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Went to install FT focuser, head twisted off screw

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#1 NicolasKL

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Posted 02 July 2013 - 09:19 PM

The internal screw that holds the stop on the old focuser was on so tight that I twisted the head off trying to get it off.

Any ideas? I can drill it out I guess but I'm worried about both metal shavings and screwing up the threads, plus now I need a new screw and don't know the dimensions of it.

#2 mgwhittle

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Posted 02 July 2013 - 10:45 PM

You should be able to use an extractor like the "ez out" or something similar to remove it with no damage to the threads. Might have to soak it with some penetrating oil like liquid wrench. You shouldn't have to drill it out so no shavings should get inside. If all this sounds too much, a machine shop should be able to get it out for a small fee.

#3 gnowellsct

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Posted 02 July 2013 - 11:37 PM

Car mechanics are sometimes pretty good at getting out old screws, particularly in the NE and MW where cars rust.

You might consider getting stainless steel or nylon screws from McMaster Carr. To get the size of the screw you need a screw checker. you can buy them (they're handy to have at home) or you can take an intact screw to Home depot in the screws department there should be a screw checker hung up somewhere that you can use. GN

#4 n1wvet

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Posted 03 July 2013 - 12:08 AM

Any part of the screw body sticking out? Try Vice-grips after soaking with penetrating oil.

#5 csrlice12

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Posted 03 July 2013 - 07:25 AM

You screwed up the screw? That's pretty screwed up. If it's broken off inside and the threads go all the way thru the focuser, you could take the diagonal and all out of the focuser, point the scope to the zeinith and start screwing in another screw, if the screw hole is all the way thru, the new screw will thread the old screw all the way out (did that with one of the allen head screws on my Scopestuff focuser when installing the finderscope foot.). If it isn't, I'd find a machine shop/auto shop where they deal with this on a fairly regular basis (broken off screw heads, not astronomers).

#6 dawziecat

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Posted 03 July 2013 - 08:11 AM

If you have a watch/clock/jewelry repair operation nearby, they might be able to do this. I just recently had a pair of eyeglases with broken screw. Walmart optical department and a dispensing optometrist were not able to help but a clock repair shop handled it easily in a few minutes while I waited. They charged me $5.00. Good luck.

#7 NicolasKL

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Posted 03 July 2013 - 08:16 AM

Should have mentioned, this is for a CPC-1100.

I'm going to see if they make an EZ out small enough, but I kinda doubt it, it's a pretty small screw.

A little bit of the screw is sticking out, but I really doubt it's enough to get a grip on with needle nose or vise grips, though I'll try that first.

May also try cutting a notch in it with a dremel and then using a standard screwdriver on it, but again I don't think enough of it is sticking out and unless I really loosened it up before I twisted the head off, I doubt it'll work.

Unless there's a properly sized EZ out that works better than I expect it to, I think drilling might be the only option, but maybe I could just drill out 1/4 of an inch of it or so and then buy a small screw. Not really sure how long the broken screw is though, for all I know it's only 1/4 of an inch itself.

#8 don clement

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Posted 03 July 2013 - 11:20 AM


If the screw is in aluminum you might try using Alum to dissolve the screw.
http://www.homemodel...-aluminum-br...

Don Clement

#9 oo_void

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Posted 03 July 2013 - 04:19 PM

Same thing happened to me. I tried all the "home remedies" to no effect. Ended up buying something like this and it worked perfectly.

http://www.amazon.co...TLK7O/ref=sr...

Alden has numerous set sizes. Just find the one that's the right size for your needs.

#10 csrlice12

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Posted 03 July 2013 - 04:37 PM

Take the focuser tube out of the focuser and see if the screw hole goes all the way thru (depends on the focuser). If it does just thread in another screw, it will force the old one out. Just be sure to keep the scope pointed up!

#11 starrancher

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Posted 03 July 2013 - 04:53 PM

Very possible you'd end up with a "cinch nut" situation in attempting that and causing damage to existing threading .

#12 don clement

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Posted 03 July 2013 - 06:31 PM

http://www.amazon.co...TLK7O/ref=sr...

Alden has numerous set sizes. Just find the one that's the right size for your needs.


