Btt Skr pro Cnc homing direction
July 10, 2022 04:19AM
Looking for a expert opinion.
I am making my first cnc, and working on the setup, however, I think I may have shot myself in the foot.
My problem regards homing direction on the Y axis.
I have the Z axis homing correctly, homing with the spindle raised to the top, using Repitier host manual controls, selecting Z up and down works perfectly.

I have the X axis homing correctly, homing with the x axis moving to the left, left and right manual controls move the carriage as expected.

The problem comes with the Y axis. I had designed and made the Cnc with the Y axis endstops at the rear of the machine, thinking this would be best to get the spindle out of the way when homed. This is the first machine I have made with dual Y steppers (with Y and Y2 drivers).

The situation as it stands:

I have the Y axis homing in the right direction on both 'Y' steppers (towards the rear). Both endstops on 'Y' (Y_MIN and Y_MAX on the Skr pro) trigger as they should, however, to get the manual control to go the right way on Repitier host, I had to select invert Y in the host settings. With that done, everything appears to work perfectly, but I'm guessing when it come to running real gcode, the Y axis will be mirrored?
I thought I could resolve the issue by inverting the homing direction on Y along with inverting the step direction on Y also. However I cant get that to work. If I try and invert the homing direction for Y, it fails to compile, and complains about the endstop not being correct. I figured I may need to tell it to use Y_MAX, but that's what the Y2 axis is set to use for its endstop.

I'm just not sure how to fix it due to it having dual endstops for Y. (Y_MIN and Y_MAX) are the default endstops on the Skr pro when you enable dual Y steppers.
Is what I have done, making Y home to the rear of the machine a real problem, or just some settings I need to get right? Will it cause problems later on with setting relative work offsets?
I have tried everything I can think of. Any help would be greatly appreciated. Let me know if I need to supply further detail. Thanks in advance.

Re: Btt Skr pro Cnc homing direction
July 10, 2022 04:50AM
Doesn't matter if you home to the front or the rear. Purely a matter of convenience.

It's very easy to have a mirrored image. I can't tell if that's the case here.

I suggest going back to the Y setup that works and then testing for mirrored operation.

I've managed to confuse myself when testing for mirrored operation. I found the best way was just to do some letters to see if they are mirrored or not.
Re: Btt Skr pro Cnc homing direction
July 10, 2022 05:11AM
Thanks for your reply. The Cnc isnt fully finished yet, so I wont be able to do a real test yet. I have just been using temporary wiring to test the individual axis one at a time, obviously having two sets of temporary wiring for the (2) Y axis. I figure the Y axis must be reversed as sending the command ie. :

G91 (relative position)
Y 50

Moves the Y axis towards the front (Away from the rear endstops), when I would expect it to move rearward. As it would do if it homed at the front?

I figure, having to invert the axis in the host cant be a good thing?
Re: Btt Skr pro Cnc homing direction
July 10, 2022 05:20AM
you don't describe your Y axes enough...

Is your Y axes a bed slinger like most 3d printers, or a fixed bed in the Y direction?

If it is a bed slinger then an endstop at the back is the min Y position
If Y is fixed then a endstop at the back is a Y max position

Edited 1 time(s). Last edit at 07/10/2022 05:21AM by Dust.
Re: Btt Skr pro Cnc homing direction
July 10, 2022 05:59AM
Thanks for your reply, the bed is fixed, and the gantry moves over it.
Endstops are positioned at the rear, and the gantry moves rearward towards the endstops when is homed. Endstops work like they should. But I feel like the machine thinks it is moving forward towards endstops located at the front. Hence why I needed to invert the control direction for Y in Repitier host.
I feel the problem lies in the machine homing to Y_min and not Y_MAX, but I cant figure out the settings due to the Y_Max endstop plug already being used for the second Y endstop (Y2), it uses dual Y steppers and dual Y endstops.
Thanks for any advice.
Re: Btt Skr pro Cnc homing direction
July 10, 2022 09:13AM
Another thing I have tried, is to assign the Y2 end stop from YMAX to the XMAX endstop (The only free endstop I have left) in configuration adv. h, Hopeing that would allow me to use the YMAX endstop for the Y endstop, but this wouldn't compile either.
Re: Btt Skr pro Cnc homing direction
July 10, 2022 09:53AM
Silly me - all I had to do was watch my 3D printer.

It has a fixed bed. Positive X direction is left to right. Positive Y direction is front to back.

Non-mirrored operation is also obtained when BOTH are flipped. Positive X direction is right to left. Positive Y direction is back to front.

