Controlling finished length on a manual lathe

[lbhsbz]

I’m constantly tasked with modifying caliper pistons….one or 2 are not a big deal, but more than that is a pain in the ass. I haven’t made a chuck spider yet mostly because it entails picking up my rotary table and setting it on the mill…it weighs about 200lbs…haven’t been in the mood to deal with that thing since I set it there 6 years ago lol.

Today’s project was to shorten some brembo caliper pistons to 26mm in length. I had 36mm and 42mm pistons to do, 20 each.

Normally for one or 2 I creep on it, shut down, measure, make another cut, confirm, etc…no time for that on 40.

I could make some 5C emergency collets, but then I’ve gotta yank the chuck and find the collet stuff…nope.

I saw a chunk of aluminum I fucked up last week when I was hired to make a 33mm turbo restrictor for a rally team (napkin sketch didn’t match sample…I referenced off the sample)…so I cut that up and made a few “fixtures”

Wall thickness I was hoping would be thin enough where I didn’t have to make slits. Concentricity doesn’t matter since I’m only working on length. It worked! Chuck jaws collapsed the adapter things enough to grab the pistons and relaxed enough to release them.

Made one for each size piston with a step to stop on the chuck jaws and step to stop the piston. Set up an indicator on the carriage and knocked out all of ‘em in 15 minutes. $10 each. Not bad.

 

[lbhsbz]

Had another batch to do yesterday, but chromed steel pistons, 24 of which I overnighted from Canada…these are going somewhere in Europe for a special project.

Spec sheet said 1.178” diameter…which is what we needed. I didn’t really pay attention, just made another little adapter thing and shortened them all. Then decided to measure the OD and pay attention..lol. All came in at 1.180-1.1825.

Fuck.

Won’t fit. They need these Tuesday.

I figured I’d try to polish them down and hope I didn’t go through the chrome. Of course, I just machined off the feature that would have been nice to grab it by in the lathe chuck…lol.

Closed the chuck and smashed the piston against it with a live center in the tail stock…we’ll friction drive it. Was able to get it down to 1.1795, and it fit in the caliper nicely (these are prototypes…they need to work for testing). The chrome changed color a little…couldn’t tell if I was looking at polished steel or chrome…so I left it in a cup half covered with water overnight. This morning…the face (that I machined the chrome off of) was rusty, but the sides weren’t. Score!

30ft of Emory cloth later and at least 3 fingerprints melted off, I’ve got 24 pistons that work to ship on Monday.

There will be a discussion with my supplier on Monday