Z Feed Rate Overriding Max Feed Rate at Start of Print

RepRap Community,

Working on a reprap that has been out of commission for around a year. People have poked it, tried to get it to run, but to no avail.

The issue is when a print starts, the part homes then starts printing. I press the home button in Pronterface and there is no issue. When I start a print, however, the part homes X and Y, then does Z. When it touches the Z end stop, the Z motors then squeal to move up, then squeal to move down.

I have decreased the max acceleration and feed rates for the Z down to 50 mm/s^2 and 5mm/s to no avail. The motors will still go to a speed faster than the max feed rates.
One experiment I found was that if the steps/mm was reduced to half rate (6400/1.25 steps/mm to 3200/1.25 steps/mm), the motor did not have an issue. It did move extremely fast in Z home section where the motors squeal, but obviously I cannot have the steps/mm wrong.

Anyone know where I can change the Z feed rate in the homing command? Or where the homing command is located?

I took the old firmware, tested it, downloaded the new firmware, tested that, transferred over steps/mm constants, and did a few other tests and bug fixes to get this thing to work, but I can't crack this bug. This same software is on 4 other printers that work without issue. This printer is unique in this bug, and has been left to rot in the corner as a result. I want this thing to live and do its job.

EDIT: I also got new drivers for it today. No change.

Edited 1 time(s). Last edit at 05/24/2014 09:18PM by BlenderGuy.

It should be as simple as adjusting the homing feedrate, which is on line 479 of configuration.h in current Marlin.

Thank you! Changed! I will be able to get an update on the reprap tonight.

Alas, no. That was not the issue.

Looking at it closer, this is what happens:

1. Home X
2. Home Y
3. Home Z (this is doing as is expected)
4. Move up in Z rapidly (And buzzing)
5. Move down Z to the first layer height rapidly (and buzzing)

When it is doing the rapid motion, it moves quickly, then buzzes. This does not move consistently, so it sometimes slams into the table or prints in air.
So it is something else. I will be looking through the config files again

Edited 1 time(s). Last edit at 05/25/2014 05:23PM by BlenderGuy.

In other news, I was working on another printer from the grave. I couldn't find the firmware, and all I needed to do was change the extruder constant (got a new extruder setup). So, unable to find the old firmware, I used a brand new Marlin. Same issue as above.

I will be trying to use Sprinter instead of Marlin. I will report what I find.

So Sprinter works fine. Just Marlin. The crux of the problem is the guy who officially owns the printer wants to put a screen on the machine, so he wants Marlin.

Anyone know what that last Up/Down that occurs after Home when a print starts is called? I don't know how to search for the term.

You can set the home retract distance in configuration_adv.h , but there's no option for home retract speed.

Home retract distance is something different. It tells the system to touch the Z end stop, move up a distance (1mm), then touch the end stop again. That is not where the issue is occurring.

What happens is the printer homes the X, the Y, then the Z. After that, the carriage is moved in the Z, a short amount of plastic is retracted by the nozzle, then the carriage is lowered to the first layer height (0.35mm). After that, the machine moves to the starting location.

The issue is the second part, after homing, where the carriage moves up and down. That section is where the feed rate is too high. I do not know what that feed rate is. I do know that if I reduce the steps/mm to half of what it is, the motors move very quickly in that section, but then the rate is wrong for the rest of the print. I do know that this occurs on two separate systems using the same, brand new downloaded and old versions, of Marlin. With Sprinter, the system does this same motion, but slower and does not have an issue. I would like to use Marlin on this system as we desire to have a screen on the machine, something Sprinter cannot do.

I did get the second printer printing with Sprinter, but there is some odd extruder feed rate issue. It takes a long time to extrude filament, despite changing the constants to 10x the original feed rate for E. I boosted it from 30 to 300 with no change, but that is a different issue that I don't want to get into here.

It sounds like it is the acceleration values and the Z jerk settings. Try using the numbers that worked from sprinter in Marlin. The defaults in Marlin are for an Ultimaker.

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I found recently the VIKI lcd control overrides whats in the firmware settings for steps per mm. Maybe this is the case for accelerations too? Do you have a LCD controller? There are lots of settings in the VIKI controller

I found a solution, but I still don't know why it did what it did, and I don't like the solution. I decreased the max frequency to 12500 on one printer, and 22500 on another and that is working. I brought it to the maximum frequency the motors could handle in that post-home Z motion. This does cause issues with the extrusion feed rate: the extrusion feed rate is limited by this. However, it does print moderately well.

It is a really patchy solution.

I do not have an LCD controller on the board, but there is one in a cupboard. It is a future plan... I know, added complexity.

found a slight solution. In Sli3er, the extra G commands in the end tell the system to move to Z5, extrude a bit, then start printing. I reduced this to 1mm, and I could increase the extrusion rate.

It is a patch solution. Not the type of solution I wanted though.