[monte55]

Hope I can get some help. I want to build a 48x48 plasma/router table.
X and y I plan to use 1 inch round shaft with open linear bearing blocks so I can support the shaft midway. I plan on four 425 oz 8 wire steppers with controller and power supply from Xylotex. I plan to use two motors on y..one on each side direct driving acme screws possibly 1/2 x10 or 3/4 x 6....any
ideas or suggestions on the acme part. I may just bush Z. I have a small
lathe and mill so I can do quite a bit of the mechanical part myself. My shortcomings are related to controllers, software, power supplies etc. I've
torn motors apart for years to make things but never messed with cnc and steppers yet. I built a 300 lb radio controlled skid steer 4 wheel robot thing after watching BattleBotts, to pick up my paper during bad weather days(only once) but used it for about everything else so I know I can make this
table. I would rather have input from people that have already success and
failure so I can learn what not to do. Any and all replies will be welcomed.
thanks..............nick :cheers:

[dertsap]

i would suggest the 3/4" leadscrew above 1/2 due to the sag and flex over that length and the lesser tpi will gain you speed above the other , i would suggest gecko drivers as well , they are excellent drivers and will handle much larger motors down the road if or when you decide to go bigger ,
good luck

[Torchhead]

Your target IPM number for plasma needs to be 300 to 400 IPM. Based on a leadscrew of 10TPI and directly coupled steppers you need to spin the motors at 4000 RPM.....won't happen with the setup you are proposing. You will be lucky to get 1000 RPM. So your top speed with the 10TPI is about 100 IPM. Fine for routing but too slow for cutting any metal thinner than about 11 ga with most plasmas. Also you have to factor in that your leadscrews (to get 48" of workspace) may have to be 52 to 60 inches long. 1/2" diameter screws spinning at 1000 RPM start to reach their "whip" limit. Centrifical force causes the screws to bow as they rotate. I have 3/4" 5 TPI ballscrews on my dual drive plasma table and about 200 IPM is all the screws will take.

In the world of CNC you are always trading Speed for torque or vise versa. To do a combo table useful for both routing and plasma you need:

Heavy rigid gantry (for router)
Good torque at moderate speeds (30 to 80 IPM)
High Speed AND high torque (for corner accelleration) for plasma to move the heavy gantry
Good smoke extraction across a wide area for plasma
Good vacuum system for sawdust and chip removal (concentrated at cutter)

You have to overbuild the table to get where you want to go. Your gearing has to change to get the high speeds but you still have to deal with having plenty of torque to sling that larger gantry around at 300 IPM and accelerate the load quickly enough not to get corner rounding. The commercial combo tables use big 600 oz-in (or bigger) steppers running on at least 48VDC to 70VDC. Lower voltage means lower speed and accel numbers. The servo tables use huge 600 to 1200 oz-in servos with 3:1 or higher belt reduction to just power their way through the problem.

I wish there had been someone around to tell me these things 4 1/2 years ago when I built my table and started cutting steel but this whole hobby CNC thing was pretty new then.

Here is some homework:

Software: www.machsupport.com www.sheetcam.com www.vetric.com
Motor Drives: www.geckodrives.com
Power Supplies, Cabinets: www.seanet.com/~dmauch/Products2.htm
Breakouts, controllers, pendants, Digital THC, etc ......: (me)

Tom Caudle
www.CandCNC.com