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DavidinFL
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Wood and Pipe Equatorial Mount
      #6096591 - 09/23/13 10:48 AM

I picked up one of the Celestron 4" (102mm) refractor telescope OTAs that was being sold cheaply that was the rage in the refractor forum. I've been keeping my eye out for something along the lines of a CG-4 or CG-5 mount but in the mean time I decided to see how well a pipe mount would work.

Hereís the scope that I picked up if you're unaware of what it looks like.



Iím going to break the mount down into two pieces: the head and tripod. This post will cover the equatorial head. Iím going to use the classic iron pipe mount.

Here's all the pipe I bought for the mount. The pieces are 1-1/4" fittings which is probably overkill for a scope this size. I might stick a larger scope on the mount at some point if all goes well. In the mean time, it should flex less than a mount made of smaller pipe.



Iíd like to have a way of adding friction to an axis if needed or a way to lock the scope in position. To do this, Iíll use a couple nylon bolts to put pressure on the rotating threads of the pipe. The first step is to mark off the location where the nylon bolts will go and center punch them. Next, using the appropriate tap drill for a 1/4-20 thread, two holes are drilled into the T.



Both these holes have threads cut into them with tapping fluid and a thread tap. Care must be exercised to hold the tap vertical to the surface so that the bolt isnít crooked.



With the pipe portion of the head completed, I turned my attention to making a set of rings. I measured the diameter of the scope tube and then added a little extra to account for felt that Iíll use between the rings and scope tube. I laid out the rings on a piece of plywood with a compass and set about cutting on the tablesaw.



The rings were split so they can fit around the scope tube. The pieces were marked to avoid mixing the pieces up.



To clamp the rings to the scope tube I plan to use a couple 1/4" diameter bolts. Itís much easier to drill straight while the pieces are still square. I donít have a drill bit that is long enough to drill both halves at once so I drilled the top first. Drilling into the side of plywood can be troublesome because the bit may wander due to the layers of wood. Using a center punch to mark the spot you want to drill will help the bit stay where you want it to.



I then clamped both halves together and used the top half as a guide for the drill bit. Once shallow holes were drilled in the lower half, the pieces were taken apart and the lower half was drilled out.



The bandsaw makes quick work of cutting out the rings.



Now it is over to the bench drill press with a spindle sander to clean up the inside of the rings.



The mini-belt sander is used to clean up the outside of the rings. The cut outs in the rings allow the bolt heads and washers to sit flat on the surface.



A base is needed to connect the rings to the pipe flange. I used another piece of plywood 12" long for this. The lower rings halves and a center transfer punch were used to locate the holes for the rings. The flange was used as a template to lay out the holes for it. Off to the drill press againÖwhich I will spare you pics of.



Next, I need a wedge that will hold the assembly at the proper angle to the ground. For me this is 30 degrees. Luckily, 30 degrees is a common angle used in woodworking so most of the saws and guides have it already marked out. I came up with a simple design for my wedge and set about cutting it out on the table saw. In the picture below, Iím about to turn the rectangular piece into another side of my wedge like the one on the right. The rest of the wedge consisted of two more rectangular pieces 1-1/4" thick. The pieces were clamped, drilled, and bolted together.



Now Iím ready to start putting everything together. The lower halves of the rings were attached to the plate using a couple screws. I didnít glue them together though because I may want to use another set of rings one day. The flange was attached with more 1/4" bolts.




Shown below is the equatorial head in its current form. The mount is connected to the wedge with a couple of pipe strapsÖbolted down of course. I couldnít find any nylon bolts and instead got some nylon machine screws. They work pretty well. I can add friction to the system and hold the pieces in place from moving on their own. I can overpower them pretty easily which was expected. All of the pipes were tightened down except the threads near the nylon bolts so they can turn. I have about four complete revolutions before the parts fall apart so I donít have any fears of it falling apart in use. I do plan to do some more sanding and finish the parts. I want to try it out before I do so I can make changes if need be.



Later, Iíll post about the tripod that Iím in the process of making. So far itís looking pretty good.


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Mirzam
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Re: Wood and Pipe Equatorial Mount new [Re: DavidinFL]
      #6096617 - 09/23/13 11:01 AM

Nice job and well documented!

Another solution to the ring problem for small scopes is to use large hose clamps with a small section of rubber hose covering the part of the clamp that makes contact against the telescope.

JimC


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DAVIDG
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Re: Wood and Pipe Equatorial Mount new [Re: Mirzam]
      #6096683 - 09/23/13 11:54 AM

You might want to read my article on the Delmarva Pipe mount that was published in the Nov 2012 Sky and Tel. I developed a simple to construct bearing system using PVC reducers and Teflon and the result is a very smooth motion, no machining and 360 degree rotation without having the issue of bearings that use pipe thread.

