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Equipment Discussions >> Mounts

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sternenhimmel
super member


Reged: 06/06/13

Beautiful Homebuilt GEM
      #6012302 - 08/07/13 08:35 PM

I have been researching the idea of building my own GEM from scratch, and have seen a number of excellent builds -- but haven't really found any good plans or CAD files just yet.

I stumbled upon this particular "light" build today:
http://www.theskyscrapers.org/jim-brenek-equatorial-mount

I thought one, the polished aluminum is absolutely beautiful, but more importantly, the design seems relatively simple to construct with a lathe and a mill. The changes I would make would be to motorize the declination axis and simplify some of the geometry (e.g. no conical shapes, fewer rounded corners, etc).

Material costs probably won't be cheap for this project, but I reckon I could still save *money* on this project in exchange for my time. Thoughts?

I would be using the mount for lightweight primefocus astrophotography with autoguiding (with what will be custom electronics to drive the axes and interface -- hopefully).

This has also been a useful document:
http://bossanova9.org/astro/ATM/8-GermanEquatorialMts.pdf


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Chucke
member


Reged: 03/12/10

Re: Beautiful Homebuilt GEM new [Re: sternenhimmel]
      #6012381 - 08/07/13 09:07 PM

I would suggest not having so much overhang on the Dec. Make everything as closely coupled as possible. You will be glad you did. If you do it right damping won't be an issue because there will not be any noticeable deflection to damp.

Look at Schaefer mounts as an example.

http://www.larryadkins.net/sitebuildercontent/sitebuilderfiles/BillInrtoducti...


Chuck


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sternenhimmel
super member


Reged: 06/06/13

Re: Beautiful Homebuilt GEM new [Re: Chucke]
      #6013976 - 08/08/13 03:19 PM

How does the overhang influence performance? Is it simply a matter of decreasing the moment arm?

So if I understand correctly, the Schaefer mounts move the large RA spur gear closer to the Dec axis? Like this:
http://www.siderealtechnology.com/atm/Logan_Gerry/MountGermanEqu/mount.German... ?


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Chucke
member


Reged: 03/12/10

Re: Beautiful Homebuilt GEM new [Re: sternenhimmel]
      #6014248 - 08/08/13 05:57 PM

Where the overhang comes in to play is that flexure varies with the cube of the overhang so you really want to minimize it.

Schaefer mounts put the gear up front in RA and at the top for Dec. The gear then acts as part of a large thrust bearing. In addition to reducing deflection from overhang it also reduces torsion of the shaft. With a rear mounted gear/clutch the shaft twists when a force is applied to the OTA. These flexures are not very large but they are greatly magnified by the lever arm of the telescope tube and the magnification of the eyepiece. The result is a springy telescope. Look at Paramounts and AP mounts. They all use front/top mounted gears for this reason. There is minimal overhang and a very short length of shaft to wind up from the point where the force is applied (the end of the tube)to the point where the shaft is restrained (the clutch). If you are interested, the formulae can be found in Machinery's Handbook. I first learned about these design issues in the 1980 RTMC Proceedings which had some simplified versions of the formulae.

Gerry Logan and Bill Schaefer were both influenced by Russell Porter's designs in the ATM books. Gerry's mounts are quite sturdy and were built without machine tools.

Chuck


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Sean Cunneen
Let Me Think
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Reged: 08/01/07

Loc: Blue Island Illinois
Re: Beautiful Homebuilt GEM new [Re: Chucke]
      #6014604 - 08/08/13 09:10 PM

I have been building mine since 2009. I can't believe it's been 4 years, but I recently found the receipt from my first aluminum order and sure enough...

If you are looking for tried-and-true, look at Opticraft mounts... The pillow-block mount is as basic, simple and reliable design. Cheap and customizeable.

I built mine because I wanted something big and stiff which I could use for potentially very large OTA's. Some folks build them because they have the capability to make very beautiful precision parts.

The basic design of a gem is simple enough, the hard part is the gearing. Most often your choice of gearing determines the aesthetic of the rest of the build. In my case, the ra gear and main bearings both fell into my lap on the same week. Since then it has been a process of refining and upgrading as I learned about materials and my own capabilities as a builder. There are very few "rights" and an awful lot of "wrongs" so be prepared for the long-haul. The reward is a one-of-a-kind build that always garners a lot of attention! You can follow the link to the build thread in my signature. Good luck!


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sternenhimmel
super member


Reged: 06/06/13

Re: Beautiful Homebuilt GEM new [Re: Sean Cunneen]
      #6014731 - 08/08/13 10:26 PM

Thanks for the insight Sean; your words of warning make me somewhat nervous though!

