You are obviously not familiar with a roll pin. Picture a
length of flat spring steel stock which has been rolled into a two-turn
roll. The ends are tapered a bit to make them easy to start, and they
are driven into the mating holes, with the spring expanding to grip both
the parts. They can be driven out as long as the hole goes all the way
through. They are available for relatively little money for large
quantities. With blind holes, people have managed to use a tap to
thread the ID and give a grip with a screw to pull them out.

It would seem to be more reliable(though not easier or cheaper) than
using Delrin rods.

It may well be cheaper than using Delrin rods. After all, these
are mass produced to standard diameters and lengths. Delrin tends to be
rather expensive (though something like 1/8" diameter rods would not be
that expensive, and you would simply have to turn them to the desired
final diameter and cut them to length.

I do have a lot of Delrin that I could probably make as many pins as
I'd need.(Though turning it down to 1/8" of an inch may be asking a lot
of the lathe). :-)

So I'll look that up. (Tapping is going to be a
subject unto itself that I'll have to study).

Indeed so.

The groove(which would have a 3" O.D.) would actually have to be made
in the 4" square piece.

But -- the groove could be off towards one corner, so it is just
barely grazing two sides, and that would result in the other sides
extending 1" beyond what would be the case with a centered plate. And
that would be 1.414" beyond at the corner. So -- what would have been a
5.65" diameter if centered would be closer to an 8.48" effective
diameter. This is why I specified the center point of the groove being
important.

Granted, I suspect that the groove *will* be centered, but I
want to point out the problems you can have if you make that assumption
blindly.

It'll be centered so that it'll be four inches from each of the four
sides.


Anyway,
I can only hope that one of the $50 bench tops will allow enough
accuracy for my needs. I suppose I'll need it to be pretty accurate if
I go with the roll pin.

The roll pin expands to fit the hole, within reason. But
without special fixturing (other than the V on the top of a bench
block), I would suggest that you drill through both the sleeve and the
rod at the same time. The hole may wind up a bit off center, but it
will be the same for both parts, so the roll pin should fit through it
easily enough.

What if I used a sharp punch of some sort to start, followed by a
center drill in the lathe, and then drill after that? since the 1/8"
hole is only 1/8" from the bottom I'd probably have to balance things
by using a tube with a 7/16" I.D. to fit over the rod/sleeve,
effectively lengthen it so it would slip out of the chuck.

Now -- if you were using a dowel pin, you would need a very
precise hole diameter. Drill it a bit undersized, and then use a hand
reamer to take it to the proper size.

Reamers happen to be on my shopping list. :-)

Yes. That is why I joned a Yahoo Group "mlathemods - Mini Lathe
Modifications". Perhaps there will be some ideas there.

O.K. Good luck there. There will be things which you will have
to design for yourself.

I already have a couple of tool post mods in mind. :-)

Thanks.

Darren Harris
Staten Island, New York.