I just got the quote for extruded MegaRail.

Based on that, it seems the retail price of MegaRail 80 will be £40 for a 1 m length, and MegaRail Z will be £4.50 for a 250 mm length, or £12 for 1 m.

To compare, this is how much the rail for a 1 m × 1 m gantry-style CNC router table or milling machine would be:

• 4 × 1 m MakerSlide (for a dual-rail gantry) + 1 × 250 mm MakerSlide: £52
• 3 × 1 m MegaRail 80 + 2 × 250 mm MegaRail Z: £129

I would say that’s not a bad price for the huge increase in rigidity.

MegaRail Z will be available in 250 mm (to be determined: could be 275 mm), 600 mm, and 1000 mm.

MegaRail 80 will be available in 600 mm, 1000 mm, 1500 mm, and 2000 mm lengths. I’ll try to get 2700 mm lengths too, but those would ship only within the UK.

Assuming reasonable carriage widths:

• A machine with a 1500 mm gantry can cut the entire width of a full sheet of plywood, MDF, or chipboard (2440 mm × 1220 mm). With indexing, it can cut a whole sheet in several operations:
  • a 1500 mm × 1500 mm machine can cut half a sheet without resorting to indexing, or an entire sheet in two operations;
  • a 1500 mm × 1000 mm machine can cut a third of a sheet in one go, and it can still fit a whole sheet through and cut it in three operations, with indexing;
  • a 1500 mm × 2700 mm machine, if it ever became available, could cut a full sheet in one go.
• A 1000 mm × 1500 mm machine can cut a third of a sheet of plywood, or an area the size of an A0 sheet of paper (but a slightly longer and narrower shape than A0).

I got quotes for the dies for MegaRail 80 and MegaRail Z, but not for the extruded and cut rail itself, yet. The die costs were about what I expected (one can buy a decent second-hand car for that money).

I am going to go with the two-slot version of the MegaRail Z.  It is actually more rigid, which is worth the extra 4 mm in width.

These are the two designs I’m considering for MegaRail Z. They’re up on GitHub, also as PDF here and here.

The right side is the same in both cases.  The only difference is that the first profile has an additional T-slot. The side T-slot can be useful for attaching shields (in certain configurations), tabs for limit switches, and other accessories like that. The larger footprint is a disadvantage.

Both profiles have exactly 15 mm between the V centerline and the base. With standard MakerSlide V-wheels, this gives 21.45 mm of space between the carriage and the surface MegaRail Z is attached to. That should be enough for smaller lead nuts (a Tr 8 anti-backlash nut is typically 20 mm diameter).

I sent all variants I’m considering out for costing, and I’m hoping to hear back from the extruder soon.

The MegaRail family of profiles starts with two members:

• MegaRail 80, shown here, is a large beam with running surfaces for V-groove wheels on all four corners.
• MegaRail Z, a much smaller profile with a single running surface, is designed to be attached, in pairs, to a flat surface, for a much wider wheel span than is practical with a single profile.

MegaRail 80

The drawing of the MegaRail 80 profile can be found at GitHub. The overall dimensions are 46.4 mm by 87 mm (not including the slightly protruding ribbing). Walls are generally 4 mm thick, although four small sections are 5 mm thick to provide more “bite” for tapping holes. The four screw ports are M6 at 32 mm × 64 mm centers. The running surfaces are wide enough for both RM1 and RM2 steel V-groove bearings (although it’s not a good idea to run steel wheels on it unless it’s hard anodized). The standard MakerSlide V-wheels work, of course. With these, the wheel span is 104.6 mm centers, the same as for OpenRail on Misumi HFS5-4080 profile, or exactly 40 mm wider than for MakerSlide. The parallel running surfaces are centered exactly 40 mm apart.

For extra strength, two MegaRail 80 profiles can be bolted together. The groove pattern on one side nests into that on the opposite side, for perfect alignment.

The profile is extruded out of 6005A aluminium alloy (to be confirmed), and weighs about 3.2 kg per meter (MakerSlide is 0.9 kg per meter).  MegaRail 80 has area moments of inertia (a measure correlated with rigidity) about 18 times larger than MakerSlide in the wider direction, and 25 times in the narrower one. It is about three times more rigid in the wide direction than in the narrow one. I don’t have numbers for torsional rigidity, but I expect an even larger improvement, because of the unbroken outer wall.

MegaRail Z

I have several candidate designs. I’m still pondering which is the best combination of features. MegaRail Z can be used, as the name suggests, as the Z axis of a gantry-style CNC milling machine, but also as the Y axis of a moving-bed machine. There are several different arrangements for the Z axis, each with advantages and disadvantages, and each favours different features (and dimensions) of the profile.

Timeline

No idea yet. I am sending the MegaRail 80 drawing to the extruder/fabricator tomorrow. They will give me an ETA, which I’ll take with a small boulder of salt.