BuildersBot: CNC Router that can also 3D print.

The $2714.00 USD, BuildersBot 3d printer, and CNC router.




A few questions arose reviewing the BuildersBot BOM.

1) What steps are required to switch between operating as a 3d printer to a CNC router utilizing:
One Arduino Mega.
One Ramps 1.4 Board (for CNC milling and 3D printing).

2) BuildersBot uses four 2A Drivers, 128MicroDriver, (a driver for each motor, so no slave stepper?), what is the advantage of this? I was thinking it would be simpler to have slave motors utilizing the master motors 3 stepper drivers. Or is a stepper driver required for each slave?

3) What advantages are there using six End Stops (3 Wires), is it a safety overrun stop?

4) The BuildersBot does not use gear reduction to increase the linear resolution. Looking at the 3d print in the video it looks rough, I suspect it's using microstepping.

For my design I was thinking of using full steps with a 4:1 reduction for about ~0.0015 inch resolution, and use microstepping for the jobs that require a higher resolution. Should I rely upon microstepping, and eliminate the gear reduction, it would simplify my design, and reduce the cost significantly, and if you choose microstepping what reduction?

20-5M-15 Metric Timing Pulley, (20mm dia pulley).
1790-5M-15 Timing Belt.
200 steps.
1.8 deg/full step.
Circumfrence = 62.83185
Linear motion = 62.83185/200 steps = 0.314 mm/full step, (~0.012 inch/full step).


Arduino Controlled CNC / 3D Printer by aldricnegrier
[www.youtube.com]
[www.youtube.com]
[www.instructables.com]

Edited 1 time(s). Last edit at 06/17/2014 09:01AM by A2.

In my experience, I like 16th step microstepping. It's been a sweet spot for me. On my Z axis I use 4th stepping. All stepping is solid and as cheap as my motors are I haven't had a stepping related problem.
I can say however that slight ridging is apparent as the motors pass each poll, and I have yet to come accross a machine that does not have this, industrial or otherwise. I wonder what gearing over stepping would do to get rid of the ridges. Personally, with the teeth of gears I think ups and downs in speed would still be there, but that's dependant upon the gearing and tolerances of such. Just some thoughts. I might play with stepping again to see what results I get.

---

Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus

Quote
MrDoctorDIV
In my experience, I like 16th step microstepping. It's been a sweet spot for me. On my Z axis I use 4th stepping. All stepping is solid and as cheap as my motors are I haven't had a stepping related problem.
I can say however that slight ridging is apparent as the motors pass each poll, and I have yet to come accross a machine that does not have this, industrial or otherwise. I wonder what gearing over stepping would do to get rid of the ridges. Personally, with the teeth of gears I think ups and downs in speed would still be there, but that's dependant upon the gearing and tolerances of such. Just some thoughts. I might play with stepping again to see what results I get.

One thing to keep in mind is that no matter what microstepping rate you use (4x, 16x etc.), stepper motors are fundamentally only accurate to +/- 1 full step. Microstepping makes the transition between steps smoother, and it allows you to more accurately specify the desired position of the motor, but the motor still is only guaranteed to be at the desired microstep position within 1 full step. In the absence of friction and dynamic loading, microstepping can give you more accurate positioning when you are stopped, but as you add any sort of load or start moving at higher speeds (ie, while printing), you are back to the basic +/- 1 step accuracy.

Gearing, however, will increase the fundamental accuracy, but you have to trade this off against the inaccuracies of the gears themselves.

Based on the info below, to reduce positional error utilizing 2 stepper motors per axis, I should be using a gear reduction, keep all the axis energized, use full step, and a driver for each motor. What steps are required to "keep all the axis energized", and is there any thing else that I should be aware of?

Tks!

Quote
Fabricate
I heard once that using a dual motor setup for one axis and microstepping is not a good idea, but I am not sure if this is also true for a dual motor + dual driver setup. Read more about this issue here.
[forums.reprap.org]

Quote
woo

Quote
woo

Quote
Vince
My mendel has two z motors and they somehow seem to get out of step quite regularly, fortunately not during a print, just between. I was determined to lock these new ones together and reduce the hassle.
I was thinking of using the 8825s for drive but will take a look at Core, thanks.

classic reprap mistake. set Z axis to full step and its solved.

its logical explanation. everybody sets two motors on same driver, and turn on microsteps. when you stop printing, your motors are shutting down, and they stay on "microstep" position.

when you turn on printer again, and motors are on some microstep position, they jump to full step position, and there is possibility that each motor jump on different side.
just change to full step and it will be ok.

[forums.reprap.org]

Quote
misan
In microstepping you cannot de-energize the motors as they cannot hold statically any other than full step positions. You can configure your firmware to not put driver to sleep mode on Z axis. My advice is to keep all the axis energized if your are using microstepping on them.
[forums.reprap.org]

In Repetier firmware I can set the timer when things shut off after idle, I can't think why any firmware would not have this feature, but Repetier is all I've customized. Since I often start a print and leave I kept it relatively short. You'll also need to change your slicer to not put out a turn motors off code at the end of a print. I can't think of anything else that would take power away from a motor.

Edited 1 time(s). Last edit at 06/18/2014 09:10AM by MrDoctorDIV.

---

Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus