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How good are the alt/az adjustors on the GM8? As someone who has to setup and tear down for each session, it’s important to me that these adjustors work well with minimal backlash to make polar alignment as straightforward as possible. Thanks! ? Greg
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circa '94 GM8. As long as you are reasonably close of course to have the play in the azimuth direction, I have never had an issue. Bill _____________ Pictor Observatory
Twitter: @pictorobs
Minor Planet 21350 - billgardner
How good are the alt/az adjustors on the GM8? As someone who has to setup and tear down for each session, it’s important to me that these adjustors work well with minimal backlash to make polar alignment as straightforward as possible. Thanks! ? Greg
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On Sun, Jan 26, 2025 at 11:36 AM, Greg Hartke wrote:
How good are the alt/az adjustors on the GM8? As someone who has to setup and tear down for each session, it’s important to me that these adjustors work well with minimal backlash to make polar alignment as straightforward as possible. Thanks!
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Greg
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Many of us here are portable mount users, the adjusters and adjustment locks work fine if you know how to use them.? My best advice.on adjustment is to only loosen the adjuster locks just enough to allow the mount hardware to move a little bit as the adjusters are turned.? Once adjusted don't apply excessive torque to hold the adjustment in position, use just enough to hold the setting no more.?
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If you follow this advice you'll have an easy time getting a good polar alignment.??
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Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
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Thanks, guys. That helps! I have plenty of experience with GEMs and know what great adjustors are like (my A-P 1200GTO) and sketchy adjustors (my MI-250). Adjustors that work properly make PA an enjoyable task and (conversely) those that are sketchy make it truly frustrating. I do indeed use Chip’s methodology (experience tells!) and I infer from Bill’s comment that the GM8 adjustors are good, but not great. They sound good enough to be worth trying. ? Appreciate the help! ? Greg ?
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From: Losmandy_users@groups.io <Losmandy_users@groups.io> On Behalf Of Chip Louie via groups.io
Sent: Monday, January 27, 2025 9:48 AM
To: Losmandy_users@groups.io
Subject: Re: [Losmandy_users_io] GM8 alt/az adjustors? On Sun, Jan 26, 2025 at 11:36 AM, Greg Hartke wrote: How good are the alt/az adjustors on the GM8? As someone who has to setup and tear down for each session, it’s important to me that these adjustors work well with minimal backlash to make polar alignment as straightforward as possible. Thanks! ? Greg
Many of us here are portable mount users, the adjusters and adjustment locks work fine if you know how to use them.? My best advice.on adjustment is to only loosen the adjuster locks just enough to allow the mount hardware to move a little bit as the adjusters are turned.? Once adjusted don't apply excessive torque to hold the adjustment in position, use just enough to hold the setting no more.? If you follow this advice you'll have an easy time getting a good polar alignment.??
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
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I can tell you the GM8 adjusters are much better than the CGEM or AVX.? The secret, as has been noted, is not to loosen them more than necessary when you're going to move them.? I installed knobs so no tool is needed to loosen or tighten.? Some backlash is probably desirable, not something to eliminate.
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Good data point, Michael. Thanks! It really sounds to me as if the GM8 might be among the best light (lighter?) weight non-strain wave mounts available today. ? You’ve been around a long time, so you’ll appreciate this: Way back in the day when I was imaging with an LX-200, I found the adjustors on the Super Wedge to be pretty bad. I modified those babies to incorporate thrust bearings which made the adjustor motions ridiculously smooth and solid with very repeatable adjustment. The result was that ?the modified Super Wedge had the best adjustors of any mount I’ve ever used, even better than those on my A-P 1200GTO. From this, I learned that good adjustors with little backlash and repeatable motions make polar alignment (drift alignment, of course) really easy. ? Greg ?
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-----Original Message-----
From: Losmandy_users@groups.io <Losmandy_users@groups.io> On Behalf Of Michael A. Covington via groups.io
Sent: Monday, January 27, 2025 1:30 PM
To: Losmandy_users@groups.io
Subject: Re: [Losmandy_users_io] GM8 alt/az adjustors ? I can tell you the GM8 adjusters are much better than the CGEM or AVX. The secret, as has been noted, is not to loosen them more than necessary when you're going to move them.? I installed knobs so no tool is needed to loosen or tighten.? Some backlash is probably desirable, not something to eliminate. ? ? ? ? ? ?
