Good Morning To All. I have browsed through the forum to see if I could find an answer to my issue and failed so decided to make a post. I have a Workbee 1010 screw drive machine with Black Box Controller. I have been using it primarily in my guitar builds and have been very pleased with the results I've achieved. I now have come up with an issue that I can't figure out. I am a real techy type of a guy but rather new to the CNC world. Here is my issue. I've reached the point in the project where I needed to slot the fretboard. I built the tool paths using Carbide Create. The correct position for the fret slots was determined using a fretboard calculator and verified by measuring on another guitar of the same scale length. Fore machine motion I use the OpenBuildsControl software. After cutting a sample fretboard and putting it on the neck at the appropriate position I was able to determine the fret spacing was off. This is easy to see because the 14th fret should be positioned right where the neck meets the body of the guitar. The fret slot was about 1/8" forward of where it should be located and I'm sure the other fret slots are wrong to some degree as well. My 1st thought was calibration issues so I calibrated the machine using the calibration wizard. After that was done I machined another test and the results were basically the same. I tried a 3rd time by manually jogging the machine the appropriate distances and cutting the slot with the same results. Any ideas? - Mark -
Certainly sounds like calibration issues. How far off are the other frets? If it's a calibration problem, each fret groove will be off by a progressively reduced amount as you approach the nut position where you started. If you started at the body end, and all the frets are off by 1/8", it's a probing/homing problem. Kinda depends on your workflow and what the other numbers say. Could maybe even be backlash in certain circumstances.
Hi Rob, Thanks for the quick response. I'm going to recalibrate the machine again. The fretboard blank is about 2.25 x 18 inches long. I made the tool path zero to be the center of the board. The slot cutting starts at the sound hole and sequentially cuts towards the nut. I just put my test blank on top of a guitar that had the scale length and adjusted the blank so that the 14th fret slot meet the body. The error increases as the fret slots move up towards the nut. The error is not a lot but I'm still uncomfortable with what I see Since you are suggested still a possible calibration issue I'm going to find a ruler that has metric markings. When I ran the calibration wizard I was measuring from the set zero point and then out the 100mm that the wizard sent the router. I was using a digital caliper to try to measure the center of a .05 mm end mill at the start and the end points and put those numbers in the Wizard and saved them. Then I went back to set zero and put a aluminum ruler marked in inches and fractions and dropped the z axis down so the bit was centered on one of the inch marks. Manually sent the router out a variety of inches on the X axis and measured where the bit fell on the ruler and it looked very good. Perhaps the error is due to not reading the caliper correctly. I'm going to try calibration again I made the post thinking that I missed something using the calibration wizard.
If the error changes over distance, it's almost certainly a calibration issue. If you clamp the fixed jaw of the caliper to the machine, drag out the moving jaw so that the depth gauge is sticking out of the body a fair way, jog the machine until a plate or a piece of extrusion or something just pushes in the depth gauge a little bit and is resting on it, zero the caliper then command say, a 50mm move... What does the caliper say? It should say 50.00, ideally. 49.95-50.05 are acceptable. Basically you're using the caliper like a dial indicator, only it doesn't have a spring return and you'll have to pull it out each time. Beyond that (and based on your description, it should say something like 51 or 52) it's time to recalibrate. Do the above test but over 100mm or more (I assume it's a 6 inch caliper), the further the better. Divide your commanded distance by your actually measured distance, then multiply by your steps per mm value in grbl for that axis. That's your new steps per mm value. Then repeat a couple more times to be sure. This recent thread has more description and pictures of this process: Precision problem with stepper motors (ox cnc)
