I have tried to cut a number of circles on different material but they all seem to come out less than perfect. The two sides in the X-direction are always a bit flat. I have tried different feed rates without any improvement. I have tried it on both aluminum and plastic. Are there any comments or tips that might get me closer to a perfect circle? Second problem is that the machine never returns to the center of the workpiece. I have registered the bit on the centre and set the zero positions. However, when I try to return to zero from where ever I place the bit it is always off center. When I was running a job it would never return to center to make the next cut in the z-axis.Any suggestions?
Hi @ricklach, there are lots of things for you to check, starting with looking for a mechanical problem. Start at the bit, wiggle it and look for things moving that shouldn't. You haven't given us any details of machine or controller, so it's difficult to be more specific but you need to methodically work your way around your machine until you find something that has play. Check eccentric adjustment, bearings (especially on the ends of leadscrews) are properly seated, lock collars tight. Motor couplers, or drive pulleys secure (fixing screw on flat of motor shaft) frame parts not moving relative to each other. It could also be a carriage binding. DON'T TURN STEPPER MOTORS BY HAND! disconnect motors from leadscrews or drive pulleys then see if each axis will slide smoothly along its entire length (you may have to remove a leadscrew to do this so leave it till last) Let us know what you find. Alex.
Thanks Alex, I did a complete check of my Workbee 1510 system including roller tension, belt tension, and router bracket stability. The problem was isolated to the router bracket which, in my opinion, does not represent the best in design and manufacturing for such a critical piece in the system. I replaced all of the screws that came with my kit (I mean all in the whole project) with a much higher quality SS screw, added two extra brackets to the top of the router bracket by drilling and tapping two new holes in the top of the bracket, adding better T-nuts that actually fit the channel snugly and provide greater surface area so they purchase better. In short, I beefed-up the entire kit to make it more sturdy. Today, I will try to cut the same project to see if all this paid off. I will keep you apprised of the results.
Hi @ricklach, if you continue to have problems post a pic of a circle (just 3mm deep) labelling X and Y axes. Alex.
Alex, Here is the photo of my cut of the circle. I watched the machine do a dry cut first and without any load on the system (air cut) I would get this slight deviation at the two points shown by the arrows. This was consistent throughout the whole cut - both an air cut and an actual cut in the materiel. It seems that there is a small glitch somewhere in the system, perhaps in the import or interpretation of the Cut2D Pro grbl file and the blackbox controller. At least that is my best guess. I centered the bit on the hole in the center of the plate and made it my home position. However, when the cut was complete I returned the bit to its home position and it was no longer in the center but off to one side by about 2-4mm in the X axis. This behavior happened before and seems to be consistent. Any suggestions that you have would be most welcomed.
Hi @ricklach, don't waste aluminium on these tests - some scrap mdf would be ideal. I am 99% certain this is not a software problem - I think there are two issues; 1) the kink in the toolpath is most likely some play somewhere in the system. I would particularly check that the drive pulley doesn't move relative to the motor shaft on the Y axis. I am assuming X axis is leadscrew - if not check the drive pulley on that as well. Even with the fixing screw firmly tightened against the flat on the motor shaft a drive pulley can sometimes move. Same applies to a motor coupler on a leadscrew - a fixing screw on the flat of the motor shaft, but also a fixing screw into the thread of the leadscrew (sometimes you have to grind a flat on the leadscrew to get a really firm grip - but don't do this yet). You should also check that your anti-backlash nuts are adjusted to take up any play in a leadscrew, although I don't think this is the issue here. Did you set the current for each stepper motor (OpenBuilds BlackBox 4X Documentation) - this could be the cause of not returning to zero (missing steps). 2) Your circle may not be perfectly round - did you calibrate your steps/mm for each axis? I have attached a test file produced in Vcarve desktop using the grbl (mm) post processor - with a slight modification to take out the unwanted tool call. The file is for a 100 mm diameter circle (just the perimeter path) 0.5 mm depth of cut, 3mm flat end mill. I haven't included a finishing path, so tool deflection may cause this to be slightly undersized, but X and Y dimensions should be identical once any backlash (play) issues have been fixed. Alex.
