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Black_Moons
10-30-2009, 05:06 PM
Hi, as one of my beginner plastic projects I thought about making UHMW drink coasters. custom made so they don't stick to the bottom of my cup and fall off soon after I lift the glass like my current marble ones.

I have a plate of UHMW plastic about 1/2" thick I was thinking of making it out of, but how would I hold it on the lathe to turn the OD without making a hole in the ID or adding a 60 degree center hole?

I suspect I could do it on the rotary table+mill by using 3 clamps and moving the clamps around the 4 slots as needed, but that seems excessive.

AFAIK glues won't stick to UHMW, so I think thats out.

winchman
10-30-2009, 05:22 PM
I'd rough out a disc, and hold it by the OD while I machined the recess where the glass sits and the top surface. That'll leave a shallow step.

Cut a wooden piece to fit the step, and clamp the disc against the chuck with pressure from a live center on the wooden piece while you machine the OD.

Glues won't stick, but double sided tape can be used to hold UHMW in place. I'd be hesitant to trust it for machining, though.

Roger

Black_Moons
10-30-2009, 07:12 PM
I assume just pining it to the faceplate with the tailstock (say a flat nose on a live center) isent gonna hold it, then again maybe I could just use a pointed live center or carve out a 0.01" recess in it for a blunt nose live center (I plan to carve some of the ID out, but not all, so a small dent is acceptable)

tattoomike68
10-30-2009, 07:39 PM
I assume just pining it to the faceplate with the tailstock (say a flat nose on a live center) isent gonna hold it, then again maybe I could just use a pointed live center or carve out a 0.01" recess in it for a blunt nose live center (I plan to carve some of the ID out, but not all, so a small dent is acceptable)

you can hold it with a coin and a pointed live center jammed on it. Iv done steel circles that way. its plastic it will do it easy. go a bit light depth of cut till they round out and then you can speed up.

RKW
10-30-2009, 10:54 PM
Hi, as one of my beginner plastic projects I thought about making UHMW drink coasters. custom made so they don't stick to the bottom of my cup and fall off soon after I lift the glass like my current marble ones.


Not sure if being UHMW will make much of a difference. The attractive force is cohesion due to condensation is it not? I would think it might be better to add concentric or radial grooves to reduce the contact surface ... just an idea.

winchman
10-31-2009, 01:36 AM
"The attractive force is cohesion due to condensation is it not?"

You're right.

The best coasters I've ever used were made by Tupperware.

http://images.goantiques.com/dbimages/ZRP8940/ZRP8940C3192.jpg

The combination of drain holes and raised radials left the bottom of the glass almost dry until the foam insert got completely soaked. There was never a tendency for the coaster to stick to the glass. They probably quit selling them because the foam insert tended to get moldy if you didn't take the coaster apart after using it. They worked pretty well without the inserts, too.

Roger

Paul Alciatore
10-31-2009, 01:54 AM
Make them from brass, about 1/2" thick. No amount of "attractive force" will cause them to lift with the glass. And absloutely no one else will have any that are even remotely similar.

Black_Moons
10-31-2009, 05:42 AM
Brass would stick, its a 'vaccum' effect, solid marbel 1/4" ones stick so bad they sometimes make it to the kitchen and back!
I am planing to use my ball nose endmills to route an X grove in the base to prevent that. or maybe i'll see if just leaving a rough finish (super fast feed) when facing the disk will work. (Would likey look cooler)

dockrat
10-31-2009, 11:47 AM
I like the brass idea. They would look great all polished up. I wonder if it would work if you faced them up with a slight taper to the center so that only the outside circumference of the glass made contact.
I just had another idea. How about doing a diamond pattern on the bottom with a small ball end mill? Moisture would drain to the grooves and glass sit on the tips of the diamonds. Do it something like this:

http://i253.photobucket.com/albums/hh67/Dockrat1/IMGP1068Medium.jpg

Black_Moons
10-31-2009, 04:46 PM
I just recently made a cool square pattren using a ball nose endmill on my mill just like that for a clamp face. but I was thinking a complex pattren like that would attract debrie so I want to minimize the pattren or make it all go one direction (spiral for example) for easy cleaning