Blanchard Grinding Tolerances

Can anyone give me some reasonable expectations for Blanchard ground tolerances for plate aluminum and steel? Thanks.

What size and how thick?

This piece in particular is 3/8 thick 8" x 17" aluminum.

+/- .003 and f&p .003 is our standard callout

Sounds good thanks. f&p??

flatness and parallelism?

sfriedberg said:

flatness and parallelism?

Click to expand...

folded and pressed

Larry Dickman said:

+/- .003 and f&p .003 is our standard callout

Click to expand...

Is that number mm or inches?
Please don't tell me inches on a 8x17 plate. One can mill that number at way above Blanchard speeds in one pass.
If mm that is very good.
Bob

engiNERD77 said:

Can anyone give me some reasonable expectations for Blanchard ground tolerances for plate aluminum and steel? Thanks.

Click to expand...

.
large plates can warp or curl. a magnet can just flatten it in machine but once out of machine and on a surface plate it can be checked for flatness. getting stuff flat to .001" when over 12" can be difficult.

A top condition Blanchard should make .0005 on steel fairly easy. I have never ground aluminum on one, just steel and carbide. But ways have to be good, machine has to be trammed square to table,chuck has to be checked to not be ground to a concave or convex top side.

Grinding to part size is difficult because of wheel wear so spotting gauges are good to be set on chuck to be painted-up to be perhaps + .001 or at or near high limit so operator has a little stock high for a spark-out to make surface finish and size.*Spotter of + .010 or .020 painted a different color may be used so to give advanced warning to be looking at finish size spotter. When grinding on only half chuck one can hear the wheel tickle the spotter so the change of sound can be the warning to watch finish spotter( set opposite side). Simple block with a tapered and sliding bar set screw locked to micrometer check size is good for a spotter. Often with a full chuck (many parts)a few of the finished parts measured to be near high limit will be painted-up to be spotters for the next load of parts. Spark out stock is important so high pressure is relieved and head can settle.

When grinding the chuck square attitude of head to chuck must grind chuck dead flat or the part (work to be ground) going over chuck center will be ground positive or negative dish when (magnet) pulled down to chuck attitude.

Adjusting (Tramming) a head square and tilt to chuck flat can be tricky. looking at grinding crosshatch is only a part of the job.
I liked to set a to set a parallel across (going with travel direction) the whole chuck with being measured in to be same from out side edges(centered) and going across center. Then look for belly or hump at cheuck center for an idea of how good or poorly it was ground or how it was wore by use.Indicating down the parallel would tell the attitude or condition of the bed ways.Setting the parallel cross way and wheel set indicator swipe can tell a little but is a combination of ways and head attitude. Tramming the head to an out of flat check is not good. A dead true blanchard is running (floating) on a on oil.. one wore out is bumping over metal to metal or over
griit and abrasive,.

That Arter or Heald type machine is much the same except one is adjusting the table angle and set for tram of wheel to chuck.

From what I have found with the local Blanchard grinders by me, the tolerance they state is one thing. What they actually hold is another.

But then most people are looking for a low price.

on a 8" x 17" plate of aluminum I would expect to see you use up the entire tolerance of flat and parallel .003"

I would look to machine something like this VS Blanchard grind.

cash said:

.....
on a 8" x 17" plate of aluminum I would expect to see you use up the entire tolerance of flat and parallel .003"
....

Click to expand...

Just for giggles how about in steel?
This is not that big and you see Blanchard ground bases and tables much bigger talking numbers tighter.
(Yes I know talking and doing are not same and setting a Blanchard head flat is not as easy as those 3 points look or just getting a pretty crosshatch.)
Bob

Thats a loaded question-

What kind of steel?

Was it stress Relieved?

How good was the stress?

Normally on A-36 anything under 1/2" I will not guarantee any flat. smaller parts of course depending on size sometimes I can. But it is on a job by job basis.

With some of the recent A-36 coming from either south of the boarder or from China this even makes it harder sometimes. We recently had some plate that covered our entire 84" Blanchard chuck. It was a bear to get thru the scale. Once thru no matter how hard of stones we put in it would not pull any load.

Now if you are talking heat treated tool steel, which I do in house, I will easily hold these flat tolerances via blanchard and or surface grind.