- Dave


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DavidinFL
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Re: Wood and Pipe Equatorial Mount new [Re: DAVIDG]
      #6096939 - 09/23/13 02:33 PM

Mirzam: Thanks! I'd heard of hose clamps being used but I thought I'd go with rings since I'm able to make them.

DavidG: I'll have to see if I can find a copy of that article. That sounds pretty nice. It's been cloudy since I got the scope and I haven't had a change to try out this mount yet.


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Pinbout
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Re: Wood and Pipe Equatorial Mount new [Re: DavidinFL]
      #6096985 - 09/23/13 03:12 PM

Quote:

That sounds pretty nice




I've tried his mount and its much better than just lapped threads.

the only trick is the adapter has to jump 2 sizes down. so 1-1/2" to 1" instead of a normal 1-1/2to 1-1/4, not something I've found stock in the big box stores. maybe order it, mcmaster carr?


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DAVIDG
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Re: Wood and Pipe Equatorial Mount new [Re: Pinbout]
      #6096997 - 09/23/13 03:33 PM

My prototype mount used standard 1-1/4" pipe tee and 1-1/4" to 3/4" NPT, PVC adapters which are common and available at my local HomeDepot for under $2 each. The 3/4" pipe I used for the shafts is just a few thousand larger in diameter then standard 1" shaft material. Here is a link to the Stellafane website were there are pictures of the scope which should give you some idea of how it works. It's the 4" f/11.5 "Scope on a Stick" http://stellafane.org/convention/2012/2012-scopes.html

- Dave


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Arjan
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Re: Wood and Pipe Equatorial Mount new [Re: DAVIDG]
      #6097041 - 09/23/13 03:59 PM

Good work!
As an alternative, you can also use copper and brass plumbing parts for a light scope. Tolerances are so good that you get very smooth and hysteresis free movement.
See here.

Edited by Arjan (09/23/13 04:02 PM)


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DavidinFL
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Re: Wood and Pipe Equatorial Mount new [Re: DAVIDG]
      #6097071 - 09/23/13 04:13 PM

Quote:

My prototype mount used standard 1-1/4" pipe tee and 1-1/4" to 3/4" NPT, PVC adapters which are common and available at my local HomeDepot for under $2 each. The 3/4" pipe I used for the shafts is just a few thousand larger in diameter then standard 1" shaft material. Here is a link to the Stellafane website were there are pictures of the scope which should give you some idea of how it works. It's the 4" f/11.5 "Scope on a Stick" http://stellafane.org/convention/2012/2012-scopes.html

- Dave




I'm trying to look at the pics to see what you've done. It appears you've drilled out the PVC adapter to 1" and then run a 3/4" iron pipe through it?


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DAVIDG
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Re: Wood and Pipe Equatorial Mount new [Re: DavidinFL]
      #6097167 - 09/23/13 05:12 PM Attachment (73 downloads)

You take the 1-1/4" to 3/4" PVC adapter and drill out the threads so the pipe slips thru. This is NOT the bearing surface so the hole doesn't need to be precise. The pipe just needs to slip thru the hole. I happened to use a 1" forstner bit only because I had it. Now you flip the reducer over and make two cuts at 90 degrees thru the threaded section down to close to the base. This makes four tabs that can move and squeeze down on the pipe as you screw it into the tee since pipe thread is tapered. You then cut a strip of Teflon and bend it into a ring. The strip is about 3/4" wide and a few inches long and made from 3/16" Teflon. This fits inside the reducer. This is the bearing surface and it wraps around the piece of 3/4" pipe that I used as the shafts. Now when you tighten the reducer, it squeezes down on the ring of Teflon which squeezes down on the pipe. The result is no play, very smooth motion, 360 degrees of rotation and you can easily adjust the amount of friction. You make four of these that screw in the ends of the two tees.

- Dave


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DAVIDG
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Re: Wood and Pipe Equatorial Mount new [Re: DAVIDG]
      #6097320 - 09/23/13 07:25 PM Attachment (89 downloads)

Here is a close-up of the back of the modified reducer and the Teflon strip bent into a ring that fits inside it.

- Dave


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DavidinFL
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Re: Wood and Pipe Equatorial Mount new [Re: DAVIDG]
      #6097331 - 09/23/13 07:30 PM

That's very slick (pun intended)! I'm going to give my mount a try in this configuration since I've already built it but I can see upgrading to your setup soon.

