56 replies to this topic

[Bomber Bob]

One Word:   DREMEL

 

I've about worn mine out carving bolts, brass & aluminum rods, tubes, etc.  Add a tap & die kit, and make your own custom threaded rods & bolts (had to do that with the Mogey).

 

Put an old towel over a counter or table, and teach that metal who The Boss is...

[NinePlanets]

In lieu of a vice, often a big C-clamp can fit the bill.

 

But truly, a bench with a vice, in my opinion, is almost as necessary to life as air or water. 

[spartan1]

Glaucoma, cataracts and trigger thumb dont help me.  It sucks getting old!  Men's shed tomorrow! 

 

I used the scope last night for and was gobsmacked. Jupiter was stunning even through the 25mm MA in Bortle 6 back-yard. I was expecting the worst but the very basic collimation I did indoors proved more than adequate for the test run and I know it can be improved.

 

There was a lot of slop in the DEC axis which I didn't notice before without the OTA and weights on. So I have stripped the mount again and will start from scratch. I'm more confident about working on the mechanics to reduce slop/backlash but struggling with the idea of a push-to Newtonian German EQ mount, having been used to large Dobs and GOTO EQ's!     

[spartan1]

The 628 came with one large weight. The 826 came with two weights, one large and one small.

 

Your 628 looks like it has two small weights in entry #1. One of your weights looks to be slightly larger, but they are both small and close in size. The Meade large weight is about twice the size as the small weight. Your scope might have shipped with two small weights instead of one big one pending supply at the factory or possibly employee error or any number of factors. 

 

Replacing the spider won't degrade intrinsic value when the old spider has disintegrated with metal fatigue. Keep all old parts that you replace if you are worried about preservation for posterity. 

The focusers on my 826 and 628 are both newer looking than yours with plastic knobs and an end ring with set screw. 

Did you replace the focuser on your 628? If so, did you use the existing screw holes and was the new curvature ok? 

 

Secondary mirror - for the 628, is there a 1.3" to 1.52" to 1.8" advantage to be gained? I am no maths expert when it comes to obstruction versus light gathering! 

 

Greasing - Lithium is ok for everything...worm, plastic shaft bearings, circles ?    

[deSitter]

Did you replace the focuser on your 628? If so, did you use the existing screw holes and was the new curvature ok? 

 

Secondary mirror - for the 628, is there a 1.3" to 1.52" to 1.8" advantage to be gained? I am no maths expert when it comes to obstruction versus light gathering! 

 

Greasing - Lithium is ok for everything...worm, plastic shaft bearings, circles ?    

For f/8 you want a 1.5" secondary in a 6". You can get away with a smaller one but will lose low-power versatility. Contrast loss at 25% will be negligible. If the secondary is too small you lose light in the outer part of the field of view at low power. 1.8" is way too big. A small secondary is usually paired with a "low rider" focuser where the image is close to the tube. This is much harder to set up correctly but results in a small gain in contrast. There are specialty f/10 Newtonians with small secondaries dedicated to lunar and planetary work. But the f/8 scope is generalist and needs a 1.5" secondary IMO. That's the classic setup.

 

-drl

[apfever]

Did you replace the focuser on your 628? If so, did you use the existing screw holes and was the new curvature ok? 

 

Secondary mirror - for the 628, is there a 1.3" to 1.52" to 1.8" advantage to be gained? I am no maths expert when it comes to obstruction versus light gathering! 

 

Greasing - Lithium is ok for everything...worm, plastic shaft bearings, circles ?    

I did not replace anything, especially the focusers, on any of my 826, 628, or Starfinder GEM 6" and 8" scopes.  I have no need to modify major parts of a vintage scope I'm fixing up because I have other scopes to use. The more major an aspect is, the less likely I am to change it. I do a lot of mods when I fix up a scope, but most are small things like hardware or clearances. I will make major changes on things that never worked from the factory or were just horribly done. I keep mods minimal on major flaws, especially infamous flaws, to preserve the factory flub as much as possible and be user friendly. This all becomes a subjective shade of gray, to each his own. A tall focuser is OK with me if it works OK and was factory, a secondary that vignettes on axis rays is NOT ok with me (major engineering flub). 

