View Full Version : mapping the leadscrew

04-17-2007, 11:32 AM
Mapping the leadscrew, how does one do it in Mach3? I couldn't find anything in the mach3 manual, but then I might be using the wrong search term. I have heard it is a long and laborious process, but I have also heard it is worth it to get a nice accurate machine.

Machine is a "Joe" style machine that is currently being updated and modifies. Current screws are acme 1/2-10, these will be changed out and will be replaced with either acme 1/2-10 2 start, or nook .631, .200 pitch double nut ball screws (rolled screws). (I'm leaning towards the ball screws now that I know what my tax return will be).

If possible a step by step process would be preferable, especially where the mach3 data input is concerned (unless it is so obvious a 6 year old can do it).

Thank you

04-17-2007, 11:46 AM
I believe it's as simple as moving to a position, and entering the position error. But I'll have to look tonight. I don't think it's in the current manual.

The hard part is measuring how much error you have.

04-17-2007, 12:07 PM
Thanks Gerry

04-17-2007, 09:21 PM
I don't have a way to check it, but it looks like it works like I said. Move the machine to 1, for instance, open the screwmapping window, and enter the actual position. Don't forget to click the save button at the bottom of the screen. The more positions you enter, the more accurate you'll get.

04-18-2007, 01:43 AM
What the heck? I swear leadscrew mapping was in the manual the last time I read it, but it sure is missing from the current manual.



04-18-2007, 09:02 AM
Thanks Gerry

Thanks Bob, it probably was there in the past. Oh, BTW, thanks for the reply on the double row angular contact bearings yesterday.

Would either of you have a good picture or sketch of a double nut ball screw setup, preferably using a spring for preload, I should only need 150lbs preload a the most. Do I need a right and a left handed nut? I assume both nuts have to have flanges (but I could be wrong about that, there might be a better way of setting them up). Would it be safe to assume that gravity on the z-axis would be enough of a preload by itself.

Application is a wood router based on the Joe design.

04-18-2007, 11:45 AM
Steven, for a Joe's wood router, I don't think I'd bother with double ballnuts or even angular contact bearing blocks. Seems like folks get great results in the accuracies wood demands without such expensive ornaments. I think part of it is the precision requirement is less, but part is also likely that cutting forces are way less than for metal.

If you do want double ballnuts, there's a lot of pictures and info on these on the Industrial Hobbies web site:




I'd also go check the ballscrew manufacturer's sites for info such as Rockford, HiWin, and so forth.



04-18-2007, 04:48 PM
Hi Bob,

Thats great to hear that single ball nuts may do the trick for me. Should I go through the effort to have then factory preloaded with oversized balls (which brings them up in price to being the same as a pair of non preloaded nuts). I figure I'll still take a look at the double nut setups too, I've come from knowing absolutely nothing about CNC to knowing enough to be dangerous... not reason to stop learning now :).

The double row AC bearing I can get on ebay cheeply, they are likely ABEC-3 rejects, but probably still better than skate bearings that joe uses.

04-18-2007, 07:50 PM
Imo, the only benefit you're likely to see vs decent 2 start acme is a gain in efficiency. Bigger motors to make up for that are a lot cheaper than ballscrews. It's very unlikely you'll see any improvement in accuracy. Keeping wood dust out of the ballscrews is another thing you'll need to contend with.

04-18-2007, 08:22 PM

That's good to know and it will allow me to spend the tax return on other stuff too. Thanks. Considering I have 665 in-oz pacsci motors they should handle things well.

Hey, I found this thing on ebay and was wondering if it will work for mapping out the leadscrews?

I'm thinking on these lines: if I attach this to my x axis on 1 end and movable brace attached to the table on the other, move the gantry an inch according to the Mach3 DRO's, read the measurement off of dro quill and use the measurement to calibrate the axis. Then repeat across the entire span of the axis. Would this thing do what I want it to do