Z axis creeping down / loosing steps on a Taig Micromill 2000 with Mach 3

Hi everyone, I just started having a new problem: as my progam is run, I notticed that the cutter cuts deeper and deeper. Attaching a dial indicator and then jogging the z-axis up and then down 0.125" inches results in the head moving further and further down (between 5 ten-thousands and a mill each time). I tried changing the acceleration on the motor from 7.5 in/s^2 to 1in/s^2 and then 10 in/s^2 but it didn't seem to make a difference. Any advice what to check? I have a Taig Micromill 2000 being run by Mach 3. Thanks,

John

Sounds like you have already checked your motor tuning. Might want to have a look at the motor belt and teeth on the belt. You cold also switch axis motor cacble reassign axis and test for accuracy issue.

Are you sure it's not a mechanical problem? Often problems like that are caused by a coupler slipping, due to a loose setscrew (Taigs are direct-drive, so it's not a timing belt or pulley issue). Are you using the stock Taig controller or something else? If it's all Taig's system, you can get them to walk you through a diagnostic process over the phone.

Continuing on the mechanical theme. How often do you use the machine and when was it last stripped and cleaned? With the standard Taig spindle there is a lot of weight on the brass nut so it does ware more than the X and Y and while backlash may be less of a problem with the weight holding things down, it can mask other problems if the vertical slide is sticking.

Like Lester implies above, if it's not slippage of some sort, another cause of a tool cutting progressively deeper is the Z axis losing steps as it tries to move up. When that happens, it thinks it's higher than it really is, so when it goes down again it plunges further than it should. Lack of lubrication, gunk in the slides or screws, or burs on sliding parts can make it too hard for the motor to turn, so steps are lost.

Thanks again everyone for your advice! I took apart the axis, adjusted the gib (slightly loose), checked set screws, and cleaned everything, but haven't really found anything wrong. How do I know if the half nut needs tightened? The machine is used a few hours a week for the past 4 years, most of which has been spent trying to run down all the gremlins. :tired: I agree with Awerby, seems like it just looses a step or two each time...

Have you tried running it since stripping it down, cleaning and reassembling it? Sometimes those gremlins just need a little attention...

What kind of lubrication are you using? The adjustable nut is tightened every once in a while to compensate for wear, but that's not likely to be your problem with the amount of use you're giving it.

You might try increasing the pulse width, if all that TLC doesn't seem to be helping. That can give the motors a little more time to respond, which might do the trick.

Actually, just got it all back together and the problem went away... Not sure what I did that helped though (chair). I've often wondered about the pulse width - the manual recommended a pulse of 2 and dirpulse of 0. I'll try setting them both to 5 if it can't hurt, or should I only change the pulse and leav dirpulse at 0? Thanks again!

John

if you don't have an oscope, set mach3 for sherline 1/2 pulse mode

i ran into a similar problem.. basically not all parallel port drivers are created equal.

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Originally Posted by littleCNCjohn

Actually, just got it all back together and the problem went away... Not sure what I did that helped though (chair). I've often wondered about the pulse width - the manual recommended a pulse of 2 and dirpulse of 0. I'll try setting them both to 5 if it can't hurt, or should I only change the pulse and leav dirpulse at 0? Thanks again!
John

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As Eldon_Joh says ... if you have had a niggle from day one it may be down to the parallel port, and a wider pulse will not hurt since it should be 10 !
taig-jams-when-rapid-traveling

Oh, I have it on sherline 1/2 pulse. Do you use a pulse of 10? Keep dirpulse = 0 since it's not used by Taig, right?

John

Quote:

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Originally Posted by littleCNCjohn

Oh, I have it on sherline 1/2 pulse. Do you use a pulse of 10? Keep dirpulse = 0 since it's not used by Taig, right?
John

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I've always used '10' with the open loop Taig controllers, and 0 for the DIR setting as you don't want to delay it changing state. On the normal mode .. i.e not using the sherline fix.

Polarity of the step pulse sometimes makes a difference with some controllers.