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The use of flat thrust bearings is really not needed, there should never be that much force on the lock knob/lever.? If you really feel compelled to mess with the adjustment locks a good cheap compromise modification is to put a ground SS washer under each of the lock knob/lever with a thin plastic washer between the new SS washer and the GM8 or G11 base.? This promotes easier adjustment movement while reducing the undesirable mount movement when the knobs start to get snugged down.?
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I mention using a precision ground SS washer because they will introduce less movement during tightening of the lock knob/lever.?
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Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
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Where does one get the kind of washer you recommend?
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On Jan 27, 2025, at 16:33, Chip Louie via groups.io <chiplouie@...> wrote:
? [Edited Message Follows]
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The use of flat thrust bearings is really not needed, there should never be that much force on the lock knob/lever.? If you really feel compelled to mess with the adjustment locks a good cheap compromise modification is to put a ground SS washer under each of the lock knob/lever with a thin plastic washer between the new SS washer and the GM8 or G11 base.? This promotes easier adjustment movement while reducing the undesirable mount movement when the knobs start to get snugged down.?
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I mention using a precision ground SS washer because they will introduce less movement during tightening of the lock knob/lever.?
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Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
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Greg,
I will be a bit of a contrarian here. ?I find there is quite a bit of slop (backlash) in the adjusters. ?Others here have commented on it before so I don’t think it is just me. ?When reversing direction while adjusting the Az there is probably a good 1/8th revolution before it starts actually moving the Az. ?There is a big change in torque needed when this happens so it is easy to know when you are actually moving it.
The Alt is a bit stranger. ?There is also what feels like 1/10th revolution of slop before it tightens and it starts moving the Alt in the opposite direction. ?However, I do find that sometimes, even when it feels like I’m in the backlash zone, I do see the Az move. ?Not sure why sometimes it move immdiately when reversing and sometimes not.
Even with this backlash, I find it pretty easy to adjust the polar alignment. ?It is not really an issue for me.
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On Jan 27, 2025, at 11:13?AM, Greg Hartke via groups.io <ghartke@...> wrote:
Thanks, guys. That helps! I have plenty of experience with GEMs and know what great adjustors are like (my A-P 1200GTO) and sketchy adjustors (my MI-250). Adjustors that work properly make PA an enjoyable task and (conversely) those that are sketchy make it truly frustrating. I do indeed use Chip’s methodology (experience tells!) and I infer from Bill’s comment that the GM8 adjustors are good, but not great. They sound good enough to be worth trying. ? Appreciate the help! ? Greg ?
--? Bill Tschumy Otherwise -- Longmont, CO www.otherwise.com
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Thanks, Bill. Very helpful! The important point is that it sounds as if the GM8 adjustors are very workable, if not as good as my A-P 1200GTO (on which they are very good). Nothing can be as bad as the adjustors on my MI-250. That’s a great mount, except for the adjustors. In fact, it’s on my list to take the scope off the MI-250 and see if I can rebuild ‘em to something better. It really is a nice mount otherwise! ? Greg ?
