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Info regarding centerless grinding

Tupper87

Plastic
Joined
Feb 12, 2019
Hey guys, so I'm new to centerless grinding and having my parts sent out to have it done. So I have a few questions. If there is a slight taper, will the grinding take the taper out or follow it? Also, if there are any high spots will the part come out round. I'm talking about .0003" if that.
 
What is / are your parts diameter and length ?

There's a massive range of sizes that encompass centerless grinding.

Are there internal features ID/ bores etc. that have to reference an external cylindrical surface ?



Curious as to what sort of quantities you may be dealing with + QC ?

Grades of steel and hardness , + possible surface finish you are going for ?


You might also want to post this simultaneously in the "Abrasives" section too maybe ?
 
What is / are your parts diameter and length ?

There's a massive range of sizes that encompass centerless grinding.

Are there internal features ID/ bores etc. that have to reference an external cylindrical surface ?



Curious as to what sort of quantities you may be dealing with + QC ?

Grades of steel and hardness , + possible surface finish you are going for ?


You might also want to post this simultaneously in the "Abrasives" section too maybe ?
Diameter is .2506" with a tol of -.0002 finish is 16 and length is 3". No bores just a tight tolerance on the OD. With a little flat. Its inconel 718 around 35-40 Rockwell. Qty is 106.
 
Diameter is .2506" with a tol of -.0002 finish is 16 and length is 3". No bores just a tight tolerance on the OD. With a little flat. Its inconel 718 around 35-40 Rockwell. Qty is 106.

Dumb question here from me... Why centerless grinding in this case ?
 
Really - the question is "what kind of centerless" grinding?

You could easily get a tapered part if it is getting plunge ground.

But a through-feed unit shouldn't even be able to get a taper if they wanted to.

It should be round after it is done - irrigardless of what it was before going in, but a good deal of that will be dependant on height of the center support.
You need to check this with a 3 point mic as you can get 3 lobe profiles at times, and that will not show up on a 2 point mic.


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Think Snow Eh!
Ox
 
Really - the question is "what kind of centerless" grinding?

You could easily get a tapered part if it is getting plunge ground.

But a through-feed unit shouldn't even be able to get a taper if they wanted to.

It should be round after it is done - irrigardless of what it was before going in, but a good deal of that will be dependant on height of the center support.
You need to check this with a 3 point mic as you can get 3 lobe profiles at times, and that will not show up on a 2 point mic.


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Think Snow Eh!
Ox

Assuming the work piece can't be held on a conventional cylindrical grinding machine...

I was wondering how many pins/ shafts do you have to go through to get stuff nicely dialed in on a cylindrical grinding machine ?

If OP wants 106 how many extras workpieces have to be supplied to get things "Sweet"..?
 
Ox is on this to a tee.
You can dress to a almost zero taper when plunge but though feed gets rid of it all if the part moves though at the right speed and you can be a lot out out alignment.
One can also make a straight end section and a back-tapered section with the wheel at a small taper and controlling how much is fed through out the back.
This is how drill bits and reamers are made.

Tri-Lobing is the bane of centerless work and the source of many people's later misery.
Due to the way the machine makes parts It will always check okay with a regular mic.
Pay heed to the advice from Ox on a tri-mike or 120 vee block and indicator.

Mostly to your point centerless grinders don't give a poop about incoming taper and will grind where they want.
Bob
 
Assuming the work piece can't be held on a conventional cylindrical grinding machine...

I was wondering how many pins/ shafts do you have to go through to get stuff nicely dialed in on a cylindrical grinding machine ?

If OP wants 106 how many extras workpieces have to be supplied to get things "Sweet"..?


I don't git'cher post?

The first part through the centerless will be right if they sneak up on it correctly.
I can't imagine trying to run this on a cyl grinder. :ack2:



BTW - this must be a "CNC" centerless grinder - right?


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Think Snow Eh!
Ox
 
I don't git'cher post?

The first part through the centerless will be right if they sneak up on it correctly.
I can't imagine trying to run this on a cyl grinder. :ack2:



BTW - this must be a "CNC" centerless grinder - right?


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Think Snow Eh!
Ox

Some of the modern-ish centerless grinding machines seem fantastically complicated to me and are based around high through put and automation. I just assumed that 20-40 work pieces 'Plop" out the other side , go to inspection, and that (in turn) informs what is dialed in on a production level machine... Maybe in a progressive way until the 'Process" is stable for making tens of thousands of something in a reliable and efficient way; day in day out kind of thing. (My ignorance I guess for the question).


So I guess from what you are saying with (maybe) older style machines as well that in process gauging is no problem ( and It's possible to "Get" it / nearly nail it on 1st workpiece for form tolerance on the centerless grinding machine and the other pieces should be a no-brainer with a careful eye. ). Curious about practical technique for 100 parts (kind of thing).

If it's Inconel 718 (with a 16 finish) and there are no ways to actually hold it for other (more common) methods then I guess centerless is the only way to go ? Right ?


I'm surprised this is not a type of pin that can't be ordered off the shelf unless the flat is in a weird place ?

I'm curious what kind of shops and what kind of rates would take on this job … Just for my own selfish purposes.

