Struggling to cut MDF ... Insights needed

LowRider CNC Advice
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Hi guys !

I’m a bit ashmed, but irritated enough, to ask for help :slight_smile:
I know, i know, the matter has been discussed before, i searched but it didn’t help my cause …
I may be stupid enough to have missed the whole point though !

So, my machine :
LR3, SKR 1.3 with 2209 drivers
Nema 17 steppers, 84 OZ/in, 2A
Makita router, speed 3 (approx 17k rpm)
1/4" single flute upcut bit

Changed a few parts in the firmware, mainly increasing motor current from 900 to 1200 mA.

So, here is my situation :
I’m trying to make myself a new subwoofer, and cut all the panels with the LR3.
This includes large round shapes, for speaker. And those suckers always fails !

Of course I did a lot of basic testing, and everything seems to work great, with different settings.
But then I try to cut this fucking round, and it fails every - single - goddamn - time.

Settings used :
3mm DOC, 1000mm/min - failed
3mm DOC, 650mm/min - failed
6mm DOC, 500mm/min - failed

I know i could go slower, but according to the feedbacks i read here, i should be able to make these cuts easily ! I appear to be on the safe side, and yet it fails every time.
What fails ? It skips steps on the Y axis ! Every time, the same Y axis.

So, I’m lost, irritated, and on the edge of giving up and just doing it by hand …

Could it be my cheap endmill ? (I’m in Europe, i sourced it from Aliexpress to avoid US import taxes)
Could it be machine related ?
Could it be speed / DOC related ?
What am i doing wrong ?

The outcome will probably be laughable, but after all I have done to make it work (changing motors, changing gears, changing firmware, doing numerous tests), i feel totally lost and have no idea what else to look for.

Many thanks guys, as always :smiley:

Laurent

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So I’m trying to picture the specific case scenario while I’m assembling mine, while you wait for someone “knowledgeable” to help you. Making sure I’m understanding the exact situation.

Are you saying it cuts the parameter of the subwoofer side panel (a square I’m assuming) just fine, but isn’t cutting a circle, with the same settings? Or it’s failing on and all MDF cuts? And more specifically skipping steps when cutting MDF, on all Y movements?

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Yeah, more or less ! :slight_smile:
I can’t say for sure “it only fails doing circles”, but i’ve done numerous test before with much more luck !
I tried squares, i tried V1 logo, all went well.
Nice and crisp, 0.1mm tolerance, amazing finish.
I try to cut the round hole in my sub, 100mm in and it fails … :crazy_face:

According to my test sheet here, i even did a V1 logo with 6mm DOC and 1000mm/min without any issue !
Tried the round with those settings, failed almost instantly … Tried reducing speed, then DOC, and reducing again, and again … and, oh god, go to hell :face_exhaling:

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Can you share a picture showing the failure?

Are you getting clean cuts before it fails?

Is Y axis the double axis on your machine?

I agree with you. This should be doing great at those settings. Especially 3mm DOC and 10mm/s.

My first question is how is it failing. The pic might have spme insights.

Some thing I would be most suspect of:

  • Are the grub screws on the pulleys tight? Slipping on the motor shaft is a common issue
  • Are the bits burning? Bits are a very important part of the machine. Finding a good 1/8" bit for starting is really helpful. They need to have the right geometry, be sharp, and be hardened for CNC. How many flutes do yours have?
  • It could be an intermittent wiring issue. These are hard to debug. Running M122 after a failure could give you the ola olb feedback from the TMC drivers. Those flags are only right when the motors are engaged, and after a failure though.

If I can only do one thing, it is tell you that you’re not crazy. This should be working better than it is. Whatever is wrong will get fixed and you will be making a ton of projects soon. You don’t have to be an expert to get this to run, and it looks like you’re already being very detail oriented in your progress so far. You’ll get there.

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Honestly use an old piece and see if slow fixes it or still happens. All steppers and drivers are the same correct? Grub screws seem most likely. Did you draw crown? Does drawing work?

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This should be easily doable, I’d have said grub screw as well. :smile:

Good endmills can be bought from www.sorotec.de, depending on where you are exactly in Europe.

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Might not be the problem, but just asking… what are gou using for CAM?

It may be that something is derping on arcs (G02/G03 commands) if you aren’t having trouble with straight lines. In Estlcam, you can tell it not to use those, and I think other CAM packages as well. It will instead change the arc commands to many short straight line segments. You probably won’t see a difference, actually. The gcode file gets a bit bigger, but there will be enough of the short segments to keep circles round.

It may be worth a try.

Aside from that, like others have said… pictures often help with diagnosis.

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900 mA is high and 1200 seems real high. Are your motors getting really hot?

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I can feel your pain. Try this: regenerate the gcode so that the toolpath is moving in a direction opposite the direction of the bit rotation. So if the bit is rotating clockwise, the circle will be cut in a counterclockwise direction. I did this on my lr3 and all the cuts came out much smoother.

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In estlcam, you can select conventional vs climb milling and it will switch direction.

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Jeez ! Wasn’t expecting so many answers; thanks guys :smiley:
I was away for work, excuse my lack of reactivity.

I’ll try and answer everyone in order; but first I have to correct myself, I wrote Y axis, but it’s in the X axis :sweat_smile:
I use my CNC on it’s side, and tend to mix the two …

@jeffeb3,

  • I will take a picture tomorrow !
  • Clean cuts all the way; i had trouble in the beginning, but now it’s all sorted out and looks amazing.
  • Y axis is double, but as I just corrected it’s not this one who’s at cause :sweat_smile: and X axis isn’t double … of course …
  • Regarding pulleys, I will double check tomorrow, but I don’t think so; I had the issue before, replaced the motors, pulleys were tights, and the issue is still there now, in the same way as before.
  • Bits looks really good; I burned my first one, by going to slow and spinning way too fast. Throw it away, adjusted settings, now it lasts and stays good. But as for the quality of it … Can’t be sure, it’s a “reputed” seller on Aliexpress, but god knows the quality of it.
    I’ll probably order some new from a “real” seller in Europe !
    I’m using only one-flute upcut bits, 4 and 6mm (5/32" and 1/4").
  • M122 ?! Never heard of it. Will take a look into it, as I have no idea on how I’m supposed to handle it.

