I am pretty new at machining.
How can I attach a disc that is larger than my jaws and machine all
sides without putting a hole in it?
An example would be a 200mm dia disc, 1/2" thick made from mild steel.
Chuck a short bar , as big as will fit. Face it off true, then
superglue your part to the bar. It helps to have a few grooves in the
face of the bar in the chuck to allow a bit of air access to the
Remove with heat from a propane torch. Don't heat it enough to smoke
the superglue, and if you do, don't breathe the fumes. It takes around
350 to 450 degrees F to get the bond to break.
Clean part with acetone.
Take light cuts with a sharp tool.
Clamp it radially with 3 or 4 set screws (see dwg above) or even clamp tabs
with the clamp bolts in-line with the lathe axis.
Strt by welding some 25mm + bar stock to some plate and build on it from
I made something that goes in the tailstock that is somewhat like a
live center, except instead of a 60 degree point it has a flat disk. I
used a roller bearing for a car front wheel.
So I can put a mandrel with a disk in the chuck and this thing in the
tailstock and clamp the two together to machine the edges of disks. A
piece of rubber or double sided tape on the disk clamped in the chuck
improves the friction.
The bit that goes in the tailstock also has some alternate parts so it
can work as a pipe center too.
Mount a large diameter chunk of something in the chuck and face it off,
and turn the OD to slightly less than the diameter of the workpiece, if
necessary. Make sure one face of the workpiece is completely flat.
Use wax, superglue, double-stick tape or whatever you have to attach the
disc to the mandrel you just made. Now, you have the other face and
the OD of the disc completely exposed for facing and turning. Obviously
you need to go easy on it of it will come off the mandrel.
Another method is to use some kind of "pusher" attached to a live center
to press the disc against the mandrel. This won't allow you to face
all the way to the center, though.
It can. You need to face one side of the thing any way you can to get
it flat, first. If it is so big that you can't get the jaws around it,
then you might need to use a 4-jaw and reverse the jaws. Once one face
is flat, you can then glue it to the mandrel. it works best if the
mandrel is at least 3/4 the diameter of the workpiece. You can also
use a faced piece of thick-walled pipe as a mandrel.
And, of course, you can't take heavy interrupted cuts when mounting work
like this. But, if you want to face and turn the OD of a part in one
mounting, you have to make compromises. The only other way to do it
is to mount a thicker piece in a chuck, face it, turn OD, and then part