+1 on the Grabit I have a set that works well.

The last resort is to take it to an EDM removal service such as : http://www.brokentap.com/services.html

Don Clement

#13 Goodchild

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Posted 03 July 2013 - 06:48 PM

If it were me, I'd send it to SI and let them fix it. Not worth messing up a nice focuser trying a DYI approach. It doesn't sound like a simple fix.

#14 NicolasKL

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Posted 05 July 2013 - 01:28 AM

All taken care of. Tried the Grabit but just couldn't get it to bite, so I just drilled out the screw and tapped new threads in.

#15 NicolasKL

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Posted 05 July 2013 - 09:18 AM

All ready to go, smooth as butter. Forecast is partly cloudy tonight, but if there's too many clouds tonight, rest of the weekend is supposed to be clear.

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#16 csrlice12

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Posted 05 July 2013 - 09:37 AM

a little off topic, but don't you just love those Baader quicklock adapters........

#17 Goodchild

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Posted 05 July 2013 - 09:37 AM

I'm glad to hear you had a successful conclusion to your dilemma.

#18 tim57064

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Posted 05 July 2013 - 09:38 AM

All taken care of. Tried the Grabit but just couldn't get it to bite, so I just drilled out the screw and tapped new threads in.

How did you take care of the shavings problem? Hope that none got inside the tube.

#19 NicolasKL

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Posted 05 July 2013 - 10:15 AM

All taken care of. Tried the Grabit but just couldn't get it to bite, so I just drilled out the screw and tapped new threads in.

How did you take care of the shavings problem? Hope that none got inside the tube.


I left the focuser in while I was drilling it out, so it caught everything. Then vacuumed everything thoroughly before I pulled the old focuser back off. Seems to have done the trick.

#20 NicolasKL

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Posted 05 July 2013 - 10:17 AM

a little off topic, but don't you just love those Baader quicklock adapters........


Yep, I'm a big fan.

#21 don clement

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Posted 05 July 2013 - 03:54 PM

Is this a focuser or an add-on to the focus knob leadscrew assembly of the stock moving mirror focuser?

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#22 NicolasKL

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Posted 07 July 2013 - 04:56 PM

It's a focuser. Has both the stock rate and a 10:1 (fine) focusing knob.

I guess it doesn't replace the rod or the entire mechanism, unlike an external focuser, but that's the nature of the beast. It's also not like its just a different looking knob that slides onto the stock focuser gearing.

Worked great last night, though I had tracking problems which I suspect are caused by the 2" Baader diagonal and the pineapple sized 40mm ES EP. Starizona balance system should show up this week.

#23 don clement

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Posted 07 July 2013 - 05:22 PM

It's a focuser. Has both the stock rate and a 10:1 (fine) focusing knob.


Is it a complete focuser that moves the primary mirror, or is it just a focus knob assembly with a 10:1 reduction mechanism replacing the stock knob assembly bearings and leadscrew nut? If it is just a focus knob assembly, then the stock moving mirror focuser is still there with the same old issues of mirror flop and wanting to dance on the pole with image shift. From the picture posted it looks like a 10:1 reduction focus knob assembly and not a complete focuser.

Don Clement

#24 NicolasKL

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Posted 07 July 2013 - 05:28 PM

It does not 100% replace everything in the focusing mechanism (which would require pretty major interior surgery) so no, it cannot 100% eliminate mirror flop (if anything can).

#25 don clement

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Posted 07 July 2013 - 06:03 PM

It does not 100% replace everything in the focusing mechanism (which would require pretty major interior surgery) so no, it cannot 100% eliminate mirror flop (if anything can).


The only thing replaced here was leadscrew nut knob assembly. The FT knob assembly replacement does nothing to fix mirror flop or image shift in a pole dancing moving mirror focuser.

As far as if anything can “100% eliminate mirror flop": I have completely replaced the stock pole dancing moving mirror focuser with my compliant moving mirror focuser that 100% eliminates mirror flop. However it is pretty major surgery as you stated.
Here is my moving mirror focuser with a 14 " conical mirror mounted on that I built that has zero mirror flop. Another picture shows the focuser installed in a C14.
Posted Image
Posted Image


Don Clement






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