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Does anybody care to educate me on centreless grinding?

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PekkaNF:
Maybe you are familiar with this?



Because grindingwhees can be hands full, mabybe belt would a way to go...something like this:


Real machines tend to be powerhungry behemonts, here is the tiny one:


Pekka

mc:
Thanks for those vids Pekka.
That surface grinding one had popped up on my feed, but I had not watched it until now. It certainly gives me one potential option if I go down this line.

The belt one, I'm going to guess is aimed more at getting a brushed/clean finish rather than good tolerance.

And yes, industrial centreless grinders all seem to be big, but then they're all aimed at big throughput with minimal adjustment. If I was to go for grinding, I'd hope to have something reasonably compact, but I'm well aware the smaller the wheel, the more adjustment it'll need to keep tolerances.

PekkaNF:
Happy to nudge a little, right direction, I hope, from the OP I suspected that you pretty much know what need to accieve:


--- Quote from: mc on January 04, 2019, 05:11:56 PM ---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).
...

--- End quote ---

If you need relatively short and are willing to do manual repetition, then Robin method is superior.

But belt grinding can be dialed in to be pretty accurate when corret contact wheel and belt is used. And obiviously has greater troughput capacity on constat size shaft. My limited knowledge on polymer bushing is that they are more forgiving on actual diameter than surface roughness, therefore I put this belt option here.

Being DIY forum that beltgrinder option seems to show pretty good DIY potential compared to proper centerless grinder.

WeldingRod:
Are you worried about surface finish or tolerance?  Roller or diamond burnishing can take a lathe finish to what you need in one step.  AND the finish will be the better-for-sliding biased type: peaks selectively knocked down.
Single point diamond burnishing tools aren't super expensive, but are also not super-impressive (at least when I tested them)  Completely flexible on diameter, though!  I was shooting for biased and around 2 microinch, so I was asking a LOT.  They need clean coolant/lubricant.  We used a whole house filter with a micron element.
Roller tools are not very diameter flexible, but super fast, smooth finishing, and controlled.
I still have the diamond tool somewhere, so I might be able to do a demo.

Sent from my SAMSUNG-SM-G891A using Tapatalk

mc:
A bit of both.
I'd like to maintain a nice constant tolerance, and I realise it's not that tight a tolerance, but I think I'd struggle to maintain it on my lathe using normal turning. The shorter parts would probably be OK, but trying to hold less than a thou (I'd ideally like to aim for maintaining within 2-3 tenths) on a bit bar at 6 times longer than diameter is likely to be a challenge.

The finish is where things get a bit interesting. IGUS provide lots of information and wear rate charts, for their various compounds. The generic option specifies 0.6Ra (N5-6 or rougher end of ground finishes) finish as being optimum (too smooth and stiction/material transfer becomes a major problem), yet their low friction compound doesn't show any greatly increased wear even up to twice that roughness (in the N6-7 area which is the overlap zone between typical ground and turned finishes). As this will be a oscillating application, they also mention the high spots will wear of the shaft, so a rougher shaft can actually give longer service as it'll wear in. Off course I need to tread the line between wearing in to give good performance, and wearing out so things start rattling!


At the moment, I've found a supplier of reconditioned roller boxes, and although it probably won't work in my CNC lathe (it would stop my turret from fully rotating which could be worked around, however I think it'll hit the enclosure when trying to part off), I'll give it a run on my manual lathe to see how things will work out.
If that works, I think this idea will have enough potential profit to justify a new CNC lathe build designed around gang tooling.

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