Catalin Paduraru

#59932

Hi guys,

This is my first post on this group. Sorry for my english, I’m not a native speaker.

I have an old GM8 mount which I want to improve. The actual periodic error is about 54 arc/sec peak to peak. I have the steel worms and two block design.  I’ve attached a picture with PECPrep graphs.

My questions are:

1) Can I improve the actual error using the steel worm?

2) If I change to a high precision worm from Losmandy what would be the best PE I can get? How much better than now? To know what to expect.

3) Can I find the mount’s year of production by viewing the serial number? The serial number is HGM299805084.

What I want to do next to gain some improvements:

1) Change the bearings with new ABEC 5 bearings.

2) Spring washer on one bearing to tension the worm between the blocks.

3) Play with the mesh to find the hot spot.

What I did till now:

1) Clean and grease the mount.

2) I found that at transport the blocks that press the needle bearing and hold the RA axis were misaligned. So I pressed them together to a true. I’ve read about this here on the group.

3) Make a version of OPW. You can see it in the attached picture.

I’ve searched a lot on internet about performances of GM8 but very few details I found. So you are my last chance J

Any suggestions are welcome.

Catalin

#59934

Your first big win will be very likely from the worm gear mesh adjustment, that's definitely worth doing.  I got a large improvement on my mount just be doing that.

Clear skies
Dave Partridge

Show quoted text

-----Original Message-----
From: Losmandy_users@... [mailto:Losmandy_users@...]
Sent: 19 January 2018 08:19
To: Losmandy_users@...
Subject: [Losmandy_users] Losmandy GM8 periodic error

Hi guys,

This is my first post on this group. Sorry for my english, I’m not a native speaker.

I have an old GM8 mount which I want to improve. The actual periodic error is about 54 arc/sec peak to peak. I have the steel worms and two block design.  I’ve attached a picture with PECPrep graphs.

My questions are:

1) Can I improve the actual error using the steel worm?

2) If I change to a high precision worm from Losmandy what would be the best PE I can get? How much better than now? To know what to expect.

3) Can I find the mount’s year of production by viewing the serial number? The serial number is HGM299805084.

What I want to do next to gain some improvements:

1) Change the bearings with new ABEC 5 bearings.

2) Spring washer on one bearing to tension the worm between the blocks.

3) Play with the mesh to find the hot spot.

What I did till now:

1) Clean and grease the mount.

2) I found that at transport the blocks that press the needle bearing and hold the RA axis were misaligned. So I pressed them together to a true. I’ve read about this here on the group.

3) Make a version of OPW. You can see it in the attached picture.

I’ve searched a lot on internet about performances of GM8 but very few details I found. So you are my last chance J

Any suggestions are welcome.

Catalin

[Non-text portions of this message have been removed]

------------------------------------
Posted by: "Catalin Paduraru" <catalin.paduraru@...>
------------------------------------

------------------------------------

Yahoo Groups Links

#59936

Hi Catalin,

If you are capable of doing the mechanical work without damaging the mount and the mount ihows no obvious damage your GM8 should be capable of pretty good tracking. With any project like this you have to be honest with yourself in recognizing your abilities and your limitations to avoid causing more harm than good. That said the basics are the most important considerations. This is what I always do with any equipment I buy new or used. Assess the baseline performance of the system in front of me to see if it meets the needs of the project or use. If the answer is yes use it as is.?

If the answer is no, document performance problems then determine what can be done to bring the system into operational condition. For a high quality mount like the GM8 this should be simple as long as there is no obvious damage, just bring the mount back to manufacturer's stock condition before chasing improved performance. To do this you need to disassemble, remove old lube fully using solvent and blow bearings and all surfaces clean and dry, inspect and assess condition of component parts, replace or repair any components that are not in top mechanical condition. Correctly lubricate (minimal fresh lube) using correct lube for expected environmental conditions and reassemble and verify correct assembly, do not rely on as received assembly order, if in doubt ask here or refer to assembly photos. Adjust worm mesh and reassess performance using the same system used for baseline data. Be sure that your measurement system is valid, if in doubt ask here or on sites that support your autoguider software and hardware.?

Once you have a good working mount and you know the mount is working correctly and is as well adjusted as possible in my experience the single largest improvement to tracking error is changing from the old silver steel colored worms to the brass colored high precision worm on the RA axis. The second option with the most impact on tracking or PE is to put that HP-worm in a one-piece worm block. Other than these two updates careful assembly and adjustment like adding Bellevue spring washers and using good clean bearings on the worms make all the difference. The most obvious issue that adversely affects every EQ mount's tracking error is polar alignment. What to you use to do your polar alignment? The best method I have seen and used is the PoleMaster camera but if you have an autoguider you can also use SharpCap 3.x which can also give you an excellent polar alignment, these two are the best of what I have used.?

