cnchillstar
super member
Reged: 12/29/08
Posts: 102
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I choose taped roller bearings for both axis.
but find that if decide a D40 mm balance bar, than will trigger a lot of unexpected clumsy design for bearings and shafts....the result is:
1.Dec: ID80,ID70 bearings
2.RA: ID100,ID90 bearings
then even a 10" scope looks small on such a mount. I think it need to be optimized to fit my goal--12" reflector. but no idea to start with....
thank you for suggestions~~
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cnchillstar
super member
Reged: 12/29/08
Posts: 102
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taped roller bearings for both shaft
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Ian Robinson
Pooh-Bah
Reged: 01/29/09
Posts: 1165
Loc: Gateshead.NSW Nth Coast,Austra...
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Vixen uses tappered bearings , I think they are thrust bearings , and they wind up with a mount capable of precision guiding with scopes larger than 12". That's a lot more compact that the one drew up.
Maybe you should change your bearings .
Edited by Ian Robinson (09/13/09 10:11 PM)
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cnchillstar
super member
Reged: 12/29/08
Posts: 102
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does anyone use a meade max mount? is the counter weight bar screwed in Dec shaft or only screwed in the interface block?
if I make a smaller bearing, it will be not enough diameter for a 38mm balance bar.
thanks a lot!
Edited by cnchillstar (09/14/09 02:13 AM)
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polaraligned
sage
Reged: 12/26/08
Posts: 233
Loc: P. R. of New Jersey
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Max Mount never got beyond prototype stage.
You don't need such a large diameter counterweight bar.
Your shafts are HUGE, and the mount will weigh a LOT.
You have no idea how to design a mount and would be a lot better off buying a used one. It will probably be far cheaper in the long run.
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Ian Robinson
Pooh-Bah
Reged: 01/29/09
Posts: 1165
Loc: Gateshead.NSW Nth Coast,Austra...
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He needs to do a study of the specs of mounts from manufacturers like Parks, Meade, Vixen, Celestron, Losmandy .... paying REAL attention to what they have in terms of bearings , shafts , gearing , rather than wasting a lot time drawing up unrealistic mounts using CAD , maybe he needs to develop an understanding of structural analysis and get a grip on this.
Edited by Ian Robinson (09/14/09 07:18 AM)
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cnchillstar
super member
Reged: 12/29/08
Posts: 102
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Hi,thanks for comments anyway, I also don't want to waste time on paper dream, but it is imporsible to touch a REAL professional mount like you did in a star party. what I own is a EQ5 without any kind of bearing.
so,study pictures and asking is the way I can found. if there is any disturbing, please forgive.
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Owen
professor emeritus
Reged: 06/21/07
Posts: 514
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Large shafts, tapered bearings, indicate large capability for later on.
As an overall design, yes this will be ok - it is a heavy weight solution, but if it is planned for your observatory, then that should be fine.
As a suitable source - timken bearings for automotive use will be relatively inexpensive, and more than robust enough 
I'd look to making the 'bars' tubes to reduce some weight with out compromise, but this 'should' (if the plate is properly welded, and the bolts suitable substaintial) be immensely solid.
Owen
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Gary Fuchs
scholastic sledgehammer
Reged: 05/22/06
Posts: 867
Loc: Easton, PA, USA
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cnchillstar - Just curious, have you considered a fork or split ring?
Anyway, good luck with the project and I look forward to your progress reports. Nice Solidworks work after a relatively brief learning time.
Gary
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neo
professor emeritus
Reged: 02/12/08
Posts: 623
Loc: Iasi, Romania
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cnchillstar ..here's a good reference material for telescopes and mounts in general but with a good chapter about EQ building with lots of technical data about shafts and bearings suitable for a large range of scope sizes.
http://www.amateurtelescopemaker.com/ATM_book/MechDes.htm
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Russian 15x50 binos
Home made 8" f/5 Newton on eq mount
Home made 70mm f/6 (Rodenstock Rotelar lens) Apo refractor
www.astronomy.ro
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polaraligned
sage
Reged: 12/26/08
Posts: 233
Loc: P. R. of New Jersey
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Have you looked at these mounts?
http://www.opticcraft.com/telescopemounts.html
Sometimes it costs more to build your own high quality item than it would to purchase it commercially. I don't want to see you pay for all this machining and have a mount that you are not satisfied with. For your intended use pillow blocks will be fine.
Why don't you start out with a solid 2" stainless shaft with pillow blocks. Your Byers gear will fit right on there. The pillow blocks clamp right to the shaft. Spend your time and money on the optical tube for now and you can go back and machine a nice mount later if you desire.
A simple pillow block mount will at least get you going and be perfectly fine for visual use and low resolution imaging.
Good luck,
Scott
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Sean Cunneen
Let Me Think
Reged: 08/01/07
Posts: 1229
Loc: Blue Island Illinois
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Quote:
Max Mount never got beyond prototype stage.
You don't need such a large diameter counterweight bar.
Your shafts are HUGE, and the mount will weigh a LOT.
You have no idea how to design a mount and would be a lot better off buying a used one. It will probably be far cheaper in the long run.
That's a little rough eh?
How about bushings instead of bearings? Bearings can introduce play into a large mount unless you spend lots and lots of money. For a DIY mount, good ol' bronze bushings and some oil will do a fine job in a large mount.
