Mini-toolmakers jaws for small 80 mm three jaw chuck

[Paul Jones]

I made my own mini-toolmakers jaws for my small 80 mm three jaw chuck mounted on my mini lathe. A couple years later, I made a mandrel for holding the 80 mm chuck in a larger 6" chuck for my 12" swing lathe (see http://www.homemadetools.net/forum/c...0262#post72147 ). This expanded the capability for holding the chuck with mini-toolmakers jaws.

The purpose for these small jaws is for machining the short threaded ends of small cap screws in the 4-40 to 8-32 thread range. All my other lathe chucks and collets (ER16 on my Unimat SL and ER32 on my mini lathe) have jaws too deep to allow holding the threads with the cap screw head-end pointing towards the headstock. Some of the screw-end machining involves facing and drilling a small hole for adding a brass pad (protection from set screw marks on sliding parts). An alternative would be to bottle bore some soft jaw ER32 collets but I avoid this class of boring whenever possible.

The parts are based on a posting at MadModder - Index. The jaws are made from 12L14 steel and use 1/8" and 3/16" long stainless steel set screws with a 8-32 thread size. The short-length sets screws can be recessed into the jaws for safer operations. Each of the mini-toolmakers jaws are numbered and registered to each chuck jaw. The righthand-side set screw on each jaw is secured with Loctite 290 (green) while the top and left-hand set screws can be loosened for removing and replacing the small jaws without changing the bore alignment.

The first photo shows the mini toolmakers jaws attached to my 80 mm three jaw chuck (BTW the insert in the lathe tool is a T-15 HSS TPMW-221 from Arthur R. Warner Co. (Arthur Warner Co. | Specialists in High Speed Steel) and fits standard carbide insert tool holders). Adding the toolmakers jaws now allows more use of the original mini lathe 80mm chuck since being replaced with a larger 100mm three jaw chuck.

The last photo shows the lathe jaws with the mini toolmakers jaws still attached resting on an enlarged photo of the source of this idea from MadModder - Index.

I probably should have hardened these parts and then lightly grind the bore surfaces with a dremel tool attached to the the cross slide but that can be a project for another time.

Thanks for looking,

Paul Jones

P.S. I made a mandrel for the 80mm chuck to be held three or four jaw chucks used on my 12" swing geared-head lathe. The mandrel makes this small chuck with the mini-toolmakers jaws very useful and easier to install and remove (see http://www.homemadetools.net/forum/c...0262#post72147 ).