 

You can stay with your original 1.3" secondary if there are no other issues with it besides size. I would go with a 1.5" if I was going to change it for other reasons. I measured my 628 (yours might have a different height focuser). I have 7.25" from the secondary to a point 1/4" above the racked in focuser. The math shows that a minimal size secondary capable of using the whole 6" primary only needs to be 0.91" minor axis. Another way to state this is that the secondary only needs to be .91"  for on axis rays. On the practical side, you need to be bigger if you view anything besides stars or planets. The original 1.3" secondary will let you see the full moon with no light loss at the edge.   ONLY for you techies: A 1.3" secondary gives a 0.56" fully illuminated field. A 1.5" secondary gives a 0.84" fully illuminated field. 

 

I suggest being leery of grease request. You are in a forum of some upper end folks that will spout specs and fancy expensive grease and lubes and such along with how awesome their product suggestion is. I use garage sale finds. You have a 6" telescope, not a factory custom 1928 Pierce Arrow automobile. Modern lithium grease should work for a generation or two, it has in the past. You can do better than lithium now. Get a small tube, you don't need a can unless you do your own car work. I find a good axle grease to work around the house in general. I use butter on door latches and strike plates because the kitchen is centrally located.

[spartan1]

I did not replace anything, especially the focusers, on any of my 826, 628, or Starfinder GEM 6" and 8" scopes.  I have no need to modify major parts of a vintage scope I'm fixing up because I have other scopes to use. The more major an aspect is, the less likely I am to change it. I do a lot of mods when I fix up a scope, but most are small things like hardware or clearances. I will make major changes on things that never worked from the factory or were just horribly done. I keep mods minimal on major flaws, especially infamous flaws, to preserve the factory flub as much as possible and be user friendly. This all becomes a subjective shade of gray, to each his own. A tall focuser is OK with me if it works OK and was factory, a secondary that vignettes on axis rays is NOT ok with me (major engineering flub). 

 

You can stay with your original 1.3" secondary if there are no other issues with it besides size. I would go with a 1.5" if I was going to change it for other reasons. I measured my 628 (yours might have a different height focuser). I have 7.25" from the secondary to a point 1/4" above the racked in focuser. The math shows that a minimal size secondary capable of using the whole 6" primary only needs to be 0.91" minor axis. Another way to state this is that the secondary only needs to be .91"  for on axis rays. On the practical side, you need to be bigger if you view anything besides stars or planets. The original 1.3" secondary will let you see the full moon with no light loss at the edge.   ONLY for you techies: A 1.3" secondary gives a 0.56" fully illuminated field. A 1.5" secondary gives a 0.84" fully illuminated field. 

 

I suggest being leery of grease request. You are in a forum of some upper end folks that will spout specs and fancy expensive grease and lubes and such along with how awesome their product suggestion is. I use garage sale finds. You have a 6" telescope, not a factory custom 1928 Pierce Arrow automobile. Modern lithium grease should work for a generation or two, it has in the past. You can do better than lithium now. Get a small tube, you don't need a can unless you do your own car work. I find a good axle grease to work around the house in general. I use butter on door latches and strike plates because the kitchen is centrally located.

Thanks for explaining in detail. I was an antique dealer and understand 'over-restoration'. You have reminded me! I think I will stay with the original focuser....its only the split eyepiece-holder that concerned me so I'll squeeze it a bit. 

Did the 628's all come with a split flange bush at the back of the axis? I have been trying to find where my 'slop' is coming from and it does not appear that the worm needs adjusting - but when the clutch is under pressure I can see a small side movement in the axis itself before it moves. The flange bush is intact and does not look worn to me, but it is 40 years old. Getting replacement parts like that here is not easy so I need to get it right. I am wondering whether I should get a standard rather than a split bush or whether the split one is the way to go.  

