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1.5" Tap Base Pillow Block Mount Coming Together

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#51 Chuck Hards

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Posted 30 November 2013 - 11:46 PM

1" Mount to a 2" mount... 8x the mass on average. double each dimension. There is a turnover point where the mass just gets out of control. That's about at a 2" mount.
My 1.5 " head weighs about 65lbs without counterweight. My 1" head weighs about 20 lbs.


I believe you on the mass multiplier factor. I'm using the 2" bearings for an equatorial fork mount. Pretty standard polar axis but the fork will probably be composite construction, with small stub shafts for DEC, and possibly only 1" dia.
I think 1-1/2" shafts is the biggest I'll go with one of these GEMs unless I build that observatory one day.

#52 Chuck Hards

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Posted 01 December 2013 - 12:56 AM

Gary you are correct. If I were substituting Hollow for
solid I would use at least a 1/4" wall thickness.For most
of our uses that probably would be adequate.


I was thinking of possibly going with thick-walled tubing for the RA shaft, which would allow using an aligned GLP to aid in polar alignment. You'd have to drill a small hole in the DEC shaft to allow the beam to pass through, though.

#53 bremms

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Posted 01 December 2013 - 01:02 AM

Well built a 1.5 shaft mount should hold a 50 lb scope. Not a large refractor. Should be good for a 6" f12 not much larger

#54 mikey cee

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Posted 01 December 2013 - 02:36 AM

I learned way back in 1978 that a pillow block mounting was what I had to have and not cut any corners. :grin: It is just a dinky 3" set up. Worked great for my 8" F/13.3 which I just recetly converted into a 10" F/11!! Those bearings cost me $90 apiece....probably a fortune in today's dollars!:help: Mike

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#55 bremms

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Posted 01 December 2013 - 08:10 AM

I like the RA plate welded to the pier. Great for an observatory installation. The simple construction of these mounts is great. I picked up my bearings (Browning) for about $15 each NOS. about $75 for Alu plate and bushings. If I was going to an observatory installation I would use steel.
Nice mount for a big frac.

#56 Norm Meyer

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Posted 02 December 2013 - 08:39 AM

Obin,
Here is a chart that I use as a guide for load
capacities. These are made with steel plate so I'm not
sure what the difference would be using AL plate. :shrug:

http://www.opticcraf...copemounts.html

Regards Norm

#57 Chuck Hards

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Posted 02 December 2013 - 08:42 AM

I like the sub-diameter counterweight shaft. It could be threaded-in for a portable mount. Interesting color choice, too.
I'm trying to figure out the DEC tangent-arm mechanism. Looks to be spring-loaded (to eliminate backlash?) and I think I see a right-angle gear setup to put the adjustment knob at the eyepiece, yes? Or is it motorized?

#58 delta

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Posted 03 December 2013 - 12:21 PM

I am a newbie here, but have some DIY experience and am considering building my GEM in a course of a year or two.
The goal is to build it for astrophotography. Therefore the precision required.

My question is how would you compare pillow blocks vs separate bearings housing in this context?

I am studying this http://www.astronomi...ca/easyweb.e... for some time already and it looks very interesting and convincing.

Alex

#59 Norm Meyer

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Posted 03 December 2013 - 01:50 PM


Alex,
I looked at the website and poured over the plans. If
you're a halfway decent machinist and have your own machine
tools you can do it. It will take a lot of time and the
cost will not be really low. My machines are old my lathes
are pretty good but my horizontal mill leaves something to be desired. I've built several mounts and I find the pillow
block mounts are fairly easy,and not too expensive to make.
As far as precision they would match the one shown. You
could make it as beefy as you like to support the weight you
want to. If you have an observatory you could make it out of steel. If you want it portable use aluminum. I made one
with 1/2" steel plate and 1" pillow blocks and it was very
rigid. The more mass you have the more rigid but that means
it will be heavy.

IMHO
Regards Norm

#60 Chuck Hards

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Posted 03 December 2013 - 03:21 PM

I agree with Norm, a pillow-block mount is as solid and precise as anyone would ever need. You can even use double bearings if desired, though that would be overkill for the light loads of a telescope, in most cases. I've seen some observatory-class pillow block mounts made over the years. For imaging you will need precise drives on each axis, and a large gear diameter on the RA axis is a plus. The larger the gear, generally, the smoother the drive. You'll throw-away fewer subs.

#61 bremms

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Posted 03 December 2013 - 11:04 PM

OK folks, I managed to spend a couple lunchtimes making the polar inclination plates. Really like the way this turned out.
The latitude is adjustable from 10deg to 50deg. Don't think I'll be moving to Canada or the British Isles.

