Pentax MZ-S remote body cap / plug

I managed to get a decent used Pentax MZ-S via an online used camera dealer. The MZ-S was in decent condition, but was missing all the plugs that go on the camera. I was able to find most of what was missing via eBay and other sources, but the cap that fits over the remote socket was impossible to find. I even tried Pentax, but I got the following email in response.

Thank you for contacting PENTAX.
The release socket cap FL (product number 31039) was considered an accessory part for the MZ-S and we no longer have any of these in our stock.  The 645nll used a different size cap, release socket cap F, which will not fit on the MZ-S.  We don't have any specifications on the cap or one to measure but you may be able to find one if you try websearching.
If you are in need of further assistance, please respond to this email or call our technical support center at 800-877-0155.

I decided to try the Pentax forum, and see if I could get some help. I started my own thread for help or if anyone had a spare one available, but nothing came of it.
Finally, a guy, probably through pity, was kind enough to loan me a cap. He sent it via snail mail - at his expense!

When I got the package, and opened it, I noticed how small the cap actually was. I knew I might have some problems duplicating the cap via my Metal Lathe and Mill. Because the cap is rubber-ish, it's VERY hard to get exact measurements. Even with slight pressure using the digital calipers, the cap would compress and squish. I tried and took many measurements, as I tried to approximate the dimensions.

In the images below, you can see my progress. All pictures taken with my Pentax K5 and Pentax SMC Macro 1:4/50 Manual lens.

The image below, is with the plug/cap on the top of a 1/4-20 camera socket screw - yes those are my fingerprints!
It's amazing at how well the K5 and an old Pentax manual lens work together!

Here is a crop to show the detail of the many ridges that are part of the cap/socket.

After looking at the images I was taking, I realized there is NO way I could make a replacement cap with all the little ridges that exist in the original part.
It is astonishing at how Pentax engineered the original part. There are something like seven separate surfaces in the cap!!!!!

In the image below, you can see the bottom is flat.

In the image below, you can see the curve of the top part. I won't try to duplicate that curve!
Well - maybe I will *try*.

In the image below, you can see the cap from the side.
Again, all pictures were taken with my Pentax K5 and Pentax SMC Macro 1:4/50 Manual lens.

Another shot

The top of the cap is smooth, with some dimples in the texture.

When I took the measurements, I estimated the measurements and cross checked on my digital caliper. Since the cap was on loan, I decided that I would make a representation of the original cap, incase someday, I could make one as intricate and detailed as the original.

My digital caliper

My first choice, since I have no rubber making equipment or rubber casting material, was to try and make a new cap/plug out of Delrin or a plastic that was similar.

No luck.

The problem working at such small sizes, is the heat from the lathe cutting tool causes the Delrin pieces to deform/melt. Normally, in a larger piece, the heat can dissipate.

I tried several pieces, with different cutting speeds, and I was getting no love.

I realized I was going to have to abandon making the cap out of Delrin. I decided that Aluminum was the way to go. In order to be successful, I needed to take the essence of the original Pentax cap, and only use the design where it worked. I went with a simple design choice of a single O-Ring, pushing against the remote socket, but staying away from the electrical contacts inside. The O-Ring would have to give "just enough" friction against the cap and the MZ-S body.

As I tested out certain diameters, I realized that while my original cap measurements were accurate - the MZ-S cap being made out of rubber - was slightly larger than the opening on the camera and allowed for a snug interference fit. I needed to make a cap that would "just" fit enough to snug up the O-Ring in the socket.

The image below is where I am trying to find the "magic" diameters!

Finally I got it right.

When using a Macro, tiny things look huge! It looks like I used a butter knife to make the parts, but the scratches are thousandths of an inch!!!

Notice how O-Rings are not perfect either!
In the image below, notice how tiny the O-Ring goes past the small aluminum that keeps the O-Ring on the cap.

Look at the detail of that O-Ring close up!

Where the cap/plug is going! The cap has to fit in that small socket, and not touch the electrical contacts inside.

Nice - Bling!!!!!

Bling! Bling!


The measurements I took, were close, but were not accurate enough. Unless the original Pentax blueprints can be found, no one will ever be able to make an exact duplicate of this part given the complex nature of the original. Because the original plug was rubber, there was enough elastic in the plug to enable an interference fit. The OEM plug was very snug on the camera. When I tried to make one out of Delrin, the exact measurements caused the plug to fall out. I managed to use an 8mm x 4mm center O-Ring. By making the O-Ring expand over a 5mm center (probably nearer to 4.5mm), I was able to get the "squish" I needed for the cap/plug to fit snugly.

I took the success of my first cap and made two others. Mark 2 and Mark 3.

Mark 3 is the smallest and roundest. It also has the smallest O-Ring retainer band. I'm going to call Mark 3 my best.
I also tried to polish Mark 3 up and make it shiny and with a better "nail/grip groove". I also believe that I am at the limit of what my Metal Lathe can do with it's limited precision.

In the image below, from left to right - Mark 1, Mark 2, Mark 3.
(Notice that in Mark 2, you can make out my reflection in the cap - The Pentax K5 and SMC 50mm Macro 1:4/50 are almost showing microscopic reflections!)

The MZ-S Plug / Cap Mark 3 in the wild.