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DavidinFL
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Re: Wood and Pipe Equatorial Mount new [Re: DavidinFL]
      #6097567 - 09/23/13 10:25 PM

I finished up the tripod enough to try the mount and scope out tonight. I'll try to get some pics up of the assembly of the tripod later. Overall, I'd say the mount and tripod are a success. It moves pretty well and once I got the counter balance weight right I didn't have to fiddle with the nylon screws much. It pushes around well and holds position. Vibration from focusing seems to die out quickly (easily under a second) and vibration from tapping on the legs dies out even quicker. There was a light breeze blowing tonight and I didn't notice it at the eyepiece. I swung around and checked out the Messier objects in Sagittarius, found M13, and looked at the Double Double. Everything looked good in the scope.

On the downside, I do think the motions could be a little smoother and there is a little bit of sticktion. It's also pretty big when all setup. I expected it to be large but it is something to see it all together. On the bright side viewing at zenith isn't uncomfortable though using the straight through finder is. I can still pick it up in one piece and move it around the yard though. I'll try to weigh it later. I also miss the Rigel on my dob. But that can be fixed.


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Chuck Hards
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Re: Wood and Pipe Equatorial Mount new [Re: DavidinFL]
      #6097964 - 09/24/13 08:31 AM

Examine any flanges that you purchase very carefully. The last time I built a pipe mount, I discovered that the face of the flanges was not anywhere near orthoganol to the threaded axis. I had to face them on a lathe.

Not a big concern on a strictly visual mount for a small telescope, but something to be aware of.

When using the pipe threads as the bearing surface, it helps to lap them with automotive rubbing compound prior to final assembly. Mirror-grinding extra-fine grit and oil can be used, as well. Spin the fittings together many times with the lapping medium generously applied, tightening them and loosening them repeatedly, until you gain another 1/4 to 1/2 turn. Then clean them with laquer thinner or other solvent before final assembly and use your lubricant of choice on the threads. It noticeably improves the smoothness of the action.


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Edward E
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Re: Wood and Pipe Equatorial Mount new [Re: DavidinFL]
      #6100500 - 09/25/13 02:13 PM

Now that is a nice looking DIY GEM!

I like your belt sander. I'm going to get one some day. What model/make & table size is your band saw?

Edited by Edward E (09/25/13 02:15 PM)


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DavidinFL
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Re: Wood and Pipe Equatorial Mount new [Re: Edward E]
      #6100554 - 09/25/13 02:36 PM

Quote:

Now that is a nice looking DIY GEM!

I like your belt sander. I'm going to get one some day. What model/make & table size is your band saw?




Thanks! It's a Rockwell 14" band saw from the 1970s. I'm not sure of the table size off the top of my head. I'll try to measure it tonight. If you'd like to see more pics of it I've got some on my site. This link and the next three posts there are about the band saw: http://somanyhobbies.wordpress.com/2012/09/15/rockwell-bandsaw/


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StarStuff1
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Re: Wood and Pipe Equatorial Mount new [Re: DavidinFL]
      #6100897 - 09/25/13 05:16 PM

Let's see: pipe fittings, plywood and PVC parts for an ATM EQ mount. MMMMmmmmm... GOOD!

Looking forward to seeing pics of the tripod.


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Rutilus
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Re: Wood and Pipe Equatorial Mount new [Re: StarStuff1]
      #6100914 - 09/25/13 05:26 PM

Nice work with the Equatorial.

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DavidinFL
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Re: Wood and Pipe Equatorial Mount new [Re: Rutilus]
      #6101641 - 09/26/13 01:47 AM

In the previous post I described the equatorial head I'd made for my telescope mount. Now I'm going to cover the tripod. First, I needed to figure out how large the tripod needs to be. To do this I measured the highest and lowest points the eyepiece would be from the floor with my scope in the equatorial head clamped to a bench. Then I measured the height of my eye while I was bent over in the sitting position. From here I figured how how much I need to raise the eyepiece at the lowest point to get it to a comfortable position. This resulted in me needing a tripod that lifted the equatorial mount 46" from the ground.

I looked around for designs of wooden tripods and came across a design I liked in a book called "Build Your Own Telescope" by Richard Berry. The book covers several telescope builds and one of them was for a tripod mounted 6" refractor. I used the design as a jumping off point to make my own design. In the book, each leg was held at an angle of 75 degree from the ground which results in me needing roughly 48" long legs. In the book, each tripod leg is an I beam made up of three pieces of wood. I decided to go with a C channel shaped beam still made up of three pieces. The legs start wide at the top and then taper to a point at the bottom in the book. I liked this element and went with it. I laid out the design for the wed of the C channel on the pieces of wood and then cut them out on the band saw.



The band saw doesn't leave a smooth surface on the edges of the pieces. A hand plane makes quick work of smoothing the sides.



