Help for those with z/x/y axis stalling

[xaruum]

Hello,

I have read through many posts over the years and have seen the many threads on axis stalling at random using 100-200 oz/in steppers but never ran into the problem until recently.

What I found is that the brass gibb's will flex if the adjusting screws are tightened beyond about 2 pounds of torque.

I have not read about this in any post, so I thought I would post up in order to help others.

I happened to find this by accident, My z was chattering as the unit got older, and it recently wouldn't lift or plunge even at velocity/accel 1/1. So I took the entire unit apart to clean/inspect/lube and found that my z nut was actually an older model brass split nut rather than the adjustable bronze nut. I got the newer nut and re-assembled the unit to "hand-tight" all around.

Everything seemed fine when moving the axis by hand, but then I snugged everything a little tighter to do stepper motor tuning. Every axis was stalling at about 10/2.5, The y axis was the easiest because of it's design, the gibb is pushed against the way, so I backed it off about 1/16th turn on each screw and it will now do 40/8.

No matter what I tried though, x and z were a mess, if I tried a simple surfacing routine both of them would stop after 30-40 lines even at the 10/2.5 rates. So after several hours of trial and error I disassembled the x and inspected everything a second time. I tried tightening the gibb adjustment screws without the axis installed on the hunch that they were slipping. What I noticed instead was that the brass wedge actually flexed out away from the saddle towards way of the table, even using just 2 fingers to tighten the adjustment screws.

So, I re-assembled the x and and played around with various levels of torque and velocity/accell settings, and found that I can get play down to .001" at 8 inches and still run x at 40/8.

I adjusted the screws on the z gibb to the same level and got deflection on the head stock down to .0005 and still run at 25/5.

This is using 269oz pac sci steppers on a 5 year old xylotex controller.

Your mileage may vary, but I found this worked for my taig.

[lsces]

The other thing that I have been wondering about in this equation is how long these stepper motors will last for? The magnets are going to get softer over time, and so how much of the stalling is due simply to the motors not now being up to the job?

[xaruum]

I don't have any precise info about the reliability of steppers as they age.

I do know motors in general will go out of spec much more quickly when they are run at high temperatures. My brushless dc motors ( akin to ac 3 phase ) are only good up to about 200f before the magnets will begin to lose strength or degauss.

I have never measured the temp on my steppers, but they do get to hot to touch after an hour of surfacing. I would theorize that over the past 5 years they probably have lost up to 30% of their rated power. I say this because I can grab a lead screw and hold tight and the stepper will stall. ( please note - I do not recommend this practice - this just happens sometimes when I clean the lead screws )

I should probably invest in new steppers, and a new controller, but money is tight right now.