I'm only going to have free access to a machine shop for the next year. After that, I'm on my own. I am hoping that I can work on this project maybe 5 hours a week over the course of 4 months and have something capable of astrophotography with a 80mm refractor, 400-500mm focal length, and with autoguiding for both axes.

I would like to take this project from paper, to CAD, and to the shop. I want it to be well thought out and have as few hiccups as possible. That means learning from other people's mistakes, and modifying only slightly existing designs. Are there any freely/cheaply available GEM CAD files out there?

The pillow block mounts seem like a good compromise if I decide the project is too ambitious. However, these mounts have the RA gear hanging below the bearings -- from the discussion above, isn't this undesirable?

Also, from your experience, am I looking at saving money for the quality of mount I produce? Or will I be producing a mount that on the market could be had for cheap. My hope is to come out financially on top of the game, and not at a loss. I don't have a good sense of material costs, but if I use aluminum for the bulk of the parts, then the bulk of the costs would be in the gearing. Unless, that is, I make my own gears. Though the trend seems to be that people purchase the worm gears, then machine the spur gears.

Edited by sternenhimmel (08/08/13 10:31 PM)


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Starhawk
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Reged: 09/16/08

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Re: Beautiful Homebuilt GEM new [Re: sternenhimmel]
      #6014791 - 08/08/13 10:56 PM

I tried asking Dick Parker if it was possible to get a drawing set for the beautiful reproduction Clark and was told no, but they'd be for sale someday, and I should figure something else out for myself. I didn't assume a drawing package would be free, but this response was a surprise. Needless to say, I was disappointed, given the amount of photos and seemingly open discussion posted from that team.

Anyway, after that, a thought I had was to look at the old Unitron clock drive mounts and maybe use one of them as a guide. I'd like to have a nice drive able to run on something like 9V batteries, and the ability to use encoders, which I think could be figured out.

-Rich

Edited by Starhawk (08/08/13 10:59 PM)


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sternenhimmel
super member


Reged: 06/06/13

Re: Beautiful Homebuilt GEM new [Re: Starhawk]
      #6015029 - 08/09/13 01:51 AM

That's surprising to me as well. If I came up with a design that worked, I think I'd make it freely available for people ti improve upon.

I don't think my design will incorporate encoders, but I also don't see it being terribly difficult to add them. I just can't be spending the money on quality encoders.

On that subject, what motors are generally preferred for small GEMs? Steppers, servos, or DC?


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orlyandico
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Re: Beautiful Homebuilt GEM new [Re: sternenhimmel]
      #6015084 - 08/09/13 03:27 AM

Steppers are easier for the hobbyist to comprehend, and can be driven with simple (non-CPU) electronics. Steppers with high gear ratios (not usable for GoTo, only for tracking) are cheap. But hybrid steppers with low-ratio gearboxes suitable for GoTo are not cheap ($200+ each, new). Also, steppers cannot detect if they are losing steps, unless you put a shaft encoder on them. The Takahashi NJP and EM400 do this, probably all the Temma mounts.

Servos meanwhile require a servo controller because they need an encoder for the closed-loop control. So more complex electronics (but no more complex than a stepper with an encoder).

Mounts like the Atlas/EQ6 etc. are hybrid stepper but have no encoders, so the electronics are simpler than the servo equivalents like the CGEM.

One thing: servos are DC motors, and usually spin at high RPM. This means you need a large gear reduction (about 50:1 at least, compared to 5:1 to 10:1 for steppers). A large reduction usually requires a more complex gearhead, with a lot of gear stages. And if that gearhead is cheap (read: CGEM) there will be intractable periodic error harmonics from that complex gearhead.

Steppers can make do with a 1- or 2-stage gearbox due to the low reduction ratio. This is why we hear about 8/3 periodic error in CGEMs but nothing similar for Atlas/EQ6.

To eliminate gearhead periodic error with servos, you need a premium gearhead, such as those made by Pittman, Maxon, Dunkermotoren, etc. I believe Roland has stated that AP mounts use an in-house fabricated gearhead with Swiss-made Maxon motors.


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EFT
Vendor - Deep Space Products
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Reged: 05/07/07

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Re: Beautiful Homebuilt GEM new [Re: sternenhimmel]
      #6015698 - 08/09/13 12:15 PM

Quote:

Thanks for the insight Sean; your words of warning make me somewhat nervous though!

