Grizzly G0704 Cnc Conversion

Sure. 200 steps per revolution with 8x microsteps. No pulley or other reduction, just 1:1.
 
A special thanks to jbolt for enlightening me on this test. You can isolate the source of your backlash by mounting a dial indicator to something other than the table, e.g. the column or the saddle then set the dial indicator tip to the end of your table. Remove the stepper motor and the AC bearings. Push the table in one direction and set the DI to zero. Now push the table in the opposite direction and note the DI reading. It should be zero but if it isn't then you have clearance in the ball screw/ball nut assembly. This is a test I have not done yet but intend to do when I get back in the shop on Tuesday.

I have done the test Dave described in his post above and I have zero screw movement in relation to table movement with the AC bearings assembled and preloaded. This is telling me my backlash problem is not with the bearings. Hopefully I will find the source of backlash is in the ball nut.

Tom S.

If you do a push test be sure to lock the Y-axis so there will be no movement there that could skew the findings.

Another way to test the ball nut is with the AC bearings in place. Lock the table and put a TDI on the end of the shaft with the base on the table, put disk on the shaft like you did before with a mark and an indicator and try to rotate the screw. If the screw rotates a little and there is no in-out movement of the shaft then the play is in the ball nut. If you can measure the amount of rotational travel of the shaft you can calculate the amount of backlash or at least a close approximation.

It would be nice to know how the double ball nuts are preloaded. Shims, springs etc. and what that value is.

In a double ball nut setup the non-flange nut, if sprung, is floating so depending on the in-use load and the spring pressure value it may be possible to exceed springs holding value which would show up as backlash when the load is applied in the direction of the floating nut. In this scenario it would not show up in a simple static test.

I'm assuming the Chinese double nuts are sprung and not shimmed due to lead errors of the rolled screws which would cause binding in a shimmed system.
 
Got home today and hopefully back in the shop tomorrow. My first test will be without the AC bearings in place. I expect to see about .007" of ball nut backlash. I've done the test you've described with the AC bearings installed and got zero ball screw movement. That's why I believe I'll see .007" of table movement doing the push/pull test. I'll also check the bearings over and determine how the nuts are loaded.

Tom S.

Edit - Sorry for jumping in on this. After reading the post again I realized it was written to the OP.
 
I accidentally attached that photo of the backlash I can feel in the handwheel of my G0704 to my previous post (#139). That's with the motor in place and table able to move. I thought I'd take a picture when I had stopped going in one direction, then reverse direction and take a pic again as soon as I could see the DTI move (it has .001 marks, so maybe .0002). I thought I could get this into some software and measure the angles.

Long story short, I tried a few things and only got a measurement in my 3D CAD program, Rhino. I got 13 degrees. This is a crude measurement. Still it works out to explain about .007 of backlash. I was able to remove that by taking the motor and mount off and just making an effort to ensure as little motion as I could get. My X-axis backlash went down from .012 to .006. I did the same sorts of things on Y and reduced it to .006 also although it started out better at .010.

Newbie question: does the tightness of the gibs affect backlash?
 
Newbie question: does the tightness of the gibs affect backlash?

Yes. Gibs should be adjusted as snug as possible without causing any binding or excessive friction. A few folks have mounted linear rails/bearings on the G0704 to increase accuracy and reduce friction.
 
I got my Y axis down to .001 and still have to work on the X.

On the X, I was doing some work on my enclosure and when the X started getting too negative (table too far to the right), it started bogging down and sounding terrible. As soon as I started going back to positive numbers, the problem stopped. It occurred to me I saw the gibs act that way when I had it in pieces. So I tightened the X gib and the problem went away.
 
On the chance that people still drop by to read this, now that I have the conversion going, the enclosure should be done today, and the other things are being added, is there any place in particular where y'all hang out? I mean other folks with CNC converted G0704 mills, or similar sized mills.

Here on the the "CNC In the Home Shop Forum"? I went to the Grizzly forum and there wasn't much in the way of discussion of how folks are using this.

One of my last decisions is whether to go with a full up flood cooling or use a mist coolant. It seems all the serious shops use flood, but my impression is that it's really for removing a lot of chips. More suited to a 3 or more HP mill than a 1 HP machine.

I have tons of questions about upgrading to a higher RPM motor, and all sorts of other improvements. I have a fourth axis ready to be added (once I figure out how to get the motor on it!), I need a bottle or two of oil for my oiler, add limit or home switches, lots of little details to read about.

Just looking for places to hang out more.
 
We are still looking, so just keep posting :grin:

I would go with mist coolant, a lot less messy. I use a direct loss system and don't try to recover any. I normally have kerosene in the tank because I machine mostly aluminum. I use about a quart in 8 hours of spindle time, most of it just evaporates. I recommend a system that allows independent adjustment of air and coolant. That way you can use more air to blast away the chips if needed. The syphon type systems are very limited on the air vs. coolant flow.

Looking forward to the rest of your project.
 
Yes, still following your excellent journey. I have never used Flood coolent but I have used both the cool-mist and fog-buster brands. I prefer the fog-buster over the two. The siphone approach is a lot of work on each job to tune it in. I guess if I was running the same parts 8 hours a day it might not be an issue but I run for an hour and then do other things before coming back to the mill.
 
Thanks for the comments. I'm not very up on the misting systems, don't know approaches or brands, just that I've heard they're easier to live with and not really a huge step down from a flood.

I ran into a stop with my enclosure, and I'm going to need to figure out just how to get out of the slight jam I'm in.

90%Done.JPG

The doors don't actually close all the way. I'm going by Hoss' videos and whatever I can pick up from the thread on CNCZone, and Hoss used some magnets to grab onto the L brackets, in the center of the panels. Then he 3D printed some little housings to hold them to the top rail. I have nothing like that. To make matters worse, to get the magnets to engage, he pulls the two handles against each other. When I do that, the handles hit each other and the doors won't close flush. I think I need new handles, at a minimum. I've tried loosening them and sliding them around to no avail. I could try that again, just because.

I think I'm going to try to find another set of handles, something smaller. Not sure about magnets or some other way of trying to snap the doors closed.
 
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