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removing captive screw from Televue 3x

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#1 bunyon

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Posted 01 February 2013 - 09:08 AM

I have a TV 3x Barlow with a captive thumbscrew. The "head" which you grab to turn snapped off and I'm now unable to turn the screw at all.

How do I go about removing this screw? I've never been faced with doing so and googling isn't really helping. However, I feel like I'm missing something obvious.

Thanks.

#2 rockethead26

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Posted 01 February 2013 - 10:04 AM

Vise grips or pliers, grabbing along the screw axis is what I would try. Twist very slowly, making sure you are going in the correct direction.

#3 FirstSight

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Posted 01 February 2013 - 10:20 AM

If it turns out the screw is truly "frozen" and can't be unscrewed with vise grips in the manner rockethead above suggested, it may have to be drilled out with an appropriately sized reverse-threaded bit. You'd of course need to pad/protect optical surfaces before proceeding. The FOOLPROOF solution is to send the barlow to Televue and have them do this for you; this is assuredly the sort of thing they've seen before in various contexts. A couple of the lens cell screws in my NP-101 refractor were completely "frozen" when I tried to collimate it myself and though I attempted to reverse-drill them myself, I decided I was taking too much risk of damaging the optics and the OTA's cosmetics and sent it into TV, and had them do it for me.

If your 3x Barlow is still under TV's warranty, i.e. you are the original owner and it's been 5 years or less since purchase, they might do it free under warranty, with you having to pick up only the shipping cost. Else, they'll probably charge at least their standard basic EP "cleaning" fee; call them and see what the cost would be.

Alternatively, you might be able to find a competent local machinist who will undertake this for you.

#4 csrlice12

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Posted 01 February 2013 - 03:58 PM

Yep, like FirstSight said, if it won't come out with the vice grips, it'll have to be drilled and tapped. You can get a "reverse thread" self threading screw and screw it into the freshly tapped "hole" in the screw and it should come out (I'd recommend sending it in if its in warranty however).

#5 bunyon

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Posted 01 February 2013 - 05:13 PM

Definitely not under warranty. I don't remember when, or how, I obtained it. I'll look into sending it back. I may just tap a new hole and supply my own screw. Even with the old bolt still stuck in the original hole it won't be the ugliest thing in my rig.

Thanks all.






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