# Thread: need help! choosing right kit

1. my machine dim. is (2400*1200*250) rack and pinion X Y with gear 2:1 or 3:1 or 5:1 ratio. used for wood, plastic and thin aluminum
i need to choose from to kits

1- 4 Nema 23 425oz 3A 6Hm with 2 power supply 60V 6A

2- 4 Nema 34 651oz 5.6A 3.4Hm with 4 power supply 60V 6A

i need advice please to obtain good torque and speed. all machin built using steel 100*100*3 box
which gear ratio is appropriate?
thanks

2. id go with the nema 23's

whats the estimated weight of the gantry ? and what size pinion you using on what mod rack ?
and what drivers ?

3. thank you for reply Blackrat

i know that name 23's is better specially for gear reduction for high speed iam looking for without loosing torque but available name23 has high inductance 6mh which mean require 78V PS and the biggest available PS is 60V only
Nema 34 has 3.4mh which mean more appropriate for 60V PS

For gear rack

1. 5:1 ratio(90 teeth-18 teeth) for Nema 34 frame only
2. 2:1 ratio (40 teeth-20 teeth)
3. 3:1 ratio (60 teeth-20 teeth

The pinion on rack 28 teeth

4 Chinese drivers 7.8A 80V

I cannot estimate the weight of the gantry because it is not yet constructed but it will be two welded steel boxes 100*100*3

i order spindle 2.2kw 5.5KG

may be this information help

4. I go to compare smallest Nema 34 stepper 651oz that is near to nema 23 425oz to keep torque drop at high speed to mininum and at the same time can move steel gantry easily

5. of course you can estimate weight of gantry

cross-section of 100mm x 3mm box section is 100*100-94*94=1164mm^2
gantry is 1350mm wide approx. so total volume of steel is 2 * 1350 * 1164 = 3142800mm^3 = 0.0031428m^3 @8750kg/m^3 = 27.5kg
add spindle, carriages, energy chain, y & z stepper, ballscrew/rack, y-rails, z-rails, etc. (all of which you can get from data sheets or calculate), and your gantry is in the order of 50kg which is typical. add 30% safety margin and for sizing purposes use say, 65kg. - its good enough to help decide what motor is needed.

6. Definitely the 23 motor

The motor you point to is not a very low inductance motor. You need similar as what Zappautomation sells:

7. Originally Posted by irving2008
of course you can estimate weight of gantry

cross-section of 100mm x 3mm box section is 100*100-94*94=1164mm^2
gantry is 1350mm wide approx. so total volume of steel is 2 * 1350 * 1164 = 3142800mm^3 = 0.0031428m^3 @8750kg/m^3 = 27.5kg
add spindle, carriages, energy chain, y & z stepper, ballscrew/rack, y-rails, z-rails, etc. (all of which you can get from data sheets or calculate), and your gantry is in the order of 50kg which is typical. add 30% safety margin and for sizing purposes use say, 65kg. - its good enough to help decide what motor is needed.

Just saw his build and did not pay attention here

He is looking at best case scenario of 100x100x3 9kg/m, just checked it, so the gantry with sides depends how he will go having in mind 300mm Z , will weight minimum ~50kg without z and rails!!!

The Z will weight around 30kg + all the rails and motors and so . Especially if he wants a sturdy machine. The lightest gantry possible as i see it is more or less the way i make it right now on my build here and is not light at all.

My conclusion for my build was to go with servos or nema 34 to be on the safe side. i went with servos.

Another point is that Rack and pinion is not the best solution so better continue at his build thread, as all is interconnected.

msacnc,

Its wise first to finish the design, then to decide the motors. Rotating ball nut on long axis will be better option. Coupled with 2510 ballscrew on your machine size.
Last edited by Boyan Silyavski; 15-09-2014 at 12:22 PM.

8. thanks riving2008 silyavski for valuable information;

Nema 23 number is JK57HS112-3004

I have a limited option for stepper and PS choice, the available stepper are JK57HS112-3004 and JK86HS78-5504 to choose one of them (low cost for me)

Rotary ball nut is not available option in my country and also dust intensity in the air is a big problem for ball screw + high cost thus rack and pinion is easy to maintain specially with big 2400*1220*30 machine

I think the design of gantry with one box 100*100*3 may be reduce the weight

i have a limited time to choose one kit (nema23 425oz+60V PS) (nema34 651oz+60V PS)
what is the best ratio 2:1 or 3:1 or 5:1
thanks

9. No one can answer your questions because we don't have enough information.

To start with, what speed do you hope to achieve? And what pitch is the rack?

Btw this probably won't be accurate enough for machining aluminium.

10. i do not determine certain speed but the faster choice is better for me

rack inf:
20 mm wide and 20 mm thick 1500 mm long Module 1.5 Pressure Angle:20°

commonly the machine is used for woodworking

I plan to reduce the gantry weight using one steel box 100*100*3 welded to two pieces of 150*100*3 gantry side

"this probably won't be accurate enough for machining aluminum" Why?

Page 1 of 3 123 Last

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•