New Machine Build- Need info on lead screw

[miwms1955@gmail]

I am in the process of getting everything together to build a 2 x 4 cnc router and need some info on a lead screw for my X axis.
How much of a benefit will I get from a 2 start(2 thread) lead screw?
I think there is an increase in speed but is it worth the increased price?

Thanks in advance
Mike

[ger21]

Probably 2-4 times faster. Assuming 1/2-8 2 start acme. Depending on motors and drives, you may even want to go with 1/2-10 5 start. I find the 60" long 1/2-8 2 start screws on my X axis whip badly over 150ipm, limiting my rapids a little.

[jsheerin]

I have the 1/2-10 5 starts, ~60" long as well between supports, and I can go a bit faster before whipping - about 250ipm or so. Above that they start vibrating but not really whipping. From theory, you should be able to go twice as fast with the 1/2-10 5 start before whipping. However because of stepper motor torque curves, that might not actually be true depending on what your cutting forces are and where on the force vs speed curve you are running.

From reading chip load information from spindle manufacturers, you'd really want to cut most wood even faster though - more in the 300-600ipm range if you're using 2 flute tools. This seems to be much more easily achievable with rack and pinion setups than screws. I've been looking at converting my router over to that lately for that reason.

[miwms1955@gmail]

I plan on using 2 lead screws for the X axis. Will this reduce the problems with whipping and vibration?

Thanks,
Mike

[ger21]

Originally Posted by miwms1955@gmail I plan on using 2 lead screws for the X axis. Will this reduce the problems with whipping and vibration? Thanks, Mike

Nope. I have 2 screws on mine. Though one of them is bent slightly, which causes more whipping. The 5 start is really the way to go. But you will want at least 300oz motors minimum.

[FandZ]

Originally Posted by jsheerin From reading chip load information from spindle manufacturers, you'd really want to cut most wood even faster though - more in the 300-600ipm range if you're using 2 flute tools.

Ouch, my best rapid is 68IPM. Gives me a lot to think about for my next build. I haven't cut that much with my router but I haven't noticed any problems cutting at 45ipm.

[jsheerin]

I've had some problems with my bit heating up. The higher chip load is supposed to reduce heat buildup because the larger chip carries the heat away from the cut. As you probably have experienced, if you sit the cutter in one spot, it tends to burn the material. Going faster should reduce that. But if you don't have enough force or power in your router, you have to take smaller depths of cut.

To Mike, I'd recommend getting a motor that has a broader torque curve. For example, the 425oz-in motor from Keling is what I have. It has a lot of low speed torque, but not as much higher speed torque. So at higher speeds, a lower rated holding torque motor with better design will actually have more force.

[FandZ]

Originally Posted by jsheerin I've had some problems with my bit heating up. The higher chip load is supposed to reduce heat buildup because the larger chip carries the heat away from the cut. As you probably have experienced, if you sit the cutter in one spot, it tends to burn the material. Going faster should reduce that. But if you don't have enough force or power in your router, you have to take smaller depths of cut.

I haven't tried taking more than a 1/4 depth inch cut yet. Maybe that is what has saved me but I haven't seen it burn anything. The last time I used it I felt the bit right after it was done and was surprised to feel it was barely over room temperature. I was useing a 2 flute upspiral Bosch bit I got from lowes on my hitachi 2.25hp router. The wood was scrap pieces of boards that I had. Not sure what type. I got a sheet of .75 MDF I was planning on useing next. I hope it doesn't start smoking.

[miwms1955@gmail]

Where would I find a 1/2 - 10 5 start acme lead screw? I have been looking on the internet and the closest I've found is a 1/2 - 8 4 start screw.

Thanks,
Mike

[ger21]

McMaster Carr

[rbarr110]

Originally Posted by miwms1955@gmail Where would I find a 1/2 - 10 5 start acme lead screw? I have been looking on the internet and the closest I've found is a 1/2 - 8 4 start screw. Thanks, Mike

Try MSC Direct as well
http://www1.mscdirect.com/Acme-Threa...000000451.HTML

[miwms1955@gmail]

Thanks for the help.
Mike