Grinding a lathe face plate with a dumore tool post grinder.

bmikkalson · Feb 25, 2017

I need to face grind a 15" cast iron surface( looks like a brake rotor, but not). Or imagine surface grinding a lathe face plate.
Has any one used a tool post grinder to get flat results . .001 over 12"
I'm using a pretty new colchester 15 lathe. Would the tool post grinder have to have a cup wheel? As I don't think there is enough room to turn the grinder side ways on the X axis. And have the travel with the carriage I need ..

P.s, no rotorary grinder or surface grinder or other.

dian · Feb 25, 2017

if its not hardened why grind it? the lathe will produce a concave shape that however might be within your tolerance.

bmikkalson · Feb 25, 2017

dian said:
if its not hardened why grind it? the lathe will produce a concave shape that however might be within your tolerance.

I need the surface finish , the shape is more like a 15" ring with. 2" part that needs to be machined. Imagine a brake disc .
So I am hoping that only moving the cross slide 2" for the cut gets me there. Other wise I could tune in the compound .
I am having trouble seing how the grind wheel is going to contact the work.

Monarchist · Feb 25, 2017

dian said:
the lathe will produce a concave shape

Not if you have need to have it otherwise. The 'usual' built-in bias to that is rather slight and can often be offset manually with staged & stepped 'spring' passes and/or by applying pressure to the cross.

Within but a 2" band, it shouldn't even be a factor.

If only ONE THOU is close enough, and for one/few item count, AND simple turning was for some reason not as good as usual, I'd finish with backed abrasives manually applied and checked.

For but a 2" band, I would not bother with the hassle of mounting a grinder, sitting through 45 minute warm-up of bearings [1], dressing wheels, etc.

At +/- a half-thou, it is just turning, the backed abrasive more for a nicer surface finish than for 'extra' precision.

Tedious, IOW. But hardly magical.

[1] My McGonegal is no more flexible than a Dumore as to mounting. The "Precise" would be. Warm-up is specified.

dian · Feb 25, 2017

if its a 2" ring i would turn it and work it on a surface plate. its faster than you might think and it will be flat.

Monarchist · Feb 25, 2017

dian said:
if its a 2" ring i would turn it and work it on a surface plate. its faster than you might think and it will be flat.

I am presuming worst-case.

For example it could be raised, or even rebated.

Access could be limited by either/both a hub or outer wall.

As an example - the finishing of a brake DRUM, not disk, insides, surrounding the hole for the hub, where the surface through, and both sides of the bolt circle must be flat.

Or similar stoooof.. I don't think he would have asked if it was simple and 'easy'.

HuFlungDung · Feb 25, 2017

bmikkalson said:
I need to face grind a 15" cast iron surface( looks like a brake rotor, but not). Or imagine surface grinding a lathe face plate.
Has any one used a tool post grinder to get flat results . .001 over 12"
I'm using a pretty new colchester 15 lathe. Would the tool post grinder have to have a cup wheel? As I don't think there is enough room to turn the grinder side ways on the X axis. And have the travel with the carriage I need ..

P.s, no rotorary grinder or surface grinder or other.

I would think you'd need a cup or a dish wheel. I don't have much experience in grinding on a lathe, although I did fab up a grinder years ago, and gave it a go. I found it surprisingly difficult to get away from what I'd call a 'woodgrain finish', I suppose due to imperfect wheel balance, or the relative tendency for the thin section to vibrate, whatever. I ended up just turning the face, and with modern ceramics for cast iron, I can get a pretty nice surface right off the get go.

Then just shine it up a bit with a hand lap: a piece of stock that is faced off flat, kind of like an air hockey handpiece, with a self adhesive abrasive sheet stuck onto the end. This is only used for a brief period long enough to sand off any scalloping from the turning tool feed marks.

Limy Sami · Feb 25, 2017

I wouldn't chew up a faceplate unless I'd absolutely had to, ..I'd go for a subplate and work that.

Monarchist · Feb 25, 2017

Limy Sami said:
I wouldn't chew up a faceplate unless I'd absolutely had to, ..I'd go for a subplate and work that.

Subplate to hold the item, yazz.

The item itself was described as similar-to a faceplate or disk-brake rotor, but is actually neither one. It could be a component for a positioner, a seal surface, a clutch - any of many things.

That the band wanting the 'good' finish is but 2" wide on a ten or so inch diameter makes it easy to not need a grinder even if done on a rather average lathe with an imperfect cross. Only kind most of us ever had hands-on - as 'employees' anyway.

Find the 'sweet spot', offset the tooling to match position to the band, brace the tool overhang. Make uber-fine chips repeatably. Tear down the bespoke setup, go back to the ordinary work.

stephen thomas · Feb 25, 2017

I like grinding stuff.
I have improvised grinding hardened rings about the size you mention by mounting to a faceplate on a Cincinnati work head, and (manually) turning them on a T & C with the work overhanging the table toward the workhead.

I would probably not bother with CI.
You mention that no grinding equipment is actually available to you.
Just turn it.

Use either an insert that you are familiar with and know it will give good results. Or, use a C2 brazed tool, and hand sharpen and hone it to a relatively acute point, slight pos rake, and a stoned slighlty rounded tip.

