[dangerousdave]

Hi guys the time has come where I now have a little funds for the bits I still need. Im building a 8x4 cnc router primarily from alloy extrusion now im using r&p for x and y and wondrring if this kit will suffice


【German SHIP& Free】3Axis 3D NEMA 34 Step Motor 11.2N.m+CNC Stepper Driver 7.8A | eBay

now ive read that z should or could be smaller but id rather get the same or is there a reason I shouldnt?

Cheers guys dave

[ger21]

Choosing the correct motors depends on the gearing your using, how much weight your moving, and your desired acceleration and velocity.

You need to choose a motor that will have enough torque to meet your requirements. With steppers, torque falls off as rpm's increase (often rapidly, especially with larger motors like those). You need to make sure you have enough torque at the maximum rpm's you'll be using to meet your requirements.

As for the Z axis. The Z axis can sometimes require a larger motor than the other axis, as it has to work against gravity. Same rules apply as above. A large motor may be a poor choice on a fine pitch leadscrew.

[dangerousdave]

Well I can't see the gantry wieghing too much as im using alloy extrusion id say around 100kg fully assembled with z?

As for gearing i think ill be making them bases on the motors I buy and others experience and advise at the time

And rapids are not as important to me as a good solid precise feedrate. Mainly on mdf and some pine but also light alloy plate work is a possibility.


cheers dave

[dangerousdave]

Well after looking around for ages now ive seen that a few kits like cncrp kits come with smaller motors now ive seen this kit..


【German Ship& Free Ship】4Axis Nema34 Stepper Motor 1232oz,6A,118mm CNC Foam Mill | eBay

Now would the drop to 1232oz be noticable? Would it be a better choice to use these motors on each axis (x2 on y)

And last question is what size wire should I order? Ive been looking around and cant seem to find anyone who ahas wrote the wire size down etc

cheers, dave

[ger21]

Those motors are far larger than you need, and will most likely hurt performance.
Mechmate builders typically use 640oz motors, and get excellent performance. CNC Routerparts sells 640 and 960 oz motors.

If you read all the build threads here, you won't find any that use large motors like that. Bigger is not better.

[dangerousdave]

I have read a lot ovrr the last few months and am under the impression that nema 34 motors are the ones I need. And I've seen a few using 1600oz motors if the big nema 23s would suit better ill order them at half the price but I didnt want to be finding out they were crap and buying the 34s after

Dave

[BuckNaked31]

The motors you choose will largely depend on what force you need to move and at what speed. If you are just looking at the torque rating of the motor, you're not reading enough. I see a lot of people buying the wrong motors because they think that 425 is better than 387. Larger steppers suck at higher rpm's and have high inductance, which means a large expensive power supply to drive them. Listen to Gerry on this one... I haven't seen him give bad advice yet Remember, it doesn't matter what the motor can hold at stop if it has no torque left at cutting speed.

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[dangerousdave]

So do you think the nema 34 motors with 878oz holding torque in bipolor (8wire motor) with 15
Mh to inductance would be better than the 1600 with 22mh inductance?

link and specs here...

878

【Year-end Promotions】4axis nema34 stepper motor 878oz.in single shaft CNC Kit | eBay

1600

【Promote&Germany ship】4Axis Nema34 Stepper Motor 1600oz.in single shaft CNC | eBay


I really appreciate all your help guys, as soon as im confident which I need ill place the order
Dave

[BuckNaked31]

I don't think 60 volts is enough to drive either motor. I have 320 oz-in motors driven by 48 volts and the inductance is under 3mH, now I'm using Nema 23 sized motors, but the idea is still the same. 32 times the square root of the inductance puts the voltage of a 15mH motor at somewhere around 120 volts. 60 volts seems a little low, unless I'm missing something. The drivers in that package will work at 80 volts, but the PS is only 60. Can you get a torque curve plot of that motor?

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[dangerousdave]

Im not sure mate everyday is a school day still regards these motors, would it have anything to do with being wired bipolar on a 8 wire system as apposed to a 4 wire? ive emailed longs motor who have agreed the 1600oz are too big for the machine but have pointed to the 1232oz motors....

what size machine do you run with the 23s? I wanted the larger motors as I could take deeper cuts at the sacrifice of some speed but I dont want it to be too slow It hardly moves haha

again thanks for your advise so far

[BuckNaked31]

I'm using the 23's on a 24x48. I bought a kit that had 425oz-in motors originally, before I knew anything about inductance. I ended up switching them out for 320's that had a much lower inductance and now they fly... I bought the CNCRouterparts kit with a g540 and a 48 volt PS. They have a NEMA42 kit, you may want to take a look at it, they match their motors and drivers well. They've never done me wrong... not to sound like an advertisement for them , but at least look at the specs , it will give you a good idea , their machines really move and they are using smaller motors. From what I understand their machines have no problem pushing the cutter through full depth cuts, of course this largely depends on your spindle, and I understand that torque is important both rotationally and linearly.

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[dangerousdave]

There are these nema 23 425oz with 3.8 inductance with smaller drivers and only 2 power supplies tho
Do you think these would be better suited to my needs?


【Germany Ship&Free Ship】4Axis Nema 23 Stepper Motor 425oz-in,3A CNC Mill Control | eBay

[BuckNaked31]

I would stick with the Nema 42's for an 8x4 router. How about these?

NEMA34 Stepper Motor ? 906 oz in 6.1A Single Shaft (KL34H295-43-8A) | Automation Technology Inc

[dangerousdave]

They do look very nice mate I cant see an inductance rating on it tho like you mentioned earlyer. What about this kit I was recomened by another ebay user (maybe wrongly.....)?...
There is 4x 60v power supplies 4.1mh inductance and 1020oz holding torque.?

【German Ship &Promote】4Axis Nema34 Stepper Motor 1090oz,5.6A,100mm CNC Foam Mill | eBay


Again thanks for all your help. ( and patience with me )

[ger21]

Those are not too bad, but 60V may be on the low end, and may limit your top speed. The drives that those come with are not the smoothest running drive. Ideally, you'd want to use Gecko drives or Leadshine digital drives. Either one will be much smoother and faster, but will add considerably to the cost.

[dangerousdave]

Would they be good to get me up and running and upgrade the drivers at a later date as and when funds permit?


Cheers dave.

[vikramjoshi24]

Hello
I do not intend to hijack this thread.
I am working on similar 8 x 4 machine and am stuck on deciding Motors and drivers. Hope to get some guidance.

Vikram

[dangerousdave]

Well I bought the 4 axis nema 34 kit 1090oz motors and ive bought some belts and pulleys to make a test belt drive system. I wired one motor ho to test then found my pc didnt have a parallel port........ so ordered a pci one from the bay to find its not compatable with win 7 or its just crap (pc wont recognise new hardware....) so ive been searching and im wondering if this.....

USB Adaptors : USB 1.1 to Parallel Printer cable


Is compatible with mach3 or if it will work in general?

Cheers guys

[ger21]

No, USB to parallel adapters will not work with Mach3. You either need a PCI parallel port, or an external motion controller like the Smoothstepper or UC100.

[dangerousdave]

Cheers bud. Ill have to have a look for a better win7 compatable pci parallel port. Any recommendations? Or any will do?

Thanks for prompt reply