Grinding on a vmc??

Does any one have any experience using a vmc as an od grinder. My part is 5.1 od and Id like to grind an elliptical barrel shape on the od. The vmc is a hass vfo e, the material would be 4140 @ about 44 rc. The profile would be a piston skirt app 1.75 in length. Only 8 parts, proto types. I know its not the best Idea , but I dont really have any other way to produce that profile and just thought Id ask If anyone had tried anything similar, and if so, what types of wheel, holder, speed , feed etc did you use. I tried searching for info on this cause I thought I had read some posts on it before, but had no luck finding them. Thanks for any input

Big consideration with grinding is where will the grinding grit go. Dedicated grinders are designed so abrasive particles can be deflected away from the works of the machine. Chip making machines don't always make this as much a priority.

If you think a few up job might damage the machine then perhaps better to send it out IMHO.

If you can't get any help. Minnesota Grinding has some Studer CNC Cylindrical grinders that could do that job for you. CNC Cylindrical & Precision Grinding | Thread, Carbide & Centerless Grinding | Minnesota Grinding Inc. ask for Randy or Harlen and be sure to say I told you please.

Alfred Lyon from AB tools grinds carbide all day on his Haas VMC's. I think he changes the ball screws every year or two.

Add a good filtration system to the coolant output, replaceable spin-on cartridge or canister style. 10 micron filtration minimum. Use plastic sheeting and water-resistant tape to make a "bib" that covers the exterior of the vise and the table and way covers, so that coolant and grinding swarf runs off directly into the enclosure. The table motions will be small enough to not displace the bib.

Use the right AlOx or CBN wheel (although the material sounds too soft for CBN), get help from a proper abrasives supply co. Keep the wheel as small as possible, and as close to the spindle nose as you can for best stiffness. Maybe 1/2" wide max. Mount a diamond point nearby for dressing as needed, make sure the grind zone is well flooded with clean coolant at as high a pressure as possible to prevent simply being tossed off the wheel by centrifugal force. Get mist collection onto the machine if you don't have it already.

And yes, you'll lessen the life of the ball screws and bearing packs, so factor that in. The better you filter the coolant, the less you'll injure the machine.

Thanks for the input everyone, sounds like I may be better off trying a reduced shank mill with some back draft and a fine step over, just not sure if I can get the finish I need that way, the skirt wall is pretty thin in some areas, .060 to .100. Thanks again everyone

How critical are the dimensions?
Can you stand a few thousants in the negative direction?

Proper setup with a reduced shank mill may get you close enough that you could use 120 grit flappy wheels in a die grinder to give it that final slicken up.

May have to get creative with your setup by filling up the inside with something to dampen vibration from the end mill so you don't get as much chatter on the thin walls.

Who knows, you may be pleased with the results from the milling and a little polishing and be just fine.

I agree with Milland but would suggest 1 micron for filtration, even that won't get it all. Go with a cartridge vs a bag filter since it is absolute vs nominal filter sizing. The only thing a little grinding should hurt on the machine is the way cover rubber and probably not much at that. Try not to dress the wheels on the machine to reduce the abrasives it has to deal with. Speeds and feeds are simple enough to figure out. How you hold the wheels may be custom.

Doing what you describe shouldn't make a noticeable difference in your machines life. If it works out and you want to do production then that is different. Would I do it on my Kitamura, hell no!

cpifer3 said:

Thanks for the input everyone, sounds like I may be better off trying a reduced shank mill with some back draft and a fine step over, just not sure if I can get the finish I need that way, the skirt wall is pretty thin in some areas, .060 to .100. Thanks again everyone

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Every think of using plated wheels for grinding? No need for dressing, no worries about grit filtering. We do it all the time. If you have a lot of stock to remove and need a good finish, no problem - use a rougher and finisher.

Generally CBN plated works best of Rc 50 and harder, but I have had good luck on 400 series stainless, especially if you are doing prototype work and aren't running long production jobs.