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From: Losmandy_users@groups.io <Losmandy_users@groups.io> On Behalf Of Bill Tschumy via groups.io
Sent: Monday, January 27, 2025 5:55 PM
To: Losmandy_users@groups.io
Subject: Re: [Losmandy_users_io] GM8 alt/az adjustors? Greg, I will be a bit of a contrarian here. ?I find there is quite a bit of slop (backlash) in the adjusters. ?Others here have commented on it before so I don’t think it is just me. ?When reversing direction while adjusting the Az there is probably a good 1/8th revolution before it starts actually moving the Az. ?There is a big change in torque needed when this happens so it is easy to know when you are actually moving it. The Alt is a bit stranger. ?There is also what feels like 1/10th revolution of slop before it tightens and it starts moving the Alt in the opposite direction. ?However, I do find that sometimes, even when it feels like I’m in the backlash zone, I do see the Az move. ?Not sure why sometimes it move immdiately when reversing and sometimes not. Even with this backlash, I find it pretty easy to adjust the polar alignment. ?It is not really an issue for me. Bill
On Jan 27, 2025, at 11:13?AM, Greg Hartke via groups.io <ghartke@...> wrote: ? Thanks, guys. That helps! I have plenty of experience with GEMs and know what great adjustors are like (my A-P 1200GTO) and sketchy adjustors (my MI-250). Adjustors that work properly make PA an enjoyable task and (conversely) those that are sketchy make it truly frustrating. I do indeed use Chip’s methodology (experience tells!) and I infer from Bill’s comment that the GM8 adjustors are good, but not great. They sound good enough to be worth trying.
Otherwise -- Longmont, CO ? ?
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I don’t have a lot of experience with mounts since I’ve only owned two Losmandys so, I have no idea what a great adjustment system looks like or how they work ;). However, on both my mounts the Alt knob is quite good with no perceivable backlash. The AZ does have perceivable backlash but it’s easy to work around it. The idea is to work from just one side so, if you are east of the pole and need to move west, move the knob a little in that direction and, the closer you get to a good PA the less you turn the knob so that you don’t go past the pole. Presumably, if you happen to go past it, it will be by a negligible amount and you can leave it like that.
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If you use digital means of PA the process is quite easy and quick. If you do a drift alignment it can take quite a while because of the necessary small movements needed to prevent switching direction, and the slow nature of the procedure to begin with
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My 1.5 cents (not enough info to make up the entire 2 cents lol)
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Jonathan
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On Mon, Jan 27, 2025 at 02:22 PM, Michael A. Covington wrote:
Where does one get the kind of washer you recommend?
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On Jan 27, 2025, at 16:33, Chip Louie via groups.io <chiplouie@...> wrote:
[Edited Message Follows]
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The use of flat thrust bearings is really not needed, there should never be that much force on the lock knob/lever.? If you really feel compelled to mess with the adjustment locks a good cheap compromise modification is to put a ground SS washer under each of the lock knob/lever with a thin plastic washer between the new SS washer and the GM8 or G11 base.? This promotes easier adjustment movement while reducing the undesirable mount movement when the knobs start to get snugged down.?
?
I mention using a precision ground SS washer because they will introduce less movement during tightening of the lock knob/lever.?
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
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Any good hardware store will carry flat ground washers as well as various plastic washers.? Use a slippery plastic, like most types of polyethylene, PTFE or in a pinch I've cut slippery washers from white plastic gallon milk jugs LOL.?
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Also McMaster Carr has these parts as well as nice adjustable handles and knobs to substitute if that's your thing.? But like I mentioned previously it takes minimal torque to reliably hold the elevation or azimuth adjustments.??
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Backlash has nothing to do with the force needed to hold the adjustment.? You should have enough preload on the locks to just hold the mount during the time you use the adjusters.?
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Think of this as two are two different operations, adjustment and locking that unfortunately interact slightly when the locks are applied.? Using ground washers with low friction plastic washers is cheap and more effective than using a thrust washer alone as they remove much of the cause of shift in the adjustment.??
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This little change works for both the old original type adjustment locks where the knob holds the threaded rod and the newer fixed stud used with a knob with a threaded insert type adjustment locks.?
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Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
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On backlash it makes no difference to how well the mount gets adjusted, the Losmandy mounts were designed with some slack in the system. It is just slack that needs to be taken up before anything happens, sort of like a 2-stage trigger. Nothing happens in the slack space or backlash just like a 2-stage trigger.? But just like a 2-stage trigger once the slack is taken up mount movement begins or the gun goes bang.?
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A good practice is to try to approach the ideal position from one direction much like an experienced SCT user will always focus by pushing the mirror up hill.? Once the desired position is achieved with adequate preload the mount won't move before the locks are snugged down.? This is the best practice with any Losmandy mount.?
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Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
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Chip Louie
Bill Tschumy