Problem- Machining not perfect holes

[greasetattoo]

Hey All,
I have a Sherline mill converted to CNC.
I just installed A2Z's headstock riser.
I have 2 of them on my machine. (an extra 4.2 inches of travel on the X axis.

I machined these parts out of Delrin.
Excuse the pictures, but kinda hard to see.
My Circles/pockets are not perfectly round.

I am running 700rpm, 15ipm.

The roundness of the gear is fine, just the cam is out of round. Same with the bearing hole on the white piece.

I use DeskCNC and VcarvePro.
Anyone have any ideas?

thanks,
Grease

[LeeWay]

Looks like backlash to me.

[greasetattoo]

Lee,
Thanks for the quick reply...
I will check into it.

Do you think on the X, Y, axis?

It would'nt have to do with the Z axis, would it?

[Crevice Reamer]

How are you tramming your Z axis? With that much extension it would definitely tend to angle forward. Cut some straight 1" cuts on x and on y. Then measure to see if these are actually CUT exactly one inch long--or if they are off.

CR.

[greasetattoo]

Yeah, that's another thought.
I might take off one of the headstock risers.

I will do the test today..
Thanks for the help!

[Crevice Reamer]

Those are two different things. Before you REMOVE the riser, (Or do the straight cut test) try to square up the column with the table. (tramming) You can get close with a good machinist square, but a dial indicator or nano tram is best.

The straight cuts are to test the accuracy of CNC setup on x/y axis.

For example: If X cut is exactly one inch, but Y cut is 1.20, holes will be out of round.

[greasetattoo]

Gotcha...

So...if I have excess tramming, I would have to bracket my machine to the back wall?

Gotcha..
I am going to perform the line test now...
I will check the backlash too!
I will keep you posted.

[Crevice Reamer]

Uh, NO. First you measure the column for alignment to X and Y. If not perfectly square to each then loosen the allen screw at the base of the column. Then you square up the column. Then you tighten the screw. Then you check the column alignment for square again and repeat until the column is square to x and y. This is called tramming.

The Nano tram from LMS:

http://littlemachineshop.com/product...2601&category=

Makes this REALLY easy and quick to do.

CR.

[Crevice Reamer]

If your column is out of alignment, this can cause the problem. It can ALSO be caused by other things, But you have to rule out the Z first. Don't even THINK about doing the inch cut test until your Z column is known to be in perfect alignment.

CR.

[philbur]

A serious question. How is it possible for out of Tram to cause a visibly out of round/square cut? By my calculation out of tram by .040" in 4" of Z travel will produce a 0.00008" out of round/square part. Am I missing something here?

Phil

Originally Posted by Crevice Reamer If your column is out of alignment, this can cause the problem. It can ALSO be caused by other things, But you have to rule out the Z first. Don't even THINK about doing the inch cut test until your Z column is known to be in perfect alignment. CR.

[Crevice Reamer]

Are you familiar with a Sherline mill with 2 throat extensions? It can be a LOT farther out of tram than .040. My point is: Tram the column FIRST, then start looking for the out of round cause. Otherwise he will be chasing his tail.

CR.

[greasetattoo]

Hey Guys...

Figured it out..

Just did some tests.
Backlash it is!

My 1" lines measure pretty dam close..

I cut some small circles too, which came out perfect!
After I adjusted my Backlash..

Also, I upped my speed.
The black delrin I had, was melting at the higher speeds.
The white is fine though..


Thanks everyone for your response and quikness!

May this post help someone in the future!