Bent centering screw

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Bryan
Posts: 93
Joined: Mon Sep 17, 2018 11:31 pm

Bent centering screw

#1 Post by Bryan » Tue Dec 29, 2020 4:54 am

I recently picked up a Leitz rotating stage that works well with my SM microscope. Everything functions great except the centering screws are both slightly bent. They only go in to a point where they bind up. One screw is normal thread the other has reverse threads, both have a ball bearing in the tip to allow for smooth rotation of the stage. The normal threaded one just barely goes in enough that I think it will work as is. The one with reverse threads is quite a bit off where it starts to bind.

These seem to be very specialized screws, I doubt I would be able to find replacement parts but if anyone knows where I can get them please let me know. The way I see it there are a few things I could do to solve this problem. One option is try to straighten the screw. I’m afraid I will either not get it straight enough, break it or damage the threads. Another option would be to grind off the threads at the point where it starts to bind. That may allow it to advance far enough to center the stage. I believe there are enough threads remaining that will allow it to be centered. This is what I’m considering but before I do anything I will regret I’m looking for advice. Any advice would be greatly appreciated.
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BramHuntingNematodes
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Location: Georgia, USA

Re: Bent centering screw

#2 Post by BramHuntingNematodes » Tue Dec 29, 2020 5:12 am

Do you have a press or vise?
1942 Bausch and Lomb Series T Dynoptic, Custom Illumination

Greg Howald
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Re: Bent centering screw

#3 Post by Greg Howald » Tue Dec 29, 2020 5:17 am

If you can put it into a soft jaw vise you may have some success. Other than that, find a machinist. They love special little challenges like that and would love to make one for you. It shouldn't break the bank.
I wouldn't think of doing any grinding until the last possible resort had been exhausted. The unfortunate thing here is that you can't have any slippage either.

BramHuntingNematodes
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Re: Bent centering screw

#4 Post by BramHuntingNematodes » Tue Dec 29, 2020 5:19 am

You want to get three small blocks of wood. Two will go underneath the screw, with a gap in the middle. The third is attached to the ram of your press. A vice can be substituted for a press, and I'm that case double sided tape can used to stick all the blocks in place. The wood will protect the threads as you work out the bend.
1942 Bausch and Lomb Series T Dynoptic, Custom Illumination

BramHuntingNematodes
Posts: 889
Joined: Tue Jan 21, 2020 1:29 am
Location: Georgia, USA

Re: Bent centering screw

#5 Post by BramHuntingNematodes » Tue Dec 29, 2020 5:21 am

And, don't worry! This is a very common, routine operation! Please don't grind off any threads!
1942 Bausch and Lomb Series T Dynoptic, Custom Illumination

Bryan
Posts: 93
Joined: Mon Sep 17, 2018 11:31 pm

Re: Bent centering screw

#6 Post by Bryan » Tue Dec 29, 2020 5:26 am

I have a large metal vise, nothing soft about it but I can try that with some wood blocks.

MicroBob
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Re: Bent centering screw

#7 Post by MicroBob » Tue Dec 29, 2020 5:48 am

Since it is only lightly bent it will probably straigthen well. These are often strange thread sizes so it would be a bit difficult to make a replacement.

PeteM
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Re: Bent centering screw

#8 Post by PeteM » Tue Dec 29, 2020 6:51 am

Bryan, The best way I've found to straighten bent screws is to observe exactly where the bend or bends are. Then thread the screw into a long nut or stack of nuts that you will hold in your vise, leaving just a bit of the bent portion proud. Lightly tap it, rotate, tap until it's straight. This operation can also be done even easier in a lathe. You should be able to get it straight enough to work as it should.

The difficulty with soft jaws is that ones soft enough to avoid damage to the threads are also so soft that you really don't have much control on where it bends when you try to force it back.

It's possible to buy nylon or brass tipped metric thumb screws that will work reasonably well holding the stage without marring it. The left-handed one, as you suggest, would be hard to find.

Perhaps heresy, but if a stage-holding screw or its female mating thread is ruined, I'll drill and tap it to the next size larger that's on hand.

Hobbyst46
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Joined: Mon Aug 21, 2017 9:02 pm

Re: Bent centering screw

#9 Post by Hobbyst46 » Tue Dec 29, 2020 12:21 pm

Here is an almost tool-free approach that worked for me to straighten metal pieces:
Straighten the screws by rolling them between two hard, flat surfaces, using your foot and the weight of your body. Find two hard, flat, smooth, 20cmx10cm (sufficiently large to lay a foot on) plates. Like 10mm thick steel or polycarbonate plates. Verify that they are absolutely flat. Place the thread between them and lay the sandwich on the floor. Step on it and roll to and fro with your foot. It can also succeed with a single plate on an appropriate floor tile, IF the tiles are very smooth and very tough (most modern floors are not... :oops: ).
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dtsh
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Re: Bent centering screw

#10 Post by dtsh » Tue Dec 29, 2020 1:42 pm

iIf all attempts to straighten it fail or it breaks, making new ones is not a difficlt task. Easiest would be to head toward a hobby machining forum, such as https://www.hobby-machinist.com, and post a request for someone to make a pair and provide as much information about the screws as possible. I'd offer to make a pair, but my lathe is mid-rebuild.

Charles
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Re: Bent centering screw

#11 Post by Charles » Tue Dec 29, 2020 2:01 pm

I have straightened many bent bolt/screws. The easiest is to screw the bolt/screw into the stage as far as it will go. Then get a socket wrench which will fit the knob end snugly. You can wrap a piece of tape to the end of the screw/bolt knob to protect it. Turn the bolt/screw until you see where the bend is and bend gently in the opposite direction with the socket and wrench until the bolt/screw is straight. You can check for straightness by turning the screw/bolt until you don't see a wobble. Be gentle when you add pressure and do it in small steps.

Note: If you question your strength and are afraid you will snap the screw or bolt by bending by hand, you can also use a rubber/plastic hammer to gently tap the wrench on the bolt screw in the opposite direction of the bend to straighten it.

apochronaut
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Re: Bent centering screw

#12 Post by apochronaut » Tue Dec 29, 2020 4:00 pm

I'm just wondering if by now, you are clear headed enough to straighten them at all?

Bryan
Posts: 93
Joined: Mon Sep 17, 2018 11:31 pm

Re: Bent centering screw

#13 Post by Bryan » Tue Dec 29, 2020 6:40 pm

I used the wood block in a vise method that BramHuntingNematodes recommended and it's now centered! I only had to straighten the one with reverse threads to get it centered. It still binds a little but since I got it where I want it I'm going to leave well enough alone before I break something. Thanks everyone for all the great advice!

BramHuntingNematodes
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Re: Bent centering screw

#14 Post by BramHuntingNematodes » Tue Dec 29, 2020 7:35 pm

Great news! Happy hunting
1942 Bausch and Lomb Series T Dynoptic, Custom Illumination

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