[apfever]

Your plastic bushing might be fine. Meade had a tendency to have the housing bores a hair too big. They fixed the oversized bores by peening them to pinch the bushings. The peening seems to have been done manually and is inconsistent with the bores ending up a bit too tight sometimes. I had one mount where the RA bore was peened so tight the scope wouldn't work. The RA axis could be budged by hand but the shaft was so tight the drive wouldn't turn it. I had to sand out the peening bumps. 

 

I don't like the peening. I'd shim the flange bush before peening the bore. I'm not sure how I'd shim a flange bush but I'd do it. I have some .0035" plastic that I think is Lexan. I could use that to make a shim flange bush. 

[spartan1]

Your plastic bushing might be fine. Meade had a tendency to have the housing bores a hair too big. They fixed the oversized bores by peening them to pinch the bushings. The peening seems to have been done manually and is inconsistent with the bores ending up a bit too tight sometimes. I had one mount where the RA bore was peened so tight the scope wouldn't work. The RA axis could be budged by hand but the shaft was so tight the drive wouldn't turn it. I had to sand out the peening bumps. 

 

I don't like the peening. I'd shim the flange bush before peening the bore. I'm not sure how I'd shim a flange bush but I'd do it. I have some .0035" plastic that I think is Lexan. I could use that to make a shim flange bush. 

The rear of the RA bore is 1.075" and the 1" split-flanged bush is 1.05" OD when compressed. So I have 0.025" of play in total. I am trying to wrap a piece of plastic file folder 0.006" around the OD of the bush which would reduce the play to 0.013" I have not succeeded yet...a very fiddly excercise - the best alternative is to find a larger OD bush but I am having difficulty finding one at all here in Western Australia.   

[apfever]

I made this quick cut demo out of paper with no lines, no layout, no measurements, just quick snip.  A carefully made one should be quite nice. 

You could make two out of your folder file material, and wrap around the outside of the original bushing so the shim is between bushing and bore. 

 

You don't have to worry about the shim being slippery. The shaft is meant to turn in the bushing, not the bushing in the bore. The only problem with using tape is that you don't want adhesive to possibly creep in to the shaft. 

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[spartan1]

I made this quick cut demo out of paper with no lines, no layout, no measurements, just quick snip.  A carefully made one should be quite nice. 

You could make two out of your folder file material, and wrap around the outside of the original bushing so the shim is between bushing and bore. 

 

You don't have to worry about the shim being slippery. The shaft is meant to turn in the bushing, not the bushing in the bore. The only problem with using tape is that you don't want adhesive to possibly creep in to the shaft. 

Yes, paper definitely easier to work with. I've made it better now using cheap copier paper around the outside of the bush. I may try thicker paper but it tends to bind up and is difficult to get the shaft to go through after fitting it. But there may also be some slop at the front end of the shaft where there is no bush, just a plastic spacer. Did you have any remedy for that end?

[NinePlanets]

Brass or steel shim is a good bet too. Easily snipped with scissors and won't swell.

 

My 2 cents...

[deSitter]

Brass or steel shim is a good bet too. Easily snipped with scissors and won't swell.

 

My 2 cents...

Make something from a beer can?

 

-drl

[apfever]

I never meant to actually use paper, that was just a demo.  I would use plastic or metal, not paper.

[spartan1]

I never meant to actually use paper, that was just a demo.  I would use plastic or metal, not paper.

I had to laugh when I read your last! Paper actually works remarkably well in this dry/non-revolving scenario but I will look out for a thin plastic to replace the paper.

[Silent_Light]

Had astrosystems make one for a 628 I restored, fits like a glove; I machined all new secondary holder assy as the original pot metal crumbled apart like a cracker....</p>

Edited by Silent_Light, 12 January 2024 - 10:01 PM.

[scribbleben]

Hello,

Thanks for all the info in this thread. I pick up a Meade pier and equatorial mount, and google image search tells me it's the same--or very similar to--Meade 628 in this thread. I'm hoping to mount a 6 inch reflector on it. The current mount is for an 8" scope.

