Before I start on a MechMate I figured I'd make myself a little machine for PCB making. Right now I have to change spindles and add a tabletop (which has to be surfaced since more than a couple 'thou deviation can blow a board). Of course PCB's need enclosures and enclosures need routing so I have to swap spindles a few times while I get the PCB and Enclosure to actually work together! In other words, I really need two seperate machines.
I have a few odds and ends laying around as well as the old gantry rails and linear bearings (3/4") that I replaced with supported rails recently so I decided to make a light duty router for engraving only. Its very light duty so I can cheap out on a lot of the components. I also decided to use a fixed gantry and sliding table. This is so I can use drawer slides (ball bearing type).
I buy copper clad boards that are 12x12 so thats what I need for a work area. I figure I'll shoot for 14x14 travel just for some breathing room and a Z travel around 4" (more to fit my hand under the spindle and pull out bits than anything about the work itself).
I'm going to try plain old 3/8th-16 allthread with two nuts arranged like I saw on a build here. Two pieces of HDPE with a (tight) slot routed out for the nuts. On fixed to the Z and the other screwed into the first. The slots face one another so tightening the screws will compress nuts against the leadscrew threads.
The Z linear bearings are skate bearings on round rod. The abnormal thing is I'm not tilting them. I'm using drill rod and the pre-load will be quite light. As for work loading... Well, cutting 0.006" deep into copper with a V-Engraver isn't exactly a high resistance task. About the worst it'll see is cutting 1/16th FR4 with a 0.063" rasp router bit at 10" minute.
I've been working all day on designing the Z itself. I have some aluminium bits and pieces around here from .25" to .75" and I'm going to use a little of it. Mostly where I need both thin and stiff - like the router mounting plate.
Anyway, here's some pics of the design and the Rhino file. Not quite finished yet as I haven't decided what I'm going to use to mount the Z-Stepper or how to get the home switch situated. I'm also half expecting to have to enclose the sides with 1/4 MDF as I'm not sure the 3/4 MDF top and bottom won't end up flapping around.
MDF doesn't thread very well at all so I'm using cross dowels and bolts. These are used for MDF furniture and are very good connectors that allow butt joints which would normally be suicidal.