Broke my NEQ6 Pro

[kbrown]

So it finally happened. The thing that I've been fearing for a while already. In an attempt to minimise the backlash my DEC axis had developed I had to loosen and tighten the four M6 bolts on the housing one too many times. One of the threads stripped completely and the other three don't look very good either. My initial thought to get me out of the trouble is to use helicoil thread repair inserts but having no previous experience with these I'm a little scared of putting them in. Three of the holes are through holes with maybe about 6mm wall thickness. Is this enough for the insert to work? The fourth hole is a blind hole with probably enough depth so I can break off the tab on the helicoil once it's fully inserted.

On the same note I noticed the latitude bolt threads on the mount are quite loose and manky too. Thinking of giving them the same treatment before the worst happens.

Has anyone here done this sort of thing before?

[Davey-T]

I've used them on stripped spark plug threads so should be no problem on your mount, there is another supposedly better type but I can't remember the name ATM.

Dave

[kbrown]

Just now, Davey-T said:

I've used them on stripped spark plug threads so should be no problem on your mount, there is another supposedly better type but I can't remember the name ATM.

Dave

Are you perhaps referring to time-serts? Had a look at them but the kits are super expensive...

[Davey-T]

That's the things, expensive to buy the kit but I think there are folk that do it for you, don't know how much they charge.

Dave

[tooth_dr]

I stipped a thread on the housing on my EQ6.  Although not the same bolt as yours, I tapped it out the next size up, and replaced the bolt with a larger one.  I've have no experience of helicoils at all to advise.  Although this seems like the worse thing right now, it can be sorted!

[Tiny Small]

You could just drill and tap the holes to M8. If you have a tap then it's a free fix and as the forces in the threads are spread over a larger area, they will suffer less stress. The one downside to this is that taps cut a sharp root tip which then acts as a larger stress concentrator than a rounded root tip, though the factory threads are pretty naff anyway. 

[kbrown]

31 minutes ago, Tiny Small said:

You could just drill and tap the holes to M8. If you have a tap then it's a free fix and as the forces in the threads are spread over a larger area, they will suffer less stress. The one downside to this is that taps cut a sharp root tip which then acts as a larger stress concentrator than a rounded root tip, though the factory threads are pretty naff anyway. 

I did think about this and may still get back to it. The problem is the heads of the bolts are in a recess in the housing:

Don't know if I can find M8 bolts whose heads would fit in there. There might be enough space if I left the heads outside the DEC axis housing and put big and strong enough washers under them...

[Stub Mandrel]

I would go for Helicoil, it's £24 from here:

https://www.tracytools.com/helicoil-thread-repair-kits/metric-thread-repair-kits/6-x-10-thread-repair-kit

You could do all four, then sell on the kit to the next person who has a similar issue - enough to fix five mounts.

 

 

[Tiny Small]

23 minutes ago, kbrown said:

I did think about this and may still get back to it. The problem is the heads of the bolts are in a recess in the housing:

Don't know if I can find M8 bolts whose heads would fit in there. There might be enough space if I left the heads outside the DEC axis housing and put big and strong enough washers under them...

You could drill to nearly final depth in the head, then use a forstner bit of the same size to flatten the hole out. Having said that, if the helicoils are only £24, that seems like the best option.

[Stub Mandrel]

The problem with M8 is that the cap head size is a fair bit deeper and wider (3.3mm in diameter and 2mm in depth). Even a carefully aligned hole made with a proper counterbore may come uncomfortably close to the scale and might not leave sufficient thickness beneath for comfort if taken to full depth.

 

[tooth_dr]

1 hour ago, Stub Mandrel said:

The problem with M8 is that the cap head size is a fair bit deeper and wider (3.3mm in diameter and 2mm in depth). Even a carefully aligned hole made with a proper counterbore may come uncomfortably close to the scale and might not leave sufficient thickness beneath for comfort if taken to full depth.

 

This is the problem.  I've looked at my own and there is little room.  This type of head might offer the best compromise:

[Thalestris24]

Useful video and, of course, Astrobaby's Page

I know it's a bit late to say it but, for future reference, you probably don't need to overtighten the above casing (or any!) bolts...

Louise

[tooth_dr]

4 minutes ago, Thalestris24 said:

I know it's a bit late to say it but, for future reference, you probably don't need to overtighten the above casing (or any!) bolts...

Louise

[kbrown]

12 minutes ago, Thalestris24 said:

Useful video and, of course, Astrobaby's Page

I know it's a bit late to say it but, for future reference, you probably don't need to overtighten the above casing (or any!) bolts...

Louise

Thanks for the links! I bought this mount used and the first time I opened these bolts when I did the belt mod they were super tight. Had a look at the threads and they didn't look very good. Part of the damage was probably already done...

[Thalestris24]

13 minutes ago, kbrown said:

Thanks for the links! I bought this mount used and the first time I opened these bolts when I did the belt mod they were super tight. Had a look at the threads and they didn't look very good. Part of the damage was probably already done...

If you've done a belt mod I don't think you should have any motor backlash but you do need to be careful about balancing accurately in all three axes. Also, the belt tension has to be just right, of course  

[kbrown]

2 minutes ago, Thalestris24 said:

If you've done a belt mod I don't think you should have any motor backlash but you do need to be careful about balancing accurately in all three axes. Also, the belt tension has to be just right, of course  

The play / backlash came from slightly loose worm adjustment (worm too far away from gear). For some reason the DEC axis has been problematic in my mount. It's really fiddly to get right without binding in a position or another. This is what I was playing with when the bolt thread stripped. The RA axis does not suffer from this and performs perfectly.

[Thalestris24]

49 minutes ago, kbrown said:

The play / backlash came from slightly loose worm adjustment (worm too far away from gear). For some reason the DEC axis has been problematic in my mount. It's really fiddly to get right without binding in a position or another. This is what I was playing with when the bolt thread stripped. The RA axis does not suffer from this and performs perfectly.

Yes, worm gear adjustments are always fiddly! I think there's a tendency to overadjust but it can be +/- quarter of a turn between just right and either too loose or binding. Can be exasperating, I know... I think the casing bolts just need to be 'firmly' tight. I don't have problems with overtightening because I'm a weak, old lady ha ha.

Louise

[kbrown]

Yay. Got it back together with helicoils. They're amazing. Used a 1.5D size for the deeper blind hole (screen right on the pic) and 1D sizes for the other three. Was a bit nerve wrecking to manually drill the holes as I don't have a drill press. The 6.3mm HSS drill bit in the kit cuts the aluminium like butter. Was a little easier after I first drilled them to 6mm. Bit of cutting oil helped too. Drill press would have helped to get the tap in straight too but I managed to do that manually too. Not really necessary but I used a drop of loctite to secure the helicoils before putting the mount back together again.

Oh, and the backlash is gone now too ?

[Stub Mandrel]

Brilliant, it will be stronger than new now :-)