- December 3, 2017 at 9:10 am #48936
I need to build a project and for that i need to work more seriously with my mpcnc.
I need to cut a lot of part on plywood, thickness 15mm.
I made a lot of try, and this is the settings i have found to complete a run without errors :
– 13 mm/s, depth of 1,5mm with a 6mm bit (1/4″)
It’s very slow and i need 2 hours of cutting to finish the cut in the picture.
What do you think about that ? Do you thing it is a normal speed ? Or do you think i have an issue with my mpcnc ?
Perhaps i have my motors not powerful enough or my stepper are not properly adjusted.
My motors :
-Wired in parallele
– 2,8 volt
My DRV8825 Drivers :
Now i have 0,9V set on all my drivers.
Calculs for Vref :
Motors : 1,68A X 2,8 V = 4,7W
So for 12v : 4,7W / 12V = 0,39A
Vref = stepper current 0,39 / 2 = 0,19
So normally i need tu put 0,38 volt for the X and Y stepper and 0,19V for the Z ?
But actually, with 9v at all my stepper, my cnc is really not powerfuul
Thanks a lot for your help !!
Attachments:December 3, 2017 at 9:25 am #48941
You can speed that up a lot with a 1/8″ bit. If you’re not worried about tearout on the upper side, then go with a 1 flute upcut bit. If you have to have the top side pretty, then consider a downcut 1/8″ dual flute. The problem with the downcut is that you can’t drill well. Don’t drill more than about 2mm deep with a downcut unless the hole is at least 2x the bit size so the chips can escape. I have hacked around this by making the doors with the bit and finishing then with the drill press. Also buy the bits from the vicious1 shop or find similar quality bits made for milling not drills or cheap router bits.December 3, 2017 at 9:35 am #48945
i have already made tests with a 1/8″ bit and it is worse !December 3, 2017 at 9:50 am #48952
I do no think this is a machine issue, lets see some pics of your machine and your gcode.December 3, 2017 at 10:08 am #48953
Thank you ryan, this is the machine : https://vimeo.com/165069935 😉
Upgraded with the new center.
Gcode and pics of the project cut are attached to this post. On the picture, i have some holes that are offset by 5mm
Attachments:December 3, 2017 at 10:11 am #48958December 3, 2017 at 10:26 am #48964December 3, 2017 at 10:35 am #48971
Most of the time, the errors occurs on the X axis. I check an re-check all the things, all is good.
I don’t know if the machine is powerfull enough, this is a video :December 3, 2017 at 10:51 am #48976
You can definitely push the machine around with your hands. I’m not sure how hard you’re pushing, but it looks like it’s probably skipping steps too easily. But it’s hard to know. Some fingers are pretty tough.
I just reread your first post. Sorry I missed this, there’s some math that conflicts with my understanding, but you have DRV8825s set to 0.9V, but you’re running in parallel. That is going to be a bit soft. If you run them in series, you can go up to 0.7V or in parallel, up to 1.4V. Where your math above went wrong is that the drivers won’t use 12V, they will use up to 12V, but be limited by the current. You can think of them as current sources, not voltage sources.
0.7V = 1.4A (for the Z), which won’t be 12V.
1.4V = 2.8A (or 1.4A for each motor).
You should also consider switching to the serial wiring configuration. It will run the drivers at a lower current. In that case, you’d set them to 0.7V ref.
There still seems something fishy though. Running a 1/8″ bit ploughing through wood will be less resistance (not quite half, but close) than a 1/4″ bit. If you’re just cutting out parts, then the 1/8″ is a good size (1/16″ would be less resistance, but more likely to break or heat up). The 1/8″ bit needs to spin faster too, since it’s radius is 1/2. Maybe that’s the issue?December 3, 2017 at 11:11 am #48978
It looks like your X axis steppers are not holding very well as Jeff suggests. How does the Y axis hold up? If it’s much better than the X axis I would double check the voltages and then perhaps try swapping over the X and Y drivers.December 3, 2017 at 11:36 am #48980
Thanks a lot for your help. I have already switched the driver. I think its because of the orientation of wood fibers.
I put my X and Y driver to 1,4V and use a 1/8″ bit (i have an active cooling for the driver).
I tell you if it’s work or not !December 3, 2017 at 1:47 pm #48985
Please do. I’m very interested to see your results.i made a looooot of tests. There is always a problem that happens
I have to say, the CNC machine definitely makes the most interesting looking firewood (even if everything is working).December 3, 2017 at 3:15 pm #49002
Your Gcode is not going to work, the firmware changed a year so so back and it will not work without Z rapid speeds in there now, you will need to use estlcam 10. I know it seems not to be the case but it crashes the machine randomly becuase it is when the bad command gets loaded, not executed. For some reason it is typically not ever in the same spot, it took us more than a year to figure it out but now that we have it is very is to verify that is the issue.
I really hope to see your new project, lets get you working again!
I am also with Heffe on this one 1/8″ should be much faster. Almost twice as fast.December 3, 2017 at 3:18 pm #49003
Heffe has caught all of this already, but we also we have switched to wiring in series, twice as strong less power needed from the Drivers. You have had your machine for a while, I forgot. I wish I had kept a better change log…December 4, 2017 at 3:17 am #49069
Thank you Ryan, Yeah, a changelog can be very helpful, i have searched a lot on the forum, i re-do all the steps of your tutorial but i have not seen this informations ! Thanks a lot for your help !December 10, 2017 at 2:56 pm #49338
Ok thank you a lot Guys ! It work !
I put my X and Y driver on 1,4V (when i have more time i put them on series, or i try the square end stop).
I have installed Estlcam 10
All’s good !
With a 1/8″ bit i can go 2,7mm deep and 13 mm/s speed on the plywood.
Do you try to go deeper or faster ?
The MPCNC go 70% faster than the time given by Estlcam, do you know why ??
First Picture, i show you the project when it is done :
Attachments:December 10, 2017 at 8:15 pm #49361
Dui, ni shuo de duiParticipant
What are you building?December 10, 2017 at 10:30 pm #49371Do you try to go deeper or faster ?
The thinking here is, deeper will use more of the bits surface, so you save some money. Plus, there’s less chance for any higher order dynamics, or ringing in the rig. Plus, of you go off course, you’ll be less likely to break everything. The disadvantage to deeper is chip evacuation. Test everything first, but deeper is generally better. I might even show it down to 8mm/s.The MPCNC go 70% faster than the time given by Estlcam, do you know why ??
Nope. If there were no accelerations, it should be perfect. The acceleration looks should slow it down, not speed it up. Unless it’s assuming some acceleration. The other possibility is that the firmware doesn’t treat cached speeds exactly the way it should, so the speeds you are using are way faster than you want.
You must be logged in to reply to this topic.