Losing Steps on Z Initialization

[johnesher]

I’m trying to do a finishing pass on my first 3D carving project. I did the roughing pass last night, and this morning I wanted to start the finishing. Not changing anything related to zeroes, I loaded and began to run the gcode and immediately began to create firewood. The bit plunged into the workpiece about ½”.

I thought okay, it’s ruined, but it was essentially a test, so let’s learn. There’s a lot of carving left and I want to see if this is a good finishing bit anyway. Now I double check the X & Y zero and find them to be good. Turned off the BitSetter (since I had previously turned on the router one step too early and crashed a running bit into the plunger on the last job) to rule that out and used a paper zero for Z. Load new gcode and same thing happens, but this time I noticed I’m losing steps on the Z initialization. The Z axis is trying to pull up past the limit causing the skips I think. Video link here…

The Z limit switch is not stuck, and now that I’m typing, I think it has something to do with safe retract height and the length of the bit. I had been using a 3/16" ball nose with an out of collet depth of 1.65" and now I’m trying to use a 1/16" tapered ball nose with an out of collet depth of 2.25". My material is 1.3" off the supplementary ¾" wasteboard. I’m using brad nails on the perimeter of the oversized blank, so the top is clear of obstructions.

I’m using Vectric Vcarve Desktop verison 10 and running CM for controller. How do I fix this?

[CrookedWoodTex (Tex)]

Not to be trite, but you have too much wood and too much bit for your machine.

[Julien]

Yep, your analysis is correct, losing steps upon retract which then translates to erroneous depth because the Z axis reference is lost.

You should reduce the retract height to the minimal value that will still clear the top of the material, try and use a shorter endmill if possible, and you may also want to temporarily raise the router in its mount for this job, to gain some Z margin.

[johnesher]

Thanks, Julien. I ended up seating the bit deeper in the collet. It’s an Amana and I initially set it to the “K” mark on the shaft. I pulled it and set it the way I do my handheld and table mounted router - bottom it out and back it out about 1/8". Gives the bit more than enough room to move when the collet is tightening.

[johnesher]

No offense taken, I’m learning 3D carving and while not overboard yet, it definitely appears to be getting close.

I’m already trying to plan for when I want thicker material since the Z height is proportional to the X & Y and I want to be able to carve bigger badges in the future.