Mill question

[higgite]

I am wondering when in my lifetime that I would ever have a project that requires a one mill tolerance.

Before I guess, how old are you now? Gotta look up your life expectancy and figure the odds. I have the month and day figured out, just not the year. Is there a prize for the closest guess? J/K.

Actually, I'm sorta with you. I'm quite happy to be within a thou, near ecstatic, in fact. But, the OP has a fun mystery to solve, so why not? I figure there's an outside chance (100%) that I might even learn something. It happened once.

Tom

 

[rzw0wr]

Hello all. I am back with this problem still.

Here is what I have done to date.

I bought new collects, Lyndex.
I bought a new vice, Gracern. Good vise.
New end mills, Made in USA.

I ran a dial indicator over my table. .002 out in 19"
Pleased with that.

Set up the vise after cleaning.
I checked the vise across the ways., .0005 or less.

I checked a parallel to see if it was parallel. OK less than .0005
Put in a parallel in the vise and indicated the top. .001 out.

I moved the vise to another part of the table.
Vise was the same. .00005 or less.
Parallel. .00005 or less.

Put stock in vise on checked out parallels. .75 thick x 1.5 wide x 9 long.
3/4" new end mill, about .003 deep cut and about 3/4 cutter width.

Nasty taper.

The table checked at X = .000 Y =.001

I got taper in both directions.

The taper on the X is always in the same direction.

I have also tried a fly cutter. about .002 to .003 deep.
About the same results.

If I run an indicator across the work piece before I remove it the indicator reads .000.

Really frustrating.

Dale

EDIT:
After rechecking my parallels I found out I really don't have anything in my shop the is parallel.
Brown and Sharp parallels ordered.

 

[hman]

The ONLY thing that comes to mind is something really stupid, so please don't be offended ... but are you sure the work piece is in good contact with the parallels? After the vise is tightened, is either of the parallels loose?

Alternatively, if you can find some precision ground flat stock (say 1/2" x 1/2" or so), you can try clamping it in the vise atop a parallel. Then indicate the top of the stock.

Best I can come up with.

 

[Janderso]

Richard King says, you have to be a detective.
Please let us know what you find out.

 

[matthewsx]

Well, process of elimination....

I have a not real good mill. Smithy.
I got it about a year ago and finally got it to working ok for what is is.

Sorry, but I had to go there. For a thousandth I'd be inclined to machine close and lap to finish.
If the budget allows why not upgrade the machine? I'm sure the Smithy is better than the 3 in 1 that I had but you may already be working past the tolerances it's designed for. You have a nice vise and collets now, I know it's a slippery slope

Definitely you are learning and thanks for taking us along for the ride.

John

 

[ThinWoodsman]

So, if the taper is happening regardless of direction, and is the same amount regardless of workpiece size, then my guess would be that the cutting tool is being pushed into (or pulled out of) the collet. This is not necessarily gong to be linear with the size of the workpiece (more cutting force used on a shorter workpiece for example, or chatter on a longer workpiece countering the effect). Mark a line on the cutter, or paint with dykem the part of the cutter that extends out of the collet, and see if it creeps out by a hair.

I would think that table, gib, and vise problems are going to vary directly with the size of the workpiece and the direction of travel.

If I run an indicator across the work piece before I remove it the indicator reads .000.

If correct (and the points about taper being not related to direction of travel or to length of workpiece apply), then either the act of removing the workpiece from the vise (e.g. vise is springing the workpiece) or the amount of time passing since the cut was made (residual stress in the metal, thermal expansion) are responsible for the effect.

Maybe: put part on table, bordered (but not held down) by clamps to keep it in position. Run DTI (held in spindle) over part. Put part in vise. Run DTI over part. Machine in one direction. Run DTI over part. Put part back on table. Run DTI over part. If indicator measurements are equal in all four cases, reverse direction of machining and try again. If the measurements are not equal in one of these steps, you have a datapoint with which to start debugging.

 

[higgite]

Per discussion earlier in the thread, we may be going overboard chasing .001” of taper, but then, who doesn’t like a good mystery?

Hello all. I am back with this problem still.
.
.
I ran a dial indicator over my table. .002 out in 19"
Pleased with that.

Do you mean that you ran the table back and forth under an indicator mounted in the spindle or that you checked tram with a tramming attachment?

Set up the vise after cleaning.
I checked the vise across the ways., .0005 or less.

Same question as above regarding how you checked it.
How wide is the vise? That’s .0005 over what distance?

I checked a parallel to see if it was parallel. OK less than .0005
Put in a parallel in the vise and indicated the top. .001 out.

That sorta makes sense, .0005 from the vice plus .0005 from the parallel.

I moved the vise to another part of the table.
Vise was the same. .00005 or less.
Parallel. .00005 or less.

First you said the vice was .0005, now you say it's the same, but .00005. Which is it?
Same question about the parallel.

Put stock in vise on checked out parallels. .75 thick x 1.5 wide x 9 long.
3/4" new end mill, about .003 deep cut and about 3/4 cutter width.

Nasty taper.

I know “nasty” is a technical term, but can you quantify it?

The table checked at X = .000 Y =.001

What exactly does that mean?

I got taper in both directions.

The taper on the X is toward the same end of the work piece regardless of which direction you make the cut?

I have also tried a fly cutter. about .002 to .003 deep.
About the same results.

If I run an indicator across the work piece before I remove it the indicator reads .000.

That makes sense if the work piece is moving under an indicator mounted in the spindle, as the indicator would just be retracing the cutter path. That would indicate to me that there was not any cutter pull out or push into the collet.

Really frustrating.

Dale

You have my sympathy. BTDT.

Tom

 

[rzw0wr]

Well, I am back.

I just cut a 3/4 x 1 1/2 x 9 piece in the vise.

Less than .0005 end to end and side to side.
Cut with a fly cutter.

I have not tried to replicate this result yet.

I think some of the problems are mine and my cutter selection.

The mill tolerance is .001.
I was just trying to figure out why I had a tape no matter how long the work piece and
why if the table is within .001 why a taper at all.

Thanks for the replies.