This is a smaller faceplate, 9" OD. Class 40 iron.

If you've never ground anything, especially with a TP grinder, it might not be as easy as you may imagine to get a uniformly attractive finish across a 2" band at that radius compared to turning without some practice either, unless you get lucky. If you have a fair amount of practice grinding, ignore these comments.

One way to approach the work is with the wheel at say 45° to the work, and dress it parallel for a small band. You don't want a large contact surface with a relatively non-rigid set up.

smt

michiganbuck · Feb 25, 2017

Guess I would check well to find the opposite side, and diameter ran within in spec, then tool bit turn make working side near as needed, then try to make finish with perhaps a .015 flat on the tool bit And a very light finish cut to remove turning circles..

Using the OD of dressed wheel is best and a wheel likely not burn perhaps a 46H grit. the cup used at face side likely will leave cross hatch grind. Think I would use coolant.

Any grinding on the lathe it may be good to have an an adjust able travel stop so controlling the in feeds and a stop for spark out. A solid stop and removing shims is a way to act like a controlled stop.

For a one-up and not common to grind on that lathe I would send it to a local grind shop even with killing the job profit.. as I think grinding on the lathe poor practice.

Taking the job to oil hone finish is better than grinding on a lathe not common to grinding. Sanding on a lathe is common but still abrasive so should have a cover up and cleaning.

Qt Stephen: [One way to approach the work is with the wheel at say 45° to the work, and dress it parallel for a small band. You don't want a large contact surface with a relatively non-rigid set up.]

smt

Very good advice...And some time if not finding the finish you need dress the other parts of the wheel not in the grind such as the Od or other side to make the wheel run smoother.

bmikkalson · Feb 25, 2017

Thanks,
It sounds like a cup wheel is going to be needed , un less I have the room to clock the grinder.
The idea of using a sharp carbide tool may be a good one. I could use the face plate to mount and shim tell I get it flat. Make a cut and flip over, repete. Than sand /lapwith paper. Realistic I could .0005 or better doing this.

Monarchist · Feb 25, 2017

bmikkalson said:
Thanks,
It sounds like a cup wheel is going to be needed , un less I have the room to clock the grinder.
The idea of using a sharp carbide tool may be a good one. I could use the face plate to mount and shim tell I get it flat. Make a cut and flip over, repete. Than sand /lapwith paper. Realistic I could .0005 or better doing this. ��

Rex 95 would do me for that task. Only have to touch-up-hone one shaped a Very Long Time Ago, so fast enough, and yes, 'split' a thou if need be.

We keep coming back to the point that it is only a 2" wide patch you've set for us, not the entire diameter of the disc. No need to make a problem out of a solution agonizing over THAT. It just IS NOT suitable TP grinder work.

Tungsten or M-series Molybdenum alloy disk? Then yes. Maybe. Even so, sending out better yet.

In ignorant Iron? First five or ten are DONE already, are they not?

HuFlungDung · Feb 25, 2017

bmikkalson said:
Thanks,
It sounds like a cup wheel is going to be needed , un less I have the room to clock the grinder.
The idea of using a sharp carbide tool may be a good one. I could use the face plate to mount and shim tell I get it flat. Make a cut and flip over, repete. Than sand /lapwith paper. Realistic I could .0005 or better doing this. 

Have faith

I turn plenty of flywheels on a largish lathe and can get within .0005" even over the hard spots, using ceramic whisker inserts. I hand lap the hard spots with a diamond lap to bring them down. On a flywheel that doesn't have hard spots, its a piece of cake, and I like cake

I've never noticed any significant concavity when facing with any of my lathes. If anything, concavity is due more to different cutting characteristics of the tool/material as you lose surface speed towards the center. On an annular ring at a decent diameter, no sweat.

James H Clark · Feb 25, 2017

bmikkalsom:

I would tighten up the gibs on the cross slide tighter than usual for this job. I would also tighten up the gibs in the compound to the point that it was almost locked up. Try to eliminate as much vibration as possible. Also try to eliminate as much overhang as possible. Lathes don't make good grinders. That's why grinders are built different than lathes. Good luck.

JH

James H Clark · Feb 25, 2017

Just a second thought, is this a one-time job? If you were to remove the face plate after grinding and then re-install it, I doubt that it would repeat back to "zero".

JH

bmikkalson · Feb 26, 2017

JH
This is a one time deal.
Gonna try a run in the am

Spyderedge · Feb 26, 2017

Some G3000 or G4000 cast iron I turned using c2 carbide. No back rake or special sharpening. Surface finish was excellent and grinding would've been much messier and dustier.

(For an r32 mk4)

Sent from my XT1053 using Tapatalk

James H Clark · Feb 27, 2017

bmikkalson said:
JH
This is a one time deal.
Gonna try a run in the am

Let us know how it went. Good luck.

JH

bmikkalson · Feb 27, 2017

Well, the one who said it would look like wood grain gets the prize. Surface finish was horrible

Tuned up a carbide bit and was able to get a 26ra finish and .0005 flat within my 2" band.

Grinding a lathe face plate with a dumore tool post grinder.

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