How to tune CNC Axis travel and Backlash in Mach4 on an AVID CNC Router
Вставка
- Опубліковано 25 лип 2024
- In this video I show how I calibrated the 3 axis' travel accuracy, and backlash on my AVID CNC router. I also show how to test for missing stepper motor steps in all axis'.
NOTE: I failed to clearly articulate that the AVID CNC machines have dual motors for the Y axis (moves the gantry). Therefore, the Y axis needs a calibration for linearity and backlash for each motor. This can be done by repeating the procedure I show in the video at both ends of the gantry, in other words, and X=0, and X = Max.
Thank you very much for all this information. You have a new subscriber :)
Wow, I didn't even think of doing this, thank you Jim for yet another excellent video!!
Looks like you are making your way through the whole video list 🙂
Incrediably useful info, so happy I came across this. I have a Avid 2x2 Benchtop and haven’t done this. Thank you!!
I am glad you found it useful Marc.
I think I found my next little project once I get comfortable with my machine. Nice walkthrough, thanks!
That's the nice thing about a CNC, there are a lot of little projects you can do. They are a great retirement hobby 🙂
This video has helped me tremendously. Thank you for taking the time to make this video.
you are welcome.
Jim - this is great info, thanks! I'm going to go check my machine and adjust it.
Glad it was helpful!
Thanks for the video I don’t have an AVID CNC but I have watched a lot of their videos. I design and built my CNC it’s 49”x52”.
Your are the first person I have ever seen state that you need to calibrate both of the Y axis motors, I accidentally finger this out. My motors are to small for the size and weight of my machine. So when cutting something heavy and fast on the left side my left Y axis motor would loose a lot of steps. When this would happen my machine could get as much as 1/2” out of square before I E-STOP it. So I install a laser point switch in parallel with the gentry and tune it to stop the machine at 0.010” out of alignment. While setting setting the laser switch moving the machine from Y-0 to Y-max this is when I realized the Y axis slave motor had to be calibrated.
What size steppers motors, and motor torque, are installed on your CNC?
Hi Jerome,
There are 3 things going on here. First, you have linearity calibration, and backlash calibration. You don't necessarily need to do those, but especially if you are building your own machine, you won't know how accurate your machine is until you measure it. The linearity you should definitely do as you can dial that in as accurate as you need. The backlash compensation in Mach4 has limitations. You want to get your machine as good as it can be to start with (fix any gross mechanical issues), then you can do backlash compensation and it may improve things some. The nature of the backlash (how freely the mechanicals will shift to the other side as you change directions) will dictate how successful you will be with backlash compensation. I can say that it works pretty well for the rack can pinion drives on my AVID machine.
The last issue that you mention is losing steps. That really not a calibration, that is an error as you should never miss steps. I have big Nema 34 motors on mine and don't have any issues with the weight on mine. If your motors are undersized, then you can try a few things. First is to slow down your cutting speed in your tool path, and your motor acceleration settings in Mach4 (or whatever control system you are using). If that doesn't fix it, then you can increase the number of microsteps you are using. You have to check your motor drivers to see if they support that. This will also give you finer step resolution.
Last, if that doesn't fix it, you may have a problem with your connectors, or noise in the control from the controller to the motor drivers. For example, I was losing Z stage steps slowly on very long runs and I have way more motor than I need. I discovered that if I changed the step direction from active high to active low I no longer missed steps. The electrical system probably was marginal on the high going side of the pulses.
If you have further questions, you can email me at jnwdwks@gmail.com and I can try to help.
Jim
Hey man awesome video and I'm definitely going to do all of these steps to get my machine calibrated. I do have a question however. I did some 1/4 dowel holes on my pro 4x8 spoilboard i did them with a 1/8th endmill 200ipm and 15 degree ramp angle the holes on the left side of the board were not perfectly round the holes on the right were much better. Could this be caused by a combo of backlash and too fast of a speed?
One thing is that is really fast for a 1/8" EM, could be some deflection on that (depending on depth of cut of course).
Not round holes could be part speed, part backlash, and even part linear calibration (if say the Y was way off compared to the X axis). The left vs. right being different could be that one of your Y motor drives is much worse for either the linearity (steps per distance) or backlash. Since they are seperate motors and rack and pinions, that is possible. I didn't really mention it much in the video, but you have to do you Y axis on both ends of the X travel to make sure both motor's linearity and backlash are optimized.
First thing is slow it down to maybe 40ipm, and make sure your acceleration settings are not the AVID default (their defaults are pretty high IMO) so that the gantry is not being slammed around, then you can go look at calibration after that.
Thanks for posting the detailed and in-depth videos - very helpful and easy to follow. Quick question, where can I buy that “grounding rod” you use in the spindle (time stamp 1:30) for alignment? Seems like it has pretty tight tolerance for the entire length.
Thanks in advance for your time!!
Hi Matt,
Here is the info for the rod and clamps. The clamps need to be tapped out for 6mm so these knobs work.
