My apologies for the blank subject field....

"Robbo" wrote in message
...
I'm looking for some ideas on how to repeatedly and hold some 20mm OD PVC
round bar in a lathe chuck. I'm turning batches of 20 pieces - they start as
a 25mm length of 20mm OD PVC rod and end up with:

a) an 11mm thru' bore
b) a 17mm x 5mm counterbore.
c) a 17mm OD step on the outside at one end.


Hopefully the cross-section below will make sense of my ramblings:

__________
_____| ____]
|___________]

11mm thru 17mm internal counterbore
bore
___________
|_____ ]____
|__________]

17mm 20mm OD
step



Is there a neat way I can fabricate some sort of jig into which I can
quickly clamp the 25 L x 20 OD PVC pieces so they will be in the same
location? Some sort of simple collet??

I need to achieve 0.5mm accuracy lengthways and 0.2mm on the turned OD and
internal counterbore diameter.
Unfortunately I dont have a milling machine - just the lathe,a CQ6230 lathe
(Chinese copy) with a 3 & 4jaw chucks + faceplates etc.

TIA
Robbo (the novice)

On Fri, 12 Oct 2007 10:08:34 +0800, "Robbo"
wrote:

My apologies for the blank subject field....

"Robbo" wrote in message
...
I'm looking for some ideas on how to repeatedly and hold some 20mm OD PVC
round bar in a lathe chuck. I'm turning batches of 20 pieces - they start as
a 25mm length of 20mm OD PVC rod and end up with:

a) an 11mm thru' bore
b) a 17mm x 5mm counterbore.
c) a 17mm OD step on the outside at one end.


Hopefully the cross-section below will make sense of my ramblings:

__________
_____| ____]
|___________]

11mm thru 17mm internal counterbore
bore
___________
|_____ ]____
|__________]

17mm 20mm OD
step



Is there a neat way I can fabricate some sort of jig into which I can
quickly clamp the 25 L x 20 OD PVC pieces so they will be in the same
location? Some sort of simple collet??

I need to achieve 0.5mm accuracy lengthways and 0.2mm on the turned OD and
internal counterbore diameter.
Unfortunately I dont have a milling machine - just the lathe,a CQ6230 lathe
(Chinese copy) with a 3 & 4jaw chucks + faceplates etc.

TIA
Robbo (the novice)

=========
Make a plate that will bolt to the faceplate.

Drill and tap the plate for a bolt that will compress the plate
side ways to clamp the plastic pipe.

Bolt the plate to the face plate and bore a 20 mm hole.

Use a hacksaw and slot one side of the plate so the drawbolt can
compress the pipe. You may also want to slot the other side of
the block so it will flex a little easier.

Burr and remount the block to the face plate and adjust for
runout.

Mount pipe pieces in hole and clamp with bolt. Machine as
required.









Bore a 20 mm hole in the plate.


Unka' George [George McDuffee]
============
Merchants have no country.
The mere spot they stand on
does not constitute so strong an attachment
as that from which they draw their gains.

Thomas Jefferson (1743-1826),
U.S. president. Letter, 17 March 1814.

On Fri, 12 Oct 2007 10:08:34 +0800, "Robbo"
wrote:

My apologies for the blank subject field....

"Robbo" wrote in message
...




Is there a neat way I can fabricate some sort of jig into which I can
quickly clamp the 25 L x 20 OD PVC pieces so they will be in the same
location? Some sort of simple collet??

Unless I'm missing some subtle point, a simple stop in your lathe's
spindle will work. You can make one that works like the opposing wedge
handlebar stem clamp with just your lathe and a hacksaw.

This is a more elaborate stop that I dreamed up that I use in my
collet closer tube.
http://www.suscom-maine.net/~nsimmon...ColletStop.pdf

Or, if your 3 jaw chuck has two piece jaws, you can make a set of soft
top jaws with a step to locate the blanks axially.

--
Ned Simmons

"Robbo" wrote in
:

Chuck spider and double-stick tape.



--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

Many thanks George, Ned , Anthony and DoN, all good ideas I had not thought
of. I spent an hour or so investigating chuck stops, spindle stops, spiders
etc. I'm leaning toward the idea of a stop located in the spindle and clamp
the work with the 3 jaw. This will give me a greater range of stop position
location - from partway along the chuck jaws to back inside the spindle for
longer jobs.

I wasn't too sure if a chuck spider was a beer & ice cream thing, I found
some good pictures here that clarified it for me:
http://bbs.homeshopmachinist.net/showthread.php?t=24007

The help and advice you guys provide is really appreciated.

best regards
r.