how to keep Z motor active when done?

So i learned the hard way that i need to be near the machine when its done to turn the spindle OFF.
I had a V-bit doing a pattern on some wood and when it finished the Z axis slowly vibrated downwards towards the table and work peice…
In the mean time i was outside helping a friend with some mechanical issues on his car. I go to show him my MPCNC and its sitting there happily drilling a hole in the waiste board and table like a dog proud of tearing up your brand new couch.

What i really should do if there is no easier option is to attach a relay to the controlled fan pins and use that to switch the motor on/off.
but lets look into keeping the Z active first since its a free option.
i looked at the post P and didnt find anything that would switch it off like it does for tool change (to which i disabled that for the same reason… not to mention i do my tool changes diffrently and if the z moves then it screws more stuff up.)

Thanks in advance for any help.

They should stay active for 6 minutes. The setting is found in config_adv.h

Ah i found it thanks Ryan!

I just changed Line 362#define DISABLE_INACTIVE_Z true to (false).
If i need to disable it i can just use my lcd controls instead of risking further destruction. lol
I need to order a relay to try to make the spindle auto off/on. That would be so much better…

You really really should not stray from the machine. There is a very recent machine fire video on youtube, he almost lots his house. There have been many close calls, please do not automate this.

Thats a good point, but…
Since the spindle keeps going even when its done and if by chance its still in the wood it would shut off and stop creating heat from friction when its automated.
So far my programs have been 30min or less as im just doing a small project right now. i dont have much time since i work 12hr/7day now, so it wouldnt sit there and burn the wood for hours if by chance something goes wrong or if the program finished and it vibrated down into the wood and started a fire that way.
Also my spindle wont slide down out of the holder mid program since it has bottom support.

Additionally we could use a sensor/endstop to detect if its bottomed out in the wood and turn off.

I think the size of my v-bit and the hole it made prevented the collet nut from friction heating the wood. So i guess thats a good thing.

what do you think about using the auto on/off as a safty measure and require people to stick around just in case?

The problem is not really the safety once the job is done, it is mostly the safety while the job is being done. You never know what can go wrong, you might have made a mistake while creating the paths, a stepper could miss steps, there can be a hard spot in your wood plank, anything can happen.

It takes about 2-3 seconds for things to catch fire, and because there is lots of fine dust the fire can spread extremely fast, even create an explosion if the room is small and the air already filled with dust.

Really, NEVER let your CNC milling stuff when you are not around.

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I guess thats true.
besides my z axis wobbles and deflects so much i dont like leaving it for long anyway. I’m about to throw it in the garbage…
I’ve wasted so much wood and time in the last 2 days because of it. its rare for me to even get a day off to work on it.
The frame for X,Y is as sturdy as a rock, but Z isnt at all. I dont know how to support it better.

Why would you throw it away, it should work perfectly fine. The point is just to never let any CNC machine unattended, even an expensive machine like a Tormach or any CNC machine you could think of.

What problem do you have exactly with your Z axis? Can you provide pictures so we can help you to fix it?

It usually takes a bit of time to get things right, but trust us, it will work fine eventually. :slight_smile:

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I was joking about throwing it out but i was pretty frustrated.
I definitely would never start a program and drive off somewhere or go to sleep when working with wood.
I’m usually close enough to hear the machine running if I do leave to go to the bathroom or kitchen.

The first pic is last 2 failures do to wobble and one decent one which was the 4th attempt the rest didn’t go so well.
1st one is just awful… it wobbled so much.
2nd one started fine in the lower right corner. the move towards the top and went deeper and wobbled.
3rd is best I have so far, but I’d like to to be a little deeper so the rest of my attempts ended in failure so far. I probably didn’t wobble on this one due to the fact it wasn’t cutting much material.
i need at least 2 of these to be good…

feed rate is 100mm/m, spindle speed is unknown. any faster on feed rate and the wobble is exponentially worse.

the second pic is all my scrap except the 2 already shown above.
1st was my bad the tool was loose. it wobbled and flew out…
2nd one went fine until a chamfer attempted. it wobbled and blew it bigger than needed. fixed by using the screws to do the chamfer instead.
3rd was fine until program error made it do a second deeper pass but surprisingly didn’t wobble. (3rd attempt)
4th misalignment when flipping, my bad. fixed. (5th attempt)
5th as seen in the first post. (6th attempt)
6th i got distracted and let the spindle drop… it gave me an unplaned corner bevel. should be fixed by keeping the z active same as #5.

also have a problem with bed leveling apparently. my second decent one has the pattern fade on one side. (not in pics)
i have 2 left and ready for the pattern but after those fail i have to buy more wood… I’m hesitant on trying it again…
the wood is cheap though.

I have heat shrink tube for the XY pipes that support the carrage but im afraid it might make it too tight. so i havent tried that as a fix yet. but it does seem that the bearings dont have enough hold on the pipes.

Well now we are in different territory.

Lets see a complete picture of your machine. What board, what parts, what firmware, What cam (better yet upload your gcode), what spindle? You are using a router bit, endmills work better. Heat shrink will not work and is not needed. The other thing, if you printed your parts can you verify it prints dimensionally accurate (do a 100mm calibration print from thiniverse), three people lately have popped up with poorly printed parts and it has completely frustrated them…same scenario, asking how to make it tighter, the parts are an interference fit they should actually seem too tight.

Lots of info please.

Can you use my crown gcode and upload a picture.

To give you an idea that part should 100% have no issues what so ever to engrave in 2-3min and another 2-3 to completely cut it out. Last night I was carving my logo into Ipe at with a V-bit from the shop at 3mm deep absolutely no issues at 10mm/s full depth.

