My trusty but heavily beaten copy of the classic Minolta MC 35 mm f/1.8 came to me with a number of – mostly cosmetic – issues. Besides a bent filter thread and a number of scratches, it was also missing the rubber focus ring grip. Like most late Minolta MC and all MD lenses, this copy used to have the typical embossed grip with tightly packed little pyramids on it, too. As focusing is a bit slippery without the rubber grip, I was looking for a replacement for quite some time. I found some ideas in threads on mflenses.com and other forums, including using leather, embossed rubber doormats, cord wraps or just duct tape. Sadly, none of the gathered ideas would have restored the original look to the lens.
I wasn’t really happy with any material I had found in hardware and art supply stores and I wanted to “do it right”. So I looked into 3D printing. There are a number of companies, which offer 3D printing “as a service” – you supply the model and select a material and the company will print it out for you. The – to my knowledge – biggest players around are currently shapeways and trinckle. To construct a model, I first measured the base thickness and pyramid length and height of the rubber grips on my other Minolta lenses. Then, I took the dimensions of the groove on the lens (d = 63.00 mm, h = 20.85 mm) and constructed a model in Solid Works. I added +0.4 mm to the inner diameter of the grip to accommodate for a thin layer of adhesive.
With the finished model, I looked for a fitting material at different 3D printing services. As they do not all offer the same choice of printable polymers, this turned out to be quite interesting. The best match for actual rubber seemed to be the sintered rubber offered by trinckle. Although not actually rubber, the material is supposed to be very flexible, soft and offer a slightly rough surface – perfect for a grip. Unfortunately, sintered rubber can only be printed with a comparatively low resolution of 0.75 mm, which is close to the thinnest features of the grip model (0.8 mm). After comparing some other options, I finally settled for sintered plastic, also offered by trinckle. The material is actually Polyamide, is flexible to some degree and offers a sufficient printing resolution (0.4 mm). Further, it can be printed in black, which was a prerequisite to get as close to the original look as possible.
[Remark: I own the copyright on these CAD files. You are free to download, use, modify and print them at no charge.
You may also redistribute them directly or in modified form, as long as you credit me and link to this post.
You may NOT use the files commercially in any way.]
The printed result arrived after about 10 days. The material is slightly shiny, looks a bit rough, has a hard surface but can be flexed. With an inner diameter of about 63.5 mm (hard to measure precisely) and a height of 21.3 mm, the dimensions were quite close to those of the submitted model. The slight surplus in height had to be reduced, though, to make the grip fit on the lens. I used 120 grit sandpaper for woodworking, placed it on a flat surface and sanded 4 to 5 strokes with slight pressure, before turning the grip about 30°. After repeating this roughly 50 times per side, the height reached a snug fit of slightly more than 20.8 mm. As it turned out, the Polyamide used for manufacturing is actually white and was likely soaked in black dye after the sintering process. Consequently, the grip is white below the surface. Not a problem in this case since the sanded sides are covered by the lens body, but still interesting to see.
After de-dusting the grip and cleaning the lens with Isopropyl alcohol to remove dirt and fat, I glued three small patches of thin double sided tape into the groove on the lens (sorry, no photo!). My initial plan was to stretch the grip onto the lens from above by heating it up to 85 °C in a water bath causing it to expand slightly and become easier to stretch. As it turned out, this was not enough to stretch it to the required 65 mm diameter of the lens. As I didn’t want to heat the grip up further or use excessive force, I settled on cutting it open on one side and just fitting the cut tightly on the double sided tape. As you can see in the close-up shot, this leaves a very small, hardly visible “scar” in the mounted grip, which might or might not attract a bit of dirt over time. It looks much more prominent in the photo than it does in real life, though – I always have trouble locating it, even though I know what to look for.
Overall, I’m very satisfied with the result you can see above. From more than an arms length away, the grip looks like the original. It’s also comfortable to hold, has plenty of grip for focusing and fits firmly – no wobbling in any direction. The only thing missing is the softer, rubbery feel of the original. Overall, it was probably the most complicated solution for restoring the lens, but it gave a nice result and for me, fiddling with the construction and manufacturing was a lot of fun.