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Sean Cunneen
Blue Island, IL
12.5" Ultralight Strut Dob
127mm f/9 refractor
35Pan, 10XW, 5XO
Member of the Calumet Astronomical Society
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Owen
professor emeritus
Reged: 06/21/07
Posts: 514
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The right type of bearing will introduce near zero play. He has chosen the right type of bearing, and whats more, they are *inexpensive* as they are used in the auto and truck industry the world over...
Last time I bought a tapered timken set it was £20... just remember to grease it properly, and tension the inner races, and you will be good to go 
Owen
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Ps191
member
Reged: 06/17/09
Posts: 43
Loc: E.OR.
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Sounds like you have a fun project.
I've never build any GEM mount but have thought about doing so. Everything I say is therefor FWIW.
From my research the quality of the bearing counts more then the type of bearing. Most types of bearings have been used at one time or another but tapered roller bearings seem to be the most popular. This may be do to the fact that they can be preloaded to reduce the error.
Unless you need high goto precision the polar axis needs to be the most error free. So you could use tapper's on the polar axis and blocks on the other.
I've used some GEM mounts who's clutch/shaft locking system introduced more error into the mount then the bearings so don't forget to consider what you plan to do in this area when you calculate the mount error.
Mount size could be reduced by using pipe for the casing. I personly think it would be easier to machine a adapter to mount bearings inside a pipe then inside a square tube.
If you are planing to build the case yourself you could increase precision and reduce size by designing it similar to those found on the mathis instruments mounts.
You probably will not save much money (if you count your time) by building your own mount. But if you have the tools, like to build stuff and enjoy doing so for reason found here - go for it. Don't be discourage by those who have never built a mount and probably never will. Many of the high quality mounts for sale today started out as someone building there own mount.
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Kevin
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Galaxyhunter
Pooh-Bah
Reged: 01/02/06
Posts: 1257
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I can tell you from experience that building a GEM is not cheap, BUT on the plus side, I know that I can do it and that it was satisfying. I don't want to sound like a snob but ANYBODY with a few bucks (or a lot of bucks) can BUY a mount, It takes a little bit of skill to build one.
If you do build a mount, one very critical area that you absolutely can not skimp on is the two ends of the axles, Where the RA shaft meets the Dec axis & where the Dec axles meets the OTA mounting plate. These two areas are prime points for flexure. When I first built mine, I used a couple of 1" aluminum plates, and that probably would have been fine for visual, but I noticed a slight field rotation during AP. So I built a pattern & had iron castings made. After I machined & installed them, my flexure is basically non-existent.
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Carl
My lousy skies at Hawkeye Observatory
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cnchillstar
super member
Reged: 12/29/08
Posts: 102
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thanks for every warm words,pictures,and links!!!
paramount ME:$14500 even an sencond hand cost 10000 I think it is not what I can offord.
what I have:
Mel&Gary control system:$1020
Byer worm and gear(9"+7.6"):$880
6061-T5 aluminium(China): $4/kilogram * 100=400
Bearings(China)normal tolerance: $15*4=60
Manufacture: estimate $1000(only mill and lathe)
total: &3000+ (scope+mount)
As a work with high precision thing, with 80 percent possibility I can get a non-satisfy result. but steps of modification will improve it...
I work for Chrysler as an engineer, safety mind of automotive industry make me coward for this design. so big shaft, traditional bearing mount method, result as stumpsy box like the pictures show. pillow bearing is easy to aligh and cheap,but I think it can't restrain the shaft for axis direction? and a hollow biger shaft will help to balance strength and stiffness.
this scope will be for free public use(children) if I can make it out. so,safty is very critical to me.
anyway, I believe right direction is more important to fast action. so, Mel servo+Byer gear+taped roller bearing are in the team. thanks for every professional suggestion!!
key mission:
1.shaft diameter(strength,stiffness,weight)
2.bearings(type,dimension,alighment,mount)
3.RA,DEC vertical assymble(better can be adjust)
4.counterweight(safty)
5.plates of body(structure to maintain strength)
6.attitude adjust(maybe learn AP's 3600 model)
7.shafts lock(no idea now, aluminium open block can do it but heavy,can friction belt brake be applied?)
I am not a person with fast action. after drinking some beer,study article and pictures, modify the solidworks model...haha~~ I will post anything I want to ask, please just keep suggesting!
thanks a lot!
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Galaxyhunter
Pooh-Bah
Reged: 01/02/06
Posts: 1257
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Quote:
Mel&Gary control system:$1020
Is this the "SiTech" servo control system?
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Carl
My lousy skies at Hawkeye Observatory
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cnchillstar
super member
Reged: 12/29/08
Posts: 102
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yes,sitech servo system:
1.controller with free softwares----350
2.two motors----310
3.handpad----50
4.two external encoder----260
total:1020
I recieve them for some time, but not very familiar now.
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Galaxyhunter
Pooh-Bah
Reged: 01/02/06
Posts: 1257
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Quote:
I recieve them for some time, but not very familiar now.
Thats what I have driving my scope. There is a lot to this system & once you get used to it, you will love it. If you have not joined the Yahoo user group yet, you can access them HERE.
One thing I would do with your proposed setup is to make some kind of rotating rings revision for the OTA. Putting a newt on a GEM if fine, but without someway to rotate the OTA, there will be times that the focuser is going to be in some really bad viewing angles. Here is my simple rotating ring design.
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Carl
My lousy skies at Hawkeye Observatory
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cnchillstar
super member
Reged: 12/29/08
Posts: 102
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Hi,hunter,thanks for reply!
did you buy software of Mel? I don't buy it, only the basic config software from Gary. still have no idea about meridian problem for GEM mount. and there is no homing sensor, how do you control your scope? through skymap?
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