Hey everyone! A little piece of info that maybe some other up and comers like myself should know... I'm sure it's floating around deep in the forum somewhere
Tiffen arms have some play (about a full 1/2 inch) in the pro socket blocks to the point where you can not use them with your Pro Vest unless you have a Tiffen socket block. O'Shea and I stumbled upon this little discovery yesterday. Could have been a disaster discovering this on a job...
Does anybody know why this is? Very interesting. And is there any way to keep the Pro socket block on the Pro vest and use a Tiffen arm?
Hope everyone is doing well! Cheers
Edited by Ryan Toussieng, 15 July 2015 - 01:34 PM.
Jerry Holway mentioned it during the SOA workshop last year and Mike O'Shea told me about it a few days ago. The PRO socket Bloch is a bit too tight (by a micron) so the socket block pin won't fit all the way in. No other option than switching to a Tiffen block.
A possible over exaggeration on my part, but it's close. Let's call it a quarter inch!
The hole on the Pro socket block where the pin on a Tiffen arm goes through is tighter at the end, not allowing a smooth fit. The threads on the socket block screws don't even get close to the lip of the arms block. I was pretty shocked, seems like an issue for most Pro socket blocks since they squeeze at the end
Edited by Ryan Toussieng, 15 July 2015 - 02:29 PM.
Yes, longstanding issue. I sanded down my Master Arm pin 5 years ago, has fit in my Pro vest ever since. I occasionally check the pin to make sure it's not rusting, as that's supposed to be mild steel under the stainless I sanded away, but I've never seen anything of concern.
Yes, long standing issue that stems from the lack of tolerances in the early CP days. What ever male socket block PRO would have measured back in the day that become their blueprint was undersized (we are talking 100th on an inch maybe - not a half inch) and that became their standard. Meanwhile when Tiffen took over form CP and became more serious about standards, they must have measured a male socket block on the larger size and that became their standard. How to fix it? File your male (arm) socket block down a tiny bit or replace your female (vest) socket block with another (standard hole pattern).
For $60, my local machinist took a couple thousandths off of the female side of the socket block. Sanding down the arm pin will work, but then you're only able to use that specific male socket block with your vest. If you find yourself using a different arm for whatever reason someday, you'll be back at square one (assuming it's Tiffen also). Shaving a little bit off of your male pin is a silly religious tradition anyway.
Good points Afton. I'd be carful about shaving any socket block (male or female) if it is Titanium though. Since back mount vests have become popular though, less and less people seem to be making them from this.
I did a little research on the socket blocks, and, for the record, it wasn't "sloppy tolerances" that caused the issue. The two parts, male and female, have been essentially the same since 1986. Tolerances were, and are still are, +/- .0005 for both the pins and the holes.
In October1986, the nominal diameters of the pins and the holes were increased .001.
So perhaps PRO had an old pin from a pre 1986 arm that they measured which was worn. Who knows?
Regardless, the solution we use at the workshops is to temporarily swap the PRO female socket blocks out for Tiffen ones, and then everything fits.