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Late
Tinkerer
Username: Late
Post Number: 3
Registered: 10-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, October 09, 2008 - 12:27 pm: | 
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Hello again from Finland,
I just bought a Welta Welmy folder, that needs some CLA. The problem is that previous owner has completely destroyed the tiny aluminum screws that hold the focus adjustment ring in place. Only way to go seems to be to drill those buggers away. I found some advice from the archives, and it seems easy enough to drill them away with a hand held drill. I'm using a drill that's almost precisely the same diameter with the top end of the screw. Should I just keep on going with the same drill, effectively drilling away the threads and making one 'big' hole all the way through the ring, or should I try a smaller one in the latter part of the task? How about getting the ring attached again after I'm done with the CLA? Any advice would be greatly appreciated. |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 698
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, October 09, 2008 - 04:01 pm: |
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There are a couple of options. If you can stay smaller than the screw, there is a good chance (if you can stay on center) that the screw will loosen once you've got a hole bored through it and you may save the threads in the chassis. Your best chance is with a left-hand drill bit if you can find one, because once the screw loosens the drill will sometimes bite and unscrew it for you. Main down side is that I like using a battery powered Dremel for this (compact and easy to handle), and they don't run backwards for the left hand drills.
If the screw is very small, a small enough drill may be fragile and hard to work with; in this case, a small Dremel bit can drill a hole down to 1mm diameter while still having a 2.3mm diameter shank for strength. |
Dgillette4
Tinkerer
Username: Dgillette4
Post Number: 245
Registered: 04-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, October 09, 2008 - 05:12 pm: |
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A small easy out the size of the hole would work if all the screw isn't gone. Don |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 699
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, October 09, 2008 - 07:15 pm: |
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By the way, the screws are not aluminum ... at least not the ones I've encountered. The chassis is generally aluminum, the screws are generally either brass or steel. Particularly in the latter case, the screw is harder than the surrounding material, so keeping the drill centered on the screw is as critical as it is difficult. If it slips off center, it will prefer to cut the chassis rather than the screw. |
Glenn
Tinkerer
Username: Glenn
Post Number: 439
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, October 10, 2008 - 08:38 am: |
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Lauri,
Your initial idea of using a drill bit just under the diameter of the screwhead is a good idea - If You Only Use It To Remove The Screwhead. You can easily drill off the head in this way, if you take care. One then takes a screwdriver whose blade width equals the thread diameter, sharpens the blade end and then gently taps the blade into the end of the exposed screw shank, cutting a shallow slot. If one then turns the screwdriver, the screw stub should easily come out.
Sometimes when dissimilar metals are involved, a drop of an 'acidic' cleaner may be beneficial in dissolving the corrosion products. Any cleaner that removes limescale will be suitable - here in the UK I have found a household cleaning product called 'Cillit Bang lime and Grime' to work wonders on all types corrosion products, tarnish and rust etc. I have found this rather stupidly named product, to be invaluable when stripping down old and corroded photographic equipment. |
Late
Tinkerer
Username: Late
Post Number: 5
Registered: 10-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, October 10, 2008 - 12:26 pm: |
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Thanks for the advice. I'll give it a try. The screws seem to be aluminum in this case. They're very easy to drill. |
Paul_ron
Tinkerer
Username: Paul_ron
Post Number: 126
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, October 16, 2008 - 02:00 pm: |
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If you do drill the old screws out, use the correct size for the tap of the same size screw so you can just run the tap in later to chase the threads out again. |
