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Old 1st Mar 2017, 3:22 pm   #1
Nickthedentist
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Default What's the best way of re-cutting the slot on a damaged screw?

Hello,

During my work on radios and clocks, I come across lots of screws (especially countersunk woodscrews) where the slot has been damaged by somebody using a poorly-fitting screwdriver, or even where it's been badly manufactured.

Sometimes, I just fit new screws but invariably, these stick out like a sore thumb or aren't quite the right size. It would be nice to be able to neaten-up and deepen the slot of the old screw and re-use it.

I've found ways and means to deal with very big screws, but what do people here recommend for the tiny ones e.g. No.4 and smaller?

Thanks,

Nick.
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Old 1st Mar 2017, 4:55 pm   #2
paulsherwin
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Default Re: What's the best way of re-cutting the slot on a damaged screw?

I use a diamond cutting disc in a cheap Dremel clone. I bought the disc from a tool store in Oxford market, but sadly they're long gone. You can probably find them on eBay.
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Old 1st Mar 2017, 5:26 pm   #3
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Default Re: What's the best way of re-cutting the slot on a damaged screw?

Thanks Paul. How thin are they? My Dremel ones someone gave me are rather too thick for what I need them for.
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Old 1st Mar 2017, 5:26 pm   #4
Mike Phelan
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Default Re: What's the best way of re-cutting the slot on a damaged screw?

I use something like this, Nick:
http://www.ebay.co.uk/itm/like/261620596449?lpid=122
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Old 1st Mar 2017, 5:29 pm   #5
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Default Re: What's the best way of re-cutting the slot on a damaged screw?

You can buy cutting discs in a range of sizes.

Mike has a point though, can't you rescue some dental cutting discs when they're no longer suitable for medical use?
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Old 1st Mar 2017, 5:30 pm   #6
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Default Re: What's the best way of re-cutting the slot on a damaged screw?

Thanks Mike, that looks promising.

It was a nice Elliott clock that I'm working on at the moment which prompted this thread. It's 70 years old and yet looks brand new... except where some clown's scratched the dial, presumably in part because of the very shallow and rounded slots on the 3 screws (hidden behind the chapter ring) which hold the movement in place.
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Old 1st Mar 2017, 5:37 pm   #7
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Default Re: What's the best way of re-cutting the slot on a damaged screw?

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Originally Posted by paulsherwin View Post
Mike has a point though, can't you rescue some dental cutting discs when they're no longer suitable for medical use?
I do a lot of that kind of thing, Paul, but cutting discs are generally something a dental technician would use. We clinicians tend to use burs and flexible abrasive discs (1/2" circles of sandpaper with a metal centre boss which snap onto a mandrel).
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Old 1st Mar 2017, 6:08 pm   #8
paulsherwin
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Default Re: What's the best way of re-cutting the slot on a damaged screw?

How do you chop off a tooth when you're doing a crown?
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Old 1st Mar 2017, 6:22 pm   #9
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Default Re: What's the best way of re-cutting the slot on a damaged screw?

I was pleased to find traditional slot (brass) woodscrews in c/sink and dome head- small sizes like No.1,2,4, and even silly lengths like 1/2" and 5/8". They were in Reeves in Maldon who are an independent, but at least it shows they are still being made in brass.
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Old 1st Mar 2017, 6:39 pm   #10
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Default Re: What's the best way of re-cutting the slot on a damaged screw?

When I had to make some special screws (ever tried to by M3*0.6mm ones?) I cut the slot with a slitting saw on a milling spindle. OK, not everyone has such facilities, but... Slitting saws come in just about any thickess from about 5 thou upwards, so you can cut the slot width you want.
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Old 1st Mar 2017, 7:21 pm   #11
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Default Re: What's the best way of re-cutting the slot on a damaged screw?

Razor saws are available from model shops and the likes of Axminster tools, who offer them with 0.25mm thick blades. Intended for wood or soft metlas, but would probably cut brass and mild steel.

http://www.axminster.co.uk/victor-jeweller-s-saw-910295


I haven't had to re-cut slots in very small screws, but I wonder if it would be possible to carefully grind either side of the teeth of a fine toothed HSS conventional or junior hacksaw blade to the desired thickness? As only a shallow slot is needed it would not be necessary to reduce the thickness of the entire blade, and in principle only a few inches need be treated. I have only had to tackle large screws where a standard hacksaw blade produces a slot that it too thin, and for this I used a suggestion I found in a book, which was to use two or more blades in the same frame according the the thickness of slot required.
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Old 1st Mar 2017, 7:39 pm   #12
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Default Re: What's the best way of re-cutting the slot on a damaged screw?