Anybody who states that the standard tolerance they can hod is .XXX is making a very broad statement and normally what I have found is once the job gets sent out then there are a lot of, oh well we can't do this or we can't do that.

If you cannot Blanchard grind a small piece of aluminum like that in 7075 or Mic 6 within +/- .001 your doing it wrong.

IAMATT said:

If you cannot Blanchard grind a small piece of aluminum like that in 7075 or Mic 6 within +/- .001 your doing it wrong.

Click to expand...

If it was mic6 why would you grind it? That said, 3/8" thick 8x17 (aluminum) sounds a bit squirrley to me for a blanchard. If you can hold that flat and parallel (.001) AND hit +/-.001 thickness that's pretty damn good. You would get my work if I had some to give out

Resurrecting this one...looking for some guidance

We machine plastics.
One of our customers spec'd out a stainless (no type) plate with .002" flatness to anneal a part on.
Part we would be annealing is 21" diameter, so I'm looking at several 24x24 plates.

Questions:
Is the .002" flatness over something this size realistic?
I'm guessing plate will be 3/8 or 1/2 thick, yes/no?
Anneal cycle goes to 600F, is it going to warp?

This is a bit out of our wheelhouse. Any insight is appreciated.
Ted

Start with low-stress plate, like MIC6 or other cast plate. Machine the plate oversize. Run it through a couple of (plastic part) annealing cycles without any plastic parts. Remachine/grind the plate to final dimensions. Should be pretty stable through subsequent annealing cycles.

No idea about thickness. How will the plate be supported in the annealing oven? That probably is relevant to the question of how thick to make it.

sfriedberg said:

Start with low-stress plate, like MIC6 or other cast plate. Machine the plate oversize. Run it through a couple of (plastic part) annealing cycles without any plastic parts. Remachine/grind the plate to final dimensions. Should be pretty stable through subsequent annealing cycles.

No idea about thickness. How will the plate be supported in the annealing oven? That probably is relevant to the question of how thick to make it.

Click to expand...

Customer is spec'g stainless for the plate, not Al...same would hold true for conditioning s/s with a couple annealing cycles, correct?

We have removable trays/shelves in our ovens, would go on top of them.
We can remove trays to give additional space if required.
My concern is how thick does ti have to be to maintain the flatness with the repeated cycling over time. We are not capable of refacing/grinding here, this would be a purchased item...

For plate thickness, I would look at it like a surface or bench plate. A 24"x24" surface plate would be 7" thick ribbed with a 3/4" top. A bench plate would be 24"x24"x3"

Is this a customer you have good communication with? If so, would they be amenable to not using stainless? You can buy an off-the-shelf cast iron plate to do what you want and then have it electroless nickel plated. Unless they're annealing at very high temperatures, this should solve the design goals of no contamination and heat tolerance.

Sorry for not noticing the SS requirement. Yes, the same protocol with SS plate (machine oversize, couple of oven cycles, finish machining) should work, although I would take off more in rough machining and probably use a thicker original plate. Most of the SS stock I use is stuff that's been rolled and sheared. I'm not sure how larger SS plate would differ in from-the-mill stresses.

I am sure you don't need the same thickness in an annealing plate as in a surface plate. You're looking to hold 2 thousandths, not 2 tenths. Also, the ribs in metal surface plates might be problematic in a temperature cycling situation. 1/2" or 3/4" is probably fine, and thicker is not necessarily better in this situation, because of the dynamic temperature changes.

In fact, let me ask a little bit about the (plastic) annealing schedule and technique. For a metal plate to remain flat while it expands and contracts during the annealing cycle, it needs to be at a uniform temperature throughout. You'll never get it perfectly uniform, but there are lots of ways to really do it badly. Ideally, the plate would be inside a muffle which provides more-or-less omnidirectional heating, and the heating and cooling schedules would be long enough to allow the plate to heat and cool more-or-less uniformly throughout. In the worst case, you'd be using direct heating on only one side, and cool with an air blast or something like that.

At metal heat treating temperatures, the usual rule of thumb is to hold at temperature an hour per inch of thickness. You won't need to hold nearly that long because your plate isn't undergoing changes in metallurgical structure, but you will need to avoid temperature profiles that don't allow the plate to "catch up" internally and on the unheated surfaces. You may need to do some experiments with your standard annealing schedule, a sample plate, a straightedge and a few pieces of shim stock to see what happens.