This is why I posted the picture of the M with the circle. This is was a second attempt to recut the M. The surrounding depth is from the first pass when the Z skipped and was shallow. So this is not really a mystery.
However,
It is very difficult to tell in the pictures but the 0.20" stepover also lost it’s Z-axis mind when cutting the M. It went much deeper. I checked the the tool was not loose - it wasn’t. I have been setting the tool to the maximum depth into the router so that it bottoms out anyway. So this did not make sense.
I know that the Z can skip when cutting at a fixed Z depth. This is becasue the force pushing up overloads the stepper motor’s ability to hold in position. This happens when the piece of aggregate is very hard and using a ball endmill.
I do not think this has anything to do with the motor torque. There is absolutely no pitch change that would indicate the overloading of the motor.
I think slowing down the helical feedrate and angle would both be a good idea.
WIth the HDZ is there a gearbox between the stepper and the shaft or direct drive? The reason I am asking is to understand how much more stability in height there will be.
First - I’m really impressed with this concrete milling.
Second - the HDZ has a ballscrew driven by the stepper so it is inherently geared down a lot from the belt drive, downside is much slower rapid retracts, upside is it can push down hard enough to bend your spoilboard and break end mills, I don’t think Z position will be an issue for you once you have the HDZ.
All clear now, thanks. @LiamN answered about the benefit of the HDZ (but you were convinced already…and I know it’s no fun that they are out of stock)
Regarding the toolpaths, I’ll regenerate a few combinations of ramp rate/angle and post them here later today.
I took this project on very naively. Thought I knew about machining and concrete cutting. I mean, how hard can it be? Once we get this all tuned up and we do the real project I will be share on this forum. I will just say that it is part on an installation project at a state park. I am getting some serious pressure for having to push the schedule out until the HDZ is available.
Thank you for the clarification on the Z-axis. Geared down is good and a thread will not slip or skip so this will be a huge improvement.
Luke - Are you saying that the Z-axis with the belt can apply 70 kg of downward force?
But you say over. How much over? At what point does the Z stepper skip?
And what does the HDZ put out in terms of downward force?
I am on my phone in a tower, so forgive any short descriptions.
I realize this might not be an efficient process, but possibly of some benefit.
To avoid the helical ramp into material, would it not be possible to predrill tool start positions? You could drill just shy of full depth, to full depth, or just past full depth(grouting in the tool mark after the fact). You could spot all of the prill drill locations with the CNC. No ramping.
Also, might be of some benefit to rough out as much material as possible with something like a flat cutter with a minor radius instead of a full ball mill. Maybe that will reduce some of the axial deflection?
@isoworks: predrilling like @Lowbrowroyalty suggests sounds like a great tip (yet drilling a lot of entry holes in each letter is not going to be fun I guess). Fusion360 has a “predrill” plunge type where you can specify where the predrilled hole is, so that it enters and plunges to full depth there.
I have generated a few new toolpaths if you want to try them to see if we can slow it down enough for the Z axis to stop skipping.
0.02" stepover, same feedrate as before (750mm/min during helix ramping, 1524mm/min during adaptive milling), but ramp angle reduced from 1 degree to 0.5 degree: MAR_AdaptiveTest_0.020stepover_0.5degreeHelix.nc (755.0 KB)
lol, somebody just got the last one. It was in my shopping cart, but nooo, I just had to go back and add some more goodies to the order. Went to pay, “item is out of stock”. NNNGAHHHHHHH
