Grinding larger parts than your machine can handle

SirRage · Apr 29, 2017

Hey there,

I was wondering if there were techniques for surface grinding parts that exceeded the size of the surface grinder? Say you have an 8x24 inch part and your surface grinder were smaller than that.

I imagine if there were breaks in the part that would allow the wheel to spin freely between each pass then you would have some options.

Larry Dickman · Apr 29, 2017

I have tried this by rotating the part a few times. Results were less than ideal. I don't think you would ever be able to hold tenths, but to get something f&p within about .002 is doable

Peter from Holland · Apr 29, 2017

I never did it but I have heard with not too thick pieces they put some weight on the overhang so that part slightly bends down a bit

Peter

adama · Apr 29, 2017

I done some 8x1" bright flat on the narrow edge circa 37" long on my J&S 540 6x18" capacity grinder, Not grinding for finish but for a flat surface to mount linear rails on. Clocked it in + shimmed it true, not sure on total accuracy, but its well under 2 thou total error - can't even detect the error with anything i have here Straight edge shows no light under it, half thou DTI shows nothing across the joint face.

Theres about 1/4" of overlap on the ground area that i used sharpie marker pen on, just tickled it off like i would picking up a face after a wheel dress.

I did have to add some weight to the table opposite the work to stop it lifting though as most grinders tables are only held down by gravity! and i had more than enough weight to lift it at full travel.

winger · Apr 29, 2017

I've ground 10" pieces on an 8" chuck. Best I could do was, close enough. Spinning the pieces multiple times wasn't any better. May be a little bit the well used grinder.

Dave

CarbideBob · Apr 29, 2017

So say a 8 x 24 on a 6x12 grinder?
Have done it, not real fun time. One side okay and trustable or both sides?
You Sharpie marker or blue the cut sides and try to blend.
Chuck needs to be dead flat in millionths and remount of part means no dust in the same range.
No hand wiping, dead skin cells puck you, no outside air, think clean room bunny suit.

Yes you can get away with much less and I even smoke around the machines.
We do use a acetone wipe on chuck and part with crazy filtered air blow off for lint/dust on such indexes.
Bob

cash · Apr 30, 2017

We do this on our surface grinders and Blanchards often.

Grind a 42" wide part on a 36" wide machine, or a 96" diameter on an 84" blanchard.

This is what separates the "A" operators from the "B" operators.

No job is ever the same when doing this so it is hard to explain how for an open scenario.

DMF_TomB · Apr 30, 2017

if part is not hardened i am often given many jobs to just use a big cnc mill to get parts within .0003" straightness, flatness, perpendicularity.
.
when parts weigh tons often gravity causes then to sag from their own weight and how they are held is important.
.
many mills have grinding attachments for higher rpm but normally a modern carbide insert facemill is all thats needed. i have milled hardened material but obviously it works better if you use cutters made for hardened steel.
.
it is called lap the different in parallel width passes height. my tolerance is usually .0003". i of course check for it with a .00005 indicator

dian · May 18, 2017

has anybody pushed a long part between wheel and chuck? i have seen this done with a belt grinder.

Larry Dickman · May 18, 2017

dian said:
has anybody pushed a long part between wheel and chuck? i have seen this done with a belt grinder.

I think the real question is, has anybody done it twice?

6061Mike · May 18, 2017

cash said:
We do this on our surface grinders and Blanchards often.

Grind a 42" wide part on a 36" wide machine, or a 96" diameter on an 84" blanchard.

This is what separates the "A" operators from the "B" operators.

No job is ever the same when doing this so it is hard to explain how for an open scenario.

Some years back, my boss gave me a job to grind on our 6x12 that was longer than the chuck, maybe 15" or so. I said "it's bigger tahn the chuck, how do I do this?" He said figure it out. Lots of patience, skill, and luck (in no certain order

) and I got it done. I don't know, but to this day I think it was a test (which I passed) and I think it irritated him because a week later he gave me something about 3-5" longer than the first one to do. Well the first one taught me a few tricks, so the second wasn't too bad (although today I might struggle trying to repeat that job).

So, make sure the table doesn't tip due to weight, make sure chuck is nice and flat, shim where needed (if needed), keep everything super clean like Bob said, and cross your fingers and you should be able to get er done, as long as the tolerances aren't 'too' tight...

michiganbuck · May 18, 2017

Agree with a good flat chuck work can be places about and off chuck.. good was the old grease markers.. they would smear with being .005 off, go liquid with about .002 , and start dusting witness at 0002 or so..The china markers found today are OK for that task of matching a grind from another location..
Many oil way machines will go longer but limited by the cross and long travel control (lead screw or what).. The B&S 13 grinder designed to go 22" long can actually go 31" long with going off the long gear rack and to a temporary cable drive.

One very important trick is with getting close is to let the part rest a bit to let the heat out.. then tickle-in to see the touch marker then spotting grind witness to match the first grind. getting .0002 is not tough but getting close is best done with hone finishing.

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