Stipped thread on focuser lock scew

[glend (Glen)]

I seem to have a focuser clamp screw that is stripped or jammed and held fast in the hole. It's in a Crayford style GSO 10-1 focuser. It became jammed up at Bretti and I have been making do with just the one (there are two). Any ideas on how to fix it, would prefer not to have to buy a new focuser.

[multiweb (Marc)]

Originally Posted by glend

I seem to have a focuser clamp screw that is stripped or jammed and held fast in the hole. It's in a Crayford style GSO 10-1 focuser. It became jammed up at Bretti and I have been making do with just the one (there are two). Any ideas on how to fix it, would prefer not to have to buy a new focuser.

Drill through and tap bigger.

[GeoffW1 (Geoff)]

Hi,

I had the same. It was caused by "galling" or partial stripping and deformation of the softer thread in the alloy body, rather than the steel screw. A brass screw might be different.

Reasoning that it would be difficult to drill out the steel screw in situ without stuffing everything by running off centre, I put drops of Penetrol type-thingo on there and let it soak, then got out my lockjaw pliers and backed out the screw forcibly.

The risk is that the screw shears off, but then you have not lost much in that case.

I then tapped out the hole with the same size thread, but no, too much damage was done, so then to the next stock size up. That worked. I put anti-seize gunk on all the threads there after that.

Good luck

[linkpng (Alfred)]

Have you tried using 'penetrating' liquid to get into the tread and help to work it loose? One example is WD40 aerosol you get at the auto parts shop or you could ask a local plumber what they use. Another example is DWF ("de-watering fluid") aerosol lubricant and rust penetrant. This stuff "creeps" into fine cracks and may help to loosen the seized points.

If easy, remove the whole focuser from the scope, spray a small amount of WD40 (or other) spray ONLY into the affected area and leave that in for half an hour. NOTE: be very careful to only spray the few mm area that needs it; do not spill the oil on any other part of the focuser. If this proves too difficult you can also: spray some of the WD40 into a small bowl and then with a small paint brush pick this up and dab it at the entrance point of the screw.

Now do two things at once: Ask your wife or a friend to tap the base (area not visible when mounted) regularly with a small hammer "tic, tic, tic, tic, tic, tic, tic....." while at the same time you try to carefully undo the screw. Keep gently hammering while you work on the screw.

If it does not come free, try again in an hour's time. With the hammering the oil may have worked in a bit further, etc. Best of luck.

[astro_nutt]

You could also chill the screw by placing an ice cube on it for a few minutes in order to shrink it before attempting to move it.
Cheers!

[rally]

Another option for a stripped thread

If there is enough thread depth and available supporting material around the tapped hole, you could use a HeliCoil or a Recoil
You retap the stripped thread with the HeliCoil or Recoil tap (special tap) and then screw and loctite in the replacement thread - it looks like a stainless steel spring, but its hardened stainless steel.

I did this on a friends EQ mount Azimuth adjustment threads - they were heavily worn and there was a lot of play in the thread and this did the trick perfectly and provided a new thread that will likely never wear.

It may not work if there are only a few threads.

Rally

[glend (Glen)]

I tried to remove it this morning and found that once I got it out that the end of it was broken off inside the hole. I rang Andrews to find out if this sort of thing is covered by warranty (it's only four months old). And was told to send the entire focuser back to them, and they will probably replace it.

Does anyone know of a better quality focuser that will fit the 12" GDO Dob, as if there is this might be an opportunity for an upgrade?

[glend (Glen)]

Sent the GSO focuser back to Andrews via Express Post, so we'll see what happens.