My Workbee is a X-Y belt driven model and Z-axis lead screw. I will check all three drive pulleys for tightness. I have already calibrated the X,Y, and Z axis steps/mm as part of my other setup. I have checked the tension in the belts. I will recalibrate the current for each stepper motor while the machine is under load. I will get back to you once I have finished the adjustments.
Hi @ricklach, re not returning to work zero, after you have set motor current - using the pointiest bit you have; Jog to middle of machine, put a strip of masking tape along the X axis. Mark bit position. Jog 200 or 400 mm to one side. Jog back the same distance. Mark bit position. Do not re-centre. Repeat. Is the bit position gradually moving to one side? Re-centre and repeat in the opposite direction. Again does the bit position gradually drift sideways with each repeat? If so the possibilities are the drive pulley slipping (unlikely with no load), missing steps - also shouldn't happen with no load, but check your stepper motor wiring very carefully for any poor connections. Can't think of anything else at the moment, but will post another message if I do. Alex.
Hi Alex, I just finished doing a complete check of all wiring, and the test you mentioned above. I also carried out a number of additional tests to carve circles and then return the bit to the center point plus move the bit in various X-Y positions and re-home it. All tests are running within acceptable bounds now and if I had to attribute the change in performance to any one area I would say that it was the wiring. I completely re-tightened all connections and thing seemed to get better from that point. I also checked the steps/mm calibration and everything seems to be ok now. Thank you for your assistance with this very perplexing issue. I shall now make a few minor adjustments to my aluminum project an re-run the program again to clean up the cuts. If you like I will post my success or failure.
Yes @ricklach, do let us know if it continues to behave itself. With belt drive you should get +/- 0.2 mm resolution, depending on how well the machine is put together . If wiring was the issue keep any mains wiring away from low voltage stuff. It's always good to see someone get their machine running properly. Alex.
Hi Alex, I still have about 1-2 mm slop when machining aluminum circles. I will continue to refine my tuneup. On wood, the circles are within tolerance so I am not going to go crazy over the issue. As an aside, do you know of a centre and edge finder that will work with the workbee and Blackbox controller?
Hi @ricklach, I have a workbee 1010 (leadscrew) which has the advantage over belt drive of (approximately) an 8:1 gear between the stepper and the gantry which means for harder materials I can apply more force to feed the bit (downside is I can't get the acceleration and top speeds you can get with belts). If you are OK cutting softer materials but not aluminium then you need to look at optimising your settings - you are probably missing steps by asking your machine to work too hard; 1) Stepper motor current settings - OpenBuilds BlackBox 4X Documentation - you need to find a sweet spot between being able to stall the steppers by hand and the drivers overheating - see BlackBox and BlackBox 2) Feeds and speeds - see Speeds and feeds start with lower feed rate than the table suggests and work up. Keep your spindle/router speed relatively low - you need to be cutting chips, especially with aluminium where you will be melting the metal onto the edge of the cutter if your spindle speed is too high. If you think the machine is being worked too hard reduce the Depth Of Cut rather than the feedrate. I assume from edge-finder you mean XYZ probe? - I made my own - Quick and Easy XYZ Probe - see also OpenBuilds CONTROL Software Good Luck. Alex.
Alex, I presume the macros will work the same with the blackbox controller? Where are the actual macros to be found?
The link above (OpenBuilds CONTROL Software) leads you to a post by @sharmstr which in turn includes a link to the Ooznest site with full instructions on XYZ macros. At the bottom of the Ooznest page there are two documents on calculating the offset you need to put in your macro (for different tool diameters) and the g-code you need in your macro. Come back to us if you get stuck with any of that. Alex.
One thing to check that I ran into was on an old CNC Shark converted to Grbl, I had a consistent offset like yours (along with other Shark related issues). The problem was that I had the step signals polarity inverted. Every movement had an extra “step” at the end that accumulated over time. Stan W
