Copy stand

An old Kodak DIY design. You need some 1/4 Whitworth bolts (tripod thread) and wing nuts, and a piece of wood.

Don Cox

D Cox wrote:

An old Kodak DIY design. You need some 1/4 Whitworth bolts (tripod thread) and wing nuts, and a piece of wood.

Quite elegant; a lot of the old Kodak guides are.

I use an old Spiratone Doubl-o-gram II enlarger as a copy stand, but this is pretty appealing as a DIY project.

The only thing not so good in this design is that it looks like they are using a flat block (E) to clamp against the rear corners of the uprights, and that is very likely to have wear problems. I'd suggest instead using a piece with a 90-degree angle for the clamping. That could be something like the F+J assembly, or even something like:

Also probably good to put some slightly compressible material on the contact surfaces to increase friction.... Note that the inside angle isn't needed; it could be a straight 90-degree angle on the inside.

D Cox wrote:

You need some 1/4 Whitworth bolts (tripod thread)

Are you sure?  As far as I know, it is 1/4"-20 UNC.  Nice design, though.

ThrillaMozilla wrote:

D Cox wrote:

You need some 1/4 Whitworth bolts (tripod thread)

Are you sure? As far as I know, it is 1/4"-20 UNC. Nice design, though.

Interesting.

Apparently Whitworth and UNC are compatible despite having a quite different thread profile: 55 degrees rather than 60 for UNC angle between thread peaks.

The ISO 1222:2010 standard says 1/4-20 UNC for tripod heads.

ProfHankD wrote:

ThrillaMozilla wrote:

D Cox wrote:

You need some 1/4 Whitworth bolts (tripod thread)

Are you sure? As far as I know, it is 1/4"-20 UNC. Nice design, though.

Interesting.

Apparently Whitworth and UNC are compatible despite having a quite different thread profile: 55 degrees rather than 60 for UNC angle between thread peaks.

The ISO 1222:2010 standard says 1/4-20 UNC for tripod heads.

Yes it's one of the few cases where different standards are interchangeable (at least in one direction)

ProfHankD wrote:

ThrillaMozilla wrote:

D Cox wrote:

You need some 1/4 Whitworth bolts (tripod thread)

Are you sure? As far as I know, it is 1/4"-20 UNC. Nice design, though.

Interesting.

Apparently Whitworth and UNC are compatible despite having a quite different thread profile: 55 degrees rather than 60 for UNC angle between thread peaks.

The ISO 1222:2010 standard says 1/4-20 UNC for tripod heads.

It seems like the wrong thread profile would wear the threads badly.

ThrillaMozilla wrote:

ProfHankD wrote:

ThrillaMozilla wrote:

D Cox wrote:

You need some 1/4 Whitworth bolts (tripod thread)

Are you sure? As far as I know, it is 1/4"-20 UNC. Nice design, though.

Interesting.

Apparently Whitworth and UNC are compatible despite having a quite different thread profile: 55 degrees rather than 60 for UNC angle between thread peaks.

The ISO 1222:2010 standard says 1/4-20 UNC for tripod heads.

It seems like the wrong thread profile would wear the threads badly.

Tolerances.

The thing I always use to explain this phenomenon is Triangle "Missing Square" Puzzle , a 3D-printed puzzle I designed based on some earlier published puzzles. Here are the pieces:

Assemble them one way, and you get:

With a rather obvious unit cube hole. However, assemble the same pieces another way, and you get:

How does that happen?

Hint: it's real, and it's all because of tolerances....

ProfHankD wrote:

Tolerances.

Yes, the threads will fit together, but not properly.  I expect increased wear and weakening of the thread, especially if it is alternated between UNC and Whitworth.

I don't really have any solid information on it.  This is just my opinion, but I wouldn't do it to my camera.  Do you have any information on this?

ThrillaMozilla wrote:

ProfHankD wrote:

Tolerances.

Yes, the threads will fit together, but not properly. I expect increased wear and weakening of the thread, especially if it is alternated between UNC and Whitworth.

I don't really have any solid information on it. This is just my opinion, but I wouldn't do it to my camera. Do you have any information on this?

I take it you didn't understand the purple puzzle -- and the concept of tolerances.

Nothing physical is exact. In the puzzle, the slope of one of the triangular pieces is 2/5, the other is 3/8. Assembling the parts one way, the "slope" of the assembled "triangle" actually bulges out slightly, the other way, it sucks in a bit -- precisely +/- 0.5 cubes of volume in total difference. That's how an entire unit cube appears or disappears. The key is that 2/5 is 0.4 and 3/8 is 0.375, and that's not humanly observable in a small example, and the resulting fit error is literally smaller than the typical accuracy of 3D-printed parts despite adding-up to an entire unit of volume difference. The volume is really 32.5 unit cubes, so the error is a surprisingly small 1.5%.

The 55 vs. 60 degree, and slight shape, difference between Whitworth and UNC 1/4-20 is less than the fit tolerance allowed, and there's no difference in pitch, so the substitution could be harmless. Of course, pairings of specific parts that were manufactured at the wrong ends of their allowable tolerance range might be a little tight or loose.

