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Orion single speed crayford slop

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#1 airbleeder

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Posted 11 January 2017 - 12:10 PM

   There is slop in my Orion single speed crayford focuser allowing drawtube to move within the focuser. My laser dot shifts about 2mm on primary as OTA is rotated. I have checked all scope components and believe the slop is "inside" focuser. Is there a way to adjust it to tighten it up?

Edit: to add that it is a crayford.


Edited by airbleeder, 11 January 2017 - 01:56 PM.


#2 Eddgie

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Posted 11 January 2017 - 01:16 PM

In most cases there is but it depends on what kind of focuser.

 

Here are the scenarios.

R&P.  Top glide is worn..  Fixed by the screws along the top of the focuser.  Not a common failure though, and excessive adjustment is a symptom of worn glides, but this is the first place to start.   If tightening them reduces the slop by give you less than smoot movement, then the glides may be bad.

 

It is a rack and pinion and the glides inside the focuser housing that support the focuser are worn out..   Difficult to fix.    You can put Teflon tape on the glides and this will help a bit or you can grease it and this will help a bit, but I have had two of these kinds of focusers that were never restored to new operation even after repeated attempts to do so.

And the Teflon Tape idea originated with me.   I was the one that got Scopestuff to start selling small strips.   My success though was marginal at best.   

 

The other symptom of worn glides is slop in the rack and pinion though there are other causes of this as well, but your problem is the tube has slop so this indicates a bearing issues. (the glides are bearings. They are curved channels milled into the inside of the focuser and they have a clear plastic film on them.  When this film wears, it creates the play).

 

Crayford.   Typically the Crayford gets loose with use and the solution is to look for the two small hex screws on on either side of the bottom of the housing in line with the pinion shaft.   Very slightly tighten each one maybe an 8th turn at a time to see if the condition Improves.   If it does all is good, but of not, you may have a bearing failure.

 

This usually only occurs with very heavy loads and the way you can identify it is to see if there are scatches on the draw tube when fully extended.  Not even wear tracks, but scratches.  This will occur as the bearing race drags on the tube.  Easy to fix, but the focuser usuallly has to come off and this is often harder than the actual act of replacing the bearing.



#3 airbleeder

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Posted 11 January 2017 - 02:07 PM

   Thanks Ed. Sorry I forgot to specify that it is a crayford. I don't see any scratches on the drawtube, but after reading your post I tried tightening the two hex screws on back side of focuser. They were pretty tight one wouldn't budge and I barely noticed the other moving, but it did seem to help some. Maybe .5 mm or so improvement. 



#4 Eddgie

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Posted 12 January 2017 - 09:27 AM

Well, something is not right then.

 

While you don't see scratching, you may want to drop the focuser and check the bearings.  If it is the front bearings, then the focuser may not rack out enough to expose scratches and you should be able to feel that the focuser is not moving smoothly. 

 

I doubt that they have failed because tiny little ball bearings would be rolling around in the tube but they could be in the process of failing.

The other thing to try would be to take the pinion assembly off and check the nylon bearing that holds the pinion shaft against the tube flat.  If this is worn, you may be able to address this by putting a thin shim between the screws that are used to adjust the bearing and the bottom of the bearing (as I recall, there is a little metal plate between the screw tips and the nylon bearing).

 

There is not much to these.  It has pretty much got to be either approaching ball bearing failure or nylon bearing wear.  There really isn't any other possibility beyond these (unlikely that the pinion shaft has worn down 2mm.)

Keep us posted.  Some of these single speed scopes have been out there for 10 years now and I would guess that sooner or later we will see some of them start to show these kinds of failures. 



#5 airbleeder

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Posted 12 January 2017 - 11:36 AM

   Thanks Ed. I will check it out and because the pinion is only riding on the edges of the tube flat it might be a good time to file it down flat.


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#6 Jon Isaacs

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Posted 12 January 2017 - 11:44 AM

   There is slop in my Orion single speed crayford focuser allowing drawtube to move within the focuser. My laser dot shifts about 2mm on primary as OTA is rotated. I have checked all scope components and believe the slop is "inside" focuser. Is there a way to adjust it to tighten it up?

Edit: to add that it is a crayford.

 

- Let me ask you some questions:

 

How is the focuser otherwise?  

 

Do you use a Paracorr or other coma corrector?

 

Do you use a Barlowed Laser technique to adjust the primary tilt?

 

Have you verified that the laser itself is collimated and does not shift when rotated in the focuser?

