Inductive touch sensor?

Check out the video:

This thing is awesome. You could mount an inductive sensor, near the bit. Put this thing on, tell some software to map out the top of your workpiece, as the metal pin pushes into the material, it moves closer to the inductive sensor. The sensor trips, resulting in a height measurement. Then you’d remove this thing, and adjust the overall height to a particular place (XY), w.r.t. the bit, and the firmware would have to follow the z map when milling. It all seems doable, and more reliable, more automatic than a touch plate you move around. The nice thing about a touch plate is that the height of the bit is also measured, but if you’re using a carving bit, for example, I’m not sure I would want to probe that fast. I’m still not sure exactly how some kind of manual mapping is done in the firmware. I would need more understanding of that first, at least. I know some CAM programs (like estlcam) can probe a surface, and then adjust the gcode to apply that map, but I think Marlin can too, and then you can use any CAM software.

Anyway, it’s at least useful as inspiration, if not directly applicable.

Interesting, I saw something similar posted on

My thinking would be that there it’s likely to be a difference in the material you are cutting into as well as the bed itself.


I’m looking at doing some engraving on the lowrider and I’m wondering if a spring assembly for the router would work at keeping depths consistent.


My other thought would be using a sensor as a lead ball (i think that’s what it’s called…) As they do in some record cutting setups. This would limit the order of paths you could take I imagine. Not sure about the processing power required either.

Oh yeah, Ryan put that website on the front page not too long ago, and I meant to look through what he’s been up to.

I highly doubt it. The bit wouldn’t push up enough to make consistent depths. Plus, the bit will pull, at some point, which will give it even more to bite into, and yank the whole assembly down. Unless I’m misunderstanding what you’re suggesting.

For engraving, it really depends on the size. You’re going to be measuring the height of the Z at one point (unless you have something like the sensor or a touchplate). The farther you get from that point, the more error in Z you will have. Some things that will help:

  • A very pointy bit. The flatter bit will mean more obvious errors in X/Y when there is an error in Z. If you have a 90degree bit, then every 1mm DOC error will mean 2mm wider cut. A 60 degree bit will be closer to 1:1.
  • Set the Z height in the middle of your work area. Because you’ll not be going that far from that spot. You can still use X/Y in the lower left corner, just move out into the middle, set the Z, and use a G92 Z0 to reset the Z height there.
  • Stay close to the corner. The z error is bigger in the middle, I think.
  • Stay small. If you have separable designs, you might even consider breaking them into different gcode files, and re-zeroing the Z for each sub-pattern.
    At any rate, if you’re talking something in the 9" or less, I think it will be fine without even stressing about it. The Low Rider has a very good Z error/X distance, it’s just capable of making some very large X distances. Going to some mesh leveling, with a touchplate or a probe like this is cool, but I doubt it is necessary in 99% of the designs.

I would use this as a stage after fastening down the material, but before carving. The surface of the material is what you’re trying to measure.

I’m not 100% sure I know what you’re asking, but if you’re using a ball to track on the material, that’s fine, except that the work is going to quickly get torn up, have dust all over it, etc. Having something ride on it while cutting will have it’s own set of errors.

Sorry, I was using the wrong terminology…and my head is still firmly in the realms of record cutting…

It’s called an advance ball, there is a photo of one here;


The idea is the at advance ball precedes the cutting stylus so the cutting stylus is always cutting at a reference point 10-20mm ahead of itself.

I guess the sensor only really needs to do a once over for every piece of material you’re cutting…