The flanges on my C channel legs are made of a 1x4 ripped in half on the table saw. To make sure both pieces were the same width, I ran all the pieces back through the saw after setting the fence to the width of the thinnest piece.



To attach the flanges to the web I drilled holes every six inches for screws. I also drilled the hole for the bolt that the leg will pivot on.



The pieces were glued, clamped, and the screwed together. I clamped sections, inserted screws and then moved down the line leading the way with clamps.



On the pointed ends of the legs, clamping is a must to bend the wood to the shape. The web at the location for the last hole isn't thick enough to be screwed into. Instead I bolted the pieces together. It's not coming apart now.



To connect all the legs together I borrowed another idea from the book. My hub consists of two pieces of 3/4" plywood in the shape shown below. I started with a 10" diameter circle and then laid everything out with a straight edge and protractor. It's always good to shade the areas you want to cut as it is tough to add material back.



Off to the band saw for more cutting. I freehand cut all the pieces because I planned to clean them up on the sander.



Here's the two pieces clamped up while the glue sets. After the glue dried the inside edges of the piece was sanded.



To go on top of my hub I cut out a 10" diameter circle. All the parts were center drilled, glued, and then temporarily bolted together so I could sand them as one piece.



To attach the legs I held them in the extended position pushed up against the top of the hub. This way the legs will jam tightly when opened to increase the stability of the tripod. I marked the location for the bolt holes by drilling shallowly into the hub with the legs in this position. I finished the holes using the drill press. I drilled down halfway on one side and flipped the piece over to drill the other half of the hole. This way, if your drilling isn't perfect the problem is inside the piece where it can be fixed as opposed to being off when you exit the other side of the piece you're drilling.



Here's everything together. To attach the head to the tripod I drilled a 3/8" hole and bolted the two together. A wing nut on the bolt allows me to move the head around in azimuth.



The tripod was very stable but when lifted the feet would come together as expected. To fix this I added a spreader in between the legs. I thought about it for a little bit and decided I'd add braces attached to each leg that would meet in the middle. I recalled a joint in a book I have around here called the Triple Lap joint that would be perfect. Here's the one I made.



How do three pieces of wood occupy the same space? Here are the piece separated for a better view.



I installed the spreader using hinges and put a bolt through it to hold it closed. The joint is meant to be stacked vertically. Swinging the arms together on an arc causes results in them not coming together smoothly. I think I'll need to remove a little material to solve this problem sometime soon. But it does come together nicely.



Here's an underside view on one of the spreader arms. The end of the arm is cut at a 15 degree angle to jam up against the legs.



The spreader can be disassembled allowing the legs to collapse for storage.



Finally, the pic you've been waiting for. This is the setup currently. I'm still testing so I haven't finished any of the pieces. No finish means I haven't put felt in the rings so I'm using a towel to take up the space.



I put it all on the bathroom scale and measured the weight of all the pieces. Currently the tripod weighs 16.4 lbs, the equatorial head weighs 11.6 lbs, the scope with diagonal and finder weighs 7.6lbs, and the counterweight is 7.5 lbs. Summed this results in about 43 lbs. I have given thought to making new legs with material taken out of the webs to reduce weight. I think I could lighten it some but I don't want to decrease its rigidity. Currently, it may be on the heavy side but it is solid as a rock. I may add a tray on top of the spreader as well. Next up will be rounding corners, sanding, and finishing.

I had the scope out tonight looking at Uranus and some double stars. I noticed a little more vibration than I did previously and still had the sticktion issues. I'm also still trying to think of ways to reduce setup time and hassle. I ordered some Teflon so I can give DavidG's design a try. Home Depot had the reducers so I should be all set when the Teflon arrives.


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Geo31
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Re: Wood and Pipe Equatorial Mount new [Re: DavidinFL]
      #6101761 - 09/26/13 06:43 AM

Instead of producing new legs, why not drill a series of holes along the length? Maintain much of the strength and rigidity but still shedding mass.

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Edward E
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Re: Wood and Pipe Equatorial Mount new [Re: DavidinFL]
      #6102140 - 09/26/13 11:20 AM

Excellent build! A very steady mount for that refractor.

I would recommend putting some self adhesive green felt on the OTA clamps to protect the OTA finish. Has always worked for me.

Drilling the holes into the legs to lighten the weight is a good idea. I have seen that done in other builds here in ATM as well as in Richard Berry's books.

I enjoyed reading your web page blogs, though I nearly cried reading about the iron skillet restoration. The rust must go but Ooooo, the removable of the seasoning layer. It would be like erasing my grandmothers memory (I have her cast iron skillets); all those biscuits, ham, bacon and pinapple up side down cake. I think I'm hunger now.