 

- Some thoughts and comments on collimation:

 

The tolerance on the axial alignment of the focuser, that is the tilt of the secondary, is 0.03/D. For a 200mm scope, that is 6mm so if you are always within 2mm, that is within tolerance. If you use a Paracorr or other coma corrector, you need better alignment.

 

With any laser collimator one should be adjusting the primary with the Barlowed Laser and not the return beam so that 2mm error does not come into play with collimating the primary mirror.

 

It is possible that it's the laser, it could be a poor fit in the drawtube, in the adapter, something could be flopping inside.  

 

If you are not using a coma corrector and use the Barlowed Laser Technique to adjust the primary tilt, you should be OK with the focuser as it is.

 

Jon



#7 gene 4181

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Posted 12 January 2017 - 01:27 PM

   Thanks Ed. I will check it out and because the pinion is only riding on the edges of the tube flat it might be a good time to file it down flat.

the  focuser on my 8in f6 was like this, took  it apart and used a flat mill file, refiled the flat  . The way they had it, it was concaved from center out . Now it works  very  well.    :)


Edited by gene 4181, 13 January 2017 - 01:19 AM.

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#8 airbleeder

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Posted 12 January 2017 - 05:32 PM

 

   There is slop in my Orion single speed crayford focuser allowing drawtube to move within the focuser. My laser dot shifts about 2mm on primary as OTA is rotated. I have checked all scope components and believe the slop is "inside" focuser. Is there a way to adjust it to tighten it up?

Edit: to add that it is a crayford.

 

- Let me ask you some questions:

 

How is the focuser otherwise?  

 

Do you use a Paracorr or other coma corrector?

 

Do you use a Barlowed Laser technique to adjust the primary tilt?

 

Have you verified that the laser itself is collimated and does not shift when rotated in the focuser?

 

- Some thoughts and comments on collimation:

 

The tolerance on the axial alignment of the focuser, that is the tilt of the secondary, is 0.03/D. For a 200mm scope, that is 6mm so if you are always within 2mm, that is within tolerance. If you use a Paracorr or other coma corrector, you need better alignment.

 

With any laser collimator one should be adjusting the primary with the Barlowed Laser and not the return beam so that 2mm error does not come into play with collimating the primary mirror.

 

It is possible that it's the laser, it could be a poor fit in the drawtube, in the adapter, something could be flopping i

 

If you are not using a coma corrector and use the Barlowed Laser Technique to adjust the primary tilt, you should be OK with the focuser as it is.

 

Jon

 

   Jon, let me start by answering your questions.

    The focuser works very well othewise, handles the ES 68* 34mm very well.

    I do not use a coma corrector.

    To collimate the primary, I either use a 2" Telecat or a Glatter 1.25/2" laser with a 1.25" Tublug inserted into a 1.25" parallizer which I leave in the scope for my 2" to 1.25" adapter. As far as checking laser collimation, I set the screw after each 90* rotation until I have rotated 360*. In the 2" mode, the laser spot stays pretty much dead on (barely any noticeable wandering), but in the 1.25" mode inserted in the parallizer, it wanders probably 2mm. 

   I have checked a couple other things and have somewhat reached a conclusion concerning the registration, but really want to check some more before I jump the gun and post something that isn't so.

   I still believe the slop is inside the focuser because I can put just a little pressure on the draw tube and laser beam moves to center, but putting pressure on the focuser housing has very little effect.

   I understand the tolerance by your post but now that I see a registration error also, I'm thinking it might be out of tolerance.

   I have company on the way but when she leaves I will look into it somemore and post. Thanks for your help.



#9 airbleeder

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Posted 12 January 2017 - 05:33 PM

 

   Thanks Ed. I will check it out and because the pinion is only riding on the edges of the tube flat it might be a good time to file it down flat.

the  focuser on my 8in f6 was like this, took  it apart and used a flat mill file, refiled the flat  . The way they had it, it was concaved from center out . Now it works  very good. 

 

Does the mill file smooth the surface well or will I need some sandpaper too?



#10 gene 4181

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Posted 13 January 2017 - 01:26 AM

 airbleeder, I just used a small fine flat mill file and didn't overdue it , just took out the high spots along the  outside edges. Re-assembled it, adjusted the allen tension screw and  it was much better .  No more rocking in the  focuser body . 


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#11 Jon Isaacs

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Posted 13 January 2017 - 08:26 AM

I still believe the slop is inside the focuser because I can put just a little pressure on the draw tube and laser beam moves to center, but putting pressure on the focuser housing has very little effect.
   I understand the tolerance by your post but now that I see a registration error also, I'm thinking it might be out of tolerance.
   I have company on the way but when she leaves I will look into it somemore and post. Thanks for your help.

