Blanchard Grinding Thin Materials

[jlinker6]

Quick question here for you guys, I have some mild steel spacer plates about 175mm in dia, that I need to make to several different thicknesses (1mm, 2mm, & 2.9mm). My problem is last time we tried this with our surf. grinder the parts bowed up and warped with all the heat and we need to keep a parallelism call-out of 0.010mm. Is this even possible to keep the parallelism within 0.010 over the diameter of 175mm with such a thin plate?

 

[tricky1975]

yes but i'm afraid you'll have to either have them lapped to size. or have one face lapped and you'll have to grind the other side.

 

[Tmoose]

It ain't just the heat. Machining both induces some surface stresses, and can remove the pre-existing stress that was in the material that is now chips.

With a magnetic chuck the thinner parts would be parallel, but not flat when done.

I wonder if it would be easier to start with nice sheet stock and limit machining to holes and shape

 

[jim07601]

You can have them lapped. If you blanchard grind you have to take light passes and use a lot of coolant. Also, You have to flip the pieces over a few times as you are thinning them down. The main problem is resideual stresss from the initial fabrication of the spacers. It will be symmetrical, so you have to remove stock symmetrically.

 

[saberblue]

You will also want to use the softest, wheel/segments you have.

 

[unclesyd]

Depending on the quality and quantity needed should determine your approach. For small lots hig quality there are sample preparation machines on the market that will handle your job. We use a very similar machine, older model, to prepare coupons in your range for both SS and CS. For SS we use Al platens with different mounting adhesives or if the run is high we can use a vacuum platen.. For Cs we use mostly magnetic platens made with Alnico magnets attached to an Al platen and ground and lapped flat. Normally we take the sample after grinding to an approbate cut off point and then diamond lap while still mounted.. Most of our polishing is done in vibratory polisher using Al oxide powder down ot 1 micron. Here is the secret to polishing this type specimen, It takes at least 24 hours to get the mirror finish. The surface will have a mirror finish but will not be a flat as when removed fro the diamond lap, shinny isn't flat. Parallelism is still good.
Depending on your production requirement you cna chalk out both approach through the surplus market . The laboratory type or the Speedfam type if production is high.

http://www.speedfam.com/en/product02.html

http://www.buehler.com/equipment/gr...polishers/products/ecomet-250-grinder-polis-1

I have concur that a very good approach would be to get the approbate shim or feeler gauge stock and start from that. One caveat is that the precision o of the different materials is quite variable. When i was making high pressure rupture disks I would have to buy 10 rolls 0.008" SS shim stock to get 3-4 that were on the money. This was considerably cheaper that ordering super precision stock
You can get an idea of what's out there from these sites.

http://www.precisionsteel.com/about-us

http://www.easterngage.com/stock-heavy-thickness-feeler-gages.asp