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10-06-2016, 01:57 PM   #1
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Help! Destroyed screws in PENTAX-M 1:2.8 35 mm

I have a PENTAX-M 35mm F/2.8. It has a slow aperture. So, I thought I should disassemble it and fix it.

But, some previous owner have had the same idea and destroyed two of the screws.
There are no crosses there any more, just two round holes.

The three other screws I have loosened without any problems. But, of course, the two destroyed
screws is a problem. First I need to take them away somehow, and then I need new screws.

So - my question is regarding those two topics.

1. What is the best way to remove the screws?

2. Where can I find new screws?

The diameter seems to be 1.9 mm (maybe 2 mm) and the length, including head is 2.8 mm.
And the head is very thin.

10-06-2016, 02:58 PM   #2
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First thing: these are JIS screws see here:

https://www.pentaxforums.com/forums/114-maintenance-repair-articles/119344-cr...s-caution.html

I assume the damaged screws are on the mount. While there are various suggestions for coaxing out damaged head screws inc using a heat source (soldering iron, heat gun), in this case I would be tempted to complete the removal of the screw head using a drill and lift the mount off, exposing the stud which can then be gripped with eg a small mole wrench.

The easiest source of a couple of replacement screws is a junk lens. Not sure where you are located, if in the USA dcshooter on this forum for example does lens work and is likely to have some. Otherwise JIS screws are metric threads and there are any number of suppliers of 1.6mm/2mm/etc dia thread machine screws. Best to take one of the screws (or the mount and test the engagement of screws in the thread) to a local engineering shop and get it measured with gauge/calipers, would be easy to get the wrong ones otherwise.

Last edited by marcusBMG; 10-07-2016 at 04:54 AM.
10-06-2016, 03:13 PM   #3
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I stripped a screw on one of my Leica lenses and ended up sending it to Eric Hendrickson who replaced the screw and finished the conversion I was trying to do for a very reasonable price.
10-06-2016, 04:54 PM   #4
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QuoteOriginally posted by mattb123 Quote
I stripped a screw on one of my Leica lenses and ended up sending it to Eric Hendrickson who replaced the screw and finished the conversion I was trying to do for a very reasonable price.
I usually put drop of acetone on each screw and heat it all up with a hot hair drier. A quick, well controlled jerk will be more effective than constant pressure and a big handled screwdriver that just fits the groves is a lot more effective than a little thin jewelers screwriver. Once you get the mount off you will likely be able to to remove the broken screws with a small needle nose vice grip.

10-06-2016, 06:35 PM   #5
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Normally you drill out the damaged screws with a screw extractor.

Micro-Tools -
http://www.metricscrews.us/index.php?main_page=index&cPath=21
http://www.micromark.com/mini-extractor-and-screwdriver-set,8570.html

You might be able to find a suitable sized screw from various sources that sell "micro screws". They need not be cross head screws.

Machine Screws - Micro Fasteners
http://www.metricscrews.us/index.php?main_page=index&cPath=98
10-07-2016, 06:23 AM   #6
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Thank you for your answers. So - it seems like it was dangerous to use my Philips driver to remove the three undamaged JIS screws. You learn new things all the time.

BTW - found JIS bits here:

K

BTW - is this a suitable screw?

MSPPS2003 - M2 x .4 x 3mm - Pan Head Machine Screws - Phillips - Stainless - Micro Fasteners

Is the head thin enough?
Is it an M2x0.4 screw?
10-08-2016, 02:55 AM   #7
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Did you get them out, yet? Not sure if it will work with screws that small, but usually you can help yourself with some rubber band that you put between screw and screw driver. Maybe you'll have to find some really thin rubber for screws that small, but I'd give it a try.
10-09-2016, 05:30 AM   #8
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I managed to get the two destroyed screws out. First I applied some acetone. Then, one of the screws was just easy to take out with the philips screw drive. The second one was harder. I hade to use a sharp "awl" at the edge of the screw head, forcing it around. So, now they are out. I have three undamaged screws. Maybe that is enough. Otherwise, I need two screws.

I have ordered a som bits, containing JIS 000, 00, 0 and 1 bits. I think I shall wait to open the lens until I have got the right bits.

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