According to :
[ ... ]
You are going to be making a lot more chips than parts, starting
from that size. A serious bit of waste in my book. And, you *will*
need the 4-jaw independent chuck to hold those rectangular pieces.
Yes. I'm thinking a 5" chuck with a spindle bore that is at least .787"
would be preferrable.
That sounds reasonable.
Hmm ... look at the MSC web site:
http://www1.mscdirect.com/CGI/NNSRIT...PMT4NO=4749765
which shows 1/8" Delrin (acetal) rod, 1 foot long, for 98 cents each.
Your choice of black, or natural (fairly white). Hmm ... that looks
like Teflon (PTFE), not Delrin (acetyl).
At 98 cents, that's obviously the better way to go. I'll save the
Delrin scrap I have for something else.
Good!
I'm assuming that Delrin would be the best choice as far as plastics,
but my first choice is your idea to use the roll pins. It would seem
that they would withstand shearing forces better.
Well ... "best choice" varies with what you need it to do. I
might consider a fiberglass/epoxy to be stronger, or even a graphite
epoxy composition. But it is not yet clear how much strength you really
*need*.
[ ... ]
I also have several 4" diameter Delrin cylinders that are about a foot
long, I'll be slicing them into 3/16" or 1/4" thick disks that I'll
need to do six plunging operations involving making different sized
holes/slots in each of six equal "pie" slices.
O.K.
BTW. If there is a way to do this using my lathe, the drill would have
to be at the headstock end, and I'd need something like a six-sided
collet block in something not only large enough to hold a 4" disk, but
also position it at varyng heights above the bed.
There are 3-jaw chucks, and 4-jaw chucks, available with 5C
collet style shanks -- designed for when a larger lathe needs to handle
smaller workpieces. Combine this with a collet block and a lathe based
milling attachment and you could probably make a go of this. The
question is how deep and how long the slots will be. If they are all
the way through, and continue out to near the edge of the disc, you will
have problems as the workpiece will collapse when enough material has
been removed.
For that -- perhaps replace the chuck with a faceplate, and find
positions in the workpiece which can accept bolts to secure it to the
faceplate (perhaps with some sacrificial material under the workpiece, so
you don't mill into the faceplate itself.
So obvious a drill press and a rotary table would be the easiest and
cheapest way to go for this.(I'd have to "overlap" drill holes to make
slots).
Smooth slots would be difficult to make this way. Drill bits
tend to bend when you're trying to partially overlap with another hole.
If you space the holes such that they are almost a full drill diameter
apart, and then make a second pass, drilling through the center of the
web between them, you will wind up with a scalloped structure which
you can then smooth out with a file.
Now. yes, the 11/16" long(7/16" diameter) sleeve will have the turned
down end of the rod already inserted into it so I can drill the 1/8"
diameter hole all the way through *both* at the same time. That 1/8"
diameter hole will be located only 1/8" from the end, so gripping it so
it could be drilled would pose a problem.
Hmm ... I would not bother with the center punch given that
setup, as long as the holder (fixture) which you describe below remains
fixed in position between workpieces.
Yes. I'd ahve to make a dedicated face palte and holder just for this.
O.K. Start collecting faceplates to fit your lathe. :-)
As I say -- the punch probably is not necessary. Just start the
hole with the center drill. (You can get them down to 1/8" diameter,
which would make a great start for the hole.
Yes. I believe that would be the #1 center drill.
That sounds right.
Ok. If a $50 drill press would be easier then I will get one.(Hopefully
better than my last one).
Your setup on the faceplate would work. But you would need to
add a counterweight on the faceplate to allow it to balance properly so
you could run at reasonable speeds for a 1/8" drill bit.
Hmm... My original thought was to drill out the solid end of the
holder(a little at a time) which at the start would be slightly heavier
than the side holding the work and Aluminum block. until the weight on
both sides of the center axis(drill point) was equal. This would be
determined by balancing the center axis on a straight edge. But if this
is a bad idea I'll entertain your suggestion.
Simply mount a lighter counterweight to one of the faceplate
slots, secure it with a bolt through the slot, and adjust it outwards
until it counterbalances the workpiece and the fixture. A lot easier
than repeated machining until you get close to the right size.
Good luck,
DoN.
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