I'm only going to have free access to a machine shop for the next year. After that, I'm on my own. I am hoping that I can work on this project maybe 5 hours a week over the course of 4 months and have something capable of astrophotography with a 80mm refractor, 400-500mm focal length, and with autoguiding for both axes.

I would like to take this project from paper, to CAD, and to the shop. I want it to be well thought out and have as few hiccups as possible. That means learning from other people's mistakes, and modifying only slightly existing designs. Are there any freely/cheaply available GEM CAD files out there?

The pillow block mounts seem like a good compromise if I decide the project is too ambitious. However, these mounts have the RA gear hanging below the bearings -- from the discussion above, isn't this undesirable?

Also, from your experience, am I looking at saving money for the quality of mount I produce? Or will I be producing a mount that on the market could be had for cheap. My hope is to come out financially on top of the game, and not at a loss. I don't have a good sense of material costs, but if I use aluminum for the bulk of the parts, then the bulk of the costs would be in the gearing. Unless, that is, I make my own gears. Though the trend seems to be that people purchase the worm gears, then machine the spur gears.




Not to discourage you, but if you are an excellent machinist with good access to materials, you might be able to come out ahead on costs for a project like this. However, if you are not an excellent machinist with materials available, then it is rarely going to result in a cost savings to build something of high quality. In that case, you undertake a project like this because of the challenge or the satisfaction of doing it yourself, not to try to save money and don't forget that your time is worth something.


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sternenhimmel
super member


Reged: 06/06/13

Re: Beautiful Homebuilt GEM new [Re: EFT]
      #6015772 - 08/09/13 12:54 PM

I am by no means an excellent machinist. I'm a beginning machinist with very little experience. I might have access to some scrap material, but a lot of it will have to be purchased. I will have the guidance of excellent machinists, if that's worth anything.

I'm a maker at heart, and if I see a way to do something myself, I'll (try to) do it myself. If nothing else, it would be an excellent project to become more familiar with the mill and lathe.

I believe I saw a video of the Atlas slewing and it sounded like a stepper motor that was being microstepped. Would that be a correct assumption? If I plan on using a guide scope, would encoders really be necessary (ignoring GoTo capability for now)?


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orlyandico
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Loc: Singapore
Re: Beautiful Homebuilt GEM new [Re: sternenhimmel]
      #6015845 - 08/09/13 01:28 PM

Yes the Atlas is using microstepped hybrid steppers.

The Atlas doesn't have encoders on its steppers. The Takahashi NJP does. I would think there is value to those encoders, but you can live without them.

BTW there is a project out there that uses an Arduino to emulate Atlas mount electronics. So you can build your own mount with your own gear ratios (not matching the Atlas), but control it using a Synscan handset or EQMOD.

https://github.com/TCWORLD/AstroEQ


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EFT
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Re: Beautiful Homebuilt GEM new [Re: sternenhimmel]
      #6015865 - 08/09/13 01:38 PM

Quote:

I am by no means an excellent machinist. I'm a beginning machinist with very little experience. I might have access to some scrap material, but a lot of it will have to be purchased. I will have the guidance of excellent machinists, if that's worth anything.

I'm a maker at heart, and if I see a way to do something myself, I'll (try to) do it myself. If nothing else, it would be an excellent project to become more familiar with the mill and lathe.

I believe I saw a video of the Atlas slewing and it sounded like a stepper motor that was being microstepped. Would that be a correct assumption? If I plan on using a guide scope, would encoders really be necessary (ignoring GoTo capability for now)?




Doing it yourself can be very rewarding, a good learning experience on the machines, and a good way to gain a better understanding of how mounts really work. That is what I do with a lot of things.

The Atlas uses steppers. Steppers are easier to deal with than servos with encoders, but they are not necessarily as accurate because they work on the assumption that the steps that the motor was told to make were actually made and made correctly. If you use any CNC machines, you may quickly gain and appreciation for this problem.


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Sean Cunneen
Let Me Think
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Reged: 08/01/07

Loc: Blue Island Illinois
Re: Beautiful Homebuilt GEM new [Re: EFT]
      #6016169 - 08/09/13 04:17 PM

Remember that time when you typed the words "GOTO"? Right there you made it more expensive to build than to buy. Commercial mounts are all--in-one packages and goto is very expensive to DIY. Structurally, Modern mounts can be purchased for approximately the same material costs as what it takes to build so the GOT functionality is basically gratis. However the difference comes in quality. You do not need to cut costs therefore your components can be the best available. Dependability and the ability to repair/replace a broken component means your mount will last for decades rather than a few years. The other benefit of DIY is the ability to upgrade and modify should better technology make itself available. You cannot rely on backwards-compatibility from commercial manufacturers. The ones that do make their equipment with upgrades in mind(AP and Losmandy come to mind) Are so expensive for that very reason. So to see the real economic benefit of DIY, you have to think long-term.