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#62 bremms

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Posted 03 December 2013 - 11:09 PM

Got my pictures mixed up. Previous pic is or will be the latitude fine adjust.
Here is the whole mount.

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#63 Chuck Hards

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Posted 04 December 2013 - 09:01 AM

Very nice, compact. Any plans for a small screw jack to help with fine latitude adjustments?

Did you mill the curved slot? I could do that with the router, but a milling machine would be preferred.

When you're done, you'll have the equivalent of a ten or fifteen thousand dollar precision commercial mount, at a fraction of the cost.

#64 bremms

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Posted 04 December 2013 - 09:20 AM

Chuck, Yes, I didn't put the jack screws in yet. I used a milling machine and a rotary table. I've made a few end cells with a router, but a high precision slot would be harder. Possible, but not easy. I was running through range of motion today and found that the rear pillow block bolt heads keep the RA plate from going past about 46 degrees. Not that it matters, since I'm at 34 anyway.

#65 Chuck Hards

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Posted 04 December 2013 - 09:42 AM

Any thought to going with flathead machine screws, and countersinking the heads? You've got plenty of thickness to work with. Harder to torque-down, though. And you don't need the extra movement.

#66 Norm Meyer

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Posted 04 December 2013 - 10:46 AM

Hi Marc,
Beautiful mount, nice work. Is the base 1" AL? The sides look like 1/2" is that correct? I think I may copy your design if you don't mind. I opted for a dividing head wish I had gotten a rotary table they come in handy. I'll have to rig up something to do a curved slot.

Regards Norm

#67 Chuck Hards

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Posted 04 December 2013 - 11:16 AM

I'm certainly going to copy many aspects of that mount. It's well thought-out and executed perfectly.

I think my friend has a rotary table for his milling machine. Might have to give him a call.

#68 bremms

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Posted 04 December 2013 - 12:58 PM

Norm, it's 3/4 and 3/8. Nice thing about the 3/4 plates is you can tap the edge no need for any brackets.
Thanks for the praise. Feel free to you any part of the design. Almost made a fixed latitude, but I might be moving in the next 5 years.

#69 delta

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Posted 04 December 2013 - 01:12 PM

Norm, Chuck, thanks for your comments.

What was stopping me from considering the pillow blocks is the possible concentricity issue due to the way the shaft is fixed - with set screws.
Although I will admit that getting the shaft and the home made housing to fit the bearings with required tolerances would be a bit hard with our equipment.

#70 Chuck Hards

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Posted 04 December 2013 - 02:22 PM

The setscrews merely keep the shaft from slipping- they are not sloppy in the bearing.

I've sometimes had to freeze a shaft overnight before it would fit into a bearing, and then had to encourage it with some gentle tapping.

Note the posts on shafting- some is oversize and has to be reduced slightly before it will fit.

I don't think this is an issue at all. There are GoTo pillow block mounts out there used for high precision astrometric work.

#71 bremms

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Posted 04 December 2013 - 09:40 PM

There is only 0.001 or so clearance. I sanded my shafts down on a lathe to fit. Not any different from standard bearings. You can get precision pillow blocks with compression collars. They are expensive though. Going from tolerances of about 0.0005 to 0.0001" costs a LOT more.

#72 Sean Cunneen

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Posted 04 December 2013 - 11:06 PM

Other kinds of bearings have their complications as well... Seating ball bearings without binding is very difficult. Tapered bearings need compression to work well. Pillow blocks self align at the expense of aesthetics. I'll take that trade any day!

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#73 Chuck Hards

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Posted 05 December 2013 - 08:59 AM

Nice mount, Sean. Lots of beef in that polar axis assembly! Is that about a 12" RA gear? I like the manual over-ride, as well.

#74 bremms

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Posted 05 December 2013 - 01:20 PM

Nice Sean. 3" RA shaft? Did you make Tap base bearings out of non tap base? I did that years ago on a 1 7/8 pillow block.
Went and looked at a bit of your mount build. You did chop the ears off and tap the base of the bearings. What does the mount weigh? Just the head and wedge without counterweights.
I want to keep the weight of each component under 60 lbs. The head is about 55 without counterweights

#75 Sean Cunneen

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Posted 05 December 2013 - 04:31 PM

That's actually an old picture, One axis is 3" and the other is 2 5/8". I paid just shipping for the bearings and I did not know until later that non-tap base bearings even existed! I suspect the weight of just the head is in the 80# range. The bearings are a good part of that!






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