Ishan Mair

On 20/12/2019 at 14:24, teoria_del_big_bang said:

Yes those are the bearings I meant.

They only need to be tight enough that the rollers are always in contact with the race. So I would not say make them loose but it is very east to over tighten them when using tools to tighten them. But unless you are a body builder then I would say it is difficult to over tighten by hand, but do not leave them loose at all.

I

Essentially they need very little pre-load, if any, you just need to sure there is no movement at 90 degrees to the bearing (I hope that makes sense). See my very bad quick sketch below.

 

I've run into a related problem on my HEQ5 Pro. When I hand tighten the RA nut with a little force, the RA axis rotates very easily during balancing. Thats the good part. Now the bad one. It is so free to rotate that a little wind or even a thin cable can rotate it. So even with axis locked, it does slip. It takes a lot of time to balance. Gets frustrating.

So I was thinking that I could keep RA nut a little loose because that seems to make axis a little rough to rotate. What would happen if  the RA nut is a little loose? Would that damage the gear teeth or motors?

Or is there any other solution to this problem?

Wow !!

Astronomyshed is the place to go !! Thanks for the links.

I dont think I will strip anything after bad experience with my mount.

So I'll start with resetting the spider. Following astro-baby's guide, I'll make a circular sheet, put a hole to it and check spider position. I agree collimation is not as bad as it seems. I have had good experience collimating my XT8.

Its just this sideways shift of secondary that got me worried. Infact, despite this problem I can do the rest of the process to get exactly the view through the collimation cap as shown in this image by astro-baby. ( Mel, I hope its okay to use the image for this purpose.)

As far as I am aware the secondary should be centred and concentric in the cap.  The offset comes in later when you align the primary with the secondary.

Cheers

Ross

Thanks Ross. Collimation has got me worried after getting squarish stars in Baader MPCC III. The secondary holder itself looked a slight displaced from the centre when seen with the cap (not up-down the telescope tube..but the other direction). I rotated the secondary, it looks ok now. How tolerant is collimation in this scope?

Ishan.

Nice image that !! Which coma corrector do you use?

I got some time off work and since I have a Baader MPIII waiting for me, I tried to collimate my scope first time in over an year. BUT A collimation question : Should the 130PDS have secondary offset when seen under the focuser? I mean when I put the collimation cap on and see though the hole, I see that secondary leaves a larger space below it than above. The circle of the drawtube and secondary mirror are not concentric. The orientation of scope is parallel to ground and focuser extended vertically away from ground.

Ishan.

Excellent! How precise are your exposure lengths? Do you time manually or tether to a laptop?

[emoji15]

I use a laptop..helps a lot with polar alignment and field selection..not to mention autoguiding when I get the Orion MMAG.

Here's my m45, m42 and m31 with 130 PDS..

All 3 min unguided subs with canon 1100d

M45

http://www.astrobin.com/140413/

M42

http://www.astrobin.com/124109/

M31

http://www.astrobin.com/122877/

Thanks,

Ishan.

Absolutely the worm gear adjustment will make a difference to rotation by hand or with the motors. If you can rotate the mount in RA with the motors without the motor clutch screaming at you then I doubt this adjustment is the issue.

The mount works okay with the motors. I have not noticed any binding or noise when rotating with motors. When I unlock the RA clutch and rotate RA axis, I see that the brass cylinder and the RA shaft at its center rotate together. Correct me if I am wrong. The motor drives the worm and that drives the RA shaft inside the clutched brass cylinder. So I dont understand how can worm be involved when the whole RA assembly is just turning in its housing.

Meanwhile, I have put in a lot of lithium grease and there was a little improvement.

Here's the video I've shot showing the problem. http://youtu.be/aqczPuRghEw

There was also a slight movement in RA axis when clutched.

Ishan.

Thanks for helping everyone.

I've merged the two threads together.
It seems the that the ra housing has been badly machined or the ra bearing is out of alignment.

Got it !!

Did you adjust the the fine adjusters (small Allen screws) to set the worm gear spacing as described on Astrobaby's site? It is a very fine adjustment and makes all the difference. It takes some trial and error to get the play correct but it's an important final fine tuning step.

The RA axis was stiff when the mount arrived. Have I misunderstood here? Does "worm gear spacing" have any role if RA clutch is off and I'm trying to rotate it by hand? Does "play" mean "With RA axis clutched there's any movement in the axis"? Sorry for noob questions.

so it takes more effort to unbalance it in RA. I can move it in RA with the scope attached using just one finger.

Louise,

but seems like mine takes almost a hand push with Skywatcher 130 PDS scope (3.6 kg)  and one counterweight. But it is not "free" by any means. It stays in almost any position I keep it in. A video will be helpful.

Can I use sandpaper on the housing? Or is there a way to correct the misalignment of the cylinder? Anyone tried it before?

Ishan.

Hi everyone.

The RA Axis on Skywatcher HEQ5 Pro was tight to rotate by hand when unclutched. Cant balance on RA Axis. So I took it apart. When i removed the RA shaft from housing, I found black grit formed by rubbing of brass cylinder with its housing.

The attached photos show black grit on cylinder and housing.  The cylinder seems to be out of centre in the third photo.

I removed it all, degreased and regreased it with yellow translucent lithium grease  and assembled it again. But no improvement in RA Axis stiffness. When I try to put brass cylinder back into housing, it stops at a point. It has to be turned around so that it can slip in.

I think that the housing is "undersized". Please help with this.

Ishan.

When clutch is disengaged, and I try to rotate RA axis by hand, the motors dont move at all. It is only the RA shaft rotating in the base of mount. So I suspect the problem to be in the shaft and base not in the motors or worm wheels or anything.

Hi.

Its an one year old little used HEQ5 Pro mounting a Skywatcher 130PDS and Canon 1100D.

The RA axis is stiff to turn by hand even when it is unlocked. So Its difficult to balance as the axis just stays into its position even if it not properly balanced. There's no play in RA axis when it is locked. Mount is tracking okay though.

I've followed Astro-Baby's strip down guide to remove the polar scope, black nut and the tapered bearings. And yet there was no difference at all. The transparent and little sticky grease is there in moderate quantity.

Now I am clueless. Please help.