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DavidinFL
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Re: Wood and Pipe Equatorial Mount new [Re: Geo31]
      #6102253 - 09/26/13 12:23 PM

Quote:

Instead of producing new legs, why not drill a series of holes along the length? Maintain much of the strength and rigidity but still shedding mass.




I've considered doing that or using a jig saw to remove bigger areas. I've also got an idea about making legs with the same flange pieces but using horizontal strips of wood as the webs. The material for the legs cost less than $15 so I don't mind making another set and keeping the originals intact in case I remove to much.

Quote:

Excellent build! A very steady mount for that refractor.

I would recommend putting some self adhesive green felt on the OTA clamps to protect the OTA finish. Has always worked for me.

Drilling the holes into the legs to lighten the weight is a good idea. I have seen that done in other builds here in ATM as well as in Richard Berry's books.

I enjoyed reading your web page blogs, though I nearly cried reading about the iron skillet restoration. The rust must go but Ooooo, the removable of the seasoning layer. It would be like erasing my grandmothers memory (I have her cast iron skillets); all those biscuits, ham, bacon and pinapple up side down cake. I think I'm hunger now.




Thanks! I've got some adhesive felt but haven't put it on yet. I'm waiting to put the finish on the wood first. I have a wide variety of topics on my site for sure. I'm glad you found them interesting. I picked up my cast iron pans from a flea market so there might have been industrial grease on them for all I know. It had to go! It'd be different if I knew the history of the pans.


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DavidinFL
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Re: Wood and Pipe Equatorial Mount new [Re: DavidinFL]
      #6104372 - 09/27/13 02:38 PM

I made the new legs for the tripod this morning. Theyíre the same shape as before but lack the large webs of the solid legs. The previous legs weigh 4lb 2oz while the new ones weigh 2lb 12oz a piece. Total, the tripod is now 4lb 2oz lighter. It still feels very rigid when the spreader is used. I hope to give it a try tonight.



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Geo31
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Re: Wood and Pipe Equatorial Mount new [Re: DavidinFL]
      #6104394 - 09/27/13 02:53 PM

Outstanding!

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richard7Moderator
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Re: Wood and Pipe Equatorial Mount new [Re: Geo31]
      #6105066 - 09/27/13 10:45 PM

Darn good looking tripod Dave.

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allardster
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Re: Wood and Pipe Equatorial Mount new [Re: richard7]
      #6105141 - 09/28/13 12:06 AM

Nice intricate triple lap joint there! What tools did you use to make these?

This is one of my favourite threads. Full of ideas to borrow. Thank you for documenting and everyone for piping in on the pipe part.


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DavidinFL
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Re: Wood and Pipe Equatorial Mount new [Re: allardster]
      #6105181 - 09/28/13 12:58 AM

Quote:

Nice intricate triple lap joint there! What tools did you use to make these?

This is one of my favourite threads. Full of ideas to borrow. Thank you for documenting and everyone for piping in on the pipe part.




I used a table saw with a dado stack and miter gauge to cut the triple lap. It's actually not to hard to cut once you see how it's done.

I did some more work on the scope this afternoon and integrated DavidG's Teflon bearings. That makes a huge difference and completely changes the way the scope feels when moving. It's much improved over the pipe on pipe setup. I also made a few more small changes. I'll post some updated pics and more info tomorrow.


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Boot
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Re: Wood and Pipe Equatorial Mount new [Re: DavidinFL]
      #6105809 - 09/28/13 12:02 PM

Quote:

I made the new legs for the tripod this morning. Theyíre the same shape as before but lack the large webs of the solid legs. The previous legs weigh 4lb 2oz while the new ones weigh 2lb 12oz a piece. Total, the tripod is now 4lb 2oz lighter. It still feels very rigid when the spreader is used. I hope to give it a try tonight.






(Reminds me of a pair and a half of crutches)

Like the tripods Ed Turco's made, shown here.

Nice work all around. Thanks for sharing.


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DavidinFL
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Re: Wood and Pipe Equatorial Mount new [Re: Boot]
      #6106414 - 09/28/13 06:16 PM

I've implemented the changes DavidG suggested for his Delmarva mount system. The mount now utilizes some PVC reducers and Teflon to provide better bearings.

The first step is to modify the PVC 1-1/4" to 3/4" bushings. The 3/4" side needs to be bored out using a 1-1/8" Forstner bit so that a 3/4" galvanized pipe can pass through it.