Edited by Sean Cunneen (08/09/13 04:20 PM)


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EJN
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Re: Beautiful Homebuilt GEM new [Re: Chucke]
      #6016469 - 08/09/13 07:40 PM

Quote:

I would suggest not having so much overhang on the Dec.




That mount looks to have similar Dec. overhang to the Losmandy GM-8,
and that is a highly regarded mount.

GM-8


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sternenhimmel
super member


Reged: 06/06/13

Re: Beautiful Homebuilt GEM new [Re: EJN]
      #6016627 - 08/09/13 09:26 PM

GoTo isn't a a highly desired feature for me but I also wouldn't see it being an expensive feature? It can be implemented with software, some driver boards, and an arduino or raspberry pi as mentioned above with the open source code. However, this is a method that requires assumptions about the position of the axes, unless encoders are used.

I'll start drawing up plans and iterating through design improvements. There are many things the details of will need hammering out...


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Sean Cunneen
Let Me Think
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Reged: 08/01/07

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Re: Beautiful Homebuilt GEM new [Re: sternenhimmel]
      #6016724 - 08/09/13 10:25 PM

Unless you get lucky with surplus or you pull them out of something, encoders will run you $100 ea, easy. Add in the boards, drivers and an oscilloscope and the price goes up. Don't forget all the tuning. But don't pay too much attention to me, I have always been a star-hopper, so my bias comes through.

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orlyandico
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Reged: 08/10/09

Loc: Singapore
Re: Beautiful Homebuilt GEM new [Re: Sean Cunneen]
      #6016857 - 08/09/13 11:56 PM

Vexta hybrid steppers with gearheads are $50 each on ebay. New they are $250+.

The link I've shown above provides GoTo electronics for UKP 80 or about $150 USD.


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sternenhimmel
super member


Reged: 06/06/13

Re: Beautiful Homebuilt GEM new [Re: orlyandico]
      #6016901 - 08/10/13 12:24 AM

Anyway, I wouldn't be worried about implementing a simple GoTo system. As orlyandico pointed out, there are affordable options out there -- encoders would be an upgrade if ever they was needed.

But I digress, the electronics I can get a grasp of, and there are lots of resources available out there for custom drive solutions for telescope mounts. The machining aspects, and the details of GEM construction on the other hand, is sparsely documented. It will require a significant effort to piece together everything and come up with something that will function well.


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Starhawk
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Reged: 09/16/08

Loc: Tucson, Arizona
Re: Beautiful Homebuilt GEM new [Re: sternenhimmel]
      #6017309 - 08/10/13 10:18 AM

How much observing have you done? If this is a starter mount, then it would be putting off quite a bit of skill building in observing for the sake of building something which may not turn out to be the sort of mount you really want.

-Rich


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sternenhimmel
super member


Reged: 06/06/13

Re: Beautiful Homebuilt GEM new [Re: Starhawk]
      #6017465 - 08/10/13 11:40 AM

Observing? A fair amount over the years, mostly with an 8" Newtonian. But my real goal is an astrophotography platform for relatively light scopes. I see the merit in buying an introductory setup like the CG-5, and going from there as I become more advanced and my appetite expands. However, I also get the feeling it would be better to invest in something more substantial right off the bat, so that it will last me years to come. If that's my philosophy, then to me it makes sense to build something myself.

Again, I'll only have access to this machine shop for another year, and I would like to become somewhat proficient in my machining skills. This seems like a good project to achieve both my goals while the resources are still at my disposal.


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Chucke
member


Reged: 03/12/10

Re: Beautiful Homebuilt GEM new [Re: sternenhimmel]
      #6023519 - 08/13/13 05:20 PM Attachment (40 downloads)

Here is an example. 0.4" overhang. I could have made it less but assembly in the field would have been more difficult.

Chuck


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orlyandico
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Reged: 08/10/09

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Re: Beautiful Homebuilt GEM new [Re: Chucke]
      #6024354 - 08/14/13 01:24 AM

That's a handsome mount... home-built?