 

 

I just wanted to point out that a 2mm shift maybe bothersome but it probably doesn't affect the quality of the views. 

 

Jon



#12 Eddgie

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Posted 13 January 2017 - 10:16 AM

I have to agree that 2mm of shift at the objective is such a tiny amount of play that it could be ignored for now if the focuser works well with light motion and no image shift while focusing at the highest power typically used.

 

For now though, he could just live with it, but if it starts to get worse, I suspect that he is getting wear on either then pinion bearing or on the roller bearings. 

 

The sign of roller bearing failure is that the image shifts when focusing at high power.  

 

If the OP does not have this condition and the focuser motion is smooth and light, as you suggest, there may be little reason to bother with it now. 

 

Me?  I would be looking for the problem.  It may be telling the OP that something is wearing.   A properly functioning and adjusted Crayford should have zero play.  It may be that the wear is not sufficient to take the focuser out of service at this time, but if it is a roller bearing wearing out,  these things don't get better on their own. :(

 

I absolutely agree though that if the focuser is otherwise working well with light smooth motion and no image shift, then there is no harm in using it. It may never get worse and if it does the OP can deal with it at that time and it will be easy to troubleshoot because the reason will be obvious.  


Edited by Eddgie, 13 January 2017 - 10:40 AM.


#13 airbleeder

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Posted 13 January 2017 - 10:27 AM

   I understood that ,Jon and I appreciate you making me aware of what the tolerance is because I didn't really know how to figure it. I was trying to clarify that I believe I have two issues going on, registration and slop. Having said that, I am now not sure if I am still within tolerance. 

   Jon, I have a couple of questions: Assuming the laser is collimated, where might the problem lie if the beam is centered in 2" mode( without any adapter), but is not centered when inserted into a 2-1.25" adapter without rotating adapter to center the beam? Is there any way the 2" adapter which screws into the top of the drawtube could cause this?


Edited by airbleeder, 13 January 2017 - 10:31 AM.


#14 Eddgie

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Posted 13 January 2017 - 11:01 AM

And I have had to replace bearings in Crayford focusers twice.  They can wear out. 

Symptom is play and excessive tension on the pinion adjustment screws is required to keep the focuser tube from deflecting away from the rear bearings under load and my bet is that if the front pair of bearings are wearing, it is only a matter of time before the OP starts to experience more serious symptoms and potential damage to the focuser

 

The front bearing pair is the pair that will wear first because it carries much more of the load.  The pinion acts as a pivot point and the load acts like the bigger kid on one side of the seesaw so that the front of the weight is being focused on the front of the focuser tube. For scopes that have a fixed orientation (Newtonians and refractors with Alt-az mounts or rotating focusers) the front bearings do all the work really. The rear bearings just kind of guide the tube and keep it from shifting side to side. 

 

And the bearings in these scopes are tiny.   I don't think they are really up the task of heavy laods.

 

I notice that Moonlight now sells heavy service Crayfords with two pair of dual bearings at each point.

In other words, while the OP only has four bearings, the heavy duty 2.5" Crayfords from Moonlight now have sixteen bearings!  

 

(The damage that occurs with front bearing failure is that the bearing will start to drag on the tube.  This drag will cause marring in the tube surface and this will cause slight roughness in the motion of the focuser. 

The bad news is that once this occurs, if it is serious enough, it does not go away when you put in the new bearings and you have to carefully smooth the roughness with suitable tools. 

 

You can't take off two much material.  Ask yourself what happens if you cut one leg of a chair slightly shorter than the other leg and you will know why I am saying this.

 

So, that is why I would be looking for the problem sooner rather than later. If you scuff or mar the tube finish it can cause a very slight degradation of the silky smooth Crayford focuser movement.

At the first sign of a bearing dragging, stop using the focuser or the damage will quickly build. 



#15 Eddgie

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Posted 13 January 2017 - 11:10 AM

And for anyone reading this  that has a Moonlight focuser, the good news is that it is easy to see approaching bearing failure in a Moonlight because you can see the tracks the bearings leave on the anodizing.

 

The tracks should all look super smooth and super even.    If any of the tracks show even the slightest sign of scratching or galling you have a failed bearing and my advice would be to stop using the focuser and replace the bearings immediately. 

 

Again, these bearing can and do fail and knowing the symptoms can save some pain down the road. 

 

I would encourage people using Crayfords on dobs with high moment loads (Paracorr and 31mm Nagler or Binoviewers to inspect the bearing tracks regularly for signs of a bearing dragging or race wobble. 

