[webgeek]

Hi all; I've got a good sized CNC mill that I love but I find it's a bit of a pain to use for small and thin stuff. It's low-ish RPM range is really limiting on what I can get away with when it comes to things like plastic, small bits in aluminum, garolite or carbon fiber. To that end, it seems I need a router. I want the router to replace some of what I do on my big mill though so I'm trying to come up with a compromise solution. Here are the requirements:

• Working envelope of 12"x18" (the hole grid is this size in the pictures)
• Ability to cut at lowish all the way to high RPMs
• Be reliable
• Be accurate
• Support coolant
• Be usable inside
• Cut aluminum reasonably - I know I won't be hogging, but I'd like some good speeds and shallow depths if possible. Not trying to push it here, but I'd like a reasonable surface finish.

Now I've got a fair bit of CNC experience, so I'm reasonably comfortable in putting together the right steppers, drivers, etc. for this project. I've never built a gantry-type design and I've come up with something a little non-traditional so I'd like to know if this is a workable solution. The specs for the design thus far:

• The base of the entire machine will be 1/2" MIC6.
• X and Y linear rods are 16mm from VXB. Not decided on the Z, but probably 12mm. 4 Linear Bearing 16mm CNC Router Bushing Linear Motion
• Spindle is undecided - I'm thinking the trim router from Rigid combined with the Think and Tinker precision collects and a Super PID to get the low RPM torque. Would love to know people's thoughts on this set up.
• Keiling steppers and drivers - I've had great luck with his stuff and plan to keep on using it.
• Roton 1/2-10 ACME screws with their anti-backlash nuts. These screws will be machined to have a flat for bearings, threads for a lock nut, and a flat again for the coupling to the steppers. I'm very nervous about the 25 lbs rating on these as I've never used anything but ballscrews in the past. Any thoughts here?
• Screws will be supported with two skate bearings on one side and clamped in place with the locknut. A single skate bearing will be on the other side. Not sure if this is good enough for a small machine or not. Would love comments on this too!
• The rods are held in place with shaft collars - not sure I like this in hindsight, but I'd like to avoid the slitting trick everywhere if possible.

Now for pictures...
The first shot is the obligitory render. I ran out of time tonight so it's missing lots of nuts and bolts but the basics are there. The last shot is the same, but just shaded for visibility. The z-axis is still in the air. The plan is to use the Mic6 as the bed combined with dowel pins to help secure things and locate them properly. I show how this works with the next three pictures with the gantry detail.

The bearing blocks have pins in them along with 1/4-20 tapped holes. The gantry base plate gets tied with 8 dowel pins and 6 bolts. In turn, the pins are shared for the stepper mount and the bearing mounts on both sides for the X axis.

I'd love any advice on any of this as it's all kinda different from what I've done in the past. Thanks much!

-Mike