2+2+3 More Plasma builds, double the joy ! 3X2M and 2.5X1.5M cnc plasma build.

tommylight wrote: ... That seems all good, and with that reduction it will be also usable as a router for sure. I did try to surf the gantry yesterday at 10m/m for over 10 minutes i was jumping on it, and they never stalled.

That is with Nema 23 motors at 1.8A, 1:3 reduction and a 15 tooth 3mm pitch pulley, so 15mm per revolution of the motor, or ideal for plasma cutting.

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Hi - been reading through this thread and others very closely as I get my head around what seems to be working and not working etc.
I "think" I know what I should be getting but I got a little confused in the series of exchanges and the numbers being used. If possible a clarification would be very helpful.

Context: looking at a "small" table with a cut area of circa 1200x600mm with gantry and Z assemblies constructed from Aluminium for minium weight. Only the base table and water try are going to be steel. Even the water tray may be ali sheet with the replaceable steel support ribbing. This is based on available space and a desire to be able to handle (in segments) the standard metric sized sheeting typically found in my area.
This is a hobby/learning/fun build. If it becomes more only time will tell.

Questions:
For this size table I THINK Nema 23 motors with 3:1 gearing from the motor (i.e. motor turns 3 times for 1 turn of the pulley on the belt) should be ok. But people talk different amperage sizes and sometimes that seems to be getting mixed up with the Holding torque?

For example I am looking at a set of motors that are spec'd as:
Current:3.0A
Resistence:1.1Ω
Inductance:3.6mH
Holding Torque:1.89Nm
Weight: 1.2Kg

Yet there is mention of 1.8A or 2A motors? I am not seeing anything like that about. Was that really 1.8Nm or 2Nm torque mottors? Or am I missing something?

Or would a motor set looking like below be preferable?
Current:3.0A
Resistence:0.9Ω
Inductance:2.4mH
Holding Torque:1.26Nm
Weight: 0.72Kg

PSU feeding either set would be 36V with DM542 digitial drivers.

Really appreciate any clarification or advice.

Thanks,
James.

For 36V supply the second motor is better due to lower inductance of 2.4mH as that will get more speed in use.
Stepper torque and current are pretty complicated but even 1.2A Nema 23 with 3:1 reduction should be enough to drive a lite gantry for plasma at 12m/m .

tommylight wrote: For 36V supply the second motor is better due to lower inductance of 2.4mH as that will get more speed in use.

Thanks for responding. The 36V supply just happened to be what was in the motor bundle from aliexpress. I have a s/s from when I did my CNC mill conversion that suggests the 3.6mH motor would be better with ~60V supply and the 2.4mH motor would like a 50V supply. It seems the 542 driver in the bundle is the limiting factor. I might be better off buying the eact parts I need instead of trying to get a bundle "deal" that is actually not optimal.

For the small/medium stepper designs that you have suggested did you ever describe the psu setup? I can remember you mentioning DM860 and DM542 drivers just not what PSU sizing you were using to supply things. I have DMA860H (they can do DC or AC input) on my mill and can take up to 80V, they might be a better option with a higher voltage supply to get the best performance out of the motors?

One of my design ponderings has been based off of some spare kit I have on hand. I have two Nema32 4A 3Nm(428Oz-in) 1.6mH 2.2Kg motors and DMA860H drivers spare with a 48V 500W PSU. I had been pondering using them to drive the belts on the X and Y. Given the gantry is planned to be long enough to support a 1200mm wide cut I believe I need to drive it on both ends. My thinking had been to use one of these motors with a 3:1 or 5:1 reduction driving a shaft that spanned the back of the grantry and drove off a GT2 (9mm wide steel or fibreglass reinforced) timing belt on each side. Idea being that the pullys on the drive shaft along with the gearing reduciton would give around 10-20mm of movement per rotation of the motor. Plan would be to have the shaft supported in a pillow block at each end and probably one in the middle to stop any risk of whip. Also to have a tenstioning/position adjusting system so that I could tune in the non motor side to get the gantry square. Given I will be using hollow aluminium rectangle section I could in theory get cute and have that shaft inside the gantry. Just gets a bit more complicated for the centre support.

Anyway, interested in more experienced perspectives on this. Bearing in mind this is a budget project of a first cnc plasma table so trying to not over invest as I learn and see how much use I will get from the resulting tool. Given the budget angle, if I can use kit I already have that would be an advantage.

Just for context I'm not limited to hand tools when it comes to making stuff. I have a lathe with 1m between centres with DRO, vertical/horizontal mill that is Bridgeport sized with DRO, a baby cnc mill and steel/aluminium welding capability. So if I need to get accurate for hole/feature placement/spacing/consistency I can.

Appreciate the advice and insights,

Thanks - James.

What you have will do just fine, just drive them at a lower current to reduce vibration and lower the power so the belts do not get torn in case of a mishap. For reduction aim at 15 to 25mm per motor revolution.

Awesome. So my drive shaft idea is not completely whacked? lol - I have a good friend who is continually giving me shit for over engineering.

That 15-25mm rule of thumb is gold! Helps with so many other decisions in the drive chain design.

Snow again....