 

I have lost all of the pictures I had of the damage on my Moonlight tube when I had to reload my computer, but once you know what to look for it is easy to see.  Tracks should all be perfect and a track that shows any deviation from the other three should be investigated. 


Edited by Eddgie, 13 January 2017 - 11:13 AM.


#16 Starman1

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Posted 13 January 2017 - 03:17 PM

   There is slop in my Orion single speed crayford focuser allowing drawtube to move within the focuser. My laser dot shifts about 2mm on primary as OTA is rotated. I have checked all scope components and believe the slop is "inside" focuser. Is there a way to adjust it to tighten it up?

Edit: to add that it is a crayford.

The focuser is likely to be a "red herring" if it is adjusted tight enough to hold your 34mm eyepiece when focusing.

The most likely culprit is the secondary shifting in the tube.

The causes:

1) a too-loose spider for the secondary mirror or a curved secondary spider.  This will allow shift in the collimation as the scope is rotated or moves up and down in its pointing direction.

The cure is to tighten the spider until it emits a high pitch when struck.  If this begins to dimple the tube, add fender washers under the nuts to distribute the pressure.

2) a secondary holder that is too loose in the spider.  If the center bolt wiggles around when the center nut is loosened, then shim the bolt where it passes through the spider (teflon tape or toothpick parts)

until it cannot move, then tighten down the nut until snug.

3) the secondary can be moving in its housing.  If it is a hollow holder with some padding behind it and a lip around the mirror to hold it, it could easily wiggle from side to side when rotating.

I suggest having enough padding material behind the mirror to hold it in place and not let it rattle in the holder.

If none of these applies, then I would loose to the truss poles and their connections.  If it's a full tube scope, that won't be relevant.

It might be in the focuser, but somehow, I just doubt it.



#17 airbleeder

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Posted 13 January 2017 - 04:16 PM

   Don, it is a solid steel tube. When I support the drawtube with my hand as tube is rotated I see no movement, but if I don't support it, I do. If I support the focuser housing with my hand, I see movement as OTA is rotated. The spider is so tight the steel tube shows signs of collapsing with the fender washers. I also have wrapped the secondary center screw with teflon tape so it is pretty snug. I was still suspecting the secondary until I tried holding the drawtube. The rear bearing hex heads are very tight as is the pinion tensioning screw. So tight I think that it might wear the bearings.

   I understand according to Jon's post that I should be ok, but I think it wouldn't hurt trying to improve it if it can be done without too much trouble. The scope is on a GEM so I have tried to tighten it up along the way.

  The primary was flopping around until I added edge supports at the COG. I added stronger springs. Tightened up the secondary. Now I am on the focuser. Before I started the scope had about a 6mm shift through rotation, now down to 2 and I'd just like to see if I can get anymore out. It's really more of a learning thing than a necessity and I don't plan to take away any viewing time with the scope. Just tinkering is all. I do thank all for advice.


Edited by airbleeder, 14 January 2017 - 10:28 AM.


#18 airbleeder

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Posted 14 January 2017 - 02:51 PM

   Don, I now think you are probably right about the focuser being a red herring. The focuser seems to be in good shape. I did file the drawtube flat so it's actually flat now and I can ease off the tension some. Still has a smooth focus. 

   I also found a 2-1.25" adapter which provides a good consistent registration, so I feel the 2mm movement is still within tolerance as Jon stated. I will leave for another day when I have nothing else to worry about. Thanks guys.



#19 Night shift

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Posted 14 January 2017 - 04:17 PM

I recently replaced my Orion single speed that had a bit of slop, for a Moonlite CR and I must say it was a good investment. Very happy with the product and performance. 


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#20 Phil Sherman

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Posted 17 January 2017 - 01:30 PM

While your focuser may have slop in it, I'd suspect that that's not the cause of the shift you're seeing when changing tube positions. The first test I'd try is to move the focuser to the full in position and look for the problem as you rotate the tube. With the focuser set full in, you have the lowest possible stress on the draw tube and the draw tube should be fully resting against the focuser body, preventing any movement. If you still see shifting of the laser dot, then the next place to look is distortion of the scope tube from the weight of the focuser. You could repeat this test with the focuser a short distance out and shims cut from a piece of plastic pipe to again prevent focuser tilting. I used this shimming technique for a number of years when attaching a DSLR to the focuser.

 

Orion recognized this is a potential problem and added a steel backing plate to the focuser area of the tube in their f/4 imaging Newtonian. You could get some lightweight steel sheet from any Home Depot (or probably Lowe's) and make a double or triple layer sandwich to add to the inside of your scope's tube The focuser mounting bolts will hold it in place and some flat  black spray paint will handle any reflections from it.


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