Need help with odd behavior

Starting from zero my spindle gradually cuts into piece as it moves towards area where it’s going to begin cutting by over 1/8.

Typically this means the Z axis is out of square but I’ve checked it several times and it’s perfect.

I wonder if it’s my settings. See last photo.

What’s odd is machine is not cutting into the waist board as you would as you would expect it would when it exhibiting this type Of behavior.

Usually cutting problems such as this are caused by insufficient belt tension — the Z-axis needs to be guitar string tight, the X only slightly less, the Y maybe a bit less, but even tension for both belts.

Also check the balance of the machine mechanically, eccentric nut/V-wheel adjustment and pulley set screws.

It behaving differently is usually caused by the difference between climb and conventional milling.

I check the belts there’s they’re tight. In fact I just tighten them .

Will pretty much nailed it here I reckon. I had the same thing on 3 separate occasions, each caused by something different…

  1. Pulley slipping on z axis stepper due to loose set screws - I pulled the pulley off, made sure the screw lined up with the flat spot (if there’s no flat file one on) put some Loctite on the screws and tightened them up

  2. Z-axis travelling too far down during job, losing its place and losing its zero - to fix I dropped the router down a bit in the holder

  3. Safe z-height/minimum height set too low, in this case below the top of the material - easy fix in software to set safe height 25mm/ 1" above material


I’m running my ice machine with the HDZ. So there’s no Z pulley or belt.

What is the Goebel code to set the safe hight to 25mm

@DCFYI How are you generating your gcode? How are you establishing your Z-zero? My first guess would be the toolpath. Zero is a bit too low and gcode doesn’t lift Z before heading to the XY start?

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I’m sure someone else has a better answer but I don’t think it’s a gcode as such. You set it in the software you create your gcode with - Carbide Create, Fusion360, Vcarve etc.

The software options all call it something different, look for something like retract height, minimum safe z distance, safe z height or something like that.

What software are you using to create your gcode?

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The safe / retract height is set in one’s CAM program — there isn’t a Grbl setting for it as such, it’s a discrete G-Code command / level to which the machine moves after each pass / as needed, so will appear in the .nc file as something like:

G0 Z25

depending on where zero is set.

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Carbide create. Using universal g-code sender to control the machine.

Carbide create. UGCS and Carbide touch probe

Interesting. It doesn’t look like your z is loosing any height as the cuts are correct, it’s just the actual machine moving to position at the wrong height.

Looks like it might be a zero setting or post processor? Usually the machine should raise the z, move to position then lower z/cut. What’s happening with yours?

It gradually lowers the bit over time. I recently left the firmware and thought it might be a GBRL issue.

Are you sure it’s not staying at zero and cutting through inconsistent material thickness of material surface not perpendicular? Can you post the gcode?

Have you actually measured the material?

The third photo down - where there is a cut in the material from the origin all the way across the workpiece. Difficult to tell but that is a single machine movement and the depth of cut gets greater over its length (ie shallow at the origin and deeper at the cut part).

That tells me that either;

  • the material you’re cutting is not a uniform thickness or;
  • your wasteboard isn’t flat, or;
  • the workpiece isn’t clamped flat over its entire area
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As a rookie I’d tell my machine to return to zero and see if it ends up where I set it originally. I think that’d give me a good hint if it’s the cnc machine or not.

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Yes. I ran my tramming tool across the surface to check for inconsistencies in thickness of the material. The material and machine are both within spec.

Post your gcode please.
The ballscrew drive on your HDZ won’t just drop.

I will post g-code tonight.

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