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Starhawk
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Re: Beautiful Homebuilt GEM new [Re: orlyandico]
      #6024791 - 08/14/13 10:15 AM

Sternenhimmel, the light weight astrophotography mount is nothing less than the holy grail in this hobby. The real problem comes down to tracking accuracy, which can be broken down a little unconventionally this way:

Mount:
Drive mechanical accuracy
Drive movement accuracy

Mount and telescope:
Telescope focal axis flexure (SCTs are famous for this issue)
Telescope to guidescope flexure
Telescope/ mount rigidity and natural frequency
Telescope and mount environmental disturbance response (wind, jarring).

Telescope:
Focal length
F/#

So, mount mass ends up being positively correlated with dealing with about a third of that list. What isn't obvious is picking a telescope with a longer focal length means any tracking error is easier to see in the image- and this is linear. However, f/# drives what you are required to do. So, an f/10 system can get to minutes of exposure time very easily, so even if the error is fairly low, the opportunity to damage the image is large. But image brightness is proportional to the inverse square of the f/#. And this is why very fast systems like the f/2 hyperstar exist. I invented this dimensionless brightness number to predict performance:

BR= 1000/(f/#)^2

BR (f/10)= 1000/100= 10

BR (f/2)= 1000/4= 250

So, the f/2 image is 25 times brighter than an f/10 one, meaning the magnitude it reaches in 30 seconds is equivalent to what the f/10 system needs 12 minutes and thirty seconds to do. So, the mount tracking burden is far less than it is for the slower telescope.

So, for small and light, you're talking about a light weight telescope, short focal length, and low f/#. This is a specific solution set more in the direction of camera lenses or things like the C6 hyperstar. Things like the Vixen Polarie, Takahashi SkyPatrol, or Celestron NexStar SE mounts fit in this zone depending on size.

Hopefully this will help for seeing what you would be trying to get with larger mounts.

-Rich


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windjammer
member


Reged: 06/02/13

Re: Beautiful Homebuilt GEM new [Re: sternenhimmel]
      #6025696 - 08/14/13 06:02 PM

Hi -

>>astrophotography platform for relatively light scopes

yes please!

You might be interested in my upgrade projects on an EQ2 to try and achieve this (I know, quixotic). One of the projects is electronic setting circles using home made encoders which might be useful for the goto aspects of your mount - you can find all the mechanicals, electronics and software on the site:

www.astrobling.weebly.com

I get totally the pleasure of machining beautiful precision parts, and some of the designs mentioned look fantastic and lovely. At the risk of sounding heretical, a lot of this is overkill - the trick surely is to combine cheap simple mechanics with smart software and electronics to get over the mechanical shortcomings. For example, any piece of junk can be made to track accurately for as long as you like if you have closed loop guiding - autoguiding.

Simon


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Chucke
member


Reged: 03/12/10

Re: Beautiful Homebuilt GEM new [Re: orlyandico]
      #6025798 - 08/14/13 07:04 PM

Hi orlyandico,

Yes, I made it in my garage. I have a lathe and a mill. It took about 6 months working about 6 or 7 hours per day. I was unemployed at the time.

Chuck


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orlyandico
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Re: Beautiful Homebuilt GEM new [Re: Chucke]
      #6025816 - 08/14/13 07:14 PM

Chuck, it is a very good-looking mount. But at 6 months x 20 days x 6 hours a day, a very expensive mount at 700+ hours of time. I get the unemployed part, but this illustrates well why AP, SB mounts are actually a bargain - if you were charging for your time, your mount would cost maybe double of an equivalent AP.

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Chucke
member


Reged: 03/12/10

Re: Beautiful Homebuilt GEM new [Re: orlyandico]
      #6025952 - 08/14/13 08:34 PM

orlyandico,

It would have been a lot quicker if I had a CNC mill like SB and AP do. Face milling those big plates to thickness takes a long time.

It is really sturdy. I had a 250lb OTA and 250lb of counterweights on it at one time and it didn't blink.

Chuck


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sternenhimmel
super member


Reged: 06/06/13

Re: Beautiful Homebuilt GEM new [Re: Chucke]
      #6026268 - 08/14/13 11:59 PM

Heaps of good information is accumulating right here.

I'll start by picking my jaw up of off the floor after seeing Chuck's mount as well as reading about how long it took. I'll get back to this in a minute. Nice scope, as well

Starhawk, your point is well received, and fast scopes certainly do change the game. Honestly the fact that most scopes in the astrophotography community tend to be refractors and SCTs is surprising. Newtonians are cheaper and generally faster (save for additions like the HyperStar), yet seemingly scarcely utilized. I see the advantages in using refractors and SCTs, but these don't seem to be performance related.

I think a good target scope for the mount I am building will be the 8" f/4 Newtonian I already own. I have also considered some 80mm apochroamtic refractors, but I suspect I'll get better performance out of the Newtonian.