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Razor saws are available from model shops and the likes of Axminster tools, who offer them with 0.25mm thick blades. Intended for wood or soft metals, but would probably cut brass and mild steel.
They do and cut on the pull stroke keeping the blade straight. Another unmentioned "maybe" problem is the existing damaged slot, fill with solder? Cut the new slot at 90 degrees?
 
Old 1st Mar 2017, 8:00 pm   #13
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Default Re: What's the best way of re-cutting the slot on a damaged screw?

Fret saw blades are very thin.
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Old 2nd Mar 2017, 6:55 am   #14
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Default Re: What's the best way of re-cutting the slot on a damaged screw?

When faced with this problem on oboes and clarinets (an everyday occurrence) we use a piercing saw with a blade of the correct thickness.
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Old 2nd Mar 2017, 9:46 am   #15
Craig Sawyers
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Default Re: What's the best way of re-cutting the slot on a damaged screw?

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How do you chop off a tooth when you're doing a crown?
We're a bit off topic, however:-

My dentist (Robin Nagi at Iffley Dental, Oxford) always removes the minimum amount of tooth and fits a thin crown. His perspective is that leaves lots of options down the line, whereas the method of chopping a tooth down to a peg and then using a massive crown leaves absolutely nowhere to go if something goes wrong later on. I've now got four or five in various materials.

Last dental hilarity was root canal work, which I was not looking forward to apart from the fact I was under so much pain. Three really easy two hour sessions and it has been absolutely perfect since.

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Old 2nd Mar 2017, 11:27 am   #16
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Default Re: What's the best way of re-cutting the slot on a damaged screw?

On some chewed up screw heads I have supported the screw vertically in something solid like a bush on my vice and 'planished' the chewed up bits back into position then tidied up the slot by one of the above methods and finally used a piece of fine abrasive paper or scotchbrite on the head.
Recovery 'can' be better than replacement!

Alan
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Old 4th Apr 2017, 7:53 am   #17
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Default Re: What's the best way of re-cutting the slot on a damaged screw?

I always use a junior hacksaw for the small ones, and a full size hacksaw for the bigger ones. May not be the best, but I have them, as do most other practical folk.
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Old 4th Apr 2017, 10:15 am   #18
David G4EBT
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Default Re: What's the best way of re-cutting the slot on a damaged screw?

Quote:
Originally Posted by Nickthedentist View Post
I've found ways and means to deal with very big screws, but what do people here recommend for the tiny ones e.g. No.4 and smaller?
Without a doubt, a diamond disc, but the problem with smaller screws is that while the disc may be thin enough to fit the slot, a standard 22mm diameter disc will be too large a diameter for c/s screws, and hence, at the depth of the screw slot, will cut into adjacent timber (or metal). No problem with r/h or c/h screws where the head stands proud of the wood or metal surface.

I've just tried a No 4 5/8" c/s/ woodscrew with a 22mm diameter diamond disc. The screw slot is 35 thou wide (0.92mm), and the diamond disc is 23 thou (0.6mm) thick, so will fit the slot nicely. The width of the screw head is 5mm diameter, and with the 22mm diameter disc at the bottom of the slot, it cuts into adjacent timber.

A junior hacksaw blade fits the slot, even with the set on the blade, but I can't possibly see how a hacksaw blade could be used to clean out the slots of countersunk screws.

To make clearer what I mean, I've attached a sketch.

16mm diameter diamond discs aren't commonplace, but are available.

The set here for example includes four 16mm diam ones and two 19mm from a UK supplier:

http://www.ebay.co.uk/itm/6pc-Diamon...-/222450496787

The other problem with most Dremel type drills is that they run at far too high a speed for ticklish jobs - typically 10,000 RPM, though the '4000' goes down to 5,000 RPM. I use a small PCB drill and a speed controller for tasks such as this.

Hope that helps a bit.
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