Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
10-06-2016, 01:57 PM   #1
Senior Member




Join Date: Sep 2013
Posts: 122
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
Site Supporter
Site Supporter




Join Date: Nov 2012
Location: North Wales
Photos: Gallery | Albums
Posts: 2,850
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
Site Supporter
Site Supporter
mattb123's Avatar

Join Date: Apr 2010
Location: Colorado High Country
Photos: Gallery
Posts: 10,864
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
Site Supporter
Site Supporter
DeepThrob's Avatar

Join Date: Nov 2012
Location: Taos, New Mexico
Posts: 295
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
Moderator
Not a Number's Avatar

Join Date: Mar 2012
Location: Venice, CA
Posts: 10,503
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
Senior Member




Join Date: Sep 2013
Posts: 122
Original Poster
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
Senior Member




Join Date: Feb 2013
Photos: Gallery
Posts: 168
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
Senior Member




Join Date: Sep 2013
Posts: 122
Original Poster
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.
08-13-2020, 07:51 AM   #9
Forum Member
Praktica*ist's Avatar

Join Date: Jan 2013
Location: France, near Paris
Posts: 56
searching for K-mount replacement screws

Mega-bump !

So, I had stripped a few screws on K-mount lenses way before. Now I'm more cautious on applied forces, for avoiding the cam-out of the screwdriver. Plus, having Japanese-made cross point screwdrivers also helps.

Nevertheless, I have several lenses, which have been badly tinkered by previous owners. Some screws here or there need replacement, and I cannot find exact replacement parts for these K-mount miniature screws.
Here is what I measured with an old caliper :

  • Apparently 2mm thread diameter, so a metric M2 thread, most probably a standard pitch.
  • 3mm total length.
  • Only about ~0.6mm head thickness, flat-type.
  • 3 mm head diameter.


In my country, I have found only one online serious supplier for general public, that provides many micro-screws, with the appropriate data. But none of them are a good match for K-mount screws.
Their nearest equivalent that I found are described like this :

  • DIN 7985 norm, mmmh OK,
  • M3 , M2.5 , M2, or M1.6 or even thinner. M2 seems about right.
  • 1.6 mm head thickness, which seems quite too thick,
  • 4 mm head diameter, flat on the inner side, slightly bulbous on the tip side.
  • Available with 3, or 4, or more total length.

So it would be maybe possible to take a 4mm length screw like this, sand the head to make it thinner, sand again the head but tangentially, in order to reduce its diameter down to 3mm or so.
And hope there is still enough material left to engage a PH0 / PH00 screwdriver properly.

I have some modelling tools to do the trimming. But it would be a lot of hassle, for each screw, and many to modify.



So if anyone has a better source for K-mount replacement screws, and confirm my measurements, it would be very nice indeed.
08-13-2020, 10:49 AM   #10
Moderator
Not a Number's Avatar

Join Date: Mar 2012
Location: Venice, CA
Posts: 10,503
The parts diagrams I've seen for many Pentax lenses usually list the diameter at 1.7mm.

Edit: looking at some of the camera parts lists Pentax uses 2.0mm diameter screws on the camera side of the mount so it is possible 2.0mm are used on the lens mount side.

Measure with an accurate micrometer to be sure.

Last edited by Not a Number; 08-13-2020 at 11:05 AM.
08-13-2020, 10:58 AM   #11
Forum Member
Praktica*ist's Avatar

Join Date: Jan 2013
Location: France, near Paris
Posts: 56
I just grabbed a Pentax-K lens, removed a screw, and my caliper lines up at 1.95 mm for the threaded part.
On maybe the 2 in M2 is about internal diameter, without the helicoid ??


Edit : after a short research, the number in metric standard screw is indeed the external diameter of the thread. The real measurement can be a little less, because the carving of the original rod from which the screw is produced removes a bit more material than intended. Hence the 1.95 mm I measured. The second number indicates the thread length, sometimes excluding the head, sometimes not (countersunk type).


So I will order M2*3 mm DIN-7985 screws, and sand the head to approximate the dimensions of K-mount ones. Unless someone has a better reference.

Last edited by Praktica*ist; 08-13-2020 at 11:54 AM.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
35mm, drill, driver, f/2.8, head, k-mount, mm, pentax lens, pentax-m, pressure, primes, repair, screw, screwdriver, screws, slr lens, tip
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
For Sale - Sold: Pentax F 50mm 1.7 Mint, M 28mm 2.8 in the box & K 55mm 1.8 Excellent. jjdgti Sold Items 8 07-18-2015 05:22 PM
Help me decide: Too many Rokkors (28/2, 35/1.8, 58/1.2, ...) Boris_Akunin Canon, Nikon, Sony, and Other Camera Brands 5 11-23-2014 03:42 PM
What should I buy, DA 35 mm 2.4 or DA 50 mm 1.8 flaviopetrone Pentax SLR Lens Discussion 30 10-25-2014 02:03 PM
For Sale - Sold: Pentax DA 35 mm f/2.8 Limited, Sigma 24 mm f/1.8 macro Vantage-Point Sold Items 15 01-03-2013 07:11 AM
For Sale - Sold: Classics - Tokina 19-35/3.5-4.5, M 50/1.7, Vivitar 28/2.8 PK/A, Sigma 90/2.8 M stillshunter Sold Items 14 03-14-2010 01:19 PM



All times are GMT -7. The time now is 08:43 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top