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Does anybody care to educate me on centreless grinding?

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mc:
I'm toying with a new product, but my problem is I need ground shaft stock (0.498 - 0.499" to be precise), as polymer bushings need to run on it (hence the ground surface to meet the recommended surface finish requirement).

Now I'm aware such things are typically finished with centreless grinders, but that's where my knowledge on the subject ends, so I'd be grateful for anybody who could at least increase my knowledge a bit.

How much material would you typically leave to be ground?

Links to more in depth information about them would be welcome. I have done a couple google searches, but other than the basics of how they operate, I've not really found that much information.

And how mad would I be to consider building one?
A quick search suggests they're typically into double kw figures for power, which is well beyond what I currently have available, so I'm thinking something maybe 3-4 foot square foot print, with a 2-3 hp motor. I'm not looking for a high throughput, and if I could combine it with an automatic parts loader, I could dump a pile of parts in it, and ignore it while I do something else.

seadog:
Can't help, other than to point you at this company - https://www.westmidlandgrinding.co.uk/services/centreless-grinding/

Lew_Merrick_PE:
Hi mc  --  You are (I hope) aware that 3 points can define a circle.  Think of centerless grinding as being 3 tangent points where 2 of those points are high friction drive wheels and the 3rd point is the grinding wheel.  Problems crop up because high friction drive wheels are usually flexible and grinding wheels tend to wear away.  This makes holding a diameter closer than (say) .0005 inch somewhat problematical.  Back in the dark ages when I did a fair amount of centerless grinding most parts had less than .010 diametral inch of clean up.  [1988 was the last time I ran a centerless grinder.]

sbwhart:
Done a bit long time ago:-

As said in Lews' post you have to watch out for lobeing due to the three point contact. You can get small fixtures that fit onto a service grinder that will change it to a centreless. the main benefit of centreless is that you can do long bars by simply feeding it through the machine we've used bars 3m long that were ground this way, also you can simply pass multiple part through one after the other. You'd leave about three thou on for finishing. If your part is relatively short say 4/5" I'd just have it ground between centres, you could do this with a tool post grinder or you lathe.

Stew

mc:
Thanks for the input guys.

The finished parts would vary between around 1 to 3", and some kind of between centre grinding setup would work for the parts with a centre hole, but not all parts would have a central hole, hence why I was looking at centreless grinding.

I spent a bit of time today looking at items that are already available, and it would appear nobody else is grinding their parts, as all the parts I've seen so far are just turned finish, so a roller box is now looking like a more cost effective option, at least for now.

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