need help with z axis

I have a I3X, which is a cheaper version of the I3. I have made over 50 really nice prints. Anyway when my Z axis rapids it grinds. This is a new problem, and just started yesterday.
when I jog the axis (with a settings/options z axis of 200) in pronterface Z move nice and quiet. If I kick that setting up to 300, they growl and I can actually see one stepper stop spinning. But its not always the same stepper.
I took the axis apart, and it glides smooth as silk. I also changed the stepstick, but nothing is fixing this except slowing it down.

Questions:
Why all of a sudden is it doing it now?
Where is the max federate for Z axis? (although I shouldn't need to change it, it has always worked before)

Any suggestions would be much appreciated.

Edited 1 time(s). Last edit at 12/11/2013 10:30PM by makovai.

Have you tried changing the stepstick current level? I'm not sure the one hour using, but the pololu driver has a trimpot on it that allows setting of the current level. Perhaps yours is set a bit too low.

To answer your question, the max feed rate is in configuration.h, but you can also interrogate the running software with the M503 command to see all settings. Further you can change the feed rate to try a few different values with the M203 command.

I have pretty much ruled out the step stick. I cranked the current up to where they got really hot when they were on, and same thing. It has somthing to do with the speed. Although the speed doesn't make sense as this is a new problem and i have been printing at this speed for months.

Max feed rate on the Z axis on a normal i3 is in the 4 or so mm/second range. It's limited by the numbers in your firmware if you try to go a lot faster.

Have you cleaned and oiled your Z axis rods lately?

Have you checked your Z axis nuts to be sure they are seated?

Is there anything restricting your Z axis thread rods from moving around (they need to swing a bit)?

Is your left Z axis down from your right Z axis (has one of them slipped)? Put another way - has your bed level changed?

I tore that axis apart twice. It is amazingly free moving and screws very easily. I put an indicator on the axis and when i jog it, it travels right on the money.
I really, really believe this is an electrical or software issue and not mechanical. But ive seen stranger things in my day. Im open to anything at this point.


However i will say the first time i tore it apart one of the z axis motors was loose on the bracket. I was sure tightening it up was going to solve my problem, but it didn't.



I was just thinking, tonight when i get home, Im going to pull both motors off the machine and try a full rapid with no load, that way i take any mechanical issues out of the loop.
That should tell me alot.

Edited 2 time(s). Last edit at 12/12/2013 02:33PM by makovai.

So I came home and disconnected the entire z axis leadscrews and clamped the z axis to the top of the printer.

The motors growl with nothing hooked to them. (In rapid only)
I then tried cranking the stepstick prox switch and it did seem like it lightened up the growl but then I crank it so high the motors wouldn't move at all, they just buzzed.

I have a Sang board, I think I will start changing axis's around and see if the problem follows the driver or the motors. I'm running out of ideas.

2 hours later. I went to start switching my axis's when I noticed my fan for the mb was still running even with the power supply switched off. I tried a search on older threads in this forum because I know I read somewhere that is a problem with PS somewhere.
I cant find anything about it now.

Edited 3 time(s). Last edit at 12/13/2013 06:29PM by makovai.

If you have a 12V fan and a 12V power supply and the fan runs with the power supply off, the power supply isn't off. It may be that it holds charge for a while, it also may not be responding to your switch.

Swapping around cables with the power still on is a good way to blow things out.....a cheap voltmeter is a lot less expensive than replacing just about any piece of your printer.

Edited 1 time(s). Last edit at 12/13/2013 08:22PM by uncle_bob.

Well i'm not 100% positive but I talked to my electronics teacher tonight and he said when a stepper motor gets older it loses its torque and higher feed rates are not obtainable anymore.
I change the M203 in the entry code to Z3.8 and it seems to be doing a lot better. (thanks for the idea jbernardis and uncle bob)
I ordered more steppers so hopefully I just have worn out motors.
I was kinda surprised they are going out after 100 hours or so, but what do you want for $10-$15 each.

When I get new motors ill swap out so I can end this thread and hopefully it will be a benefit to someone else in the future.

I've designed steppers into applications where they are used for hours a day / 365 days a year. They don't seem to slow down. The bearings wear out eventually. I know of no physics that would back up an electrical wear out on them. As far as I can tell, the $15 steppers we put on these printers are not a lot different than the stuff I've worked with in the past.