help with a 4' by 9' cnc build

[soyeb]

What i am looking for is a variation of sign manufacturing and cotinuous production of items. from very large to small. I am looking for reasonable cost but at the same time something which is fast as what i can get. I have done some research and would like to follow the plans off www.buildyourcnc.com. I have the actual make covered more or less and just need help with the electronics.

thanks a million

[irving2008]

What i am looking for is a variation of sign manufacturing and cotinuous production of items. from very large to small. I am looking for reasonable cost but at the same time something which is fast as what i can get. I have done some research and would like to follow the plans off www.buildyourcnc.com. I have the actual make covered more or less and just need help with the electronics.

thanks a million

OK, pleased to see you're not going for 9' long leadscrews! It just doesn't work (with sensible sized motors and screws) as he discovered...

[soyeb]

Only problem i have is he is making a 2 x 4 foot machine while i want to make almost twice that size. what is going to be the best with regard to electronics for my machine or is there a chart or someone who has made a similar size??

thank you

[irving2008]

Only problem i have is he is making a 2 x 4 foot machine while i want to make almost twice that size. what is going to be the best with regard to electronics for my machine or is there a chart or someone who has made a similar size??

thank you

If you hunt through his site you will find information on BlackToe, his 8' x 4' design using chain drive.

If you want to go with leadscrews you will need a ballscrew of 25mm diameter with fixed bearings at each end holding the screw in tension. With a 5mm pitch this will give you 1200mm/min (50ipm) cutting speed and 3200mm/min (125ipm) rapids (limited by screw whip) using an 8Nm NEMA34 stepper with decent drivers (50 or 60volt drives).

For the short, 4', axis a 16mm x 5mm ballscrew simply supported and a 2Nm motor would suffice.

[phooddaniel]

If you hunt through his site you will find information on BlackToe, his 8' x 4' design using chain drive.

If you want to go with leadscrews you will need a ballscrew of 25mm diameter with fixed bearings at each end holding the screw in tension. With a 5mm pitch this will give you 1200mm/min (50ipm) cutting speed and 3200mm/min (125ipm) rapids (limited by screw whip) using an 8Nm NEMA34 stepper with decent drivers (50 or 60volt drives).

For the short, 4', axis a 16mm x 5mm ballscrew simply supported and a 2Nm motor would suffice.

Quite correct. There have been some interesting ways to stop wild whipping of lead screws, but the expense and efforts are generally futile. Rack and pinion, timing belt and roller chain seem to be the best methods to move at long distances. I have tried with great success both the roller chain (at #40 size) and timing belt. My intension was to try to eliminate as much mechanical backlash as possible and these two really do the trick. Rack and pinion, although the best for the longest distances, can still exhibit some backlash due to the possibility of space between the two gears. Backlash is almost eliminated since the roller chain and the timing belt are both tensioned and the drive pulley/sprocket are fastened to the motor.

By the way, thanks for supporting the efforts over at buildyourcnc.com. This is my first post on this site.

[irving2008]

Quite correct. There have been some interesting ways to stop wild whipping of lead screws, but the expense and efforts are generally futile. Rack and pinion, timing belt and roller chain seem to be the best methods to move at long distances. I have tried with great success both the roller chain (at #40 size) and timing belt. My intension was to try to eliminate as much mechanical backlash as possible and these two really do the trick. Rack and pinion, although the best for the longest distances, can still exhibit some backlash due to the possibility of space between the two gears. Backlash is almost eliminated since the roller chain and the timing belt are both tensioned and the drive pulley/sprocket are fastened to the motor.

By the way, thanks for supporting the efforts over at buildyourcnc.com. This is my first post on this site.

phooddaniel,

Welcome to MyCNCUK.

I note from your site you achieve 1500ipm rapids on BlackToe, thats pretty impressive!. What cutting speed do you generally recommend?

What size motors do you use for the X-axis to get these rapids and what is the gantry weight on your BlackToe design? Assuming you drive it from MACH3 can you say what acceleration values you have set up for cutting and rapids?