Yes, we are, sorry for a topic change. I don’t think changing that line of code helped keep the z active at all. it still drifts down with the spindle on.
Also thanks for your help again. I finally had time today to work on my MPCNC and 3d printer after my guest left.

Spindle: 53mm 500w spindle motor w/er11 adapter.
Control Board: Ramps MKS base v1.4. (planning on getting a duet wifi later)
Firmware: Marlin MPCNC813 GLCD T8. I had to half the steps per unit for each axis or it would go the double distance.
Cad/Cam: Auto desk Fusion 360 with mpcnc post processor. (some personal edits for my sanity)
I did not see an endmill Vbit so I got a router bit.
I got the heat shrink because when I torque the spindle on one axis the carriage moves slightly and I can freely spin a bearing by hand.
it seemed loose but I have not put the heat shrink on it.

I cant find the “100mm calibration print” you’re referring to. but I did print and spray paint my own parts.
I used “100mm calibration block” I has 100mm on xy as well as a 20mm block with a 10mm hole 5mm tall.
X = 99.75, Y 99.76, Z 5.05/5mm, and the hole is 9.91mm. Not extremely accurate but close.
for a 90° angle its actually 91° or my cheap plastic protractor is crap. I’ve tried to adjust the printer for days to be square but nothing works.

I tried the crown with a 1/8 flat endmill and the vbit.
the endmill wobbled so much I was ready to kill the power if it went too crazy.
vbit cut smoothly but there is clear evidence of tool deflection.

I included a pic of my crude but working stepper motor splitter board just because I think its unusual.

1003-Keymod-Panel-P2-1.gcode (10.2 KB)

Are you sure you are spinning spindle in the correct direction? Looks pretty bad, something is wrong for sure.

The gcode is odd, it is missing feedrates in what seems like random lines.

Steppers in series or parallel?


It’s spinning clockwise which at very low rpm looks correct. the cutting edge would be leading into the material.
I believe the steppers are parallel. i don’t have them wired directly from one to the other.
The wire goes from the controller board and splits off from my splitter board to each stepper individually.
I rewired the steppers myself with an 18/4 cable, because they were originally quite short and separate mess of unbound wire.
they sound fine when running and not missing steps. I need to permanently attach everything to the table when i get more filament to print a box.
My belt has 5 steel wires inside so belt stretching is near impossible. The tension seems okay not sure.

here is a video showing the wobble when pulled with around 5-8lbs of force.



Series will be better but does not matter for now.


These will fail prematurely, that is why we don’t use them. They can not handle repeated tight bends. May or may not be contributing to the issue. Your pictures do not show the ends of your belt to judge tension, but if they are too loose they could be adding to the issue as well. Too tight and you will skip steps.


That is because you have a really tall build. Definitely contributing to the issue. 2-4"…primo, every time you half the length of any of the parts you double the rigidity. Extra braced legs…there are already 4 of them, the part that suffers the most is the Z axis, no way to brace that. The longer it is the more it flexes the XYZ parts.


Did you use PLA for the XYZ parts? All other materials are more flexible (that is why people say they are “stronger” they flex instead of breaking). We desire rigidity in our parts not flexibility. I ask because I think all of this individually isn’t usually a problem, add too many up and then you get issues.

This could all be adding to make up the issue but plenty of people have had no issue at that size. Make sure your gantry is build well, and all the bearings are making solid contact.

Just to make an observation. The flat endmill that made the crown while removing much much more material looks completely better than the vbit. Try raising your material up on blocks as close as you can get it to the gantry and try a proper cut with the regular endmill.

Use estlcam to make the gcode as your gcode above is incorrect.

Another thing to try is raise up your spindle until the collet is flush with the end of the rails, only the endmill needs to stick out. Every bit shorter helps.


If you have done much wrenching in your life think Breaker bar, the longer it is the more force you can break loose. The further your cutting tip is away from the crossover point of the gantry tubes, the less force it can exert on the material, like holding a new pencil at the eraser end and trying to sign your name.

My Z is 200mm I thought that wouldn’t be too high when planning. I can cut it down not sure I would ever use that height for milling actually. I probably over estimated there…
I found about a 0.5mm gap with the bottom bearing on the Y axis on large black XY part towards the front. that lets it wobble a bit more than the x-axis. Not sure what can be done about that. the pipe is 23.5 and I printed the correct version for it. I tried doing something about it but it didn’t help much. even if I cut it down or moved things up or down that would still be an issue I need to solve first.

yes, it’s in PLA I cant print ABS very well my bed temp cant reach the recommended temp for it so everything warps badly.
I’m not sure what another filament to try that prints as easy as PLA.

I don’t have much time to mess around with it today I have to work for the next 12hr.
I might have an hour or two when I get back.

This is in the FAQ’s page. This is by far the most common issue. Take the center apart and rebuild it. Everything is an interference fit, if they are not touching you have some improperly tensioned bolts. All the assemblies should should actually seem a bit too tight for the rails, never ever loose. You verified your printers dimensions. So just rebuild it paying close attention to keeping all the tension bolts as loose as possible and the others ever so slightly snugged as stated in the directions. We worked this whole problem backwards, took the long way to the actual problem.


I think my comment was unclear. PLA is correct. Don’t change it.



“We worked this whole problem backwards, took the long way to the actual problem.”
I deserve that for not reading the direction… the assembly was easy to figure out but with apparent small things to miss.
I’m sorry for wasting your time like that…

I’ll take it apart and reassemble it when I have time.
Thanks for the assistance.