Thanks for the kind message and help ! I’m not letting it down.

@RockinRiley,

  • all motors are the same, bought brand new last month.
  • crown drawn, I actually draw a lot of things and it all went well. I even machined a few part with no noticeable issue.

@Tokoloshe,

  • Definitely going to check grub screws !
  • And thanks for sorotec, never heard of it. I’m from Belgium, but buying in Germany shouldn’t be an issue.

@ SupraGuy,
Damn, that’s an interesting opinion ! I’m using Fusion, but have no idea how the pp handles the arcs part. Will take a look.

@ DougJoseph,
900mA is stock value, straight for firmware … I looked around here, to see what’s the recommended value, and from what i saw 1200 mA seemed acceptable; some even going higher than that.
But I have to confess, I didn’t checked for the motor temps ! That’s … a valid point … I’m definitely gonna check !
Should I check them under load ? Or can I simulate work (in free air) and check ?

@ Autonomous and @ jeffeb3, I did try it at some point. Switched from conventional to climb, didn’t saw much of a improvement, but rememberd Ryan recommending conventional for the noobs like me.
So, I went back.

Again, thanks for the help guys !
It’s very much appreciated ! :grin:

[edit] Can’t mention more than 3 peoples … Damn it. :grimacing:

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The TMC drivers can get too hot. If they do. They will drop the current setting automatically. So you need to be keeping an eye on it if you are craving it up. 1200 is much higher than 900. Something like 950 or 1000 can be enough to see a big improvement.

If you connect repetier host or cncjs from a computer at 250000 baud rate, you can send M122 that prints out a big report about the motors. Including their current current setting and any records of over temp warnings, open loop warnings, or shorts to ground warnings. There are stall guard threshold things you can ignore. It uses a lot of acronyms.

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I had a stepper motor (on short axis, aka X axis for most users) get hot enough to soften its PLA motor mount and saw significant warping. I was using stock settings at that point I think. It was when my LowRider was still a version 2.

I’m not an expert on the steppers (other guys here on the forum are much more knowledgeable), but it’a my understanding that just engaging the motors is enough, however, time is a factor. Leaving them engaged for a longer period and then checking, is probably a better test.

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I would go a bit slower, 10mm/s, to start with a 1/4". 1/8" is a better way to get your feet wet honestly. It can rip way faster but we need to get a working cut before it gets put to real work.

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Slow down the RPM even slower.

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Guys, guys, guys !
It’s working :crazy_face: :heart_eyes:

You have no idea how thrilled and grateful I am right now …
After all the issues I’ve had with the machine, finally being to let it work, come here and type this message is so damn satisfying :grin: Because, yes, it’s working next to me as I’m writing
And it looks SO good.

But now, update and answer to everyone who helped me here !

@jeffeb3 I did some pictures, which speaks for themselves :
https://imgur.com/a/vUIFqV2

Regarding the current, I heard your advice and lowered it to 1000 mA. I had no idea it had such a big impact.
Then, I dismantled the X axis motor to look at the grubscrew.
And … Yeah … Of course, you were right (as @ Tokoloshe), it was the screw !
I had no idea it could fail. It had turned on the shaft, made marks in it, it was pretty bad …
All cleaned, red loctite this time, tighten as hell, put back together.

And it woooorks :heart_eyes:

@DougJoseph
Damn ! That’s definitely too hot :flushed:
Mine’s been working for the last hour or so, and the motors gets barely hot; feels like 35-38°c.
I can’t check the stepper, will get my IR thermometer here quickly to check them.

@vicious1
I’d like to use 1/8 instead of 1/4, but didn’t find (so far) a bit long enough to cut through my 22mm MDF boards.
I found a 40mm one, but it’s too dangerous to even try.
I’ll end up ordering bits from Sorotec, they might have something that fits the bill !

And regarding the RPM’s, if i try to go below 3, my whole router starts to shake when cutting … I suppose it’s too slow, or my bit isn’t sharp enough ?

Anyway, i cut a few panels this morning, everything went perfectly with those settings :

6mm single flute upcut bit
600mm/min or 10mm/sec
4mm DOC

What would be the next step to test ? Incresing DOC, or rather speed ?

Again, I want to thank all of you, for helping me sorting this out ! It has been amazing to get such precious help. It wasn’t that complicated, but I felt so powerless and was ready to give up … So, you saved me on this one :grin:

Cheers guys !
Laurent

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Speed first. DOC adds way more load and speed is, in my opinion, the easier variable. :slight_smile: With a 6mm you can go pretty fast, depending on the RPM.

See here (It’s a 6mm 2-flute though!):

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Great to hear! Glad you have success! :+1::blush:

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Plus it’s easier and safer to test…
Just put the feedrate to something like 1000mm/min and then adjust the speed during the cut using “feed rate”
No need to re-generate the gcode each time…

When you it the limit, just add 1mm to the DOC and re-iterate until you find a good middle point

6mm DOC per pass @ 2000mm/min?! That’s sick!
Currently I’m using 1500mm/min at 2.5mm DOC (with a single flute 3.175mm bit though)

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Not normally doing this, but didn’t have any time so it had to go quickly. :smiley:

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