Troubleshooting and Fixing Backlash in the G0704 CNC Mill 

I was thinking about doing the exact same, do you have your code and interface documented anywhere?

@@philiprisser938 Hi Philip, I'm afraid I don't have the code etc. on the internet anywhere, just on my pc. I don't have any problem in giving you my stuff but not sure how to do it. Any suggestions?

Hello, interesting implementation. That sounds like a closed loop system. Did you modify the original GRBL code?

Hi, Yes you are correct it is a closed loop system. The GRBL code was not modified (to be honest I don't understand a lot of it) I just use the step and direction pulses from the GRBL controller and feed them into an Arduino Mega. The 'step' pulse of the GRBL is set to be the same as the resolution of my DRO i.e. 0.005mm/step and it drives a 'set point' in the Arduino, this is compared to the DRO position which produces an 'error'. The Arduino then drives the stepper motors to reduce the error to zero. It is a bit slow, my max table speed is approx. 250mm/min before the steppers stall but I think that's down to a combination of too small stepper motors (NEMA 23) and a relatively slow Arduino. Still it does everything I want it to do with very good accuracy, + or - 0.005mm, and it's been doing it perfectly for at least 5 years now. One of the demo's I like to do is to physically push the table away from it's position with the backlash (approx. 0.1mm) and it immediately bursts into life and returns the table to its previous position, very satisfying. Thanks for the interest.

@@TurbineTed I didn't quite get it. You have a second arduino which does the closed loop and it reads the DRO? From where the stepper driver gets it's step input? Maybe you can do a video or a schematic.

I can live with what I have, but I'd like it to be better. The slip-stick in the dovetail ways on Z is tough to overcome on a machine like this.

If everything appears to be tight you may want to look at your lead screw nut or ball screw nut specs there could be back lash in those. A high quality system will provide the specs that you need, Chinese systems very rarely if ever provide you with the information, and the quality is rarely what they claim it to be. I’m not saying they can’t make decent product, I am leaning more towards you get what you pay for.

Now, that there is funny ARW

I'm sure both are. It's better with the 28lb spindle than it was with the original 70lb head, but it's still an issue.

Most of the backlash comp changes the way the mill with move and can cause more issues.

Mach 3 does have backlash compensation. I believe all it does is add the amount you specify to the amount of movement, but only when changing directions. That way the backlash is taken up on the first move.

It's only time and money. When I did this conversion, I had more of the former. At this moment in my life, it's the other way around. Not sure I'm up for building completely from scratch.

@@Clough42 After a while I got tired of chasing backlash on my G0704 conversion and tightening loose items on the ATC and mill. Ended up buying a used 5 axis Robodrill in good condition for almost the same price I put into the conversion. I don't think I'll buy another machine without an ATC or do a conversion again if I'm serious about making good parts.

Yeah. Maybe not a bad idea. Also servos. And better ballscrews. And maybe a better mill. You know, a Tormach 1100MX would fit in basically the same space in my shop...

@@Clough42 yeah I guess but tormach is still just a dovetail machine and I personally am not a fan. And for the price of tormach, there are better options but it's your choice

@@chrisadesigns yeah I can't get over the dovetail. Obviously it works but I keep thinking of it as WW1 technology.

@@Clough42 Haas has a TM-0 coming out in Q3. Same size and they are shooting for the tormach price target.

Mobile vactra no2 is the way to go

No. You could contact contact CNC Depot. They manufacturer it.

it's an amphenol brand connector. cnc depot has close-up pictures of the connector on their website

the gib is a wear item; adjust it so there is no play and also no binding. you can't eliminate stiction altogether

@@ikbendusan Thanks for Your reply! Your fully right. I was thinking about the wear on the column, caused by the gib. Is it Your opinion that I should tightened the gib to make the column "hang" on the gib tension and some force from the vertical handle, including fine tuning, will "force" the column down? Now I place my hand on the column and force it to the "down position" in order to avoid "an unexpected free fall". My old dictionary don't know the word "stiction".....

For a large, heavy system like this, the dial preload will have little effect. I have used several indicators, including a $500 Haimer on this setup and seen similar results. Questioning the tool is a good thing though--especially when results are inconsistent.

Good suggestions. In my case, I think most of the backlash is slip-stick causing the nut mount to flex. Not a lot of easy solutions, unfortunately.

and loose nuts....

Hey Yuchol are you home now?

It's all just metal, so yes. Is that practical? Don't know. Maybe.

@@Clough42 I would think milling off the dove tail and using the main base could make for a really interesting video. Would eliminate all head nod too. Pending results could open possiblitys for doing the X and y axis though you may loose z travel due to heights. But could you then make up the travel with extended z liner rails. Into the deep end fast.

@@forgeperformanceand4x4 yeah. I'll have to think about it. That does sound interesting.

this is exactly what i'm doing to my machine

You're supposed to eliminate as much mechanical backlash as possible before using backlash compensation.

i've read that it doesn't work for milling operations in mach3

It's a Grizzly G0704 conversion.

I think he said "two tenths is not the five tenths we're looking for".

@@jjbode1 i think you missed a very obvious and well known movie reference.

Champion!!!!!

If the backlash is in the nut.

mach3 supposedly does not support backlash compensation during milling operations. this excerpt is from the manual: 5.6.3 Configure Backlash: ''The Config>Backlash dialog shown in Figure 5-24 lets you provide an estimate of the distance the axis must back up to ensure any backlash is taken up when the final “forward” movement is made. You can also specify the speed at which this movement is to be made. Mach3 will attempt to compensate for backlash in axis drive mechanisms by attempting to approach each required coordinate from the same direction. While this is useful in applications like drilling or boring, *it cannot overcome problems with the machine in continuous cutting where changes in direction occur.* you would need another controller (i have an edingcnc which does do proper backlash compensation)

Yup. Very likely.

@@Clough42 what are you using for way lube? Try loosening the gib a lot and see how much backlash that removes. When setting the gib tightness on my G0704 I have a DTI on and check back lash as I tighten. I tighten until I start to introduce backlash into the system. My screws are double nuts that I custom shimmed, they account for about .0005 of my back lash.

@@michaelalcocer6778 Quick Slide 68. Essentially the same as Vactra 2. I did basically what you suggest, and found a happy .001" setting. This seems to be pretty temperature dependent, though. It was worse again the next morning when the shop was 20 degrees cooler.

@@Clough42 yeah I should have waited till the end of the video to comment. The gib will grow and shrink with the outside environment. Set it for when you would most likely be using it. I have spent hours chasing my G0704. I am over it unless you scrape it, it will have one issue after another. Linear rails if I keep it. Just trying to finish up my TC22 retrofit.

nice

Congratulations