Stepper Motor Advice

For general topics and questions that do not fit into any of the other categories or forums.
Post Reply
HanSolo
1/2 Star Member
1/2 Star Member
Posts: 4
Joined: Thu Oct 10, 2019 10:25 pm

Stepper Motor Advice

Post by HanSolo »

Hello Everyone,

I have been doing a lot of research on building a cnc plasma cutting table and just wanted some advice if my choice of stepper rack and pinion are correct before I start buying things.

The gantry I am planning to build will weight about 30 - 50 kg. I am planing to use a rack and pinion with a mod 1.5 teeth and a pinion with 40 teeth. By my calculations that means for one revolution of the pinion it should move 60mm or 2.36 inches.

I have chosen the following stepper motor: https://www.ebay.com.au/itm/272817359627

Manufacturer Part Number - NC86STH98-6004A
Step Angle - 1.8
Holding Torque - 7.5Nm(1050 0Z)
Rated Current/phase - 6A
Phase Resistance - 0.4O
Recommended Voltage - 24-70V
Inductance - 3.1mH +-20%
Temperature Rise - 80 Degree Max

I will be using a 60v power supply so from my calculations that means the motor will give me 483 RPM I will be using a 5 : 1 reduction to increase torque and accuracy with the large 40 tooth pinion that gives me a max travel speed of 5803 MM a Minute or 228 inches per minute and each step will be (0.06mm)

My questions are:
- Is my calculation of 228 inches per minute correct?
- Is enough for good enough for cutting 1.6mm and thicker?
- Is 0.06mm step accuracy good enough for cnc plasma?

Any help is appreciated.
User avatar
Blackslacks
2 Star Member
2 Star Member
Posts: 87
Joined: Mon Apr 16, 2018 10:16 pm

Re: Stepper Motor Advice

Post by Blackslacks »

Im no expert but I did build my own 4 x 4 earlier this year. It sounds like your over building. Why is you gantry so heavy? Not sure if your calculations are right or what cutter your planning on using but my Hypertherm 45xp charts says you need 6150 mm/min for 1.5 MS. Those motors are absolutly huge. My gantry weighs about 45 lbs (20.5kg). I use 300 oz steppers everywhere and Mod 1 helical rack and 20 tooth pinion. No reduction. It flies. It will does 325 in/m. easily. It will go faster but no need. Absoluly no acceleration/de-acceleration problems. Make your gantry as light as possible and you won't need huge motors or reduction.
HanSolo
1/2 Star Member
1/2 Star Member
Posts: 4
Joined: Thu Oct 10, 2019 10:25 pm

Re: Stepper Motor Advice

Post by HanSolo »

I like to overbuild things usually but in this case less might be more. With your setup you are getting about 0.1mm per step do you find that the accuracy is good enough?
Rodw
4 Star Member
4 Star Member
Posts: 780
Joined: Sun Aug 21, 2016 1:49 am
Location: Brisbane, Australia
Contact:

Re: Stepper Motor Advice

Post by Rodw »

If you are going to a Nema 34 becasue you've found a prebuilt 5:1 reduction belt drive (which is what I did), I would suggest you look at this stepper which gives me rapids at about 20 metres/min. (I think is the one I used at 48 volt).
https://www.omc-stepperonline.com/nema- ... -fili.html
Otherwise a NEMA23 with 3:1 to 5:1 is a better choice.

Your distance travelled per rev as its a bit on the high side. I make it:
(40 teeth x 1.5 mod x pi) /5 = 37.7 mm/rev. The sweet spot is around 15-25mm/rev I think the smaller motor will let you get away with it but if you could get a pinion with a few less teeth, it would be better.

Also I would suggest you consider using LinuxCNC and its Plasmac configuration which is included in Linuxcnc versions 2.8 ad 2.9 as your motion controller. Used in conjunction with a Mesa 7i96 (or Mesa 7i76e) and a Mesa THCAD board would give you a high performance THC for a low price. Many people have found it is superior to Windows based configs.

I see from your ebay link you are in Australia somewhere. I am in Brisbane, so feel free to PM me.
User avatar
Blackslacks
2 Star Member
2 Star Member
Posts: 87
Joined: Mon Apr 16, 2018 10:16 pm

Re: Stepper Motor Advice

Post by Blackslacks »

I have no problems with accuracy. Im using a Gecko G540 which has 10x micro stepping.
Also accuracy can be adjusted in the control software.
HanSolo
1/2 Star Member
1/2 Star Member
Posts: 4
Joined: Thu Oct 10, 2019 10:25 pm

Re: Stepper Motor Advice

Post by HanSolo »

Thanks for the suggestions. I think I calculated the distance per step wrong because I calculated the distance covered by the pinion per revolution wrong. Is it 1.5 x 40 x PI? Because I saw somewhere it was 1.5 x 40?
Rodw
4 Star Member
4 Star Member
Posts: 780
Joined: Sun Aug 21, 2016 1:49 am
Location: Brisbane, Australia
Contact:

Re: Stepper Motor Advice

Post by Rodw »

Definitely need to multiply by pi as I made the same mistake
HanSolo
1/2 Star Member
1/2 Star Member
Posts: 4
Joined: Thu Oct 10, 2019 10:25 pm

Re: Stepper Motor Advice

Post by HanSolo »

Thanks have go through my calculations again. Glad I haven't purchased all the parts yet :)
Post Reply

Return to “CNC Plasma Cutters General Forum”