Z Depth issue for 2 sided cutting

[MCochrane]

I've only had Cut3D for about two weeks, but that's been enough for me to spoil quite a few prototypes. I'm trying to cut a Greenland-style kayak paddle, which is perfectly symmetrical, top and bottom. Each attempt I make seems to produce the top cut properly, but the bottom cut then shows that either the top or the bottom (or both) has been cut too deeply in the Z dimension. The bottom cut breaks through the top cut, making the blades too thin and small.

The measurements I've made after each failure seem to show that the rough toolpath is cutting at the depth I set up in Cut3D. Looks the the finish toolpath is taking the cut about 5mm deeper than the midpoint of the material. (The paddle fills a 2x4 in both the Y and Z dimensions. The X and Y dimensions have not been a problem.) As you see, I'm working in millimeters.

Is there something I am missing or doing wrong in the setup screens that I've attached below? If not, then I've got to look more closely into a hardware issue.

Thanks for the help all of you so reliably give!

Mike

Paddle dimensions

Material sizing

Roughing toolpath

Finishing toolpath

[kilrabit]

Could you post a picture of a paddle that was cut too deeply? Sometimes a picture is worth a thousand words.




Roy

[SSCNCROUTERGUY]

MCochrane:
Not to oversimplify things, but are you re-zeroing your Z height between bit changes?

[MCochrane]

Hey! I take no offense at simple questions. It would be just like me to forget to Z zero between bit changes. Glad you asked.

But this time I think I've got a hardware issue (which is why I haven't posted pictures). Yesterday I Z zeroed at the material surface using the ShopBot Z zero plate (that's my machine, and ShopBot has a handy routine for Z zeroing by placing a metal plate of known thickness under the bit and running a sensing routine). I then drilled a 20mm hole and measured it with a depth gage. It's 25mm deep. I changed to another bit and another collet and did the same thing. What should be a 20mm plunge is always a 25mm plunge.

So, either the machine, which I recently bought used, has a wrong value for the zeroing plate thickness or the Z axis unit values are wrong -- so it seems. I'm looking into it.

The fact that nobody called out an obvious error on the setup screens I posted also helps me troubleshoot this. Thanks!

Mike

[esteeme1]

It sounds like you have a 5mm offset entered for the Z axis.

[ssflyer]

While this could be a stepper value issue, the first thing I would check is the actual plate thickness... The nominal is 0.121", but mine was 0.124" - it does make a difference.
I simply measuered mine with a dial caliper...

[MCochrane]

It did, in fact, turn out to be a stepper value. The unit value for the Z axis was off by 20%. After I did a number of measurements and processed the math, I put in a new value (which, interestingly, matches the values I found in the file for the X and Y motors) and its cutting accurately now. Thanks for the suggestions, all who helped.

Mike

[esteeme1]

That's great, glad you found the problem.