Understanding bitsetter and job thickness

Trying to understand the order of setting zero for my z axis, I still ‘cut air’ sometimes and trying to wrap my head around the order of setting zero. Does carbide motion take into account the job stock thickness when calculating z axis zero?
I have both bitzero v2 and bitsetter installed and working. Do I still need to be setting my z axis zero with bitzero or manual jog to top/bottom of stock? Or just load a job with the thickness correctly defined and only use bitsetter to measure the initial end mill - then start the job?

Watched a vid or two where the blank 1/4 mill ‘zeroing blank’ is inserted and used with bitzero to set z axis, that’s confusing to me because that blank end mill in no way represents the length my actual mill that I’ll be using.

I read Unexpected Z-Axis Plunges and that makes sense about being careful when changing tools. It’s the initial z axis zero order of operations that I’m confused about.

If the origin is set at the bottom of the stock, then yes, the stock thickness is assumed to be accurately measured and is used when the toolpaths are cut.

The BitZero is used to set the origin relative to rectangular stock.

The BitSetter is used to manage the length offset of the currently installed tool.

The way it works is:

  • the machine homes/initializes — it determines where the top right corner is
  • the machine measures the current tool (presumably a probing pin) using the BitSetter— this determines the length offset of the current tool based on how long it is from the Z-axis machine zero
  • set the origin using the BitZero by probing with the current tool — this will set the zero relative to the stock based on the current length offset of the currently loaded tool
  • load a file and start it — the user will be prompted for the first tool, which should be loaded and will then be measured by the BitSetter to determine its length offset — that length offset will be used to cause the machine to move relative to the established Z-axis zero
  • at any given tool change the new tool will be loaded and measured by the BitSetter

As @WillAdams said the job thickness is not important. If you use the top of material then where you set zero is used as a starting point. If you set the bottom of material lets say .5" then the cutter will start at .5" from the bottom of the material. Either case measurement of the material is very important.

When you initialize the internal coordinates the system uses are set. Then during initialization the router comes to the front and prompts for a bit. Any bit will work. Then the router goes to the BitSetter and plunges twice. The second time the system is calculating an offset from the internal coordinates to the point where the bit trips the BitSetter. That trip point is compared to the last time you physically set Z zero. That could have been the last time you used your machine. The X Y and Z zero points are remembered over power cycles of the Shapeoko. Then the router returns to the front center and waits. This is the time to set the X Y and Z zero for the next job. The previous job X Y and Z are forgotten. You load a new job and the router comes to the front center and prompts for the tool in the c2d file. You insert it and the router goes to the BitSetter and does the offset from the internal Z zero and calculates the offset from the last time you physically set Z zero. When you hit start the router moves to where it is going to start cutting and Carbide Motion knows where you set Z zero and the carving starts. If you told CC the material was .5" and used the top of material and you set the Z zero on top of the material the router starts cutting. The first cut is the depth of cut of the tool you set in CC when choosing the tool. If you are going to do a through cut then the router will cut according to the depth of cut of the tool you are using and stop at the .5" mark. So if you measured your material carefully and set the Z zero properly at the top of the stock .5" will be cut away.

The BitZero function has two positions to set X and Y and Z from. If you only set X and Y then the BitZero hangs over the edge with the lip hanging over the edge. If you are only setting Z then the whole BitZero sits on top of the stock with the lip on top of the material. When you select which zeros you are setting another offset is used and the depth of the lip on the BitZero is calculated using the internal coordinates. So an X Y and Z zero on the lower left corner the lip goes over the edge. The X and Y are probed and then the Z and the origin is set to the lower left corner. Then when the c2d file is read the cutting starts at the Z zero you set with the BitSetter and/or manual paper method.

If you turn your BitSetter on and off then you need to power cycle the Shapeoko after going into configuration and turning the BitSetter on/off. The turning the BitSetter to off when it was on during initialization does something strange to the internal coordinates. Also setting bottom of material but setting Z zero on top of the material will result in an air job.


@gdon_2003 @WillAdams Thanks, mainly trying to confirm the correct flow for when to set the Z zero, appreciate the explanations!

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