Cutting Undersized (Resolved)

[Mkelcy]

I've got a weird one. I'm trying to pocket cut several stepped holes to receive locating pins for a jig on my Acorn equipped router. I did a simple VCarve drawing with two concentric circles, the outer one at 0.560" diameter and 0.075" deep, and the inner one at 0.430" diameter and 0.48" deep. The larger hole is being cut about 0.040" undersized, and the smaller one is being cut about 0.030" undersized.

IMG_1933 small.jpg (17.18 KiB) Viewed 3954 times

Thinking I had an issue with the calibration of my X and Y axes, I programmed and cut a 14" square and a 14" circle. Both were spot on.

I looked at the G-Code generated by VCarve and it appears to call for the correct size hole. I'm using a 6mm endmill. From the center X0/Y0, the X and Y axes move positive and negative 0.1619", for a total movement of 0.3238" and with the width of the 6mm bit (0.2362") should cut a 0.560" hole.

I suspect I've got something set up incorrectly in Acorn, but I'll be darned if I can figure out what.

[mick41zxr]

Been a while since I looked at V carve but do you have a stock to leave setting left on in your cam file as 0.040 is approx 1mm. Enough to be a finish pass.

[martyscncgarage]

Use Intercon to create a hole and test it. If the created hole is fine, then its your software. If its the same, then its the machine, or possibly a resharpened bit? Check its diameter.

[cnckeith]

post the problem g code program please.

[Mkelcy]

I'm sorry, I can't find the original g-code file, having overwritten it several times as I tried to figure out what was going on. I tried to regenerate it, and that file is attached. My incredibly simple minded analysis (maximum -X travel added to maximum +X travel, plus bit diameter should equal the hole size; it doesn't) makes me think that VCarve is creating the issue.

[Gary Campbell]

VCarve Pro may be passing thru an issue, but it is highly unlikely that it is creating it. Can you post the vcp file?

[Mkelcy]

The Vcarve file? The site won't let me attach it. It's got a .crv extension, which the Centroid site says is an invalid extension.

[Gary Campbell]

So make it a .crv.txt file and post it

[Mkelcy]

LOL. Good work around. Done.

[cbb1962]

I've got a weird one. I'm trying to pocket cut several stepped holes to receive locating pins for a jig on my Acorn equipped router. I did a simple VCarve drawing with two concentric circles, the outer one at 0.560" diameter and 0.075" deep, and the inner one at 0.430" diameter and 0.48" deep. The larger hole is being cut about 0.040" undersized, and the smaller one is being cut about 0.030" undersized.

Interesting story:
I use that exact locator pin in my work. A few years ago, before I got my CNC router. I went to a local gut that had a huge Onsrud machine running Vetric Aspire and asked him to cut out a template for a part out of 1/4" plywood that had two of those locator pins in it. I got the part back and all of the holes were slightly undersized. I had to sand and hammer them to fit. It'll be interesting to see what the root cause is of your problem.

I know in Fusion 360 that there is a setting that adds 0.04 axially and radially to the part and I have had that bite me in the butt a few times.