 

I'm a bit confused about its behavior. The vertical (declination?) axis has a nylon threaded rod with an aluminum knob that tightens it but doesn't quite lock it.

 

The equatorial (x?) axis moves freely and doesn't seem to have a lock knob. The scale spins freely relative to the axis.

 

The electric motor runs but doesn't have a switch or a lock knob that I can see. 

What am I missing? Is the worm gear in the motor box stripped? People have mentioned a clutch in this thread... could there be clutch in the motor box that needs some love?

Is there a way to use the mount without the motor?

 

Has anyone seen a user's manual or parts list for it?

 

And finally … the one I purchased also has slop in the pitch setting (FYI). Nylon, Delrin, or brass washers will tighten it up I think.

[spartan1]

Hello,

Thanks for all the info in this thread. I pick up a Meade pier and equatorial mount, and google image search tells me it's the same--or very similar to--Meade 628 in this thread. I'm hoping to mount a 6 inch reflector on it. The current mount is for an 8" scope.

 

I'm a bit confused about its behavior. The vertical (declination?) axis has a nylon threaded rod with an aluminum knob that tightens it but doesn't quite lock it.

 

The equatorial (x?) axis moves freely and doesn't seem to have a lock knob. The scale spins freely relative to the axis.

 

The electric motor runs but doesn't have a switch or a lock knob that I can see. 

What am I missing? Is the worm gear in the motor box stripped? People have mentioned a clutch in this thread... could there be clutch in the motor box that needs some love?

Is there a way to use the mount without the motor?

 

Has anyone seen a user's manual or parts list for it?

 

And finally … the one I purchased also has slop in the pitch setting (FYI). Nylon, Delrin, or brass washers will tighten it up I think.

 

I have sent you a pm regarding the manual. The electric motor does not have a switch, it runs constantly. It is basically a 'push-to' scope, rather like a Dobsonian. Open the plastic box and all will be obvious. I doubt the worm is stripped and its probably that the clutch screws need adjusting for the necessary grip. The worm casing may also need some adjusting.  For a 6" scope, just buy a set of rings...they are just threaded attachments. You can take the whole mount apart in 5 minutes...it is not difficult. I renewed bolts and nuts and tightened everything up. I have not managed to get rid of all the slop yet.  That is a fine art. Test the motor without any weights or the OTA mounted. Leave it running for an hour and check the movement. Then put the weights on and then the OTA...balance is VERY important if you want the motor to run and the clutch to do its job. Mark the OTA tube with a line where the rings are when you have perfect balance (dont forget to put an ep in).   Dont use WD40 anywhere near the clutch. Then take her outside and see how the tracking goes.  Yes, you can use the scope without using the motor...it can be pushed/nudged.    

[spartan1]

I have forgotten much of my school maths, calculating moments of force, fulcrums, etc, etc. So I am going to ask the question here.

 

My 628 has two counterweights...it needs them both in order to balance the OTA...but only marginally. So really I am loading 2 counterweights just to get a few extra ounces onto the shaft.

 

Is it better to just add a small magnet to one of the weights and locate that weight at the furthermost end of the shaft - rather than have two counterweights located midway along the shaft. Whilst the turning momentum maybe the same, the extra weight must put additional pressure on the shaft bearings and place more strain on the clutch?  Or do I need to go back to school? 

 

Thanks...

[deSitter]

I have forgotten much of my school maths, calculating moments of force, fulcrums, etc, etc. So I am going to ask the question here.

 

My 628 has two counterweights...it needs them both in order to balance the OTA...but only marginally. So really I am loading 2 counterweights just to get a few extra ounces onto the shaft.

 

Is it better to just add a small magnet to one of the weights and locate that weight at the furthermost end of the shaft - rather than have two counterweights located midway along the shaft. Whilst the turning momentum maybe the same, the extra weight must put additional pressure on the shaft bearings and place more strain on the clutch?  Or do I need to go back to school? 

 

Thanks...

