Make a jig and use some software for repeatability
If you are looking for the Mach3/Romaxx version of this page, please see here.
When I bought my ShopBot, I found it came with a Zzero plate and routine (C2) for finding the surface of my material, and a routine (C3) to find the corner of my table using the X and Y limit switches. I quickly found that I didn't like using offsets to locate smaller projects that I wanted to place out on my table, vs. in the corner, so I wrote a new routine. It is a modification of the C3 routine to use the same input that C2 uses, plus combines the Zzero from C2 into the code. You use it as follows:
- Locate your project wherever you wish on the table
- Use the jig shown below and hook it onto a corner of your work
- Run the routine available below (I called it C4 on my system), and enter Y in the first prompt, which lets you move your spindle around
- Locate the tool over the copper cap, and lower it slightly into the cap. It does not need to be centered in the cap
- Hit escape, and the routine finds the center of the cap, then finds the bottom of the cap, and updates your zeros.
For all the pictures, click to get a high-res version.
Below is my jig in use on the ShopBot. It is simply a 1/2 or 3/4 inch copper cap inserted into a tight fitting hole in a piece of wood, centered over two machined lips to catch the edges of your work piece. The first picture shows the tool moved into the cap, which is how it needs to be before the routine does the measuring and zeroing. Note you don't need to be centered. Next is a picture of the whole set-up, from the bottom side of the jig, showing the lip, and showing the alligator clip attached to the Zzero plate. As a one time activity, after you build the jig and insert the cap, you must measure the distance between the inside bottom of the cap and the bottom of the jig cutout (don't include the lip. Enter this measurement on line 23 of the routine. In my case, that number is .088 inches (3/4 inch version). This number directly affects how accurate your Z zero is.
Here are three pictures showing the results of running the routine. The first is the tool centered, then the Y and X centered results. I turned the tool between the pictures, ant it shaved a tiny piece of wood off, which makes the Z look high in the X picture, but it was my fault.
The next picture shows the positioning screen you get when you first run the routine (click for a readable view).
I made a video of the routine running. You can see it on YouTube:
The PartWorks file for the 1/2 inch jig.
The PartWorks file for the 3/4 inch jig.
The ShopBot code for the routine.
I made one of these jigs for my friend Chuck. He decided it could be improved, and with the help of a Bridgeport and a friend, here is the result.
