Problem disassembling 300mm lens

Roka · Expire: 2017-04-07

I've run into a problem attempting my first disassembly and re-greasing. The lens is a Minolta MC Tele Rokkor-HF 300mm f/4.5. I got it disassembled to the where I had to remove 6 body screws. 5 came out but I think I've stripped the head on the 6th one. My only idea was to use my Dremel Tool to try and open the slot a bit. Any other ideas or suggestions?

The lens:

The screw:

Lloydy · Expire: 2022-01-01

the Dremel should be your last resort.
My first option would be - soak the screw in lighter fluid or acetone, there might be thread lock on the screws - if there are traces of white dust on the screws that came out then it's probably thread lock.
Second, get a small electrical soldering iron with a pointed tip and heat the screw. The screw is steel and the lens aluminium and the have a different coefficient of thermal expansion - the screw will expand and the aluminium around it should expand slightly more
Third, and this might help with any attempt to remove the screw, tap the top of the screwdriver before turning it. Maybe sacrifice a screwdriver and make a sharp chisel point on it, tap it into the slot, then use a good screwdriver - maybe tap that in to get it into the 'new slot' - and turn that.

I've sheared the tops of screws in the past, but never failed to get the remains out - eventually

Gerald · Joined: 25 Mar 2014 Posts: 1196 Location: Brazil

In my experience, a hot air gun is much more efficient than a soldering iron. The reason is that a typical soldering iron with fine tip is a low-power heat source.
With a hot air gun, the procedure I usually use is:
1) Cover the screw head with an adhesive tape with a hole slightly larger than the screw head. The adhesive tape is important to protect neaby plastic or rubber parts that could be damaged by hot air.
2) Adjust the hot air temperature to about 250 °C.
3) Heat the screw head for about 30 seconds.
4) Apply acetone on the screw head with a cotton swab.
5) Try to unscrew the screw.
6) If the screw looses, great. If not, repeat steps 3, 4 and 5 until succeed.

Roka · Expire: 2017-04-07

Thank you both for the replies! I'm glad I didn't immediately break out the Dremel Tool as that probably wouldn't have ended well. I don't have either a soldering iron or a heat gun so I just ordered a small heat gun which should arrive on Wednesday. I also have to get some acetone as my wife doesn't do her nails - neither do I. Wink

After I get both I'll try again on the screw and let you know how it goes.

Jiaming · Joined: 09 Mar 2016 Posts: 107

There are tiny screw extractors for sale, either on amazon or on ifixit. Do give them a try before you turn to heavy duty machines.
If the screw is already loose, you may try to turn it with a needle or whatever sharp tool that can provide enough friction, slowly. When there is enough length for a pair of tweezers, use a pair of those to remove.
I was once very lucky to be able to remove a dead screw with a needle, but this is unlikely to hold true for every case.
Good luck!

Roka · Expire: 2017-04-07

Gerald · Joined: 25 Mar 2014 Posts: 1196 Location: Brazil

A 10mm heat gun nozzle is ideal, but be sure to protect the plastic parts and paint with a tape or kitchen aluminum foil. You can use a higher temperature, up to about 350 °C (662 °F) for particularly difficult cases. The tip of the screwdriver must have sharp edges to reduce the chance of tip slip and consequently damage of the screw head. If necessary sharpen the screwdriver tip with a sandpaper or a small grinder. The most important thing is to have patience.