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04-06-2017, 11:13 AM   #1
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To 3D print a PK mount?

Hi!

After reading various posts it occurred to me that 3D printing could help converting lenses to PK-mount.
One can easily print plastic mounts but also 3D metal printing is reality now.

Question: which mounts could be printable?

Seb

04-06-2017, 11:26 AM   #2
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It's definitely feasible for Nikon, Olympus-OM, and Leica-R if removes the mount ring from the old lens, scans it in 3-D to get the dimensions and mounting hole pattern, and then creates a K-mount replacement. Canon is less feasible due to the differences in registration distances.

Any 3D-printed mount replacement ring will still need a little machining to get the right dimensional tolerances and surface finish or risk being too loose or too tight.
04-06-2017, 11:47 AM   #3
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Plastic would seem to not be strong enough for this application, at least based on the 3-D printing I have seen. How readily available is 3-D printing of metal?
04-06-2017, 12:03 PM   #4
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QuoteOriginally posted by leekil Quote
Plastic would seem to not be strong enough for this application, at least based on the 3-D printing I have seen. How readily available is 3-D printing of metal?
Definitely true of today's consumer level 3D printers but there are some industrial grade ones that might be up to the task. The big issue is cost. The printers that would technically be able to do the job would most likely be a cost-prohibitive solution.

04-06-2017, 12:06 PM   #5
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QuoteOriginally posted by bassek Quote

Question: which mounts could be printable?

Seb
You could print anything, if you choose all the dimensions correctly. M42/M39 mounts would be difficult in plastic, because the threads wouldn't last very long, and they would need to be produced after printing. CNC milling and metal would be a better choice, because plastic shards will likely chip off over time and land inside the camera, on the sensor etc. Not to mention that support material is kind of hard to get rid of. I am always left with a thin layer that I have to remove manually.

A fun project I keep wondering about is printing the entire lens with a off the shelf components from thorlabs. This could be a very nice, light lens if designed correctly. The problem is that off-the shelf lens elements are quite pricey and the process is not cost effective.
04-06-2017, 12:11 PM   #6
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QuoteOriginally posted by rrstuff Quote
CNC milling and metal would be a better choice
This ^ ^ ^


Steve
04-06-2017, 01:07 PM   #7
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The difficulty with reverse-engineering of any type is that of tolerances and accuracy of measurement. All mass-produced items are subject to variation, so it would only be a fluke if you selected one that measured precisely to the base dimensions specified by the manufacturer. Well-calibrated image scanning or touch-probe measurement will get you close to precise measurement, but it'll still be subject to some error, if only very small.

After the measurement phase, making the item introduces variations of its own. The whole basis of mass production is to keep those variations within design tolerances, so any two mating parts will fit together within the specified dimensions of the assembly.

There's no substitute for getting the maker's specification, if you want to manufacture your own, but that generally involves payment of some kind. However, if you're willing to accept that you'll sometimes make a reverse-engineered item that doesn't fit correctly, then it's all well and good.

If I was doing this for lens mounts, and I used to do similar things as part of a job in manufacturing, I'd get as many specimens to measure as I could, and decide on base measurements and tolerances from those, and then I'd get the items CNC machined, rather than 3D printed, even in metal, as the accuracy of finish would still be much better.

04-06-2017, 03:58 PM - 1 Like   #8
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Agree with everyone here about doing it right.

However, that said, I have successfully printed K mounts in plastic for non-precision use with only very lightweight attachments.
04-06-2017, 04:51 PM   #9
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3-D printing in titanium is available with accuracy of 0.2mm and surface roughness of 0.075mm. Provided you uploaded the 3-d file then the cost would only be around $70-100 per mount.
Of course, that may not be a tight enough tolerance. Not sure. Based upon the original K-mount drawings posted here - https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/209239-loo...-drawings.html - that accuracy may be enough.

Last edited by MarkJerling; 04-06-2017 at 05:02 PM.
04-06-2017, 05:13 PM   #10
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I understand some of the latest machines will give accuracy of 0.05mm. But, costs for using those are likely to be higher. I know someone with a DMLS machine - I must check with him what his tolerances are. I know he can print up to 245x245x280mm maximum size, but I'm not sure of the tolerances.

Last edited by MarkJerling; 04-06-2017 at 05:36 PM. Reason: Max size corrected.
04-06-2017, 05:13 PM   #11
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QuoteOriginally posted by MarkJerling Quote
3-D printing in titanium is available with accuracy of 0.2mm
That error on a 50mm K lens would change the subject focal point from 100 metre to 11 metre.
04-06-2017, 05:25 PM   #12
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QuoteOriginally posted by wombat2go Quote
That error on a 50mm K lens would change the subject focal point from 100 metre to 11 metre.
Would you care to provide your maths for that? I'd venture that the resulting error would be much smaller than that. If the register distance is 45.5mm then a 0.2mm difference would move, by my maths, the focal point from 100m +- 0.44m, so 99.56 to 100.44m. Or is my maths wrong? (Maths was not my best subject at school)
04-06-2017, 05:39 PM - 2 Likes   #13
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QuoteOriginally posted by MarkJerling Quote
Would you care to provide your maths for that? I'd venture that the resulting error would be much smaller than that.
The classical thin lens function:
(1/f) = (1/v) + 1/u)
units [mm]
where f : focal length = 50mm for example
u = distance from n2 to film plane
v = distance from n2 to the subject being photographed

Case 1 : Adaptor Error = zero, subject : 100 metre = 100000 mm
(1/50) = (1/100000) + 1/u) > u=50.025mm

Case 2 : u = 50.025 mm from case 1. Adaptor Error = 0.2mm, subject : to be calculated as v
(1/50) = (1/v) + 1/50.025) > v = 11161 mm; v= 11.161 metre`
04-06-2017, 05:48 PM   #14
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Wow. Thanks for that. I'll stick to my knitting.
04-06-2017, 05:52 PM   #15
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3d print rough, bring important dimensions to tolerance with a mill
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