I don't understand your compile failures. Please attach a failing configuration & I'll see what is wrong.
Re: Btt Skr pro Cnc homing direction
July 10, 2022 07:08PM
Thanks for your interest in solving my issue. I have had many differing compile errors depending on what I tried. But this is the config where it all started, just changing the direction of homing for Y from -1 to 1 (line 1367 in Configuration.h).
As stated in my post, I figured if I changed that, along with inverting the step direction (something I achieved by changing the dip switch position on my external stepper drivers themselves) it would solve the issue, but alas it didnt.
Leaving the Y axis with a value of -1 shows no compile error, and the homing sequence works perfectly, albeit needing to invert the manual control setting in Repetier host.
I think the whole issue revolves around the fact that the Y axis should be homing to YMAX, not YMIN, however, I cant plug in the Y axis to YMAX due to YMAX being assigned to the Y2 stepper endstop. (something I have tried to fix, but to no avail).

I have tried to include a compressed version of the config as a attached file, but no matter how small I compressed it, it would not let me attach it. So I will try and attach a link to my Google drive (the first time I have tried this).
If this fails, I think I may be better off just doing what it takes to move the endstops to the front of the machine, that may just be a better option.


Kind regards

Re: Btt Skr pro Cnc homing direction
July 10, 2022 11:01PM
The compile error you're seeing is because you told it to home to Y max (changing the direction of homing for Y from -1 to 1) so Marlin assumed that Y the Y_MAX endstop would be used but you told it the second Y end stop was also Y_MAX. This confused Marlin.

Homing direction assumes that the axis direction is correct. "invert the manual control setting in Repetier host" is finally making sense to me. When you tell the machine, via Repetier host, to go positive 20 mm you're actually seeing movement in the negative direction. That means you need to invert the stepper direction. Doesn't matter if the invert is done via Marlin, the external driver or by a wiring change.

I recommend you do the following:
  1. Get the X & Y directions correct.
  2. Set the homing directions to what you want.
  3. Move the endstops as needed.
  4. Setup the config files to match.

I noticed that all your stepper drivers are set to TMC2209. Only the ones that have SPI communications should be set to TMC2209. TMC2209 without SPI communications should be set to TMC2209_STANDALONE.

You mentioned having an external driver. I suggest you set those steppers to TB6600. That's the fastest external driver supported by Marlin.

I see 7 stepper drivers defined. I thought the BTT_SKR_PRO_V1_2 only had 6 slots. I'll bet the E1 assignment is being ignored because you've set the number of extruders to zero.

I see that you're running Marlin Marlin is now up to 2.1.0. I suggest going with the newer release.
Re: Btt Skr pro Cnc homing direction
July 11, 2022 01:34AM
Thanks for your replies, I really appreciate it.
I have decided to just move the endstops to the front, and have it home there, hopefully that fixes my issue.
I am wondering if I sent you the right config, Im sure I did? but I'm unsure now. My reason for saying that is the fact you say the config showed TMC2209 drivers specified, however, the config I am working with has the drivers listed as A4988, also I only have 5 drivers specified. Strange. I really only need 4 stepper drivers, X Y Z and E0 that is used for Y2.(Just need to undefine E1 I think).
Yes, with the drivers set as A4988 the external drives would not even move, I had to force the minimum 'step' pulse time to 3ms, this started the drives working, but I will take your advice and specify the drives as TB6600, as this may also have better timings for 'Dir' timing etc, worth a try!

Thanks again for your help. Hopefully all goes well.

Kind regards

Re: Btt Skr pro Cnc homing direction
July 11, 2022 03:18AM
Update. After some investigation, I found I had sent you the wrong config. Silly me.
I took your advice and downloaded Marlin 2.1, I tried to simply copy my Configuration.h and Adv Configuration.h files to the new Marlin directory, however, when trying to compile, it came up with a whole bunch of new errors. Including saying my Configuration.h and Adv Configuration.h were outdated, and something about not needing to define dual steppers anymore. So I think at his stage I will just continue with what is working.
I figure the only way to Update to the new Marlin would be to go through and manually update the changes (Using the compare feature)? Is that how you would do it?


Re: Btt Skr pro Cnc homing direction
July 11, 2022 07:50AM
Yes, using a compare feature is how I do my updates. A pain in the rear but much better than the alternatives.

The only files we normally care about are configuration.h and configuration_adv.h . Next time just ZIP up those two and attach.

"just continue with what is working" - that's a reasonable approach.

Did you ever get X, Y & Z moving in the direction Repetier Host thinks they should be moving?
Re: Btt Skr pro Cnc homing direction
July 20, 2022 10:39PM
Thanks for your help.
Haven't done that much on my machine over the last few days. Back into it today!
Yes, success! I moved the endstops to the front of the machine, and everything is now working as expected. I have been teaching myself the workflow for a cnc, as I have only had previous experience working with 3d printers, and although similar, there are some differences, as Im sure you are aware. I even managed to attach a pen to the machine, and draw some things. So all in all I'm happy with progress.
Thanks again for your help.
I have another issue (a minor one) Im trying to sort now. It involves getting my neopixels going correctly. They are the RGBW type, and I can only get the RGB working, no luck so far with the White led. However, I'm going to start a new topic, as I think that is the right way to go about it.
Hope your day is going well.


Re: Btt Skr pro Cnc homing direction
July 20, 2022 11:00PM
Great news!

Yes, a new topic is best for the neopixel problem.
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