Gear reduction understanding

I have built several plasma tables. I’ve use direct drive though, I have never used a gear reduction or stepper reduction box. Though I have been told they give better quality and accuracy. I would like to incorporate them into my next build. Though I’m not sure I understand fully what they do and how they improve the quality when using a stepper motor.

(Simplistic answer)
Gear reduction:

• Increases the stepper motor torque transferred to the gantry & head
• Increases mechanical resolution
• Increases acceleration
• Increases "smoothness" (8x microstepping will become 40x with a 1:5 reduction system)
• Increases backlash
• Increases inertia (both rotational and basic system weight)
• Decreases top speed of gantry & head

(Complicated answer)

• Reduction systems can be great, or horrible.  It depends on a number of factors:
• Motor torque curves
• Motor top speed
• Reduction system quality (backlash, sloppy, springy belts)
• Reduction system type (belt, planetary, spur, harmonic, cycloidal, etc.)
• Gantry/head weight

For consideration:
Figure out the maximum cutting speed you anticipate - really thin aluminum perhaps - then add 10% to that number.  That's the max speed you need.  Anything faster is a nice-to-have for rapids (repositioning between cuts).

My experience with plasma cutting is that acceleration is king.  Top speed doesn't matter as long as you can reach the programmed cut speed.  After that high acceleration will permit very fast direction changes, leading to improved corners and smaller corner radii able to be cut cleanly.

 

Another answer. Assumes rack and pinion with approx 30mm pinion diameter:
Nema 34 5:1 reduction on each side of the gantry,
Nema 23/24 3:1 reduction on X axis across the gantry.
You should also not have the stepper moving in its resonance zone with the reduction

These were designed at a cut speed of 10.24 m/min max cut speed.

Motor selection and voltage are pretty important to get max performance.

Acceleration should be at least  3 m/s/s, you can get to 5000 m/s/s with steppers but you need a very very rigid table to handle the inertia! eg accel to 2200mm/min cut speed will be  30 milliseconds.
 

so if you plan on using a hypertherm45 xp it states that the recommended speed for 1/10” aluminum would be 240in/min or 7890mm/min. Therefore if you want a machine that can maintain that you should the top speed should be 264in/min or 8,679mm/min. I have only used stepper motors, NEMA23 570OZ/IN to be exact. My rack and gear has always been 20 Degree Pressure Angle, Round Bore, 20 Pitch, 15 Hardened Teeth. Like I said I’ve always done directs drive. I haven’t had an issue with quality at all. Or speed. Would a stepper reduction box really make a positive difference for me?

Aldenflorio wrote:

so if you plan on using a hypertherm45 xp it states that the recommended speed for 1/10” aluminum would be 240in/min or 7890mm/min. Therefore if you want a machine that can maintain that you should the top speed should be 264in/min or 8,679mm/min. I have only used stepper motors, NEMA23 570OZ/IN to be exact. My rack and gear has always been 20 Degree Pressure Angle, Round Bore, 20 Pitch, 15 Hardened Teeth. Like I said I’ve always done directs drive. I haven’t had an issue with quality at all. Or speed. Would a stepper reduction box really make a positive difference for me?

FWIW, I run the exact same setup, stepper size, rack and pinion, etc. I too have had very positive results. I've also considered doing a reduction (mainly due to people here saying it's necessary), to the point where I designed it, but have yet to create it. I've been kind of waiting for something to break, or provide more indication that the current setup is lacking something. I have also considered that "I dont know what I'm missing", but it goes hand in hand with "if it aint broke dont fix it".

If you decide to go the reduction route, please share your results, I'd be very interested to hear from someone who is running the exact mechanical setup I am.

Also, acceleration gets talked about a lot, but I'd say that keeping the gantry weight to a minimum is equally important.

Aldenflorio wrote:

Would a stepper reduction box really make a positive difference for me?

Not really, if everything is working as you expect.
Get us some pictures of the cuts done on some thicker material.