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MotorradMike
02-27-2011, 02:57 PM
Hi guys:

I've got a couple of not quite round 1/8" thick plastic disks I need to true up and turn down to about 1-1/2" diameter.

Is there an accepted method for this? They won't go in a chuck and I can't have a hole in the center.

The Artful Bodger
02-27-2011, 03:08 PM
Glue? Double sided tape?

My suggestion: Put a scrap of something, wood maybe, in the chuck and face it off. Stick on first disk, stick on next etc, finally stick on another bit of scrap and bring up your tail stock and with a live centre put some pressure on your sandwich.

RKW
02-27-2011, 03:13 PM
Pinch the oversized discs between two high-friction posts, one in the chuck, the other in the tail stock. Then machine to size.

Keith

dockrat
02-27-2011, 03:14 PM
Well if it was me I would turn a plastic sacrificial backing disk that would fit in the chuck and then mount the discs to be turned on that with 2 sided carpet tape. I would also use a DCMT or CCMT cutter to avoid having to cut too deep into the sacrificial disc that you would have to with a triangular cutter.
I'm sure others here will have better ideas though.

Edit... yup other ideas were coming through while I was typing this LOL

small.planes
02-27-2011, 03:46 PM
Something like this http://bbs.homeshopmachinist.net/showthread.php?t=31473
should do it.
I superglued the blanks to a faceplate, but double sided tape would probably be better for plastic.

hth

Dave

DICKEYBIRD
02-27-2011, 04:08 PM
Chuck up & face off a 1 1/2" rod, make up a 1 3/8" dia flat face adapter to fit onto a live center in the tailstock, sandwich your disc between the chuck piece & the tailstock adapter with a piece of paper on either side and apply enough pressure to hold the disc firmly. Use a parting tool and make your cut.

That's how I'd try it 1st. I hate cleaning glue or 2 sided tape off a part.:rolleyes:

MotorradMike
02-27-2011, 04:49 PM
Thanks all!!

I made a sandwich using two 1" maple dowel posts. I have a live center so didn't have to cobble that up.
It worked a treat without tape or glue, I clamped it pretty hard and took light cuts.

Al Messer
02-27-2011, 05:36 PM
See what I mean about this forum is Educational? I learned something today!! Thanks guys!

winchman
02-27-2011, 06:15 PM
I had to true up a 4" diameter 1/8" aluminum disc recently. I opened the three-jaw so the outer edges of the jaws was just a little inside the OD, then ran the live center up against a piece of scrap to hold the disc to the face of the jaws. Worked like a champ, and I was even able to make a little shoulder on the disc in the same setup.

Black_Moons
02-27-2011, 06:26 PM
Pinch the oversized discs between two high-friction posts, one in the chuck, the other in the tail stock. Then machine to size.

Keith

Thats the exact reason I had to beef the hell outta my tailstock clamp for :0

Standard camlock tailstock.. Sucks for this. I turned a new cam that was about 1/2 the offset as the old cam, and made a new bottom clamp plate that was uhh.. 6x as big and protrudes out the back of the tailstock incase I wanna put a bolt on top clamp plate.. :P (have not needed to do that.. yet.)

macona
02-27-2011, 06:47 PM
Watch this video, he shows machining discs.

http://techtv.mit.edu/videos/172-machine-shop-10

Mcgyver
02-27-2011, 06:57 PM
Standard camlock tailstock.. Sucks for this.

agreed, the old fashion bolt through is more solid....my big lathe has both which has been nice.


Pinch the oversized discs between two high-friction posts, one in the chuck, the other in the tail stock. Then machine to size.

that's how i've done it, a faced pad in headstock and one sandwiched between work and centre in the tailstock. Not for plastic but for steel some fine emery paper folded over provides all the friction you'll need.