NEQ6 Pro DEC Axis bolt stripped - Help!

[OzDave]

Since Christmas/New Year was rained/clouded out here, I decided, after inspecting my mount, that it didn't rotate very easily and so a service might be in order. So I followed Astro Baby's EQ6 strip down and rebuild guide for the DEC axis. I got everything stripped down, cleaned and re-greased, and reassembled without issues. However, the final part is adjusting the worm carrier. I had done this and eliminated all play in the DEC axis and proceeded to start tightening the DEC worm carrier cap head bolts. I got 3 of them tight but not as tight as they were to undo originally. However, the 4th bolt managed to strip the female thread with almost no force at all. It didn't even get anywhere near tight, just kept turning in the hole. I took it back out and found a neat spiral of metal wrapped around the bolt.

I have to conclude from this that the thread was basically ruined before I started messing about and undoing and replacing the bolt was just the final thing it needed to fail.

Looking down on the DEC axis saddle, with the cap head bolts below the saddle, the bolt in question is the 3rd one counting left to right. All the others are secure enough without being overnight I believe.

Should I be worried about this 3rd bolt not being tight? The DEC axis seems perfectly functional with no play, so it seems not to matter too much. However, I would like to hear what people think.

Also, supposing that I want to fix it, what are my options? Can it even be fixed in some way? Presumably I'd have to replace the 3rd bolt with another one slightly larger in diameter and have a new thread cut to suit. I'm not sure what else would be required in terms of enlarging other holes. No idea how to cut the new thread either.

Advice please....

Oh...and happy new year!

David

[Merlin66]

Dave,

Bumma!!!

The easiest long term solution may be to get the hole re-tapped and use a Helicoil thread insert to bring it back to the original thread......

[perfrej]

Although helicoil is a great solution in engine blocks and such, I am not sure it will be that great in aluminium. I would simply bore the hole to one size up (is it M5 or M6?) and thread it. On the other hand, I think you may well do fine with just the three

/per

[Peter Drew]

Helicoils are used as standard in the aircraft industry for helping to prevent thread stripping in aluminium components. Probably the best option for the OP, but in view of his declared lack of experience in such matters, three good fixing screws will probably be adequate. 

[thanders]

Helicoils are used as standard in the aircraft industry for helping to prevent thread stripping in aluminium components. Probably the best option for the OP, but in view of his declared lack of experience in such matters, three good fixing screws will probably be adequate. 

Yes, helicoils in aluminium is the standard procedure. It will be better than before. Why not fix all of them?

/Thomas

[Hungran]

Yes, helicoils in aluminium is the standard procedure. It will be better than before. Why not fix all of them?

/Thomas

Thread inserts are standard procedure for "soft" or "brittle" materials, as mentioned by other posters. Perhaps you have a friend or a machine shop nearby where you can have it fixed. If you decide to fix the bad thread, fix them all. It will be the same effort or cost.

/Mikael

[sbooder]

I have just done the exact same thing while tuning the RA. 

If you are lucky and the bolt you have stripped is not one that is level with the motors you can get a slightly longer bolt and add a nut & washer inside the motor housing as the bolts protrude in it anyway.  If on the other hand you are unlucky like me and have stripped one below the motors you can't.  So tapping looks the most likely as mentioned above.

[OzDave]

I think the bolt I stripped might be "saveable" with a nut and washer inside the chassis as you suggest.

Following my RA strip down I took the mount out to test the guiding performance. I found DEC was significantly improved but I was getting random stalls in RA although RA guiding was generally good except for regular periods where the graph would just go totally nuts with displacements of 5 pixels of so. Eventually this would correct and things would be normal again for a while.

I attributed yhis to having the RA worm tweaked too tighly, so I've backed it off a bit but have yet to retest. Oddly I seem to have zero play in the DEC axis now, but maybe half millimetre or so of play on RA. Try as I might, I cant seem to get RA any better and having to back off the grub screws in RA has made things marginally worse.

Have others also found things go like this?

David

Sent from my iPhone using Tapatalk

[sbooder]

I think the bolt I stripped might be "saveable" with a nut and washer inside the chassis as you suggest.

Following my RA strip down I took the mount out to test the guiding performance. I found DEC was significantly improved but I was getting random stalls in RA although RA guiding was generally good except for regular periods where the graph would just go totally nuts with displacements of 5 pixels of so. Eventually this would correct and things would be normal again for a while.

I attributed yhis to having the RA worm tweaked too tighly, so I've backed it off a bit but have yet to retest. Oddly I seem to have zero play in the DEC axis now, but maybe half millimetre or so of play on RA. Try as I might, I cant seem to get RA any better and having to back off the grub screws in RA has made things marginally worse.

Have others also found things go like this?

David

Sent from my iPhone using Tapatalk

Try backing off the worm retainer nut 1 eighth of a turn to allow more float on the worm shaft, this will allow you to eliminate more play in the RA axis by tightening the grub a bit more.

[sbooder]

Does anyone know what size the hex bolt is on the worm carrier for the NEQ6 Pro so I can buy the Helicoil kit for this repair please?

[OzDave]

Try backing off the worm retainer nut 1 eighth of a turn to allow more float on the worm shaft, this will allow you to eliminate more play in the RA axis by tightening the grub a bit more.

I just gave this a shot and managed to remove all the play in the RA axis. I'm yet to put the motor back, and haven't tightened the worm carrier down yet, but the worm screw turns easily in my fingers with no play. Excellent! Now to get it all tight and run the motors to test!

Thanks for this tip!

I had seen a website which advised securing the worm screw before adjusting the worm spacing, because if you don't, there would be two variables at work making things difficult. However, Astro Baby recommends the opposite. Adjusting the worm retainer nut after the worm spacing is done.

Moral of the story: Do not fully tighten the worm retainer nut before adjusting the worm carrier. Otherwise you'll probably end up with play in the axis.

[sbooder]

I tend to have the retainer nut set so I can just turn it with my fingers before I re-assemble the worm carrier and then set the worm mesh so I have about 1/2mm play in the axis (as best I can judge 1/2mm).  And then go from there.