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  #1  
Old Fri 15 August 2008, 11:13
Mcyoda
Just call me:
 
1/2" or 3/4" rack

I am planning to build a 8' x 20' router table and the gantry would be weight at least 250 to 350 pounds I would think.

Do you think the 1/2" gear rack is strong enough pull that much weight?

I can use the next size gear rack would be the 3/4" with 16DP but is not 20DP as most people here is using.

Do you think is fine with 1/2" rack?

Thanks

Rocky
  #2  
Old Fri 15 August 2008, 11:35
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The 1/2" 20DP rack is a good match for the stepper motors that we recommend here. If you are going for much more powerful motors then you will need stronger gears.

The gantry weight is not directly relevant. You will be able to move the 8' gantry with one finger. The rate at which you want to stop that gantry, or the cutting force you want to apply, are related to motor power and thus to gear tooth size.
  #3  
Old Fri 15 August 2008, 12:58
Mcyoda
Just call me:
 
I am planning to use nema 34 servo motors with 1100 oz/in with some belt pulley speed reducer. So is the 16DP is stronger than the 20DP? Will I lost any accuracy due to the less bigger teeth on the rack?

The other alternative is to use belt and pulley.

Thanks

Rocky
  #4  
Old Fri 15 August 2008, 13:09
Leko
Just call me: Leko
 
Kaukapakapa
New Zealand
Wouldn't it take like a bazillion pounds to break the teeth off the rack? The pivot spring would be the weak point, correct?

I would be more concerned about the connections between the rack & rail as well as the pinion to motor.
  #5  
Old Fri 15 August 2008, 13:10
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
If I wanted a bigger rack than 1/2", I would use metric module 1. It is 5/8" wide and has a finer tooth than DP20. That is what us metric people are using for our MechMates.

What Nema34 servomotor with 1100 oz/in are you thinking of?
  #6  
Old Fri 15 August 2008, 15:07
Mcyoda
Just call me:
 
The servomotor is from Kelinginc model #KL34-180-90 with around 1125 oz/in peak.
  #7  
Old Fri 15 August 2008, 20:57
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
From their spec sheet:

Clipboard01.gif

As far as we are concerned, that is only a 226 oz-in motor, and then only if you can feed it 7.8 Amps at 90Volts.
  #8  
Old Mon 18 August 2008, 19:26
Mcyoda
Just call me:
 
Thank you Gerald for the clarification.
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