Windjammer I like your philosophy and the website is full of helpful information. The mount I am using now is a barndoor tracker, and I've even considered guiding with it, which would be ludicrous. Yet, it could be done with a few changes. I have also considered buying a cheap mount second hand, like the CG-4, and modifying it to do accurate guiding.

Anyway, I digress, and here is what is important. I talked with one of the machinists today about this project. I showed him the photos from the original link, and discussed techniques to make the various parts. This was incredibly helpful, and I now believe that this project could be reasonably completed in 100 hours. He seemed to think material costs would be cheap, but I am suspecting at least $200 in aluminum. One question I have: should any of the parts be steel? Perhaps the shafts? It also would seem wise to purchase the worm gears, and possibly even the spur gears (at least the large one for the dec axis). Thoughts?

One aspect I had not carefully considered is the need to create tools/rigs to accurately make/position certain parts. This will consume more materials and more time, and this is something I am learning is where real machining skills come into play.

Edited by sternenhimmel (08/15/13 12:04 AM)


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TxStars
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Re: Beautiful Homebuilt GEM new [Re: sternenhimmel]
      #6026286 - 08/15/13 12:13 AM

You can get some gears from Ed Byers and not have any tracking issues.
Make the CW shaft and weights from stainless and you should be good to go.


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EFT
Vendor - Deep Space Products
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Reged: 05/07/07

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Re: Beautiful Homebuilt GEM new [Re: sternenhimmel]
      #6026307 - 08/15/13 12:29 AM

Axis shafts and counterweight bar should be stainless steel. Worms and wheels are an art form and for the best result should be purchased rather than trying to make them. Aeroquest Machining is one source, Byers is another (but they are harder get). They should be good sized and will not be cheap.

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Starhawk
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Re: Beautiful Homebuilt GEM new [Re: EFT]
      #6026331 - 08/15/13 12:48 AM

From another thread, this is probably be closer to your mental image of what a beginning machinist can have done in a year:

http://www.cloudynights.com/ubbthreads/attachments/6025789-Optic-Craft%20COPY...

-Rich


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TxStars
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Re: Beautiful Homebuilt GEM new [Re: EFT]
      #6026340 - 08/15/13 12:58 AM

Ed Byers can be reached at 760-221-2127 and has several gears on hand so they are easy enough to get (for now).
You can get them with or without a slip clutch just give him a call and talk to him.


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sternenhimmel
super member


Reged: 06/06/13

Re: Beautiful Homebuilt GEM new [Re: TxStars]
      #6026350 - 08/15/13 01:09 AM

Starhawk, a pillow block mount may still be the route I go, but I think it's a little disingenuous to say that a beginning machinist can't come up with something a little more sophisticated in that time frame. We'll see what things look like when I draw them out, then I'll access feasibility.

I checked out Byers' ebay store and some classifieds for drive systems. Expensive, yes, but more reasonable than I thought. I would probably invest in just the wheel and worm, and make my own slip clutch (if necessary) and and buy spur gears to link to the steppers, or direct drive the worm.


Edited by sternenhimmel (08/15/13 01:14 AM)


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orlyandico
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Re: Beautiful Homebuilt GEM new [Re: sternenhimmel]
      #6026451 - 08/15/13 03:44 AM

100 hours

I wish I had that kind of time to throw around.


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Starhawk
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Re: Beautiful Homebuilt GEM new [Re: orlyandico]
      #6026822 - 08/15/13 10:14 AM

I've been machining for 9 years for my own stuff, and the only "Better" I could add to that project would be some details like a finishing pass with a fly cutter to make parts pretty, making sure the support for the upper section was statically determinate, and cleaning up finishes with a sanding pad. It's very easy to imagine building something extremely elaborate, but every setup you haven't done before takes quite a bit of time to get right, and complex parts with a stack of operations are hazardous- I have a nice dovetail replacement block I made for my AT66ED with the 15 degree dovetail sides, radiused interior corners and the works, and was doing the last operation- tapping the last of 6 tapped holes and broke off a solid carbide tap in the part. So, I'm remaking it. I do have a jig I made just for doing vixen dovetails, but this will take time. I've had a project I'm doing to convert a NexStar8GPS to a trapeze, so all I had to to was make two end plates to take the place of the original one, a trapeze to go between them, a dovetail locking mechanism for the dovetail clamp, and a modification to a second dovetail I made earlier to produce an over and under arrangement. I've been working on that off and on for two years, now.

So, use as many bought components as you can. A year is a lot less time than it sounds like for this.

