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Author Topic: Z drive confusion  (Read 1491 times)

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Z drive confusion
« on: April 18, 2016, 10:01:16 PM »
Hello All,
First post on this forum. Thank you for looking.
I have been running a 5x10 router for a few years. I bought it off of craigslist for cheap. It took some work to get it going but it was well worth it.

It's a camtech with mdrive steppers all around. I use Mach 3 to control it, and sadly boobcad to create CAD files.

Here is the rub-
I was 3d engraving a skateboard deck for grip (similar to a gun grip) each pass got deeper and deeper.
So checked the tool to make sure it was tight. Check the z drive to see if it got sloppy (newer ball screw installed, still very tight) - all good.

So I checked the steps per unit on the z drive. This is what I found-
I can set the steps perfectly so each time the needle splits the line on my dial indicator. Then I set the z drive back to the physical point from where I started.
Now zero z on mach and my dial indicator. Use the jog function to raise z. I moved z according to mach .100" using the jog function.  The dial indicator says it moved
closer to .1125"  Repeated multiple times- same deal.

I put the dial indicator on the y axis and it moves exactly as it should. If mach says it moved .500" then we are within .0005". I checked the step per inches on y and it was perfect. The movement
between setting the steps and the jog function is the same.

All that being said I recently swapped motors, ballscrew, bearings......on the z drive. I have cut multiple 3d molds without issue-as far as i know. I'm a bit hesitant to cut a mold until I
figure out what I'm doing wrong at this point. Suffice to say I make a lot of skateboard and longboard molds and spring time isn't a good time for cnc issues. So any help would be much
appreciated. you can see my stuff on instagram if interested pushmorelongboardsLLC


Offline Tweakie.CNC

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Re: Z drive confusion
« Reply #1 on: April 19, 2016, 02:02:16 AM »
Hi Vince,

Welcome to the forum.

The fact that it used to work good but now it doesn’t is a bit suspicious.

From what you say it is my understanding that…

If you zero the Z axis DRO and your dial test indicator then MDI a command Z 0.100 the Z axis moves ~ 0.1125 but the Z axis DRO now shows 0.1000 ?

It is unusual for a Z axis to move further than commanded on the way up (assuming there is not a counter-balance system in use).

Try the same thing on the way down. Zero everything then MDI  Z -0.100. Do you still get approx. the same error between the dial test indicator and DRO ?



Offline RICH

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Re: Z drive confusion
« Reply #2 on: April 19, 2016, 06:14:36 AM »
If the steps per unit are correct the move will be correct.
Assuming that there is no skipping, then there is backlash.
Backlash can be due to  the mechanics of how the axis is installed / mounted.
You will have some backlash, but, certainly not .012" if done correctly.