Sunday, December 3, 2017

A Followup On Soft Jaws for the Lathe

It seems hard for me to believe it has been almost five weeks since I posted (on Halloween) about a coming small project of making soft jaws for my lathe.  Particularly since I've been done with them since the middle of last month (16th) and never mentioned working on them.  Here they are mounted on my lathe's 4" chuck.
First off, none of the dimensions I'm going to talk about are critical and need to be within even 1/16".  These are made from a piece of 1-1/4" hex bar of 6061-T6 aluminum that I bought from an eBay seller.  I bought a foot long bar and cut off about 1-1/2" of it.  First, I put the cutoff piece on the lathe and drilled it down its axis with a couple of drill bits through my largest drill bit, 1/2".  The hole that clears the jaws needs to be close to 0.7", so I used a boring bar to open it the rest of the way.  Next came slicing it into three pieces about 3/8" thick, then I faced the saw cut sides, flipped them, and cut to final length right there on the lathe.

The original article showed tapped M8 (metric) holes on all six sides of each slice.  Mine are tapped 8-32 on three sides.  You can see the three screws each, so that they don't interfere with each other.  Drilling and tapping nine holes was an easy "drill, rotate, repeat" setup on the big mill using it as a very precise drill press. 

What I wanted to mention was that if you intend to make these, it might seem the idea is to put the aluminum slice on the chuck jaw and tighten the cap screws down.   Don't do it that way.  Leave them loose, tighten down on the stock you're going to machine first and then tighten the screws on the soft jaws.  It works better to use the chuck's own self-centering properties to reduce runout in the the piece you're working on.  That's a DAMHIK.

At least for a handful of test cuts, they work fine.  Non-marring on steel, yet hold well.  I haven't threaded anything, just used them to hold 1/4" steel round rods for test cuts. 


  1. Several years ago we got new vices for our shop tables and we had the machinist fabricate aluminum jaws to replace the steel ones that came with the vices. It really did help prevent damage to aluminum stock. When we were real paranoid about damaging material we would even use a thin sheet of G111 to help buffer the material.

    1. That's on my "gotta do" list - putting aluminum jaws or jaw liners on the bench vise. It really helps. Maybe even the milling machine vise.