I have updated (3/24/2019) this thing to include jigs for J, F, and C size MPCNC tubing. Also I provided jigs for both 4mm and 6-32 screws. All size variations are included in this one download.
I am building a MPCNC J:https://www.thingiverse.com/thing:1671517 It is a beautiful design; I tip my hat to Allted. But I got stuck when trying to drill the holes in the z-axis pipes. This Jig helps drill those holes.
This jig helps drill the two holes in each Z axis tube at the correct spacing, using the skate bearings and fasteners used to build the MPCNC. The only part you would need is a 5/16" center drill that you can buy in a package of 5 at Harbor Freight, item 60381. Or an 8mm drill may also work, but I don't have one of those to test. It should fit within the bearing.
.1mm layers, 1.2mm wall (3x .4mm nozzle)
I had trouble figuring out how to drill the two holes with proper spacing. I experimented with a couple different drill guides made out of PLA, but they just got chewed up or melted by the drill while trying to drill through the wall of 1" OD Stainless steel pipe. Then I started thinking about how to go about using metal drill bushings. Finally I realized that I could use the MPCNC 608 skate bearings as drill bushings. They have an 8mm bore that closely fits the 5/16 center drill. The smaller diameter of the center drill is a good size for the 6-32 screws. Though I think I followed up the pilot hole from the 5/16 center drill with the next size center drill.
To use the drill guide just line up the end of one of your z axis pipes with the end of the guide. The guide is symmetric, so you don't have to worry about which end you line up with. I clamped the lobes with a couple c-clamps with the guide sitting firmly on the table while I drilled the holes with a handheld drill motor. But you could also clamp this in a vice. You could also use a 6-32x3/4" or M4 screws and nuts (the size used in the MPCNC) to clamp this together. My photo above of the jig I used didn't have the holes for the 6-32 screws modeled in, but I included it in the stls I uploaded.
I uploaded this in a rush, so I only have a small piece of pipe loaded into the jig. obviously your z-axis pipes would be longer.
I printed it with just a skirt, with the face the bearings press into oriented down on the build plate. This doesn't need structure to print on my printer, but I also print slow for high quality. 20mm/sec.