Next, the 1-1/4" end needs to be bored out to large enough so that the 3/4" pipe with Teflon wrapped around it can fit. I used 1/8" thick Teflon which required me to bore bushing out to 1-3/8". I did this on the lathe as it is easier to find the center of bushing. When boring the bushing you want to bore down only as far as needed so that a shoulder is left in the bushing to keep the Teflon from sliding out.



The thread on most plumbing pipe is tapered. This can be used to our advantage to increase or decrease the friction on the bearings. If the bushing is slotted as shown below, as it is tightened it will bend in pushing harder on the Teflon and pipe. The bushing on the right has the Teflon bearing material installed.



To use the new bushings I had to redesign the mount. Some of the parts are still there but Iíve added a few new pieces. Instead of pipe threads acting as bearings on each other, 3/4" galvanized pipe is held by the PVC and Teflon bushings. The 3/4" pipe is threaded into a 1-1/4" to 3/4" galvanized reducer and the whole piece spins.



Previously to get the scope rings apart I had to remove four 1/4" nuts. To speed this process up I put small hinges on one side of the rings.



On the other side, I put some well nuts. I stumbled upon them at Loweís and they work well for this purpose. Theyíre made out of rubber with a 1/4" nut set into the bottom. Theyíre easier to get a grip on than the hex nuts.



Viewing with the scope is much improved over the previous design. The scope now turns smoothly and stiction is pretty much nonexistent. On the downside, the mount gained another 2.6 lbs bringing the total weight up to 41 lbs with scope and counterweight. This was definitely a worthy modification though.

Edited by DavidinFL (09/29/13 11:40 AM)


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DAVIDG
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Re: Wood and Pipe Equatorial Mount new [Re: DavidinFL]
      #6106676 - 09/28/13 10:28 PM

Dave,
Great job, and glad to see that the Delmarva Mount worked well for you as well. I'm a little surprised that you had to bore the back side of the reducer out for the Teflon. I used a couple of different thickness of Teflon when I developing the design and all worked well without any boring of the back side of the bushing. I just cut the length of the strip of the Teflon so it would fit inside the bushing when it was bent into a ring and had a gap in the end so the Teflon could have remove the move as it was squeezed down around the pipe. The taper of the pipe thread gives a wide range of how much it can be screwed into the piping fitting, offering a simple way to compensate for different thickness of Teflon, within reason. I designed the system so that only simple hand tools are required to make the bearing. One could, for example uses a file to just remove the threads in the bushing so the 3/4" pipe would slip through. My goal was a system that worked very well but also kids or someone with the access to power tools could build.

- Dave


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Rougeaux
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Reged: 08/15/13

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Re: Wood and Pipe Equatorial Mount new [Re: DAVIDG]
      #6107430 - 09/29/13 12:50 PM

Do you think the equatorial axis would move freely enough to be motor-driveable? I'm looking at building a mount for my 102 and it would be great if I could do some rudimentary astrophotography experiments with it while I save up for something good. My current designs involve ball bearings but I get the feeling PTFE will probably end up being better on both the cost and workability fronts.

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DavidinFL
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Re: Wood and Pipe Equatorial Mount new [Re: Rougeaux]
      #6107822 - 09/29/13 04:36 PM

Quote:

Do you think the equatorial axis would move freely enough to be motor-driveable? I'm looking at building a mount for my 102 and it would be great if I could do some rudimentary astrophotography experiments with it while I save up for something good. My current designs involve ball bearings but I get the feeling PTFE will probably end up being better on both the cost and workability fronts.




Yes, it moves freely and the amount of friction can be varied. I've considered it as well.


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Dick Parker
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Re: Wood and Pipe Equatorial Mount new [Re: DavidinFL]
      #6108192 - 09/29/13 08:56 PM Attachment (55 downloads)

David -

FWIW, I have used wood and pipe mounts since the 1960's and my primary mount is still the wood and pipe mount that I have iterated since then. I have tried every sensible type of bushing and bushing material in the attempt to get a clock drive to work. Yes, even the PVC and teflon and ebony star etc. I was not successful getting a clock drive to track well until I put a ball bearing on the North polar shaft end. At one point I did get the mount to track before I added the ball bearing, but with the clutch very tight which was a strain on the gears. For best results, the polar shaft must be absolutely frictionless.

Now, I was using a worm and gear type drive with a synchronous motor. Don't know about steppers etc.

Good luck
Dick Parker


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Boot
wildly diverse musical tastes
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Re: Wood and Pipe Equatorial Mount new [Re: Dick Parker]
      #6108306 - 09/29/13 10:08 PM

Dick - That is stunning.

Any plans available for that beauty?


