Vertical cuts not straight

[difalkner]

I've noticed I sometimes get stair steps in what should be straight walled vertical cuts.  This is using 2D Contour for the toolpath.  I am not certain if I get it from other profiles.  Feed is 100 ipm, 18k rpm spindle, 1/4" downcut spiral bit, everything seems to be tight on the machine which is a very rigid welded frame 2x4 CNC router.  Ideas?

Thanks in advance!

David

Steps -

Stair steps on vertical walls

Straight vertical cuts on same toolpath and same piece

Straight walls, same toolpath

[LibertyMachine]

On the "stair steps", what does the other wall look like? Is it steps in the other direction or are they growing towards the middle of the slot as it approaches the top surface?

What is the difference between the parts? Same exact toolpath, material, routing bit?

What is your control?

I'm suspecting that your machine is losing steps or that the part is moving.

[difalkner]

It's the same piece, just some places are straight and some are stepped.  I have attached the file if that helps.  Same toolpath with everything cut in one setting.  I'm using Mach4 for control, the piece is locked down tightly with 4 screws and doesn't move. If it's losing steps wouldn't that mess up the rest of the cut?

Here are a couple of examples -

Letters 'F' and 'A' -

Smooth sideStepped sideOrientation in machine

Toolpath

[daniel_lyall]

@difalkner Dave your link is locked or dead 

[LibertyMachine]

@daniel_lyall

That's an odd one. It gives you the first name, but doesn't auto-fill the rest. Give it an extension of .f3d and you can save and open it

[difalkner]

That's interesting; I just clicked on it to download and saved it with a different file name to place it in the same folder as the original and when I clicked on it the file opened just fine.  I have since modified the file to make the letters floating and not cutting all the way through the work piece.  I'll be using 3D adaptive clearing and I'm eager to see if I get the same results going that route.

Just for grins I am attaching the same file with a new name, so if you get the chance I'd love to know if it's something in the file or whether it's my CNC giving me the problems.

Thanks!

David

[daniel_lyall]

It's my computer being an Ahole Microsoft have stuffed something up again 

[daniel_lyall]

It's not the code this is looking at the Gcode from the top in https://ncviewer.com/# 

 

Do you have the clearpath servos set to send a fault signal to Mach4. They could be strutting then when the load comes off they are catching up or its crabbing in the Y axis slightly then when there's enough pressure they are releasing and the clear paths are catching it so it's not over shooting.

Or the machine needs a good clean 

Here's a adaptive toolpath for this pick the adaptive toolpath is attached.

[difalkner]

Thanks, Daniel.  I'm using steppers and Ethernet Smoothstepper with Mach4.  I was afraid it might be mechanical, or possibly missing steps.  But if it's missing steps wouldn't it throw off subsequent movement?  The file finishes and seems to do just fine in most places.  Ugh...!

David

[daniel_lyall]

I think I got you mixed up with a different David.

It could be mach4 It's got the same trajectory engine as mach3 whats only a 3rd order planner some times it just does stupid stuff then you slow it down and it comes good.  you cut 2 axis moves with it all day flat out and it's fine add the 3rd axis and it's not fine.

Try slowing down to 1/4 slower than it's cutting now and see if it happens, if it does not happen or it is less it's the speed and feed. my small machine whats built like a tank it goes balls to the wall at full wack it runs good as gold the big machine is restricted to a slower speed, it can not handle fast 3 axis moments at all.  when I have some spear coin I am going to change it over to UCCNC. unless they have a new engine in Mach4 by then.

[difalkner]

You mean there's another David??!!  And all this time I thought I was the only one - wow! 

I can try slowing it down but I only have it going 100 ipm now, so it's not setting any speed records.

Thanks, Daniel.  Happy Thanksgiving!

David

[daniel_lyall]

The dude I am doing the 4th axis stuff for in his machine brochure it say his machine can cut at 100in/min yer not even close 50in/min no problem 60in/min nup the Z axis starts to lose steeps vecticly.

