I am having issues getting uniform cuts on colorcore hdpe. I read a lot of threads on speeds/feeds as well as work holding and am still not satisfied with the finished product.
Shapeoko pro xxl
1/8 2 flute upcut
doc is .065, speed is at 215 ipm.
This gave me a nice clean cut after some trial and error. The chipload is .006 and its no longer leaving fuzz, so thats awesome. However, the cut depth is not unifrom. I have the material clamped down well and being its only 12" x 12", 1/4" thick, I can’t imagine it flexing. The areas are pretty random and not just in the center.
My questions are
Any clue what would cause the irregularity?
What is a good double sided tape? Most thin tape doesn’t stick and 2 sided mounting tape is too thick.
The most common irregularity causing inconsistent depth of cut is the top of the job not being perfectly flat. The cool thing is you can easily test this. Move your cutter to about a dozen different positions on the job, jog the tool down to the surface & note what it reads. If you have a dial indicator that would make it a bit quicker.
I use the “Duck” brand 2-sided tape, as well as “IPG” from my local hardware store and like them both.
There’s another brand with a name similar to “Duck” that is not very good. (I can’t remember & the roll is gone)
Don’t use VHB, you’ll break the job trying to pry it loose.
Excuse my ignorance, but can you explain how the top surface of the piece affects the cut surface?
I use my CNC machine to “face” end grain cutting boards all the time. The top surface is not perfectly flat, but after I do a surfacing pass on my CNC the cutting board is perfectly flat.
yeah, while I appreciate the input my issue has nothing to do with the top surface. If you look at the pics you can see the cut pass is at different hieghts. I have used both upcut and downcut bits with similar results.
Did you check if you have any slop in the router/Z-axis ? i.e. if you grab the endmill shaft and try to move it around while the Shapeoko is turned on (motors locked in place) do you feel any play ?
That was the first thing I checked. If the bit is set in the collet too shallow, will it flex? That could cause it to appear to be cutting deeper in spots. I had it set so the top of the cutting blades flushed to the bottom of the collet, but perhaps it could be set deeper making it stiffer?
Thoughts?
Also am planning to run a job with a 1/4" endmill to see what happens.
tool deflection increases as the stickout (remaining tool length outside collet) increases, however this typically translates mostly to X/Y dimensional errors, not Z. Also, deflection in HDPE (a.k.a. butter…) will be minimal in your example
That’s the limit. Don’t push it further in, you may damage the flutes and/or have tool slippage.
That will be an interesting test indeed. Maybe also try and cut a simple pocket with your 1/8", see if you get depth inconsistencies on a simple example like that.
Also try shallower passes, just in case. 215ipm is a great feedrate to run in HDPE, and 0.065" is not that deep, but just for the sake of the investigation.
