Centerless grinding questions

elysianfield · Feb 10, 2021

Hello,
I am investigating the purchase of a small centerless grinding machine...Royal Master size, or perhaps, even one of the small fixtured devices to place on a surface grinder to perform centerless grinding on an occasional basis. I know nothing about the process.

What I need to know, at least, is how fast these systems can grind a small part to size...a .312" diameter piece of 1018, 1/2" long, to a diameter of .257". I know there are innumerable variables...but what could I expect with a Royal Master, or even one of the fixtures? Thank You.

tdmidget · Feb 10, 2021

Why would you have that much grind stock? .055" is ridiculous! A Royal Master is not a hogging machine. I can not picture it taking off more than .005" per pass. The Royal Master can hold .0001 all day with an experienced operator. It is not for lathe work. You really need to get closer to final size before grinding. The tinkertoy rigs for a surface grinder chuck are a make do. I don't see a wheel that narrow removing more than tenths per pass. What is the situation that requires such heavy grind stock?

CarbideBob · Feb 10, 2021

tdmidget said:
... What is the situation that requires such heavy grind stock?

I'm guessing standard raw stock size.

tdmidget · Feb 10, 2021

Kind of what I thought but there must be an operation prior to the grind that could have a pass to reduce the OD to a manageable size for the grind op.

CarbideBob · Feb 10, 2021

Metric dia. stock to start with?

tdmidget · Feb 10, 2021

Could be but still too much to grind under normal conditions. I suppose it could be done but with a bigger machine and the heat would be huge. 1018 would not be through hardened but could be case hardened but hardness would suffer . It would light up the room when one goes through!

tdmidget · Feb 10, 2021

Also need a bit more info. What is your tolerance on these? Finish? I don't see any way to do this in one pass. I'm thinking they are not hardened as a surface hardening would be removed. There are larger machines that might do this but not a Royal Master. That would be abusing a nice machine. The one I ran had .00001 graduations and it would take that much off. I have run 50 parts consecutive and not vary .0001. That was a production environment, no babying.

Lost in LA · Feb 10, 2021

A Royal Master centerless grinder-- or others of similar size--can easily remove .005/pass on a 3/8 dia part.
Grind 10 passes + a couple of finishing passes of .002 +/-.

On that short length you can easily run 10 to 20 parts /minute maybe lots more.
Inspection and set-up and parts washing will eat more time. That puts you between 3 and 6 seconds/pass for a sooth running job.
Figure 12 passes and your time is between 36 and 72 second /part finished + unknown like inspection etc...

Heavy duty centerless grinders can reliably remove .010/pass on this size part.

Lost

tdmidget · Feb 10, 2021

Lost in LA said:
A Royal Master centerless grinder-- or others of similar size--can easily remove .005/pass on a 3/8 dia part.
Grind 10 passes + a couple of finishing passes of .002 +/-.

On that short length you can easily run 10 to 20 parts /minute maybe lots more.
Inspection and set-up and parts washing will eat more time. That puts you between 3 and 6 seconds/pass for a sooth running job.
Figure 12 passes and your time is between 36 and 72 second /part finished + unknown like inspection etc...

Heavy duty centerless grinders can reliably remove .010/pass on this size part.

Lost

True and if the size tolerance is wide enough something like a Cincinatti EA can probably take .025 with a 10 inch wide wheel but why? This is really lathe work. If the size is open enough then that would be an option but the OP seems concerned about space, although I don't see that much difference. If there is potential of more or larger centerless work then the EA is a better option. We also need to know if there are features that need to be concentric to the OD and how much? These old machines can do serious work, heavy stock removal and last forever. Again, though is this the best way?

elysianfield · Feb 10, 2021

Hello,
You have provided the information that I needed...it is little different than cylindrical grinding. The part in question comes off a screw machine...either grind them individually, or perhaps process a 12 foot stick to the proper dimension and use nylon fingers...go figure. They are thru holed, and are difficult and time consuming to do on a lathe...turret or otherwise. Just looking for a solution for a job we where we use a cylindrical grinder with a very marginal solution to work holding. It is open tolerance work...+/- .001

Thanks for all the replies.

sfriedberg · Feb 10, 2021

If they're coming off a non-Swiss screw machine, use a box tool, a hollow mill, or a skive tool to reduce the diameter. The skive tool can even be made to work behind shoulders if that's the problem you're dealing with. If this is a Swiss screw machine, just turn the things to the right diameter.

Gsharp10 · Feb 11, 2021

When you say occasional use would this be a production run. If so, sending them out in 12' bars would be the way to go. I have Dedtru, Cincinnati OA,EA, and Cinco centerless grinders in my shop. Dedtru (surface grinder type) are best used for light stock removal to precision tolerances. As said earlier it would not be practical to remove that much stock as blade set up would be very time consuming. What is the ID and wall thickness of the through hole? If possible we would gang them up on an arbor and plunge them down on a Cinci. Very fast. Figure the cost of the machine, wheels, blades, coolant, dressers, diamonds and learning curve for an occasional use???...just my .0005" worth.

elysianfield · Feb 11, 2021

Hello,
Yes, non Swiss machine...older Brownie. Problem is I am a half-assed screw machine guy...got it running about 80% of the job, and have tried box/balance tools, would try a hollow mill, but I ran out of lobes on the cam, and have major conflicts with existing Y axis tooling....

Had I spent years running the old Brownies, this would be easier, I know. P.S. I also have a Swissie in good condition (Traub A25), but with only one operation from the tailstock...where I need four. Back in the stone age, I was buying products from "Cams by George"...life was a lot simpler, then with the Brownies.

Cheap excuses, I know.

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