-Rich


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orlyandico
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Re: Beautiful Homebuilt GEM new [Re: Starhawk]
      #6026845 - 08/15/13 10:27 AM

I think that is the challenge of every would-be mount maker out there.

They have to develop the jigs, the techniques to manufacture the pieces efficiently and cost-effectively...

This is why nobody can challenge the incumbents, who already have the in-house skills, designs, techniques, and have amortized those over hundreds or thousanfs of mounts. The last guys to try that - Morning Calm - quit. I also remember the William-Optics GT-1, which proved too expensive to manufacture.


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sternenhimmel
super member


Reged: 06/06/13

Re: Beautiful Homebuilt GEM new [Re: orlyandico]
      #6026948 - 08/15/13 11:23 AM

Once optimistic, now I feel I should heed these warnings and go more conservative on the project.

I am a graduate student, but not in a field that normally utilizes the machine shop. That said, my time is probably worth less than most. I don't dare speculate on how much I actually get paid/hr I work, because the hours tend to be long. Thus, it's more difficult for me to justify spending $1,500-2,500 on a decent mount than it is for me to justify spending 4-5 hours in the machine shop a week and learning some new techniques.

I still naively believe that this project could cost less than $800.

Edited by sternenhimmel (08/15/13 11:26 AM)


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Sean Cunneen
Let Me Think
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Re: Beautiful Homebuilt GEM new [Re: Starhawk]
      #6026977 - 08/15/13 11:40 AM

I have something like $1500 in mine, half materials cost and the other half machining costs. Had I not gone through so many revisions, I suspect my cost would be more like $700-800 but I don't believe anyone can build a mount for the first time without any revisions.

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orlyandico
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Re: Beautiful Homebuilt GEM new [Re: Sean Cunneen]
      #6027080 - 08/15/13 12:30 PM

OP: I would suggest to look at some of the classic mount designs in ATM documents etc.

http://www.astrosurf.com/re/unusual_telescopes_russell_porter.pdf

I don't know where to get a hold of these but German equatorial mounts are a multi-hundred year old design. I'm sure all of the design problems have been ironed out, unless you want some holy combination (e.g. super high precision and light weight).


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Starhawk
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Re: Beautiful Homebuilt GEM new [Re: orlyandico]
      #6027124 - 08/15/13 12:52 PM

Find a good scrap metal yard- the good ones sell by the pound, not some guy looking at what you've got and trying to ratchet the price on you. If there are other machine shops in your area, they will be discarding stuff similar to your parts. So, there is one of these here in Tucson (Tucson Iron and Metal) I hit on Saturday mornings from time to time. What I am looking for are scrap aluminum pieces which have dimensions and features close to what I am trying to make. This is an enormous improvement for being able to get parts made since it can eliminate a huge amount of sawing pieces off, machining odd shapes to the right starting configuration, and limiting total material removal.

And yes, keep it really simple. If you want to put beautiful surface finishes on, hold that to last. Get everything cut and fitting together. You can buy a little grinder very cheaply and put a polishing wheel on it and continue the work at home. Conversely, polishing is slow work- if you put that in your build path, you will have half the mount built when you run out of time.

-Rich


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sternenhimmel
super member


Reged: 06/06/13

Re: Beautiful Homebuilt GEM new [Re: Starhawk]
      #6027243 - 08/15/13 01:54 PM

Okay I'm convinced. I'll start sketching out a design based around pillow block bearings, but try to capture some of the recommendations given here. I'm also going to see if I can track down some of those books, or at least, PDF versions if available.

Here's an instructable that I am finding to be incredibly helpful and inspiring:
http://www.instructables.com/id/Homebuilt-6-F15-Refractor-and-Mount/?ALLSTEPS


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Sean Cunneen
Let Me Think
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Reged: 08/01/07

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Re: Beautiful Homebuilt GEM new [Re: sternenhimmel]
      #6027256 - 08/15/13 01:58 PM

Aw shucks, I'm blushing. The build thread here on CN is WAY more detailed though, click on "Fred" in my signature...

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sternenhimmel
super member


Reged: 06/06/13

Re: Beautiful Homebuilt GEM new [Re: Sean Cunneen]
      #6027281 - 08/15/13 02:09 PM

Oh, doh! I should have recognized it in your avatar! This is excellent Sean, and Fred is a beauty. How does Fred perform as an astrophotography platform? Perhaps not with that scope, but in general.

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Starhawk
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Re: Beautiful Homebuilt GEM new [Re: sternenhimmel]
      #6027285 - 08/15/13 02:10 PM

The instructable you found is an unusually good one. I would suggest making the mount head a type of dovetail, though- that makes it vastly easier to swap scopes.

