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wrote:
The plan is to build a sliding table type router table for making
raised panels for doors on a furniture project. I am going to use a
couple of linear bearings on shafts attached to a large aluminum plate
for the sliding table, then use an 3/8" x 10 tpi Acme precision lead
screw to advance the sliding portion of the table. The plate will have
the wooden workpiece attached and feed the wood hanging off the edge
into the panel raising bit. The last time I raised panels I sent a
couple of workpieces across the room because they weren't fixtured well
enough to my plywood jig, so I really need a rigid sliding table for
safety and better results.

I definately don't have the skill or thread cutting attachements to
make my own lead screw and nut, and the prices on a complete assemby
with support flanges and flats milled on the leadscrew are pretty
steep. So I am looking at just buying a 3' length of lead screw with
an oversized nut. My question is about how to finish the ends of the
lead screw. Can I just weld a sleeve, with a tight fit between the OD
of the screw and the ID of the sleeve, over the ends of the lead screw
- then slide that into a pillow blocks to support the ends of the lead
screw? Of would I be better off trying to chuck the 3' lead screw into
my HF 3-in-1 and turn the screw shaft down to a smooth round surface
that fits into a smaller bearing in my pillow blocks? I have never
tried to turn a threaded rod and don't know if the threads would catch
on my cutter. I'm quite new to machining metal, and could really use
some advice.
You'll need to fabricate a support for the far end of the leadscrew.
This can be something pretty simple lashed together, with a piece of
water pipe to hold the end of the screw. Better make sure the screw
can pass through your spindle hole! You won't have to worry about the
cutter "catching' on the thread. It will be an interrupted cut, and a
bit rough, but it should be able to do it unless the screw is hardened.
If you are buying Acme or allthread stock, it won't be hardened.
Put the screw all the way through the spindle, so only an inch or so
is sticking out of the chuck. That will give solid support to where
you are making the cuts.

You may want to rig a Dremel tool or air die grinder to the toolpost to
finish the ends. (A toolpost grinder is the tool of choice, but I doubt
you have one of these.) You put a small grinding wheel on the tool and
grind the OD and flange of the leadscrew to proper dimensions with a
fine surface finish. Depending on the screw material, you MAY be able
to cut it to a good finish with cutting tools, but it is not guaranteed.
Removing the last .001" by grinding will give accurate dimensions and
a fine finish for sure. (Protect the lathe from the grinding dust with
damp cloths.)

Jon