[Generic Default]

Sadly the only boring bars I have right now are those cheap little Chinese brazed carbide box of 9 types things, complete junk. They don't even have a relief angle. Definitely can't take any heavy cuts in steel with them.

Pariel, I went with aluminum for quite a few reasons. As shown in the video, the machine weighs about 560 pounds. If I had made this from cast iron or steel, it would be 1600 pounds and would require a special table or stand. Plus I wouldn't be able to move it without a forklift. The individual components would weigh several hundred pounds. The large bearings are there to ensure that there is no flex at the rotational axes. I'm of the mindset that overkill doesn't hurt; if anything, it reduces the possible points of failure.

The weakest points on this prototype machine are where the motor shafts couple to the pulleys. Since the motors are 6384 outrunners, the motor shaft is 8mm with a length of ~90mm from the point where the shaft couples to the rotor to the point where torque is transmitted via set screw or plum coupler to the pulley.
This 8 x ~90mm steel shaft doesn't have the torsional rigidity I want. It's easy to fix with a larger shaft or by driving the pulley from the motor bell near the connection (which will be done on the production machine) but on this prototype, the spindle motor torsion is the weak point.

"but the lack of hard numbers on capacity reinforces my suspicion"
What kind of hard numbers do you want? I've been hesitant to list things like max turning length or diameter because it depends on what chuck/collet nose is on the faceplate, and the 4:1 ratio ect. I also don't want to be one of those people who lists the accuracy of the machine as the minimum theoretical micro-stepping resolution. Numbers like this are reminiscent of the way digital cameras are thought of by average consumers, where the megapixel number is seen as the only thing that matters.

[Pariel]

Pariel, I went with aluminum for quite a few reasons. As shown in the video, the machine weighs about 560 pounds. If I had made this from cast iron or steel, it would be 1600 pounds and would require a special table or stand. Plus I wouldn't be able to move it without a forklift. The individual components would weigh several hundred pounds.

Weight in a machine tool is a *good* thing. Yes, it makes it hard to move. The weights you're talking about are pretty standard for the larger benchtop mills, small knee mills, 12x36 lathes, etc. which many hobbyists have in their garages and basements. In addition, the vibration dampening characteristics of cast iron when compared to aluminum are probably valuable even in a machine this small.

The large bearings are there to ensure that there is no flex at the rotational axes. I'm of the mindset that overkill doesn't hurt; if anything, it reduces the possible points of failure.

I'm an engineer, my job is to optimize. An overly large bearing is expense that could be used elsewhere on the machine, and in either case doesn't make up for the lack of rigidity elsewhere.

What kind of hard numbers do you want? I've been hesitant to list things like max turning length or diameter because it depends on what chuck/collet nose is on the faceplate, and the 4:1 ratio ect. I also don't want to be one of those people who lists the accuracy of the machine as the minimum theoretical micro-stepping resolution. Numbers like this are reminiscent of the way digital cameras are thought of by average consumers, where the megapixel number is seen as the only thing that matters.

Real life speeds, feeds to calculate MRRs.

Measurements of repeatable tolerances.

Longevity of the PTFE on anodized aluminum boxways.

It's an impressive piece of hardware, especially for one person to come up with, but I'm not convinced it's a product that's ready to compete on the open market. Frankly, I think Kickstarter functions as a crutch when it comes to differentiating products that can't last, and I would definitely not buy a machine tool through KS. Other people sitting more tightly in the hobby end of the spectrum may disagree, although I don't think you'll be able to price this machine low enough to focus primarily on hobbyists. When it comes to a highly custom machine tool like this, the other question is whether your company will be around to sell parts in five years (or preferably 10 or 20). Until you have enough installed capacity to convince serious businesses of your longevity, that will be a struggle -- just look at some of the FADAL guys attempt to relaunch as FADEC.