Vacuum turning Chucks

[Twisted]

Has anyone had any experience with Vacuum Chucks for turning. I am in the process of building one to help with the machining of Green Ceramic, it has the consistency of Chalk and crushes even in a pot chuck.

[toastydeath]

I've never had the chance to use one, but most diamond turning lathes use them exclusively, and have spoken with folks who designed the very first high precision vacuum chucks.

They hold the part with the smallest amount of force and deflection, even when compared to magnetic chucks.

[Oregon Rob]

In the shop where I work, vacuum chucks are used 90% of the time on some product lines. It all has to do with the shape of the part. You need surface area and light cutting forces. The nice part is that you can acces 5 sides of the part.

[Twisted]

Thanks I will post pictures as I build it.

[ImanCarrot]

Toastydeath is right. I use a Diamond Turning Lathe and almost exclusively use vacuum when turning- works a treat.

Watch out for thin components- the part will deform under vacuum if the chuck is slightly say convex then the part will spring back after demounting and will be concave.

[NEATman]

Twisted-
How porous is the green ceramic?
You may need very high flow rates to compensate if the mateial is porous. Also, make sure you use the largest tubing inner diamater and the shortest tubing run you can when designing the chuck. If the material is exceptionally fragile, it may be best to make the chuck from a porous material. Be careful if you do this, as some porous material will "smear" and seal itself off when you go to machine the surface flat.

How flat is the side you want against the chuck? It will greatly affect the holding force if it isn't extremely flat.

On Diamond turning lathes, the chucks are usually 6061-T6 aluminum with concentric grooves machined in. They are radially cross drilled and tapped so that the tapped hole breaks through the concentric rings, so the effective diamater of the chuck can be altered. I believe plastic set-screws are usually used for this, as they affect the balance less. Standard practice is to "true" the surface and the OD of the chuck each time it is mounted back on the lathe. Also, the cutting force on a diamond turning lathe is tough to measure as it is so small. The chip load can be so thin that the aluminum chips will float through the air on the air currents.

NEATman

[Twisted]

Thanks for the tips, the parts I am holding are 1" diameter pressed powder slugs, very flat on the backs which is the face I am going to put the vacuum on.

Thanks for the Hints and Tips will consider them all in the build.

[Oregon Rob]

Since vacuum is pressure= f/a You have limited pressure and your area is very small. ø1" is less than one sq inch.

BTY I machine mostly pressed powder.

[sc brian]

Another option, if vacuum doesn't work due to porosity, etc., is to bond the part to a "block" using blocking wax, and then hold the block in a conventional chuck. There are various waxes available. I am assuming that the green machining is dry, so water solubility is not a problem. If it is, you need to use a wax that is not water soluble.

[ImanCarrot]

One other thing- make your vacuum adjustable. I use a venturi system which causes less vibration than a conventional vacuum pump (vibration is the diamond machinists true enemy).

If it's adjustable you can apply a light vacuum, tap your piece into position, clock it and then whack the vacuum up.

I also use UV curing gum (like adhesive but you can peel it off) and tippex (typing correction fluid)- that sets like concrete.

However, as stated above, my cutting forces are almost non- existant, the swarf (chips) are so light they float through the air (usualy ending up in my coffee, hair, eyes etc lol

Oh, if you're using a water based coolant with a vacuum system you'll want a foreline trap to capture any that gets through to system. Geoff built one and posted about it on these forums- it looked well smart.

[sc brian]

Can you tell me more about this? Who makes it, how does it work, etc?

[ImanCarrot]

The UV curing stuff was called ColdBlock or ColdLock I think, I'll check my records, came in a black flat container with a nozzle and was a clear amber colour. Set in about 5 mins exposure to UV light (get protective goggles) and could be peeled off with your fingernail when needed to be removed.

They sell it in the States, but the UK supplier stopped stocking it- wasn't worth it for the low volumes.

I'll get back to you when I get time to dig out my records.