?

Chip Louie

?

#59937

开云体育

Catalin,

?

My experience was with a used (made around 2006 I recall – it has the 25 year sticker on it) G-11. I was the second or third owner. I think the first owners bought it and did not know how to adjust it properly.

?

I started out in the same place with about 40 arcseconds of swing in the pattern and it included the dreaded 76 second ?(of time) spike in the pattern, which PEC can not take out. That is usually a result of miss-alignment of the bearing blocks on the worm.

?

I did the following:

?

Replaced the steel worm gears (I did both) with the brass high precision worms. So of course this meant I cleaned and re-greased the worm wheels as well.

?

Replaced ?the worm shaft bearings with upgraded ones like you are talking about. ?I also replaced the bearing blocks (two per worm) because the prior owner had seriously over torqued the bearing blocks. Since the metal is thin and the bearing blocks were cheap I replaced them. Perhaps not necessary.

?

Carefully aligned the bearing blocks by installing them with the mounting bolts finger tight. Then I clamped a metal angle bracket to them (with small soft-jaw clamps) to keep them parallel. Then I adjusted the worm to worm wheel spacing (often referred to as the ‘lash’) to find the high spot on the worm and carefully tightened the worm blocks in place. This took a bit of practice but I was able to completely eliminate the 76 second problem . This was before the one-piece worm blocks were available. But I haven’t had to change it since 2007.

?

Carefully mounted the motors so the Oldham couplers were square and parallel.

?

By doing the above I got the PE down to about +-4 arc seconds, which put it well within range of an autoguider since the slope would be about 4arc sec/60 seconds. So during a three second guider exposure the accumulated error would be 12/60^th = 0.2 arc seconds, which you’ll never see given the atmosphere.

?

I hope you are not trying to image moderate to long focal lengths without guiding.

?

I assume you have a non-Gemini mount. You didn’t say if it was the 492 or the Gemini drives. Some of the other responses, I think, assumed you had the Gemini since they talked about gearboxes. If you have the Gemini, of course, that is something else to worry about.

?

Hope this helps you.

?

Choi,

?

Mark Christensen

?

Catalin Paduraru

#59938

Hi guys,?

Thank you for your feedback.?

Chip

I think I can do all this improvements without damaging the mount. At least part of the hobby is improving my gear and I have experience over the years :)?

I believe?the mount has it's stock specs now. All I want to do is to improve a bit the periodic error. If I'm not happy with the results I will buy the HP worm. At least this is the plan. I don't think I need the OPWB for what I do but will see.

For polar align I'm using the Losmandy polar finder. Is good enough for now. I will try SharpCap also.

I couldn't find belleville washer in my country or ebay so I ordered wave washer. I hope they will do the same job.

Mark

I have the stock mount with?492 digital drive. And using the mount to do astrophotography using 600mm focal length and DSLR camera.?

You have good improvements with your mount.?

For the next clear night I want to try and get the best mesh setup for this worm. And after this I will do the same with the DEC worm. And I have another worm from a friend and try his worm to. And see which worm performs better.?

And I will return with the error to see how good it can be with steel worm, ABEC 5 bearings, wave washer and my version of OPWB.?

Catalin

#59942

Hi Catalin,

Have you read Michael Herman's document in the files about how to optimize your G11 mount? It is the definitive piece for the G11 and GM8 mounts! Shoot me you mailing address and I'll send you the correct Bellevue spring washers. Wave washers are not going to work.

Chip

??

Catalin Paduraru

#59943

开云体育

Hi,

?

Yes, I know the paper Michael made and that was the main reason I started modifying the mount. And I have to admit I love this part J Also because I have I friend with the same mount and we are a team on this journey J

?

The hard part now is waiting for parts.

?

Catalin

?

__

Catalin Paduraru

Tel: (004) 0722.22.75.94

?

Show quoted text

From: Losmandy_users@... [mailto:Losmandy_users@...]
Sent: Sunday, January 21, 2018 10:47 PM
To: Losmandy_users@...
Subject: [Losmandy_users] Re: Losmandy GM8 periodic error

?

Hi Catalin,

?

Have you read Michael Herman's document in the files about how to optimize your G11 mount? It is the definitive piece for the G11 and GM8 mounts! Shoot me you mailing address and I'll send you the correct Bellevue spring washers. Wave washers are not going to work.

?

Chip

??