Hello. I'm pretty new to CNC milling and I got a 1500x1500 CNC with an Blackbox controller. I bought it from a guy who build Openbuilds. It is with lead screws and Nema 23 motor The left side on the Y-axis is stuttering when its moving - its not running smooth at all. The right side is running smooth. I have check the pinol screw on the motor and the lead screw and it is where is should be. When I move the Y-axia (both motors are off) it is really tight on the left side (its really hard to move it) and on the right side it is running smooth. Is it the wheels that are too tight or is there some other things that are causing the problem. I hope someone can help me, since I have not used my machine jet. Thanks.
Do NOT turn your stepper motors by hand if they are connected to the controller - back emf from the stepper motor can damage your stepper drivers. If you unplug (or plug in) a stepper motor ALWAYS do so with the power off - same reason. You could try loosening the eccentrics fully to see if that helps. Check next that you haven't overtightened the nut blocks - let them align themselves with the leadscrew as you tighten them to the gantry plate, and as you tighten the second one GENTLY squeeze them together - the aim is to have each nut block touching one side of the thread, not gripping it tightly. If that doesn't fix it, it may be that you have a tight-fitting nut block - they are often stiff when new. If so, disconnect the coupler from the leadscrew on both Y axes. Remove the end plates from the end opposite the motor and slide the gantry to that end so that the leadscrew sticks out. Spray the leadscrew with a DRY ptfe or silicone lubricant, grip the end of the leadscrew in a battery drill at slow speed and run the leadscrew back and forth several times. If none of that helps come back to us. Alex.
It helped loosen the nut blocks. Now it runs smooth again. But is the nut blocks the ones that help get it run more smooth and make better circles? It still makes imperfect circles, when its small circles - it is slightly off. Is it possible to get small perfect circles. - When i make larger circles they look more perfect.
The backlash adjustable by the nuts is in the micron range, you wont have noticeable symptoms on new nuts, only after some years of wear (when its then time to readjust by the way) If its big deviations look for something else that is too loose (shaft couplers slipping on motor shaft or leadscrew, loose stop collars, loose wheels etc)
The backlash is still there only it spreads on a larger circumference and is therefore way less noticeable. I use Mach3 and it has a setting to compensate for the backlash.
If you now have the nut blocks loose then they are not correcting for backlash, and are probably introducing some. Watch your leadscrew carefully as you tighten them to the gantry plate - if the leadscrew is being pulled out of line that would explain the stiffness you had on the left Y axis - either your leadscrew is slightly bent or you may need to add spacers between the nut blocks and the plates - don't overtighten them. I assume that this is not an Openbuilds machine or has been modified as it is a 1500 x 1500 leadscrew, and some suppliers don't always match the tolerance levels that Openbuilds do. Alex.
How small of circles? Are they being cut out, or drilled out? If you are drilling (or helical drilling) and your plunge rate is too fast, the z axis may be flexing back making them oblong. I notice this when I cut aluminum when I helical drill small holes too aggressively, which is why I do a roughing and finishing pass. The finishing pass 0.20mm to 0.30mm left behind for the full depth finishing pass make them round again.
Hello all and thanks for all your replays. I have now used some hours to get a better circle by adjusting the screws. - It is not 100% perfect jet, but its the best that I got - and think that will work for what I have to do. I might have to do some small adjustments to see if I can get it even better. My new problem is that the holes that I am making is not the same measurements as in the drawing - when using Fusion360. (PP: swarfers Openbuild GRBL-1.1 post V15 for Blackbox...). I have some T-nuts they are 7.75 mm - and the hole is 7.75mm In the drawing the circle has to be 8.60mm I have done the calibration on the blackbox controller and y/x axis is correct at 100mm in each direction. I have tried using Aspire - when I do that, the holes are more equal in measurements to the hole in my drawing. But when I use Aspire the holes are not as good as when I use F360They are more square. (this might be because i'm not used to Aspire and have not set up the settings right. And the only post processor I have is "grbl 0.8c (mm)"
Maybe too aggressive on the feedrate? (deflection of the frame from cutting forces) Or Use a Roughing then a Finishing pass (so the finishing pass just makes it perfect, the Roughing pass removed most of the material
@Brian reklame try and slow the plunge rate down a bit especially in denser materials. I noticed when cutting aluminum, the smaller (3.175mm) end mills will flex as well as the x axis beam if I plunge too aggressively. The would lead to oblong holes. I also noticed this in some hardwoods. To counter this I would slow the plunging feed rate, and do as Peter suggested above and cut a roughing pass first and leave about 0.2 - 0.3mm to be removed by a finishing pass. What size endmill are you using? I try to use as large as possible. For your 8.6mm hole, I would use a 6.35mm end mill because the larger end mills cut better due to less deflection. I have an 8mm collet and some 8mm endmills, but there would not be much left for a finishing pass and I would basically be drilling straight down whereas with the 6.35mm I could run a helical drilling tool path. I also choose larger endmills for cutting out the parts, especially in aluminum. They seem to cut much cleaner.
