Stow-A-Way Plasma Cutter Table

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10 Sep 2021 14:09 #220133 by joeslide
I want to be able to stow 4’ by 8’ sheets of steel away underneath my welding table (which of course will be slightly larger than the sheets of steel). The sheets will be stacked on a custom-made low profile trailer that will be parked underneath the welding table. I’ll use this trailer when I go buy the steel  (⅜ inch 4’x8’ sheet weighs about around 500 lbs). After parking the trailer underneath the welding table, I want to pull out a selected sheet and cut it with my plasma table that is stored just above the trailer. So I need a frame with linear rails (2 axis) to support the plasma torch and cut out the selected dimensions (all straight cuts for now). I’m thinking of using steel tubes to support the rails.  I would like to use a Jog Pendant to control the cutting (for now).Questions
  1. What length of linear rails do I need for 4’x8’ sheets?
  2. What length of T8 lead screws do I need?
  3. Suggestions on torque motors? 17 or 23? Torque Spec?
 Thanks for your time,Joseph

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10 Sep 2021 17:02 #220144 by tommylight
1. Minimum of 10% more than the required travel, 15% are nice.
2.T8? This can be used only for Z axis, X and Y should be rack/pinion if you can find smooth running ones (i could not) or belts at least 15mm wide HTD3 or HTD5, with 1:3 to 1:5 reduction, depending on the end pulley. Aim for 15mm of travel per revolution of the motor.
3. Nema 17 for Z is OK between 1.2 and 1.7A ones, for X and Y Nema 23 at 2A are enough with reduction.

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10 Sep 2021 18:51 #220163 by rodw
Replied by rodw on topic Stow-A-Way Plasma Cutter Table
For a 2400 sheet, I'd suggest 2500 travel minimum. That gives you 50mm each end so sheet placement is not critical
The length of the linear rail would be 2500 plus the distance between the outer edges of the linear carriages plus an allowance for home and limit switch travel (25-50mm). 2800 rails should go close with say carriages 275mm apart..

Nema 23's are adequate. But the extensive engineering we did showed small NEMA34's were required for optimum acceleration (if your table is rigid enough to handle the inertial forces) with a 5:1 reduction and 40-60mm pinion diameter.

I run 2 x NEMA34s with 5:1 reduction the Y axis and a 2 amp Nema 24 with 3:1 reduction on the lighter x axis

These are NOT entry level chinese motors.
 
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12 Sep 2021 19:44 #220362 by joeslide
Thanks for your response. Trying to understand the difference in these two designs:






Why the difference in dimensions and material selection in the gantry?
Is the second design better immune from vibration?
Are both designs equally capable?

Thanks,
Joseph

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12 Sep 2021 20:36 #220365 by Joco
Replied by Joco on topic Stow-A-Way Plasma Cutter Table

I run 2 x NEMA34s with 5:1 reduction the Y axis and a 2 amp Nema 24 with 3:1 reduction on the lighter x axis

These are NOT entry level chinese motors.

 

Don't forget the voltage Rod.  From memory you are tickling those motors with some pretty angry blue pixies.

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12 Sep 2021 20:55 #220367 by rodw
Replied by rodw on topic Stow-A-Way Plasma Cutter Table
Yeh, 64 volts AC on the same drivers as shown in the second video which gives about 90 volts at the motor..

First video uses a cheap parallel port, 2nd video uses Mesa hardware and high end Lam stepper drivers.
If you are going to build a 2400 long table, please go with a Mesa 7i96 or 7i76e with a Mesa THCAD.
The extra $200 it will cost you is insignificant in the total budget and provide vastly superior results.

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12 Sep 2021 21:19 #220369 by tommylight
The second video was using 72V DC to power the drives, Sanyo Denki Nema 23 motors at 2.4A.
After finishing that machine i did push it to 68 meters per minute with 3000mm/s/s acceleration, the reduction belts failed after about 4 back and forth! :(
Oh and the difference, the second one can cut all day every day without a hitch, even 24h days.

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13 Sep 2021 06:13 #220400 by Joco
Replied by Joco on topic Stow-A-Way Plasma Cutter Table
68m/min!!!  Yikes. I was feeling adventurous doing 30m/min at 3m/s/s.  Which in all honesty is way more than I can possibly hope to cut at given the amps I can bring to bear. Even from a rapids point of view its more than is needed.  The table is not that THAT big that it needs to whizz about at those speeds to get into position. 
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13 Sep 2021 11:16 #220424 by tommylight
All that speed is useless for plasma, max speed on any Hypertherm chart is 7.8m/m !
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