right motor for a cnc
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hello,
I'm planning to build my own CNC and I wanted to know with stepper motors are the best for me.
In general:
Size 100x100x10cm
Balscrew:
https://www.ebay.de/itm/250-1550mm-SFU1605-Kugelumlaufspindel-Mutterblock-DSG16H-kupplung-BK-BF12/233164312490?var=532646499289
linear rail:
https://www.ebay.de/itm/2X-SBR20-1000mm-1m-Linear-Linearführung-Welle-4X-SBR20UU-Linearwagen-CNC/232998989290
Motor: your suggestions
As Spindel:
https://www.amazon.de/Makita-RT0700CX2J-Oberfräse-und-Trimmer/dp/B00CKYCG8SI will have dual X, one Y, one Z motors.
As a result, I want to be able to mill wood and aluminium.
can you recommend sufficient stepper motors, my idea was to use:
https://www.ebay.de/itm/Promotion-Schrittmotor-Nema-23-Stepper-Motor-270-oz-in-3A-76mm-Flat-shaft-CNC/163855575007
or
https://www.ebay.de/itm/ACT-MOTOR-GmbH-1PC-Nema23-Schrittmotor-23HS2430-3A-112mm-425oz-in-Bipolar-8mm/253725110697?hash=item3b1331f1a9:g:Em0AAOSwgvFbOeZY
but I read that the duet 2 wifi is limited to 2A.thank you in advance.
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@eduardschlegel said in right motor for a cnc:
i use something similar for a 300x400x80mm router, and it cuts aluminium with a reasonable surface finish for a "toy". Rigidity on the body and the power and speed ranges of the spindle is probably more important than the stepper motor.
The duet 3 is more powerfull, but also more expensive. I'd either go with Duet 3 or see how far away a next generation Duet 2 with new stepper drivers. Although 2A can work fine, your cuts will be shallow and slow in any case, just a little slower with 2A instead of 3A.
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okay thank you soo far, I think I will go with the duet 3 then, do you know when the shipping will start and if it will be possible to use sensorless homing, that would be very nice to zero out the workpiece.
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@eduardschlegel said in right motor for a cnc:
if it will be possible to use sensorless homing
the duet 3 supports sensorless homing. but it might not be suitable for your case
see
https://duet3d.dozuki.com/Wiki/Stall_detection_and_sensorless_homing
specifically this pointThe stepper drivers only update the stall detection state every 1 or 4 full steps, depending on configuration. So the actual position of the stall is uncertain to either +/- half a full step or +/- 2 full steps. This means that when using stall detection to replace endstop switches, the position defined by the stall is much less accurate than with typical endstop switches.
in germany there are some shops where you can get cnc supplies of higher quality
https://www.dold-mechatronik.de/
and
https://www.motedis.com/shop/ -
@eduardschlegel said in right motor for a cnc:
do you know when the shipping will start
This is the pre- order for the first full production run of the Duet 3 Mainboard 6HC. Delivery for this pre order will be starting towards the end of November 2019.
https://www.duet3d.com/Duet3Mainboard6HC -
@eduardschlegel said in right motor for a cnc:
but I read that the duet 2 wifi is limited to 2A.
That is very old information. It supports up to 2.4A if you cool the board actively (from the back, that's important). And in that case 2.4A are the proposed 80-85% current of a 3A stepper - though this is mainly for temperature reasons and if you are mounting these on metal it won't matter.
Thus: if you can go with up to 2.4A a Duet 2 will work. If you need more than you can pre-order a Duet 3 6HC to be shipped end of November.
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@eduardschlegel said in right motor for a cnc:
if it will be possible to use sensorless homing
Sensorless (stall detect) is absolutely unsuited for CNC. Simply not repeatable enough.
Notice that even 3D printers that stall detect x/y, they all use something else on Z. This is because x/y on a 3D printer need only be accurate to 0.1mm? 0.5mm? 1mm? and Z needs to be repeatably accurate to 1/2 layer height or better, so 0.05 for 0.1 layer height (which almost any printer can do), or 0.03 for 0.06 layers. Really. 0.01 or 0.005 is best for Z on most printers. So they do not stall detect Z.
Example: Prusa Mk3 i3 series. Stall on x/y, inductive on steel plate for Z.
Back to CNC: CNC machines need this on ALL axis. You want precision microswitches or optical or inductive. Some way to get to 0.005 repeatability. Even on a basic CNC machine.
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oh okay so I can use the duet 2 wifi und drive the motors at 80% (thats also recommended to avoid overheating?)?
I don't want to go over 3A motors anyways.
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2A v 2.4A vs even more is HIGHLY dependent on cooling the back of the board. In a 30C+ workshop, with no cooling on the board, in an enclosure, 1.5A can burn a driver.
I'd suggest heavy heatsinks applied with thermal epoxy to the BACK of the board (this is how Trinamic drivers are designed to cool, through the back), with a dedicated fan blowing across them. A big fan, like from a PC, not the little tiny fans we use on 3d printers.
With that setup, I wouldn't hesitate to set the current to 2.4.
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thanks for your advice.
one last question, can I drive the two x-axis motors over the Z1 and Z2 connector -
@eduardschlegel said in right motor for a cnc:
one last question, can I drive the two x-axis motors over the Z1 and Z2 connector
Yes. However, that will "split" the current between the motors, or, if you prefer "double load" the driver chip.
MUCH better to put them on separate drivers, and configure those as one axis in duet (like X3:4).
