What can i expect from my CNC?

[nikbrewer]

I am building my first cnc to cut parts for speaker boxes that i sell. It is apporx 2' x 4'. I ordered plans but have changed a few things. It suns on pipr rail ( crome tubing in my case. I am using a rack an pinion on the x, 1 start 1/2" acme thread on y and z. i have a 20 t pinion on the x, geared down about 3.5:1 to the motor. direct drive on y and z. Stetters are 400 oz for x and y, 260 oz for z. i got the kit from probotics. 24v 7 amp power supply., thier control boards,ect. ROuter is a variable speed 3.25 hp porter cable. What kind of feed rate can i expect. i was wanting 120 ipm, but not sure if thats possible. I wil lbe cuttng varius thckness of mdf, probally with 1/2" upcut 2 flute bit.

thanks and any input would be great

[ger21]

You'll probably be lucky to get 80ipm on the axis with the acme, but the rack and pinion might be a lot faster, not sure.

[nikbrewer]

is the fact of the acme thread whipping, or drag, or just max rpm limiting me on the acme screw? i am using pullys, so i could gear the y 1.5:1 t oget more speed if thats the issue, or is 80imp all the thread can handle

[ger21]

Probably rpm first, whipping second, and inefficiency third. If you gear it, the screw will spin faster, then whipping may become an issue. Although if it's only 2ft you may not see any whipping issues.

1/2-10 acme is only about 30% efficient, so 70% of your torque is wasted. If you geared it 2.5:1, it would be equivalent in turns per inch to 1/2-8 2 start. But 1/2-8 2 start is about 65% efficient, even though the turns per inch would be the same, the 2 start would deliver twice the force on your machine.

[nikbrewer]

i see, i am still fairly new to all this. Well, i will see what i get with what i have, and replace lead screws are needed.

[acondit]

Originally Posted by ger21 You'll probably be lucky to get 80ipm on the axis with the acme, but the rack and pinion might be a lot faster, not sure.

Nik, Ger,

I am using 3/4"x5 precision acme screws (single start) and I can jog about 200 ipm and cut at up to 75 ipm. Actually I can jog 210 ipm on the X and only 180 ipm on the Y axis. I have a very slight bend in the Y axis screw (about 0.020 over 34").

Alan

[nikbrewer]

cutting at 80 is not bad. what is limiting you cutting faster? torque? what size steppers are you using?

[acondit]

Originally Posted by nikbrewer cutting at 80 is not bad. what is limiting you cutting faster? torque? what size steppers are you using?

Fear and lost steps. I am running a 32 volt power supply. The drives are max 3.5 amp and 40v. The motors are Nema 34 round steppers (200 oz. in.).

Alan