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DavidinFL
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Re: Wood and Pipe Equatorial Mount new [Re: Dick Parker]
      #6108466 - 09/30/13 12:02 AM

Quote:

David -

FWIW, I have used wood and pipe mounts since the 1960's and my primary mount is still the wood and pipe mount that I have iterated since then. I have tried every sensible type of bushing and bushing material in the attempt to get a clock drive to work. Yes, even the PVC and teflon and ebony star etc. I was not successful getting a clock drive to track well until I put a ball bearing on the North polar shaft end. At one point I did get the mount to track before I added the ball bearing, but with the clutch very tight which was a strain on the gears. For best results, the polar shaft must be absolutely frictionless.

Now, I was using a worm and gear type drive with a synchronous motor. Don't know about steppers etc.

Good luck
Dick Parker




Hmm, thanks for the info. That could complicate things. I've already ordered some stuff to construct a drive so I think I'll give it a try even I will be walking the unsuccessful path you walked before. Was there to much friction for the motor to work or did it just grab and release? Or something else?

I like the tangent arm fine adjustment knob on the declination axis. Nice scope overall!

Edited by DavidinFL (09/30/13 12:04 AM)


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careysub
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Re: Wood and Pipe Equatorial Mount new [Re: DAVIDG]
      #6108619 - 09/30/13 02:52 AM

Do you think that 3/4" wide, 1/8" thick UHMW

http://www.mcmaster.com/#8702k22/=oq84z1

or 3/4" wide. 1/4" UHMW might serve in place of the Teflon?

http://www.mcmaster.com/#8702k62/=oq84if

I ask for two reasons, this material is quite cheap (about 1/10 the cost of the PTFE), convenient (already cut to width), and it has superior wear resistance (about 8 times that of PTFE).

It would be nifty if this could be used instead of 3/16" PTFE.


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StarStuff1
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Re: Wood and Pipe Equatorial Mount new [Re: careysub]
      #6108704 - 09/30/13 06:10 AM Attachment (34 downloads)

The triple lap joint for the tripod leg spreader is very nice.

A slightly simpler solution is to arrange the leg spreaders to connect by the thickness of the wood. I hope this pic makes this clear.


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DAVIDG
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Re: Wood and Pipe Equatorial Mount new [Re: Rougeaux]
      #6109015 - 09/30/13 10:28 AM

Quote:

Do you think the equatorial axis would move freely enough to be motor-driveable? I'm looking at building a mount for my 102 and it would be great if I could do some rudimentary astrophotography experiments with it while I save up for something good. My current designs involve ball bearings but I get the feeling PTFE will probably end up being better on both the cost and workability fronts.




Dick Parker is a good friend of mine, and one of THE BEST telescope makers around, along with being an excellent engineer so I value his opinion. At the same time I'm also an engineer and the designer the Delmarva mount, so I do believe that the friction is low enough that one could make a clock drive and have the scope track well. Mounts like the Poncet type use a simple bearing system similar to the Delmarva system and can be made to track well. It is going to come down to how well the drive is engineered. There are many examples of commerical mounts that used either a simple Nylon or Teflon bushings as the bearing which is the principle used in the Delmarva system that also came with clock drives and would track

All the Best
- Dave


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MKV
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Re: Wood and Pipe Equatorial Mount new [Re: Dick Parker]
      #6109622 - 09/30/13 04:57 PM Attachment (40 downloads)

Dick Parker's and DavidG's solutions are both easthetically beautiful as well as fuctional. I wish some manufacturers were offering mounts fashioned after Dick Parker's example shown, or something simple as teflon pipe mount bearing mounts DavidG made. The difference is that Dick's beauty required a machine shop while David's doesn't.

However, Dick is right about the R.A. axis having to be smooth and for that, some kind of frictionless bearing is required for a telescope to track correctly. If the desire was to come up with something that an ATM without a machine shop can do, then a combination of pipe fitting and pillow block bearings seems to be the easiest solution to pursue.

Two-inch pipe flanges and a 45-degree fitting is ideal for mounting on a tripod and also for mounting the R.A. axis on it. The declination axis can be flanged using hardwood bored with Forstner bits, and making sure the steel axis goes all the way through the declination plate. Using oak for both plates and the tripod is the way to go.

The mount will weigh a ton but that is actually good!


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magic612
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Re: Wood and Pipe Equatorial Mount new [Re: careysub]
      #6111108 - 10/01/13 12:18 PM

Quote:

Do you think that 3/4" wide, 1/8" thick UHMW

http://www.mcmaster.com/#8702k22/=oq84z1

or 3/4" wide. 1/4" UHMW might serve in place of the Teflon?

http://www.mcmaster.com/#8702k62/=oq84if

I ask for two reasons, this material is quite cheap (about 1/10 the cost of the PTFE), convenient (already cut to width), and it has superior wear resistance (about 8 times that of PTFE).

