Acme thread 1/2-8 (8 start or 2)

[rmubaja]

The title saids it all, Mcmaster has both in 6foot segment for a dollar differnce between the 1/2-8 8 start and the 1/2-8 2 start. One is 1 turn per inch and the other is 4 turns per inch. The problem is which one? My stepper motors have 380 oz-in till 600rpm then it starts tapering off.
My gantry should weigh about 28 pounds, and If I'm right (I'm not a engineer)
1/2-8 8 start(1 TPI) 1 * 200(steps) = 200 | 1" / 200(steps) = 0.005" (resolution?)
1/2-8 2 start(4 TPI) 4 * 200(steps) = 800 | 1" / 800(steps) = 0.00125"

The second bit is my linear bearing for the gantry, I have eight 20mm linear bearing but no 20mm rod, and I cant find any 20mm rod in my budget.
But I also have a bunch of 1/2" linear bearing what kind of deflection do you think a 1/2" drill rod would have over a 48" span?

I know plasma is not the most accurate process (0.03" resolution?)
But this table is only going to be use for plasma 3 times out of 10 the rest its going to be a router table.
I have to order the acme rod in the next day or so to get it in time of which would be best?

[rmubaja]

Any suggestions? the order to Mcmaster needs to go in today by 12 o'clock and I still cant decide between the 1/2-8TPI 8 start or the 2 start.

[ger21]

8 start will give you at least double the speed, probably more. depending on how long the screws are, the 8 start will have less chance of whipping with longer lengths. I have the 2 start, 60" long, and it whips a lot at 150-170ipm. The 8 start should easily get you 300+ipm.

[rmubaja]

I ordered the 8 start I hope my steppers have enough torque to get it up to 300ipm, I was wondering about the resolution but looking at the tech manual for the steppers I can take it up to 3200micro steps per revolution so 0.0003125"

Now its to just find a 45 to 75 volt 8 amp power supply.

Copied the chart from the manual: