How to avoid stripping Screws when disassembling a Camera

[Poisson Du Jour]

You put Wartner on plastic and it will literally burn a hole in it, then you'll have much more than a stubborn screw to cry over.
The stuff is fairly nasty on plastic (corrosive by nature, which is why it's effective on some, but not all, warts). Another trick is to soak a cotton bud tip in WD-40 and press down against the screw to allow penetration. Leave for 1 hour. WD-40 is also excellent for dissolving adhesive residues.

 

[guitstik]

Cold applied to the screw would make it expand and make it tighter in the threads. It would be better to apply heat as with a soldering iron to the screw to make it contract and apply cold to the area around the screw hole to make it expand. Simple physics. Parts machined for close tolerance press fit are assembled this way.

 

[lxdude]

Wartner?

I guess it would work, but it risks making the metal more fragile and prone to stripping (worst nightmare)

I suppose you mean more brittle from being chilled, rather than more fragile. It is not likely to make it more prone to stripping, but could conceivably make it more likely to break. However, torque must be applied judiciously to anything that small, so I doubt it's a big worry.
If the material is soft, therefore more likely to be damaged by the screwdriver, the chilling will make it harder and more resistant to damage.

The shrinkage is key. If it is still tight, more force should not be applied. Letting it warm and chilling it again would be sensible. The repeated cycles will work, unless the screw has some kind of locking material in the threads. In those cases, heat from the tip of a soldering iron used carefully will be most effective, followed by letting the screw cool enough to shrink back to size, or subsequently heating the area around the screw as well. The problem could also be corrosion; the thermal shock and penetrants can usually free those up unless the corrosion is excessive.

 

[Steve Smith]

Cold applied to the screw would make it expand.

It would be better to apply heat as with a soldering iron to the screw to make it contract.

I think you have that the wrong way round: http://www.engineeringtoolbox.com/thermal-expansion-metals-d_859.html


Steve.

 

[lxdude]

I think you have that the wrong way round: http://www.engineeringtoolbox.com/thermal-expansion-metals-d_859.html


Steve.

I definitely agree, Steve. Simple physics.

Also, press fit parts are press fitted together. Parts assembled with chilled and/or heated mating parts are commonly referred to as interference fit, shrink fit or stress fit parts.
A press fit is a type of interference fit but the parts are not heated or cooled, just pressed together.

I remember one time at a place I was working someone got the bright idea to grease press fit parts to make them press together more easily. A little unclear on the concept. Lots and lots of scrap from that one.
I was the inspector who caught it. All the parts had a little grease on them right at the mating point. If they'd used oil I'd never have seen it.

 

[fotch]

Cold applied to the screw would make it expand and make it tighter in the threads. It would be better to apply heat as with a soldering iron to the screw to make it contract and apply cold to the area around the screw hole to make it expand. Simple physics. Parts machined for close tolerance press fit are assembled this way.

You got it exactly backwards. Cold contracts, Hot expands.

 

[guitstik]

Put a bottle of water in the freezer with the cap on and see what happens.

 

[guitstik]

Ok, I got my physics bass ackwards. Heat causes the atoms to move faster causing expansion, I stand corrected.

 

[John Koehrer]

Wasn't Wartner developed from used developer? You know, "Warts&all" I think it was German and lasts for years in the bottle.

 

[lxdude]

Put a bottle of water in the freezer with the cap on and see what happens.

That is due to a very unusual property of water, which is due to the way the molecules join at freezing.

 

[Christopher Walrath]

My advice would be to use a large enough screwdriver for the slot in the screw's head. Many a time have I employed a screwdriver that I estimated too small for the screw and the force of my attempting to turn the screw with the smaller blade dug right through the head. I have also had this ill-fated combination of too small screwdriver and screw actually strip an unwitting screwdriver rendering it useless for future work. So, take a few screwdrivers and fit them to the screw before exerting any force at all.

 

[TerryM]

... I remember one time at a place I was working someone got the bright idea to grease press fit parts to make them press together more easily. A little unclear on the concept. Lots and lots of scrap from that one.
I was the inspector who caught it. All the parts had a little grease on them right at the mating point. If they'd used oil I'd never have seen it.

You know the old saying: it's so hard to find good help these days.

 

[John Hermanson]

User proper fitting screw drivers. Press tip FIRMLY into screw so it does not ride-out and deform the head. If stubborn, possibly TIGHTEN slightly first to "un-seize" the screw. Sometimes apply "liquid wrench" or heat from a soldering iron (some screws may be "crazy-glued" in). Freezing screws? Have NEVER had to do that. John

 

[TerryM]

... Sometimes apply "liquid wrench" or heat from a soldering iron (some screws may be "crazy-glued" in). Freezing screws? Have NEVER had to do that.

The colder the screw is, the more the shrinkage, the more the bonds of friction will break, and the looser the screw will be in the seat. The hotter the metal is, the softer it is, and the more likely to warp or break. This happened to me when heating a rusted bolt on my car with an acetylene torch. The bolt sheared off. I had no problems whatever with freezing the screws in my camera.

 

[patrickjames]

I have used P.B. Blaster before for some tough problems. One was a stuck retaining ring on a lens that the manufacturer refused to touch (too old, no parts) so there was literally nothing left to do. You may have some cleaning to do afterwards, but at least it works. I spray it in a cup and apply it with a toothpick or a needle. Warning- a little goes a long way.

 

[lxdude]

I have used P.B. Blaster before for some tough problems. One was a stuck retaining ring on a lens that the manufacturer refused to touch (too old, no parts) so there was literally nothing left to do. You may have some cleaning to do afterwards, but at least it works. I spray it in a cup and apply it with a toothpick or a needle. Warning- a little goes a long way.

It's good stuff. And the warning is very apt.

 

[mgb74]

The OP's approach of rapid, short application of force would appear to imitate the effect of an impact wrench.

Check out gunsmith tools for a variety of screwdriver sizes (i.e. http://www.midwayusa.com/viewproduct/?productnumber=510765). One problem with cheap screwdrivers is that the ends are ground at an angle (looking from the side) so that only the top edge of the screw slot contacts the screwdriver. Better screwdrivers are ground so that there is contact the full area of the screwdriver bit.

PB Blaster is well known to anyone who drives a old British car.

 

[lxdude]

PB Blaster is well known to anyone who drives a old British car.

Like say, a masochistic owner of a '74 MGB?