[difalkner]

Yep, I have limited my machine rapids to 600 ipm and have cut at 400 ipm a few times, up to 250 with this 1/4" downcut spiral bit with no issues.  That's why I felt 100 ipm is very conservative, almost seems like it's crawling. 

Here's my machine - a 600 lb. beast!

Right after installing dust collectionThanksgiving 2017

[daniel_lyall]

100 in/min is slow, when you need to make $$.

Do you have a earth wire on the dust collectors piping, you can get some big spikes on them what can make a machine do all sorts of things if you have active low settings 2.8vdc is easy to produce from the static they put out, if the dust collectors power supply is sunk to ground you just connect the end off the wire to the motor casing if not you have to earth it.

[difalkner]

I don't have it grounded but probably should.  The hose has a wire but I've not seen any evidence of static or gotten shocked by it.  It should be fairly easy to ground it to the motor, which has a grounded plug.

David

[difalkner]

Bringing this up again - this is something I have noticed in some jobs but not others; the side wall of the cut should be straight but it has steps in some areas, smooth in others.  It doesn't happen on every job I cut and on some it doesn't matter because there are subsequent operations that will remove the steps but it shouldn't be there.

I'll tell you what I know -
1) drive belts are tight
2) the machine is lubed sufficiently
3) there is no visible change in motion or jerky movement
4) the simulation in Fusion 360 doesn't show this stepping effect
5) nothing on the machine appears to be loose
6) the DC hose is grounded at the DC
7) there is no audible change when this happens
8) has happened with both downcut and upcut spiral 1/4" bits
9) using Mach4 although not the latest release, it's probably 6 months old and I need to update it, and using ESS
10) the jobs start and finish as designed in Fusion 360, no interruption or appearance of missing steps and being off from that point forward.  This one is a 2D Contour profile.
11) spindle speed is 18,000 and feed is from 100 ipm to 150 ipm with depth of cut 0.125" to 0.150" in hardwood
12) the bit is tight in the collet and the work piece is well locked down, no movement at all

This is what I was cutting today, B-52 tails for a trophy shop, 2 up per board of Walnut, cutting time is about 6 minutes, 4 boards and 8 tails total, and the stepped area of cuts is in the same place on each one although more so on the first than the last -

The red area cuts are very smooth and the green area cuts are stepped -

Right after that I cut the antennas, 10-up, and two of the bases; cuts are smooth except for some fiber tear but that's ok because these get completely rounded over -

Here's the finished piece so you'll get an idea what I'm building out -

Ideas?

Thanks!
David

[daniel_lyall]

It looks constantly the same, check your wiring at that point on the machine if it was losing steps it would not be constant and it's only a 2 axis move by the look of it mach has no problems with 2 axis moves that I have ever seen on a properly set up machine only multi axis moves like 3 or more.

Did you post this on cnczone ger21 or one of those guys may have an idea of what it could be.

[difalkner]

I posted it on CNC Zone but Gerry hasn't chimed in yet.  From what I can determine the wiring is sound throughout.  It was the same place on the tails but the letters I showed earlier at the beginning of this thread were in a different location on the machine when they were cut.

Thanks, Daniel.

David

[difalkner]

Gerry suggested it might be the CV angle feedrates in Mach4.  I haven't set those, not sure what to set.  I know there's a Wizard but that's about it.

Here are some more photos after taking the tails out of the board -

Pretty obvious when placed side by side -

You can see how it's smooth coming down from the top but starts right after the curve of the leading edge of the tail -

Waste side of the good cuts -

Waste side of the stepped cuts -

David 

[daniel_lyall]

The CV thing is there's from 1 to 179 degrees what you do is if you know your machine can do a 45 degree angle change at full whack and at 46 degrees it starts to play up.

You would set from 1 to 45 at full whack and then from 46 to the next angle it gets worse you put in a slower speed all way to 179, It counters Mach not being able to handle big angle changes fast, 179 is usually rubbish on 2.5D cutts it drifts.

It's more useful than what it is in Mach3.

Are you use R or I and j