Re: Yet another welding/machining/misalignment problem on Saturn 2. Sigh.
Originally Posted by
he1957
Are these variations caused by the box section steel frame or something else?
Thanks,
It's a combination of errors, IMO. I believe the errors in the rack and rail mount alignment are due to the lack of a machined datum in the steel frame. As I said before, that practice is an industry standard anywhere there's a rack or rail or ballscrew or other precision component mounted. It is near impossible to get alignment tolerances in a welded frame anywhere near what FLA quotes on their website without machined datums. No doubt the cost of doing so is a factor. Again, the FLA machines are SO close to being great that it should at least be offered as an option, and at a minimum be mentioned on the website. A steel frame should be welded, stress relieved (normalized) then machined. Not doing so will require shimming, not just when the machine is initially assembled, but down the road once time has done the stress relieving. I've begun to think that time is the factor here. The frame is gradually stress relieving itself and as a result, changing shape.
Another factor is how the bolt holes for the rack and rail are machined once the frame has been painted. Too many comments on this forum indicate to me that it's not a precision controlled process. The table holes certainly aren't. There are some really big (visibly off) variations in those, which make it a pain to mount, but in the end don't contribute to the tolerances of the machine. They do indicate to me a somewhat careless approach to the build in general, though.
In a post about a year ago I went through a detailed approach to squaring the gantry on the Saturn 2 when we initially set up our machine. It was out by almost 1/4". Maybe it got knocked around in shipping, but more likely the build methods used did little to ensure it was close. Some of the mounting holes for our gantry plates are double drilled side by side because the first hole was off by 3/16" or so. The plate welded to the gantry itself is visually out of square to the connector plate that the bearing cars are bolted to.
The whole process reminds me of my earliest days as a woodworker. I look at some of the pieces I made that I was so proud of at the time (they look nice) and cringe when I see the now obvious errors I made. I'm a much better woodworker now not because I have better, more accurate equipment, but because I started paying attention to how things should be done to guarantee better alignment, precision and better fit. It does not take me any more time to make something right - just the opposite - it just takes better practices. I said earlier that I'm at fault for assuming that good practices were followed in the construction of these machines when I decided that this was the machine for us. For example, I was impressed that Nate used 25mm rails on a machine in this price range. But putting $40 Blumotion slides on a drawer that's out of square does not make it any more square. It simply makes the out of square drawer open and close a little more smoothly.
My whole purpose for bringing this to the forum is not so much a rant for ranting sake. We knew and discussed at length the pros and cons of this purchase beforehand. It took over a month just to get a quote from Nate. I posted because this could be a great bang for the buck with just a few improvements. If I were buying a Chinese machine sight unseen I would know going in that making these adjustments, corrections and modifications might be likely. I didn't expect it to be the case here.
Saturn 2 4848
CRP Plug & Play NEMA 34, 2.2kw Spindle, Mach3