Knobs
smile.amazon.com/gp/product/B07KPG6RBB/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
Rod Clamp
smile.amazon.com/gp/product/B07RLL6V9X/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
Rod
smile.amazon.com/ReliaBot-Hardened-Chrome-Plated-Linear/dp/B07DPF612G/ref=pd_sbs_2/146-0220186-6498654?pd_rd_w=fYMa8&pf_rd_p=690958f6-2825-419e-9c16-73ffd4055b65&pf_rd_r=9KPMCZKWJQ68B740W06P&pd_rd_r=e9572b38-4203-4808-9435-611afc46243b&pd_rd_wg=msqln&pd_rd_i=B07DPF612G&psc=1
@@JNWoodworks - awesome, thanks again for all you do for the maker community! Much appreciated!!
When you were experimenting with your acceleration parameters, how did you ultimately decide on the setting you went with? It seems like you have a similar use case as I do; I don't really care about cutting large panels quickly as much as I do cutting things with a very high degree of accuracy and precision.
I think that the acceleration aspects of these machines is something that is misunderstood or not at all considered by the overall user base. If you're making panels, or just using for general hobby use, that's most likely perfectly fine, but in my case... I question it.
Ya, the feedrate is what really matters for long cuts (like cutting panels), and acceleration doesn't really matter since you aren't changing directions a lot. For Vcarving and laser work where you are changing directions all the time, the feedrate and acceleration both matter because the faster you are going (feedrate), and the harder you speedup/slow down (acceleration) the more vibration you get. The acceleration really doesn't seem to affect the overall machining time much. I timed a few jobs with different accelerations and they were pretty similar. So I cut my acceleration numbers to 25in/min (I think AVIDs defaults were 50 or higher). That reduced the vibration some without giving up much in machine time. Then I just adjust the feedrate on a per job basis (depending on what kind of operation it is) to get the best tradeoff between vibration and machine time. The only jobs where i really care about machine time are 2.5D carvings and laser rastering because those can run many hours, and sometimes slab flattening. Everything else is usually less that 20min, so I will always choose a speed based on cut quality (where the bit is cutting best) and where I don't have excessive vibration.
Now you have me thinking about doing an experiment where I measure the overall machine time vs. acceleration on something that has a lot of tight turns to see what that looks like when you go way down to say 5 or 10. Maybe a new video to do :-)
Curious, what was your method to get the micrometer lined up perfectly parallel with your X and Y axis when taking the measurement?
It doesn't have to be perfect. I just moved the axis to both ends of the caliper's travel and checked that the caliper's body was about the same distance from the dowel that was pushing on the caliper jaw.
But that is a good point that I didn't mention, you do want to ensure that the caliper is roughly parallel to axis travel.
If you're off a degree, 9.000" becomes 8.999"
No big deal.
Thanks , this is great idea!
love the video, thank you! sorry if i missed it in the video, but how did you ensure that your calipers were linear with the axis of motion to avoid sin error?
Hi, thats a good question. First thing to remember is that it is not that sensitive to this. If one end of a 12" caliper is 0.25" off axis wrt the other end, you are only off by 0.002" in the distance measurement your caliper will give you over the full 12". So I just jog the rod over to nearly touch the caliper body, and then jog to the other end to ensure I have the same gap from the dowel pin to the body of the caliper on each end. That will get you to within 0.010" pretty easily, which will make the caliper axis alignment error negligible.
@@JNWoodworks thank you so much! ordering a digital caliper now.
@@bloho_design I like the Shars brand. Good quality vs price.
I had no idea that I needed to do this at all. I assumed that they had the numbers correct for the setup. I guess it's nominal.
I've had years of issues with small circles, let's say 30mm in diameter, being longer in the y axis. I wonder if running in this manner would fix it. It's square and trammed and avid hasn't been able to help me with the issue and never suggested doing this.
Mine is late 2017 and running mach3.
Yes, that could be the issue. Mine wasn't bad enough to notice in that large of a circle, but I could notice the backlash in alternating lines on the same axis when cut in opposite directions. Backlash will usually make very small circles have squared edges, so if yours is turning a larger circle into an oval, then its probably the travel accuracy of either X or Y that is off. Let me know how it turns out :-).
@@JNWoodworks I'm about to start doing this today. Did you calculate the step differences somehow, or just throw a value in and check until correct?
@@MichaelWoodrum I did a rough calculation to get started. For example, if your axis says its 2041 steps per unit, and your unit is an inch, then each step should be worth about 0.0005". So I started that way and just changed the numbers until i got the best linear accuracy.
@@JNWoodworks well, I just ran through this test a bunch of times on my x and y. I averaged the readings and was off on the x axis by 0.0125 over and inch.
Y axis was off by 4 ten thousandths. I have not yet got into backlash but I have corrected this to around 0.00009 per inch.
This does not fully explain my issue and hoping that backlash could be the problem. Considering that my holes are off by more than the error within the same distances, I assume it is either backlash, deflection or possibly Cam from fusion.
thanks for the information. Avid needs to add this information as part of the setup. They never mention it other than the claim of the error in movements mentioned in their site.
@@MichaelWoodrum 12 thousandths in an inch is a lot and good you are fixing it, but I agree that what you described previously would indicate a lot more error than that.
7:12