I agree on that, they get more done a week than I do in a year. Their "get to it", "make it happen" drive is impressive.
On the build though, meah. Some bad information and while it looks great at a superficial level, is it? I really hate the guy who, on the sidelines, watches someone run through walls and get 95% of it right and then sits from the armchair criticizing the 5%. However, for posterity and to make it an interesting discussion, today, I take one for the team, and will be that guy
. My critique is based the claimed goal, being an alternate to a "professional grade" cnc mill, which implies a level accuracy. I don't think they could have possibly achieved anything close to that.
A major, catastrophic flaw is nothing was done to insure the accuracy of the way geometry. Parallelism of the linear bearings means nothing (except they won't bind). What matters is, are they straight? The rails are very flexible and will conform to whatever you bolt them to. You cannot make much of a machine if you are relying on the flatness of hunks of cold or hold rolled (or your floor lol) For that matter, the material will have a high level flex over that length. The fundamental accuracy of the machine is determined by the flatness of whatever the rails sit on, and achieving flatness, to the leveled needed for a reasonably accurate machine tool, is far from trivial
. Its a key element in ending up with a good machine, and one the most expensive and time consuming aspects of creating a machine. They skipped/ignored that as far as I could see.
Epoxy granite is amazing stuff and holds great potential for machine tool builds, especially when combined with fabrications. EG is comparatively weak and flexibly compared to steel or cast iron, but it brings vibration damping ability to about 2x that of cast iron. btw, they should know, vibrations are damped, not dampened. No water is involved. This works because energy is absorbed as the wave goes through the boundary layer of two unlike materials - stone and epoxy. His lecture says the rock is added because its cheap filler and second it adds mass. No, its because its presence creates the boundary layer, the large surface area, between the epoxy and granite, that is absorbing the energy - basically converting motion into heat. In cast iron this happens the same way: the boundary layer between different materials - the graphite and the metallic structure. Calling it "dampening", thinking the granite is just filler and using stone rather than sand (far more boundary layer) is a not a huge fail, but still, its says they don't really undertabnd what they are doing and that qualifies as armchair comment worthy
He's also dead wrong with the claim that casting have to left for several years. That's a once upon a time, old wives tale. Currently engineering/science is that they don't move about on their own. (they or any material can move if you machine it, that's movement as internal stresses are changed and a new equilibrium of forces is reached, but they don't keep wandering about on their own). Manufactures do not age machine tool castings and have not do so for a long time. Once they are stress relieved they are stable. I take offense at lecturing when you don't know what you are talking about (hopefully I'm not too guilt,y too often
More use of steel (for rigidity) combined with EG (for damping) would imo be better. They did some, but they didn't normalize or stress relieve the fabrication. That puppy's going to move as its machined and won't end up an accurate structure.
Same with the table. A big slab of stress relieved case iron would have been a lot better, but if using steel it should have be sent for stress relieving first. Even hot rolled; machine a slab like that on one side and its going to spring into new shape.
I've used those low budget linear rails before. They are not worthy of spot in a $15k machine tools....which I'd say is really is 40,000+ machine tool....who's time is free?
I didn't see how they got everything square. Maybe the did, but this not easy and is critical to performance. There is no mention of it in the video and it would have been challenging and a mission critical step...makes think because of its absence, like flatness, that it was skipped.
I do admire what they were able accomplish, so feel a bit like schmuck being so critical. However these finer points of machine design and manufacture are what cost the money and are what makes the machine perform (accuracy etc). They deserve mention in the context of understanding of whats going and what needs to into a machine tool.
I just scrapped out a Mazak. Japanese, best of quality cnc mill with a tool changer. With whatever wear was present it still would far more accurate than lengths of hot rolled steel would provide. Box way vs linear rail. Japanese servos and spindle. Mostly it need someone to put a bunch of time into working out and fixing/replacing the control system....but you can't give them away. I think rebuilding that, even if scraping was required, would yield a far better result for less cost.