It's worthwhile noting there are lots of thread differences in similar camera parts that are NOT harmless. A good example is the slight pitch difference in 39mm "Leica Thread Mount" (LTM) threads from Leica vs. some USSR clones; Leica used 26TPI (threads per inch, roughly 0.977mm pitch) whereas some USSR clones were metric 1mm pitch. You can screw them together a little, but the pitch error accumulates the deeper you thread, so things get bad. BTW, Canon "J-mount" is also 39mm, but insanely 24TPI! Similarly, some people mistake a T-mount for M42, because they're both 42mm major thread diameter, but the pitch isn't even close, 0.75mm vs. 1mm, so they bind almost immediately.

ProfHankD wrote:

ThrillaMozilla wrote:

ProfHankD wrote:

Tolerances.

Yes, the threads will fit together, but not properly. I expect increased wear and weakening of the thread, especially if it is alternated between UNC and Whitworth.

I don't really have any solid information on it. This is just my opinion, but I wouldn't do it to my camera. Do you have any information on this?

I take it you didn't understand the purple puzzle -- and the concept of tolerances.

Aw, come on, that's not very friendly.

The 55 vs. 60 degree, and slight shape, difference between Whitworth and UNC 1/4-20 is less than the fit tolerance allowed, and there's no difference in pitch, so the substitution could be harmless.

I'm not an engineer, but I notice those weasel words "could be".  Is there any engineering guideline that says Whitworth and UNC threads are interchangeable?

I don't see anywhere that it says there's a whopping 5-degree tolerance in the angle. A Whitworth bolt in a UNC receptacle would wear the base of the female threads, and almost the whole stress would be born at the base (and the tips of the male thread). The difference between inside and outside is on the order of 0.0015", and that seems like a pretty big mismatch.

It's worthwhile noting there are lots of thread differences in similar camera parts that are NOT harmless. A good example is the slight pitch difference in 39mm "Leica Thread Mount" (LTM) threads from Leica vs. some USSR clones....

This is not a difference in pitch. This is a totally different problem.

ThrillaMozilla wrote:

ProfHankD wrote:

ThrillaMozilla wrote:

ProfHankD wrote:

Tolerances.

Yes, the threads will fit together, but not properly. I expect increased wear and weakening of the thread, especially if it is alternated between UNC and Whitworth.

I don't really have any solid information on it. This is just my opinion, but I wouldn't do it to my camera. Do you have any information on this?

I take it you didn't understand the purple puzzle -- and the concept of tolerances.

There's no need to be insulting.

It wasn't intended as an insult, but you apparently ignored the bulk of my post you commented on.

The 55 vs. 60 degree, and slight shape, difference between Whitworth and UNC 1/4-20 is less than the fit tolerance allowed, and there's no difference in pitch, so the substitution could be harmless.

I notice those weasel words "could be".

Again, everything I've seen says for 1/4 Whitworth and UNC there's generally not a problem. I said "could be" because I have occasionally even had problems with different commercial 1/4-20 bolts and nuts not fitting each other too well. Also, I'm an engineer, so I try to be precise in my language, and cross-compatibility is merely very likely for specific components, not certain. Again, screw threads are never perfect.

Can you or can you not point to an engineering code or guidance that Whitworth and UNC are interchangeable?

Different standards rarely acknowledge each other, but companies making compliant parts discuss this; for example:

https://www.bolts.co.uk/guides-and-tips/heads-threads-and-finishes/can-bsw-and-unc-threads-be-interchanged/

https://britishfasteners.com/threads-bsw#:~:text=However%2C%20the%20thread%20form%20is,where%20BSW%20should%20have%20been.

Also keep in mind that there are other British standards for threads that are wildly incompatible, even at the same thread pitch, due to very different thread profiles.

For Tripod Mounts in particular, the compatibility is not entirely coincidental. Apparently, before ISO 1222-2010 , the Royal Photographic Society recommended the Whitworth version. Here's the tolerance image from the standard:

Looks roomy enough for Whitworth to me.   BTW, the standard also gives a table with upper (es) and lower (ei) bounds on the measurements for the major, pitch, and minor diameters of bolts and nuts (and nothing about the angle accuracy).

I suspect otherwise. I don't see anywhere that it says there's a whopping 5-degree tolerance in the angle. A Whitworth bolt in a UNC receptacle would wear the base of the female threads, and almost the whole stress would be born at the base (and the tips of the male thread). The difference is on the order of 0.003", and that seems like a huge mismatch.

The tolerance is the gap between mating surfaces and cavities, not angles. A 5 degree angle difference over a tiny distance does almost nothing -- the exact same principle my purple puzzle clearly demonstrates.

I regularly 3D-print fully functional 1/4-20 threads using up to around 0.25mm extrusion height -- some are significantly worse than that mismatch. In fact, I often deliberately print with up to a 45 (instead of 30) degree overhang to control sag of the extruded plastic, and that works great; I even presented that at an additive manufacturing conference as one of the DFM (design for manufacturability) tricks I was trying to automate. Of course, plastic has some flex, so it's a bit more forgiving than metal.

