[Torchhead]

Thanks for the reply Tom!
That is some great info! As for the wheels I am in the process of making some leveling jacks so when i put the table in place i could raise it a little and also level it. For the gear reduction what would you suggest? I have a 20* rack gear and a 15 tooth pinion gear. I could easily add belt drive gear reduction to my carriages. This is my first gear rack build and would like to get the most out of it. My plan is to have a well built table but low cost (the best of both worlds).

While you can use the number of teeth to figure a gears diameter it's just a lot easier to either look it up (pinion are sold in "DP" sizes (diameters). it is the precise diameter (centerline of the tooth contact circle). Just a quick measurement of the diameter works fine for the estimate formula:

"You get a speed gain of PI times the pinion diameter"

So a 1" DP gear will give you 3.1416 for a number (which is the actual circumference of the gear} . Round it off to 3. That indicates you need a belt reduction of 3:1 between the motor and pinion gear. While you can get into complex formulas that involve "reflected inertia" the rough method works pretty good since you have a pretty wide window of torque with a dual drive setup.

The numbers end up being a nice balance with steppers with plasma for getting good speeds coupled with good acceleration at the higher speeds. With steppers it is more difficult because you have a continuously changing torque curve so any calculation you do only gives you the optimum at a given speed.

Acceleration is all about time. It is the length of the curve that is important. (time it takes to go from the initial speed UP/DOWN the new speed) You have to set a target upper speed (feedrate) and you want to hit it in the shortest time possible. Obviously the curve is a lot longer if your target speed is 300 IPM than if it was 30. That is why one way to get sharp turns is to slow everything down, BUT in plasma cutting that has consequences. Some vendors have offered "corner slowdown" to combat the issue that they don't have the torque to get the level of acceleration. While it cures the corner issue it changes the dynamics of the cut to the point that you get wider plasma kerfs (changing the size of the part), and THC reactions to the resulting higher voltages , etc) Without dynamic anti-dive built into the hardware the torch will dive to the plate further changing the cut dynamics.

In one corner slowdown scheme ti turns off the THC until it makes the corner. All of that works to a level but it is a band-aid for a mechanical issue (lack of sufficient acceleration).

And you thought building and cutting with plasma (simple contours) was going to be easy!

TOMcaudle
www.CandCNC.com

[travmc1]

Thanks Tom!
So you are saying if the DP is .75 and the number would be 2.3562 round it to 2? So a 2:1 ratio would be good. did I figure that right?