I don't think OP's tolerances/ form tolerances will be an issue. (Like everyone has said). Input variance ----> output form tolerance(s).
 
It's not nearly whatever it is that you think it is.


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Think Snow Eh!
Ox


That's good to know...

Typically I don't approach a lot of shops as I figure for small numbers there's virtually no point. I.e. they don't want the hassle or the price is prohibitively expensive for a job like OP's

centerless-grinding-machine[1].jpg

^^^ This looks complicated to me (lol) … And it's not even as nearly as complex as some of the modern production oriented machines that handle OP's type of work envelope.


I kinda get the sense that the small batch high precision shops (really hands on stuff ) are kinda dying out a bit. But that does provide a GOOD market for "Peeps" hanging in in that space (perhaps).

Not to create problems where there are none, just wondering who OP goes to for this ? (In this case and what they would quote for that ?).


Wondering about functional design of OP's pins if it really is the case that grinding between centers is impossible vs. "Centerless"...
 
The condition of the spindles also affects the quality of the parts coming out of the machine. Is there a straightness tolerance on those parts too? I ask because inco can move around.

Sent from my SM-G930V using Tapatalk
 
Some of the modern-ish centerless grinding machines seem fantastically complicated to me and are based around high through put and automation.

Cameraman

I think you really need to get into a C'less shop and ask if they'd let you look at a setup.

Like Ox said, for an experienced guy, creeping-up on a dimension is pretty easy on a C'less, and once set it is pretty darn stable.
As far as automation for a few thousand pieces, how' bout a clapped out vibratory bowl feeder to present the incoming pins onto an angle iron, and then a long wooden dowel
to push them between the grinding and regulating wheel by hand?

I don't know much about setting up a centerless, but have watched a few setups.
With a properly trued up regulating wheel, dressed grinding wheel and correct support height setting ( all these are on the expertise of the operator ), they are one of the simplest
looking machines with deadly accuracy!

For short-length through feed work like what the OP is asking about, I don't believe my go-to shop has ever lost a single piece.
For full bar lengths, the only issue I've ever had is when he didn't take the time to set-up the input-output support rails and the bar ends were slightly
over/under size due to whipping.
Grinding to a shoulder ( plunge ) is where things seem to get trickier with certain part geometries, but even then I prefer to have the centerless shop tell me to F-off first
before sending stuff to a cylindrical grinder.
 
Cameraman

I think you really need to get into a C'less shop and ask if they'd let you look at a setup.

Like Ox said, for an experienced guy, creeping-up on a dimension is pretty easy on a C'less, and once set it is pretty darn stable.
As far as automation for a few thousand pieces, how' bout a clapped out vibratory bowl feeder to present the incoming pins onto an angle iron, and then a long wooden dowel
to push them between the grinding and regulating wheel by hand?

I don't know much about setting up a centerless, but have watched a few setups.
With a properly trued up regulating wheel, dressed grinding wheel and correct support height setting ( all these are on the expertise of the operator ), they are one of the simplest
looking machines with deadly accuracy!

For short-length through feed work like what the OP is asking about, I don't believe my go-to shop has ever lost a single piece.
For full bar lengths, the only issue I've ever had is when he didn't take the time to set-up the input-output support rails and the bar ends were slightly
over/under size due to whipping.
Grinding to a shoulder ( plunge ) is where things seem to get trickier with certain part geometries, but even then I prefer to have the centerless shop tell me to F-off first
before sending stuff to a cylindrical grinder.

That sounds very worth while, I'll definitely check it out...

I'm just more familiar hands on with cylindrical grinders/ grinding and know the kinds of subtle tweaks that you can make... So I tend to design for what I know can be made. I usually associate centerless grinding with much larger work pieces also (as well)... And something more "Widget like" I order from a catalog. Kind of the same with companies that specialize in honing / honed precision tubes etc.

I may be wrong here but I kinda thought better form tolerances can be done with cylindrical grinding, but centerless can theoretically offer better surface finishes but smidge lower control of form tolerance. (Depends on process/machine / grind hand / actual part/ Material / complete over generalization lol.)




Funny just looking at some second hand Cincinnati (centerless) grinders... Not badly priced lol.

Seems that Op's concern was with part variation and taper of what he / his company would supply as parts to be ground... I wonder how common it is for a 'centerless" shop to just fabricate the whole article in Op's case ?

In my area there IS a lot machining going on but tends to be behind closed doors / aerospace/ United Launch alliance /Lockheed Martin etc. etc. but have yet to fully engage with some of the " Grind houses" / firms as there are so very few... I tend not to bug them unless I come in hand with a really good or worthwhile job to begin with, build a relationship from there.

OP's question was good one, wish he'd chime back in lol ;-) With his tolerances sounds very doable but again wonder what they would charge.
 
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You had me at hello, and then I've gotten lost!

Check out these centerless guys: Micro Grinding Systems

( Sidenote: I despise Glebar's corporate attitude! )

Certainly makes sense !

Thanks , it's been a long and complicated day... (sorry about the rambling).

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Going through that link and site, looks pretty damn excellent/ useful … Nice one :cheers:
 








 
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