There is no preset answer. Every position of the weights will have different vibration modes. In general it is better to have the weights out of phase with the counterweight shaft, that is, not on a node where the bar is divided into integer intervals. All the way to the end is not good. You are almost always better off with more  weight and shorter shaft. The moment arm is the same for the same scope payload so the torque needed to get it moving is the same.

 

-drl

[apfever]

Going back to school is a noble thought regardless. I used to teach math in college up through post calc, but that was over 30 years ago. Math is not like a bicycle, it's more like a foreign language. If you don't use it, you lose it.  I've lost a lot.

 

I prefer less total weight.  In a case like yours that just exceeds one weight, I put as much as I can against the mount and adjust with the other. It is more personal preference with how much you change things accessories, how long you want a weight shaft to be, aesthetics can count.  My Meade 6" Starfinder GEM came with the single larger weight. My 8" Starfinder GEM came with one large and one small. My Starfinder mounts and 826/628 mount have the same length shafts and weight(s).

 

EDIT: drl's comment about harmonics is a blast to the past and makes sense but I don't recall the shaft ever being a place to finger dampen vibrations. I'm strictly visual and that helps. I'll dampen by hand on the OTA and pier/mount. I'll also finger dampen a windy spider assembly on larger newts. 

Edited by apfever, 21 January 2024 - 09:17 AM.

[scribbleben]

I have sent you a pm regarding the manual. The electric motor does not have a switch, it runs constantly. It is basically a 'push-to' scope, rather like a Dobsonian. Open the plastic box and all will be obvious. I doubt the worm is stripped and its probably that the clutch screws need adjusting for the necessary grip. The worm casing may also need some adjusting.  For a 6" scope, just buy a set of rings...they are just threaded attachments. You can take the whole mount apart in 5 minutes...it is not difficult. I renewed bolts and nuts and tightened everything up. I have not managed to get rid of all the slop yet.  That is a fine art. Test the motor without any weights or the OTA mounted. Leave it running for an hour and check the movement. Then put the weights on and then the OTA...balance is VERY important if you want the motor to run and the clutch to do its job. Mark the OTA tube with a line where the rings are when you have perfect balance (dont forget to put an ep in).   Dont use WD40 anywhere near the clutch. Then take her outside and see how the tracking goes.  Yes, you can use the scope without using the motor...it can be pushed/nudged.    

Thanks for the PM and all the info. I have rings for the 6" ready to go, no problem there. I'll open up the motor box and have a look at the clutch. From the conversation below it sounds like I'll have a bit of an adventure balancing the scope and the counterweights.

Thanks for the help! I really appreciate it :-)

[bjkaras]

Indeed!  Thanks for the first-hand info.  I wonder... did Tasco apply the same mark-up to the scopes they sourced from Vixen (like the 8V) around that time??  Heck!  I thought PARKS was a rip-off... Tasco may have beat them.

I can attest to Parks being kind of a rip off. Not for the scope, because I thought the price at the time was reasonable. The issue came later. I bought mine before the latitude adjustment became standard, so a few years later I contacted them about buying the parts to install it myself. I was quoted $450, so I said thanks but no thanks.

[spartan1]

After a good amount of faffing around with nuts/bolts/bookcase shelf supports/grinders (neighbor), I went to the local men's shed and they made me four new vane holders out of brass rod, turned and threaded to fit. A donation of $50 (US  ) was accepted. Good result all round. Wish I hadn't wasted time trying to figure out how to do it cheaper!  And I have the original assembly/mirror still in place, so I am pleased. 

 

Now looking at castors for the GEQ. The threaded holes are 1/2" but M12 will do. I am looking at 2-3" wheels with a levelling adjuster.   

https://www.ebay.com...tm/134471718387 look ideal...I am preferring these to a locking wheel type with no adjustment, especially since the scope is really a 'push-to' - I dont trust the wheels to be rigid enough to stay still whereas the screw down levelling system should provide that stability plus a leveler? I'll need to buy a longer M12 bolt. 

 

 

 

 

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[deSitter]

I think you want softer rolling wheels! That will clatter along and affect the optics. Semi-soft wheel, not solid plastic.

 

-drl