On the other hand, metal can be permanently deformed/shaped by a same-pitch mismatch, effectively cutting a matching thread.

It's worthwhile noting there are lots of thread differences in similar camera parts that are NOT harmless. A good example is the slight pitch difference in 39mm "Leica Thread Mount" (LTM) threads from Leica vs. some USSR clones....

This is not a difference in pitch. This is a totally different problem.

Yes, and MUCH LESS SEVERE. My attitude on the 1/4-20 UNC vs. Whitworth issue is definitely "expect it to work, and if it doesn't, you have a good guess at what's wrong."

Thanks for posting this. I learned a lot about threads.

I read the material you posted (except for the ISO standard). The consensus seems to be that they guess it's OK for casual use, but "threads should only be interchanged in non-critical applications."

I guess if I couldn't get anything but Whitworth, I would probably use it, but I'm still skeptical.

Some specific comments follow.

ProfHankD wrote:

It wasn't intended as an insult, but you apparently ignored the bulk of my post you commented on.

I know what tolerance is, but I'd rather discuss the bolt. For brevity, I have edited out comments that I'm not commenting on.

Again, everything I've seen says for 1/4 Whitworth and UNC there's generally not a problem. I said "could be" because I have occasionally even had problems with different commercial 1/4-20 bolts and nuts not fitting each other too well. Also, I'm an engineer, so I try to be precise in my language, and cross-compatibility is merely very likely for specific components, not certain. Again, screw threads are never perfect.

Good to know. I suppose they could be sloppy.

...Here's the tolerance image from the standard:

Looks roomy enough for Whitworth to me. BTW, the standard also gives a table with upper (es) and lower (ei) bounds on the measurements for the major, pitch, and minor diameters of bolts and nuts (and nothing about the angle accuracy).

If the angle is the same, the stress is distributed over the whole thread.

...The tolerance is the gap between mating surfaces and cavities, not angles. A 5 degree angle difference over a tiny distance does almost nothing -- the exact same principle my purple puzzle clearly demonstrates.

Here's what it does. The part in red shows the angular discrepancy. You can calculate the gap due to the angular discrepancy. The length of thread contact is 0.028". The gap is 0.0012".

The red line shows the 60-degree angle of a UNC thread, superimposed on a Whitworth thread. For a 1/4"-20 bolt the gap is 0.0012".

...On the other hand, metal can be permanently deformed/shaped by a same-pitch mismatch, effectively cutting a matching thread.

Yes, exactly. On your camera.

ThrillaMozilla wrote:

Here's what it does. The part in red shows the angular discrepancy. You can calculate the gap due to the angular discrepancy. The length of thread contact is 0.028". The gap is 0.0012".

The red line shows the 60-degree angle of a UNC thread, superimposed on a Whitworth thread. For a 1/4"-20 bolt the gap is 0.0012".

Nice diagram.

However, 0.0012" is 0.03mm, and if I'm reading the standard right, the basic tolerance (max-min) range on the pitch diameter is 0.185mm. In other words, assuming your number is right, the difference between the ideal values in the standards is significantly less than the variation allowed in the standard.

...On the other hand, metal can be permanently deformed/shaped by a same-pitch mismatch, effectively cutting a matching thread.

Yes, exactly. On your camera.

Minor thread-cutting happens all the time, especially as tiny specks of dirt get into a thread... not a bad thing. High surface area contacts between similar metals could even spontaneously weld, and the surface inaccuracies actually prevent binding. Also keep in mind that 1/4-20 aren't normally being used where a gas-tight seal is needed.

ProfHankD wrote:

ThrillaMozilla wrote:

Here's what it does. The part in red shows the angular discrepancy. You can calculate the gap due to the angular discrepancy. The length of thread contact is 0.028". The gap is 0.0012".

The red line shows the 60-degree angle of a UNC thread, superimposed on a Whitworth thread. For a 1/4"-20 bolt the gap is 0.0012".

Nice diagram.

However, 0.0012" is 0.03mm, and if I'm reading the standard right, the basic tolerance (max-min) range on the pitch diameter is 0.185mm. In other words, assuming your number is right, the difference between the ideal values in the standards is significantly less than the variation allowed in the standard.

I think that .185mm tolerance has little to do with how the threads fit when tightened. If the angles on nut and bolt are the same and the pitch is constant, those tolerances can result in a gap of zero, not 0.185 mm, when the thread is tightened. A matched angle spreads out the stress; a mismatched angle concentrates the stress. It doesn't have to be perfect to even out the stress.

I just found out that there is something call "Unified Standard Thread" (U.S., Great Britain, Canada). The angle is standardized on 60 degrees, and there must be a reason why they standardized it. I assume that no one really needs to use Whitworth.

That's my case for being persnickety.  I think we've both stated our case, and readers are going to get impatient soon.

Cheers.

I'm getting an old Bessler 23 enlarger. It's pretty simple to remove the head and put a quick release on it. IT has a nice, strong, rectangular crank-driven tilted column.

I had this exact thing before, but had to do a panic move due to health reasons, and left it behind. Luckily, I was able to score an entire darkroom setup — including the Bessler, and a nice easel for holding copy work down — for $60.