It would be nifty if this could be used instead of 3/16" PTFE.




The coefficient of friction for PTFE/Teflon is lower than UHMW. Given the small range of motions and extremely low speeds these are used at, I think Teflon is probably better, despite the lower abrasion resistance. I've used UHMW on Dob mounts before - there is some "stiction" that occurs. PTFE/Teflon is more expensive, but it generally works better for telescope applications, too. At least that is my experience with it.


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DavidinFL
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Re: Wood and Pipe Equatorial Mount new [Re: magic612]
      #6120671 - 10/06/13 02:09 PM

I worked on the drive for my mount some over the past week. I decided to go for a tangent arm style drive. I don't want to do long term photography so I care about the errors associated with a tangent arm over time. If I could hold something pretty much steady for a little bit I'd be happy.

I have a 2.5" tangent arm being pushed by a carriage on a 1/4-20 bolt driven by a 0.5 RPM motor, from Servocity.com, geared down to 0.3 RPM. Ideally, I need to run at 0.218 RPM according to the math. To vary the speed I'm using a simple potentiometer. The arm is made of wood and I clamp it down on the RA shaft via a bolt. To increase the friction between the wood and shaft I used a strip of sandpaper. Ideally, I'd move the object I want to track in place, turn on the motor and then tighten down the clamp bolt.

I'd say I've met with moderate success. It works intermittently. To test it I stared a Altair a lot through my 7mm eyepiece at 144x magnification. Most of the time I could decrease the rate at which it was moving and only rarely could I arrest the motion or push the star in the wrong direction. The few times I got it to track well I really had to crank down on the bolt holding the arm onto the RA shaft. Still there were a few times the star moved off to the left instead of down indicating it was working but that my RA shaft wasn't pointed perfectly at the celestial north pole.

There are a couple issues that I think are giving me trouble. The first is that getting the arm to clamp tightly on the RA shaft so they turn as one is tough. Yeah I know, soft wood on steel is an issue. Making this piece of out metal would work better I think. To get it really tight though I think I'd have to have some sort of tool to use on the clamping bolt. The second issue I'm having trouble with is flex. As most of the drive is made out of wood there aren't super tight tolerances. As the drive runs it removes these tolerances by jamming everything together but that takes time because the carriage only moves at 0.01"/min. I also have a spring on the threaded 1/4-20 bolt so I could unlock the gears to rewind the carriage. I'm pretty sure this is compressing some as it runs.

To fix things I need to increase the friction between the RA shaft and arm. I can't permanently join the together and I'd like to avoid having to use something like an Allen wrench to tighten something like a set screw. To fix the tolerance issue I can try to make everything tighter or make the tangent arm longer. Making the arm longer requires the carriage to move faster which would remove the slack faster. Getting the carriage moving faster would require me to order some more gears if I want to rotate faster than 1 RPM. Of course making the whole thing out of Aluminum would probably work too...but thats beyond my current capabilities.

All that aside, if I had a normal style spur and worm gear setup on this mount the motor would drive it ok.

Here's a couple pics of the current setup.




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calypsob
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Re: Wood and Pipe Equatorial Mount new [Re: Edward E]
      #6121416 - 10/06/13 10:21 PM

how are you going to adjust latitude?

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DavidinFL
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Reged: 08/28/09

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Re: Wood and Pipe Equatorial Mount new [Re: calypsob]
      #6121468 - 10/06/13 10:52 PM

Quote:

how are you going to adjust latitude?



My mount is set at 30 deg and my local latitude is ~30.5 deg. So, for casual viewing the mismatch isn't huge. Still, if I wanted to vary the latitude on the mount some I'd elongate the holes on the front bottom bolt of my wedge to allow some adjustment. I could put a large bolt in between the top and bottom of the wedge to provide fine adjustment if needed.


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DavidinFL
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Reged: 08/28/09

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Re: Wood and Pipe Equatorial Mount new [Re: DavidinFL]
      #6123831 - 10/07/13 11:32 PM

I made some improvements to the drive. I went by the hardware store and found a grounding pipe clamp. It has a machine screw coming out of the top of the clamp perpendicular to the direction the pipe would go. I replaced the machine screw with a bolt and cut a washer to act as the pin for the drive. I also attached the aluminum piece to the carriage more securely and took a little of the play out of the drive bolt.

This time tracking was much better. I was able to track Altair and Uranus after waiting a bit for the slack to be removed. The drive bolt and housing all flex some under load which is still causing me issues. I'll turn my attention to getting rid of the flex next.

Here's a picture of the drive with the upgrades.


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