Fine-thread lens assemblies - best way to avoid cross-threading?

jay moussy · Jun 26, 2022

When working on lens parts, like a front lens assembly (like with my Isolette, cleaning underway), what is the best technique(s) to avoid cross-threading these very fine pitch threaded parts?

I understand having very clean parts for positive feel, calm approach, and relaxed body.

Other tips?

GRHazelton · Jun 26, 2022

Turn the piece in the wrong direction, and hope that you can feel when it "drops" down at the beginning of the threads. I've used this technique successfully, of course it may depend on how fine is the pitch..... As always, YMMV......

pentaxuser · Jun 26, 2022

It is a useful question and I have never tried or don't think I have, threads as fine pitched as those on cameras but as someone who has experienced the problem of cross threading with possibly more coarse threads then other than what you have mentioned, all I can say is that very slow careful turning is required and the need of being mindful of the slightest of changes in the torque needing to be applied by your fingers. Once you feel even the slightest of tightening before you have turned enough to have this kind of tightening beginning then ease back instantly, unscrew and start again

Every time I have got into trouble it has always been because I hadn't maintained my sensitivity to the torque. I had allowed my senses to dull

pentaxuser

btaylor · Jun 26, 2022

GRHazelton said:
Turn the piece in the wrong direction, and hope that you can feel when it "drops" down at the beginning of the threads. I've used this technique successfully, of course it may depend on how fine is the pitch..... As always, YMMV......

This. Also the other comment about being mindful of torque changes.

Dan Daniel · Jun 26, 2022

GRHazelton said:
Turn the piece in the wrong direction, and hope that you can feel when it "drops" down at the beginning of the threads. I've used this technique successfully, of course it may depend on how fine is the pitch..... As always, YMMV......

I will add that for a large number of threads that I have run into, it is the >second< drop that is the start of good threads, not the first time it does that little drop. Very very closely spaced, but still the second drop is needed. I guess it's a minor offset in the cut of the last bit of threading on multiple threaded pieces. Experiment going backwards and you might find that there are two very closely spaced 'click' drops, then nothing, then another, etc....

Of course on a bolt with a single thread, no second drop.

GRHazelton · Jun 26, 2022

Dan Daniel said:
I will add that for a large number of threads that I have run into, it is the >second< drop that is the start of good threads, not the first time it does that little drop. Very very closely spaced, but still the second drop is needed. I guess it's a minor offset in the cut of the last bit of threading on multiple threaded pieces. Experiment going backwards and you might find that there are two very closely spaced 'click' drops, then nothing, then another, etc....

Of course on a bolt with a single thread, no second drop.

Thanks for the clarification. Dan Daniel is an expert; his method is to be followed.

Sirius Glass · Jun 26, 2022

Dan Daniel said:
I will add that for a large number of threads that I have run into, it is the >second< drop that is the start of good threads, not the first time it does that little drop. Very very closely spaced, but still the second drop is needed. I guess it's a minor offset in the cut of the last bit of threading on multiple threaded pieces. Experiment going backwards and you might find that there are two very closely spaced 'click' drops, then nothing, then another, etc....

Of course on a bolt with a single thread, no second drop.

My experience it is usually the first drop but I give about half a turn or a full rotation and that usually enough on the first attempt.

Dan Daniel · Jun 26, 2022

GRHazelton said:
Thanks for the clarification. Dan Daniel is an expert; his method is to be followed.

( lots of experience and expertise around here, and I would never claim the final word on anything.)

gone · Jun 26, 2022

The key, along w/ the sound advice that you've already received, is to go slow. If at any time something binds, back it off and look at things closely w/ a magnifying glass, a good one that doesn't have you squinting. That will almost always show you where the problem is.

Sometimes I've had to put the slightest bit of a light oil on the threads and screw things all the way in, or on, just to confirm that the threads are actually OK before fully reassembling something. Just remove it w/ a Q-Tip and alcohol if it's supposed to go together dry.

AgX · Jun 27, 2022

GRHazelton said:
Turn the piece in the wrong direction, and hope that you can feel when it "drops" down at the beginning of the threads. I've used this technique successfully, of course it may depend on how fine is the pitch..... As always, YMMV......

My approach too.

Sirius Glass · Jun 27, 2022

I would avoid putting even a little oil on the threads especially for camera equipment.

AgX · Jun 28, 2022

One could consider a dry lubricant as graphite etc. or lubricating wax.

But especially with the wax I see disadvantages too.

jay moussy · Jun 28, 2022

I am stuck at the lubricant part.

I have access to an auto parts store and and a well-stocked bike shop.
A quick reconn at both. I saw Permatex "Ultra Brake Lubricant at auto, and two other options at the bike shop, "Finish Line" Dry Lube with Teflon and something else.

I told the shop guy about my project, and we went behind the counter, where he gave a tiny amount of his shop grease, which is, you guessed it, green. I had to tell him about the Agfa grease!

