Facing the wasteboard issues

Hi all.

Don’t know what terms to use in the search engine. So bear with me…

After facing the wasteboard, satisfied with a smooth surface without any ridges I can feel with my hands, I moved a couple steps to the right and noticed that I do have an issue. I could only see it at an angle.

The gray lines are cut deeper than the rest, at regular intervals. If I put a rules acrosse the wasteboard along the X I can just see that there is a slight difference in depth. For my wood projects this issue is irrelevant, but I would like to understand the cause …


Are they following the toolpath you created to surface your wasteboard? If so, your Z axis may need trimming

Facing operation is cutting a strip long the X axis before moving on the Y to do the next strip, so the “bands” goes against the direction of cutting.

Also Z depth is set outside the wasteboard and the facing bit moves into the wasteboard from the side. There is no Z depth change during cutting at all.

If that makes sense… :smiley:

What material are you using for your waste board? Typically I use MDF, but if you are using something with grain such as plywood, you may get tiny variation.

What is the diameter of the cutter you are using to surface your board?

If the spindle axis is not exactly perpendicular to your waste board you will have problems. Your passes might slant a little and you would then have a noticable step where you go from one pass to the next. Tipped another way you might be cutting coves in the wood where the deep part is in the center of the cut.

If I am reading your comments correctly, it seems that the low spots are perpendicular to the direction you are cutting. This does seem strange. Are you cutting deep enough that all of the surface is freshly exposed?

I am using MDF for my wasteboard and the facing bit is a 20mm diameter 2 flute flat. Wish I had a larger one… :smiley:

And yes, I am cutting deep enough, whole surface is freshly exposed.

I am starting to wonder if one or more of my X carriage wheels are not round anymore.

The bands of these deeper cut areas indicates something is forcing the bit a tiny amount deeper on regular intervals. With a flat bit a slight change in angle of the bit, in relation to the wasteboard, would cause the outer cutting edge to dig a little deeper.

If a wheel while rotating is no longer truly a circle, could it be causing a slight tilt in the X axis carriage while moving the X direction and thus plunging the outer edge of the cutting bit deeper? If this movement was on one side of the X carriage then the angle of the Z assembly would have to change in relation to the wasteboard I think…

Does my theory make any sense?

Edit: typos

What’s your stepover size? Are you sure you’re not just seeing where each pass is overlapping?

stepover size is 45%


Red is the path the cutter is following, gray the deeper areas I am trying to get rid of. Overlapped areas due to stepover would be between the horisontal red lines.

Something is causing the cutter to change ever so slightly in angle so the cutter goes deeper on regular intervals along the X.

Can you post a pic of the cutting board?

Grain changes, direction change of CNC travel and tramming issues is your prime suspects :slight_smile:

I was thinking tramming issue too, but the direction of the tool path doesn’t look like it supports theory.

True, which is why I suspect grain direction to at least be a part of the issue :slight_smile:

My guess is Vwheel out of round OR debris in the Vwheel.

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Only camera I have is my smartphone and it is not cooperating with me…

This illustration shows a front view of my wasteboard. Placing a ruler on top and shining a light behind the ruler I can see a small depth change on a regular basis along the X axis.

The issue is miniscule and will not affect the wood based projects I have coming in any significant way so I am not stressed out by this. When I have time I will disassemble the x carriage and check all the wheels to see if one or more of them are no longer round.

A wheel out of round would seem to be a likely cause. If you have a way to measure the trough to trough distance this should correlate to the wheel circumference.

Thanks for the tip! :+1:

I’ll check it out then I get the time

The depth change along the X axis is solved. I replaced all the V-wheels on the X carriage with new ones.

Now I have a tilted bit in the Y direction and it gives a stepped look to the wasteboard. Should be easy enough to fix with some shimming, but here is the thing that puzzles me:

The stepping is like a gradient getting progressively worse towards the front of the machine… In my head the stepping should be consistent across the wasteboard from back to front.

What am I missing in my thinking here? I bet it’s obvious :slight_smile:

Thanks for all input thus far!

Here is a bad drawing illustrating the problem. Stepping get progressively worse towards front of wasteboard

Do your Y rails run parallel to each other? If not, that could maybe explain it?

According to my measuring tape they do run parallel to each other…

You go back to front? Is there a Z lift between passes? Could it be lost Z steps due to something not tight on the Z?

Toolpath goes like below with no Z changes


The only reason I can think of is for some reason the Z-axis tilt/shift while riding the Y-axis.

Bowed rail?