Ai Conversion - Getting the mount off

[Roland Vink]

I have a couple of K (New Nikkor) lenses and managed to obtain original AI conversion rings for them. Yesterday I tried to install them. I borrowed a solder iron to heat the screws (to soften the loctite) but has no success, they wouldn't budge. I only have a regular set of small screwdrivers - probably Phillips (not JIS) and the screwdrivers have a narrow handle so I wasn't able to apply much torque. Any tips on  getting them out? I probably should invest in some JIS screwdrivers - what would you recommend? Thanks.

(not sure if this belongs in the "nerds" section ?)

[Bjørn Rørslett]

Maintenance or modification of Nikkors is suitable for the "Nerds" board.

You definitively need a set of JIS screw drivers. Standard Philips drivers can easily rip or damage the screw heads when the screws are tight. Use only JIS drivers and press hard, then first try to slightly tighten the screw further before you flick the driver in the opposite direction.

You might want to soak the mount by a solvent such as hexane overnight before next try, even with the proper JIS tools.

Microtools.com is a good source for JIS screw drivers.

Early Nikkors can really be a tough challenge. Often the loctite bonding has almost petrified after decades. If soaking doesn't suffice, try putting the lens in the deep freezer over night, then immediately apply heating with the tip of a narrow solder iron.

Last resort is using a small hammer to make sure the screw driver is well and truly stuck in the slots, then apply lateral torque. Or use a narrow drill bit 1-1.5 mm in a solid chuck and drill out the screw. Be warned this should be done with the drill in a jig not hand-holding it, as the screws can be *very* hard and unless you do this carefully, the drill bit can easily skid off the target and cause a lot of damage in the mount itself.

[Øivind Tøien]

My experience with the soldering iron is that it may take lots of repeats varying heating time, with immediate wiggling back and forth of the screwdriver  (not necessarily with maximum force, but with high downwards pressure) at each try. The keyword is repeated thermal expansion/contraction. A cold pack might be useful to cool things down between repeats. So there might be hope even if there is no initial success. And yes, definitely use a JIS driver.

[Erik Lund]

Most important is to; Have a stable table top to work on, remove lens hood filters etc, select a screwdriver that fits 100% into the screw, stand up so you have your uppere body weigth over the lens, unscrew the screws...

[Øivind Tøien]

Erik, which JIS driver # do you find fits best into the mount screws?

[Erik Lund]

I use a handful of different screwdrivers some JIS some Phillips form different makers, and select one that fits the particular screw best...

Sorry i don't hve the sizes at hand, I can check later...

Also i buy replacements quite often as they wear or break

I have some special ones; for instance for the contact block screws, it's very thin so it doesn’t touch the munt contact surface or the rear of the rear of the bayonet

[Bjørn Rørslett]

Can attest to the statement that JIS drivers often have short longevity. It is not unusual they only last a few months if used frequently. The old screws are amazingly hard and really test the screw driver's strength.

The middle sizes are best for mount screws.

[Øivind Tøien]

Yes, I am already on my second set in spite of only occasional use. I got some with shorter blade then - much less rotational elasticity in the smaller sizes.

[arthurking83]

I have two questions for the masters:

1. I have a lens with a totally chewed out screw, as in it's totally unusable as a cross head screw(in any meaningful way).
I'm pondering options to eventually get it out to effect an eventual CPU conversion.
My two thoughts were
a/. epoxy a sacrificial small well fitting screw driver of some type just to remove it once and for all, or
b/. dremel out a slot in the screw to fit a larger slotted screw driver.

(the other 4 screws come out with ease)

Either way this one screw itself is dead, so the next question is, where can the correct screws be found as replacement parts?
Are they stainless steel, or any other material.
I know of a couple of possible local suppliers of screws, but don't hold my breath that they will have an appropriate part.

The lens is the 105/1.8 Ais.

[Erik Lund]

First try with the correct size of screwdriver, and as above apply a lot of force down before unscrewing.

Or simply drill off the head of the screw and use pliers to remove the stud that is left when the mount is off.

Then re-use screws from a donor lens.

[Erik Lund]

BTW first clean the 'socket' part of the head completly and use a brand new screwdriver!

Or send the lens to me for chipping I have new screws at hand ans well...

[Bjørn Rørslett]

In addition to what Erik said: yes, these mounting screws appear to stainless steel, and made of a very hard material as well. So if you want to drill a recalcitrant screw out, use a small bit first to get a "starting hole", then switch to a larger size but not as large as prone to damage the threads below the head.

[Hugh_3170]

Arthur, your option (b) might work.  I have successfully used it in other applications.  I guess that it could also be combined with your Option (a).

There maybe an Option (c) as well if a sacrificial screw can be spot welded onto the screw with the chewed out head.  You would need to protect the rear lens elements and have someone with MIG or TIG skills to do the weld for you.  This way you can get a good unblemished head to work with again.  Earlier advice about heat / cool cycles and use of a soldering iron with a suitably (re)shaped tip still applies.

This method is frequently used to remove studs and broken bolts for engines.  That said, the spot welding is actually easier for larger sized screws and studs that are usually not made of stainless steel.

 Erik's suggestion should work if there is enough of the screw left after drilling off the old screw head.  Best to make this assessment by looking at one of the removed screws.

Good luck.

[Erik Lund]

If drilling, only drill as little as possible until the head pops off. Done this many times!

In 99% percent of the cases you will have plenty to grip onto by a new sharp JIS screwdriver, since when you misuse a Phillips screwdriver on a JIS screw you just grind away the central portion of the four grip surfaces, so clean up the 'hole' and procede to unmount the screw. Done this many times as well....

I would love to see an image of the spot welding removal on a lens mount screw!

[arthurking83]

The cross slots are almost completely rounded. Who ever tried to remove the screw before I acquired the lens did a brilliant job of killing it.
I reckon they've just tired successively larger non fitting screw drivers and kept rounding the slots with each attempt, you can't see any slots easily except under a magnifying glass, and you can feel that the slots are very minimal.

Only drilling or one of my two methods would probably succeed.

I suppose I could even try some spot soldering as another alternative. Quicker than epoxy. I have no idea how strong electrical solder is tho.