Removing stripped screws from Nikkormat lens mount

[George Mann]

Hi. I have a Nikkormat that has stripped screw heads in its lens mount. I want to remove it to fix the ASA lock, and possible clean the resistor ring (difficult?).

Should I just tap them out and replace them, or do you have other things to try first?

 

[runswithsizzers]

Just to be clear, it is the cross-point (aka Phillips, aka JIS) screwdriver-part of the screw head that is stripped, and not the threads?

I assume you have tried a proper JIS screwdriver of the correct size rather than the more common (in USA) Phillips head screwdriver?

If the head slots are too badly damaged for the JIS screwdriver to work, my next step might be to try some kind of "easy out" (there are several types, and there is nothing "easy" about any of them). The easy outs require drilling a hole of the correct size into the screw and then using a reverse twist bit to unscrew the screw. When you get down to screws of this size, it's exacting work, and success may depend on great skill and some luck, as well.

Another possibility: if you can drill out the screwhead (only the head), and remove the lens mount, there *may* be enough of the headless screw sticking out to allow grasping it with some kind of grippers: pliers, visegrips, etc.

Finally, I've had some success using a thin abrasive wheel (cut-off disk) on a Dremel-type rotary tool to cut a slot in the screw head for removal with an ordinary slotted screwdriver. I will be difficult to do without marking up the surrounding lens mount, but if you don't care about cosmetics, it might work.

 

[George Mann]

Just to be clear, it is the cross-point (aka Phillips, aka JIS) screwdriver-part of the screw head that is stripped, and not the threads?

Yes, and apparently, whoever damaged them really cemented them back into place.

 

[MattKing]

Just to be clear, it is the cross-point (aka Phillips, aka JIS) screwdriver-part of the screw head that is stripped, and not the threads?

If someone has been trying to use a Phillips screwdriver on JIS screwheads, there is no surprise that they have been stripped.
Different size and angle.

 

[runswithsizzers]

Yes, and apparently, whoever damaged them really cemented them back into place.

Uh oh. If they used Loctite, the strong kind: blue, or may the heavens forbid it, red, or epoxy - then a little heat may help. Carefully go at them with a clean, fine point soldering iron. I forget the target tempertures, but do a search.

As a bonus, cutting a slot with the Dremel cutoff wheel, or even drilling *may* generate enough heat to help with the glue.

 

[runswithsizzers]

Re-reading my first post (#2), I would re-prioritize and move "easy-outs" to the bottom of the list. With the skills and drills available to me, I would probably not attempt to use an easy-out on any screw with a diameter of 1/8 inch (3-4mm) or less. I am guessing your lens mount screws are more like 2mm or a little less, yes? no? I am talking about the threaded part. Have you been able to get ANY of them out to measure? If not, see if you can find out the correct size via an internet search or discussion with a camera repairman.

However, I see several positive reviews on <this type> of screw extactor, which is one I have never tried, so might be worth a try. Says:
"4 double-ended, reversible screw extractor blades, sizes (each end listed): 1.1 mm x 1.5 mm; 1.25 mm x 1.25 mm; 1.5 mm x 1.5 mm ; 2.0 mm x 2.0 mm"

 

[George Mann]

I am guessing your lens mount screws are more like 2mm or a little less, yes? no? I am talking about the threaded part. Have you been able to get ANY of them out to measure?

They are as small as you assume. 2 of them may come out without trouble. The other 3 feel like they have cement in the threads.

 

[George Mann]

I thought about drilling their heads off, and removing whats left with vice grips once the mount was removed.

 

[runswithsizzers]

I thought about drilling their heads off, and removing whats left with vice grips once the mount was removed.

Considering the lens mount is somewhat thick - several millimeters, right? - you might have a half-way decent amount of screw to work with once the lens mount is out of the way. Still, it's kind of a one-shot deal. The screw extractors I mentioned above work on the head of the screw, so once the heads are drilled out, that is no longer an option.