AgX · Jun 28, 2022

Finish Line Wax for Dry Weather (solvent based) is my bike chain lubricant all year trough. But I am still unsure about it being beneficial at applying at fine mechanics as dry lubricant. But still it would be my only alternative to pure C/MoS2 particles or Teflon particles in varnish.

BrianShaw · Jun 28, 2022

For fine threads like lens cells I generally clean scrupulously and leave dry, but some seem to never get smooth so have used this product. Probably what AgX mentioned. Works great if applied judiciously. good on view camera rails and sliders like speed graphics.

Finish Line - Bicycle Lubricants and Care ProductsDry Lube

www.finishlineusa.com

Tel · Jun 28, 2022

I used to think I was good at this until I tried reassembling the multiple helicoid threads on a Nikkor 55mm macro. Thankfully it was a junker and I was using it to practice--I never did get it right.

BobUK · Jun 28, 2022

I also use the reverse twist until it drops into place.
If you definitely need lubricant on a thread that doesn't usually have any on it, use a soft drawing pencil to rub the threads with.
A 4b pencil is soft leaded and should work fine.

jay moussy · Jun 28, 2022

BobUK said:
I also use the reverse twist until it drops into place.
If you definitely need lubricant on a thread that doesn't usually have any on it, use a soft drawing pencil to rub the threads with.
A 4b pencil is soft leaded and should work fine.

I like this, even though I could use the product on post #15 above in other applications, as described by @BrianShaw

What about the old classic, nose grease?

BrianShaw · Jun 28, 2022

Pencil lead ~~is mostly~~ contains various amounts of clay. Why use substitutes of uncertain qualities when a properly engineered product is readily available and affordable? It’s like using Vaseline on helicoils rather than real damping grease… penny wise and pound foolish, IMO and IME. I won’t even comment on “nose grease”…. LOL

EDIT for clarity. "mostly" is an overstatement that really needed to be corrected. No. 2/HB is about 25% clay. 4B, mentioned by @BobUK is about 15% clay. A 8B is about 5% clay. All seem to have about 5% of some sort of wax, also. Per https://onlinelibrary.wiley.com/doi/abs/10.1111/1467-8659.00386

AgX · Jun 28, 2022

BrianShaw said:
For fine threads like lens cells I generally clean scrupulously...

I hardly got lens cell threads to clean, but a lot of lens-mount threads. Here after cleaning in addition I meticulously check the threads themselves, for dents or burrs, which I correct.

Dan Daniel · Jun 28, 2022

This is a nice helical grease-

1oz HELIMAX-XP Camera Telescope Optical Instrument Focusing Helicoid Grease PTFE | eBay

Excellent lubrication in a light and clean formulation perfect for helicoid service. HELIMAX-XP Contains Lithium Stearate (Lithium "Soap") and sub-micron PTFE for superb lubrication in a light and clean formulation perfect for helicoid service.

www.ebay.com

NLGI- #1 is a key bit of info. #1 is the lowest viscosity, lower 'stiction' or whatever term you'd like to use. I'll put some on and wipe 90% off, see what happens.

There are assorted helical greases out there for cameras. Mainly from Japan. A few different grades. I don't know the terminology so can't tell why one is different than another, etc. You find many here-

Lubricants

Shop COT, Lubricants, Origin - USA and more Lubricants at Micro-Tools

www.micro-tools.com

This Park Tool grease comes in tubs and is common in bicycle shops. Very likely what the bike shop gave out-

PPL-2 PolyLube 1000™ Lubricant (Tub)

A durable all-purpose grease for bearings, threads, or surface preparation, in a handy 16 oz. tub.

www.parktool.com

Be aware that most 'bicycle' lubes are repackaged versions of common industrial lubes. For example, Phil Woods Waterprooof Grease was boat trailer bearing grease repackaged from 55 gallon drums into 3 ounce tubes, according to someone familiar with the company.

BrianShaw · Jun 28, 2022

Hi Dan. For sure there is repackaging in most consumer sized items that we buy. Are you aware of any problems with the bike lube? I know there is rampant adulteration/misrepresentation of olive oil so for that and most items I buy only from reputable companies and wary of “private labels”.

Dan Daniel · Jun 28, 2022

Brian, I think it depends on what it is being used for. Your dry lube, for example, might be teflon or such suspended in a wax with solvent carrier (if it emerges with any liquidity, I'm not sure). The nice thing there is that with threads most of the material will be pushed back in assembly. And the stuff inside the threads will stay there. With little or no gassing off, a problem with oils and greases in lenses as most of us have seen.

The main concern I have had with bicycle products is density and such. A bicycle part is usually under higher stress and pressure, motion, etc, than a camera part. So the lubes I have seen and tried on cameras often were simply too thick, etc.

But I haven't spent time collecting assorted products, from bicycle shops or most other places. I'll hear about things from places like here and might try them if something seems a little off. All in all my best rules are- thinner and lighter is better; if it spins- oil, if it rubs- grease; less is always better.

Fine-thread lens assemblies - best way to avoid cross-threading?

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