Tool Post Grinder Out Of China Mill Spindle

[Ianagos]

So I was just looking on eBay and I saw some dc spindles that go from like 3000-12000 rpm and whatnot that look like they would be easy to make a tool post grinder out of. I also saw some ac ones but they needed a vfd and whatnot so too bulky for my liking. I'll put a link later in but does anybody think this would work? I have a dumore and a bigger tool post grinder (I've never used it it's huge) so this is more to see if anybody else wants to try it. I also thought about making one and a quick change mount so it could go on my CXA tool post so it would be easy to throw on and off. There are tons on eBay but the one I'm linking looks like it will be easy to mount via the face and won't require grabbing the OD.
https://www.ebay.com/itm/321818577027
This one also looks suited and can be water cooled but is faster and requires a vfd.
https://www.ebay.com/itm/391544299765

Well just wanted you guys opinion on this and if you think I'd be able to mount this right up on my lathe.

Also tho it about making and er collet shaped arbor just to get any accuracy I could for it. Because I'm guessing the China thing won't be super but maybe It could be.

 

[rgray]

I think it could work. Not sure the face mount would be rigid enough. I made a mount for my lathe but I remove the QCTP and it mounts to the compound T slot.
I thought it would be real handy and it is but you quickly learn that the lathe is not the place for grinding dust.
I now try to not use it on the lathe unless absolutely necessary. Recently used it to true a 5c collet adapter that is marked so it can be installed in the spindle in the same place every time. There is really no way to match that grinding it off the lathe so that was an instance where I used it but if possible I always do grinding on a grinding machine.

From the Dumore site was a wheel speed calculation RPM=3.82 x sfpm divided by wheel diameter(in inches) 6500 sfpm is a good number according to them. That means the small spindle at 10,000 rpm would be limited to about a 2 3/8 in. wheel and the larger vfd driven a 3 in wheel at 8000 rpm.
They have an example calculation and their math is wrong...or I'm to old to run my calculator. Not sure which.

 

[petertha]

I've had the same thoughts but never got around to trying one. The appealing aspect is it the motor/spindle combo is relatively small so would be very convenient to plop it on the tool post & commence finishing. OTOH I see lots of guys adapting anything from pencil grinders to Dremel-type tools, but I usually don't hear much tangible follow-up about how it actually performed and on what kinds of jobs. Yes, its shiny alright but...

- Grinding actually consumes substantial power. My own interest was precision dressing teeny amounts off smallish things where lapping is a PITA. But taking couple thou passes off longer lengths, the HP requirement goes up pretty substantially. Which explains why commercial toolpost grinders are substantially bigger even on hobby size lathes. If motor is undersized, presumably heat will be an issue for the little motors. Now, whether that's just a matter of taking your time or allowing cooling periods, I cant say.

- I wonder about the bearings in these? If they are just plain with no provisions to take up play, then the assembly will simply pass that deviation onto the part. ie hard to reliably control a 0.001" finished grinder depth when the bearing floats 0.002". One fellow measured runout on his (similar aliexpress motor spindle) shaft & it seemed pretty tight, but darned if I can fid that link. When you see the innards of commercial Dumore or Themac spindles, it kind of starts to click what's going on. I've seen homebrew spindle designs mitigate with multiple bearings & axial tensioning mechanism. So my gut tells me this effort must be for a reason.

- from my very limited grinding experience, you really need an accurate dial setup on the lathe which accurately shows in feed progress independently (like touching off the cross slide). Your lathe dials are pretty much useless at this scale depth of removal. I mounted a 0.0001" increment dial & it was rather revealing. A vibrating needle shows imbalance, vibration or things are not locked down properly. Even the act of locking my carriage was showing deviation I just always assumed was staying in position. Setting the compound at an angle to work can get some better resolution, just need to do a little correction math. The stone type & dressing & accounting for wear... are all things I'm learning. The results are definitely worth the headache.

Well, I hope you get one so we can see how it goes!

 

[Ianagos]

Yea my main worry on these was the rigidity

My lathe is pretty sloppy but I'm planning on getting some rebuilding done so that should be that

On positioning a dial indicator on magnetic backing is what I was gonna do and set the compound at the right angle so .001" in feed only feeds .0001"

Haha my lathe has seen years of mill scale grinding dust and all kinds of nasties a little grinding dust here or there with me wiping it up and the automatic pump floating the ways in oil I should be fine. I'll be installing new way wiper and such so that should keep it cleaner.