Vice grips are great when they work, but when they don't, what's left is sometimes not pretty. Consder getting a new pair, smallish, the best ones you can find, then dress the tips of the jaws with a grinder to make a crisp hard edge. If it wasn't for the glue, once the head is removed, the screw is no longer in tension, and it should take much less force to unscrew it. If it wasn't for the glue.

Can you see enough glue residue to guess what kind of adhesive was used?

 

[George Mann]

The screw extractors I mentioned above work on the head of the screw, so once the heads are drilled out, that is no longer an option.

I will try to extract them first.

Can you see enough glue residue to guess what kind of adhesive was used?

Unfortunately not. Regardless of whatever else the said individual did, I just wish whoever was in there the first time didn't break the asa lock.

Everything else but the mirror lockup works on it.

 

[AgX]

If someone has been trying to use a Phillips screwdriver on JIS screwheads, there is no surprise that they have been stripped.
Different size and angle.

I ONLY use Phillips designated ones on those tiny japanese screws and they fit perfectly. Here in Germanmy nobody knows of JIS.

In any case, with whatever screw head: either look for a screwdriver with perfect fit, or make one oneself.

Yes, I make screwdriver tips myself, if necessary.

 

[AgX]

Back to the OP's question:

For such tiny threads the standard approach of drilling a hole and inserting a special screw-out bit (conical with counter-orientated helical ridges) likely does not work by lack of such tiny bits.

There are however screw-out bits with special counter-orientated low-angle drill heads, such might grasp a worn out cross-head.

In case such fails the next approach I see is drilling a hole with a drill that got a counterwise orientation. By the counterorientation the screw may come free. Problem by the small size is to get the drill right in center and axial, not to damage the thread.
A drillstand (best with milling table) is a necessity here for centering. However the counter directed forces (screw against drill-stand) will likely keep te screw from coming out. Thus move the drill axially by hand.

If that fails, a bigger thread must be cut.

 

[George Mann]

Understood AgX. Thanks for your help guys.

 

[shutterfinger]

Factory thread sealant was Glyptal or similar sealant that dissolves with Acetone. Glyptal is clear.
Loctite 242 Blue breaks loose with 40 inch pounds of torque.
Loctite 271 Red has to be heated to 500°F to break loose.
Soak with acetone (some nail polish removers are acetone based and work) for 5 to 15 minutes then try to unscrew them. Its likely the previous person was unable to remove the screws. Nikon does not like its lens mounts coming loose! I had a similar problem with a FA.

 

[John Koehrer]

I'm of the opinion fwiw that the best option is this one*.
Another possibility: if you can drill out the screwhead (only the head), and remove the lens mount, there *may* be enough of the headless screw sticking out to allow grasping it with some kind of grippers: pliers, visegrips, etc.
*Used it several times. using a dremel on a lens mount is not going to be a clean job.
I't also reasonable to use a screw slotting file on the remainder of the screw when the head is removed.

Could've used the Moody screw extractors when I was working.

 

[AgX]

Another possibility: if you can drill out the screwhead (only the head), and remove the lens mount, there *may* be enough of the headless screw sticking out to allow grasping it with some kind of grippers: pliers, visegrips, etc.

Good point. one even may cut a slit into the shaft for turning it out.

HOWEVER, in this very case we got sunk-heads. Taking off such thead will not leave a thread shaft.

 

[George Mann]

Its likely the previous person was unable to remove the screws.

I believe he/she/it got in there alright. The lens-mount assembly is slightly loose (but doesn't rotate), and the asa lock has been disabled.

 

[Sirius Glass]

With patience and care, drill a hole into the center of each screw, then use an easy out, I use a tap holder to hold it, slowly turn it counter clockwise and the screw may come out. A tiny bit of WD-40 or penetrating oil may help.

Take a look at these videos: https://www.google.com/search?client=firefox-b-1-d&q=easy+out/tap+set+tool