-Rich


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Sean Cunneen
Let Me Think
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Reged: 08/01/07

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Re: Beautiful Homebuilt GEM new [Re: Starhawk]
      #6027310 - 08/15/13 02:31 PM

I am in the midst of adding steppers and driver hardware. Once that gets in place, I'll give AP another shot. Optically, AP was a blast. Setting up the mount for a run was a process, but once dialed in, I could track at 500x for 20-30 minutes, no problem. The crazy thing was with all the extensions, I had the equivalent of 1100x to stack those shots. The disk of the planet to me was little more than an amorphous blob. I took about 6000 frames of which I stacked 1000 good ones to get that level of detail.

I stopped AP because I couldn't keep up with buying new laptops and new cameras AND keep building scopes, so I sold my AP gear and got into classic scope resto's. I feel the itch every now and then, we'll see...


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Sean Cunneen
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Re: Beautiful Homebuilt GEM new [Re: Sean Cunneen]
      #6027328 - 08/15/13 02:37 PM

I just checked and none of my Signature links worked, The threads have been archived... That means either: I am getting old or: My scopes are getting old!

Off to the scrap heap I guess!


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Starhawk
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Re: Beautiful Homebuilt GEM new [Re: Sean Cunneen]
      #6027478 - 08/15/13 03:46 PM

Here's something which shows the guts of a CG-5 , and will let you see how the clutches for the RA and DEC axis are done to leave the drive engaged with its gearing yet allow the axis to move.

http://www.astronomyboy.com/cg5/

-Rich


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sternenhimmel
super member


Reged: 06/06/13

Re: Beautiful Homebuilt GEM new [Re: Starhawk]
      #6028331 - 08/16/13 12:16 AM

Sean, you should put the links back up, just link to the Archived posts. I was reading through the build thread, and it seemed like you had a lot of wobbles you were fighting. Your mount look so beefy, that this was a surprise to me. I know you replaced the Dec axis completely, and that the RA axis was what, 6"?

I'm looking at a load of roughly 25lbs. What size shafts could you recommend from your experience? Also, I saw the altitude adjustment for the wedge portion, but how did you incorporate lateral adjustments?

Starhawk, it's definitely nice to see the guts of tried and proven mounts, and it's not something I get to see very often.


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sternenhimmel
super member


Reged: 06/06/13

Re: Beautiful Homebuilt GEM new [Re: sternenhimmel]
      #6028410 - 08/16/13 01:30 AM

I also found this in the depths of the internet. Another beautiful homebuilt GEM:

http://home.comcast.net/~charles.wicks/GEM.html


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dmcnally
sage
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Reged: 03/17/12

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Re: Beautiful Homebuilt GEM new [Re: sternenhimmel]
      #6155537 - 10/24/13 01:06 PM

I just found this thread and it's been very interesting, and informative, to read.

sternenhimmel: Please post an update. I'd be interested to see what kind of progress you've made, or if you've decided to abandon the project.

Sean & Chucke: Your mounts are awesome and thanks for sharing.

As for me, I've got the "bug" to build a mount, but I'm still in the research and idea gathering phase.

Dave


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hjd1964
member


Reged: 05/24/12

Re: Beautiful Homebuilt GEM new [Re: Sean Cunneen]
      #6219382 - 11/27/13 01:33 PM

I DIY'ed a GoTo system for my G11, it works well (meeting my expectations) and wasn't terribly expensive. Not in terms of dollars spent anyway. Check my website, it's easy to setup (as these things go) and runs on a lowly Arduino micro-controller with the help of two Allegro a4988 (or similar) bipolar stepper drivers. Still need to tackle building in multi-star alignment. I use my T-Point like system to overcome this limitation for now and plan to roll it into the micro-controller eventually. Slew speeds were topping out at 1 or 2 deg./sec. (best case), but recent improvements make it fast enough that your motors (and fear of damage to your telescope/self/others) will likely be the limiting factor. Use an Android phone as a hand-controller, ASCOM driver, partial Meade LX200 protocol compatibility, PEC, etc.

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Megabusa
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Reged: 05/28/12

Loc: Page ,AZ
Re: Beautiful Homebuilt GEM new [Re: hjd1964]
      #6219672 - 11/27/13 03:40 PM

I wish I had the smarts to make that ,I did steel and Aluminum fabrication work most of my life so I've been around Machinist ,but never thought to try to pick it up ,Now when I look back I wish I had ,

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