After building a ‘c-beam plate maker’ I’ve gotten a case of, as we call it in boating ‘biggerboatitis’ and I’ve been thinking about adding a 1000mm c-beam for an x-axis and using the leftover 500mm c-beam and extending the y axis for a c-beam XL. This then got me thinking about moving forward to a Sphinx design. Then I asked myself just what are the pros and cons of each design ie the movable vs fixed stage, a long movable gantry vs dual long parallel beams moving a shorter movable gantry. So, without considering cost (which is always to be considered) what are the pros and cons of each design
One pro of moving gantry is you can feed long sheets in and mill it in sections using pin-hole registration. Another is that you can build a larger cutting area in the same amount of space with moving gantry.
Put simply, if you want more than 12 to 14" usable on the y-axis, you are best to go with a fixed bed. Moveable platforms have increasing issues with flexure with increases in size. To counter this additional trolleys are added to support the platform which in turn reduces the effective movement length of the bed. You wind up building a whole lotta machine and not getting a whole lot of usable length in return. On the opposite side of that, with fixed platform machines you only lose 8 or 9" because of the gantry length no matter how long you make the y-axis.
However, with the Ox Type moving gantry CNC, probably 85% of any problems arising, will be in the moving gantry area. Just the principal, of moving a weight, which is under high and variable stress, on rubber wheels, can logically only lead to weaknesses surrounding the moving gantry. We are all aware of the additional twist and unwanted movement in the X axis and the Z axis adding to the likelihood of unwanted movements whilst cutting. So, unless you are ready to considerably beef up your CNC, or move to Linear rails with carriages, to counteract these effects, the fixed C-Beam Gantry with a moving bed is logically the next evolutionary step. We still have rubber wheels to contend with, but the stresses are different and much reduced. Flexing in the moving bed is easily corrected by having outriggers to add additional support, or two Linear Actuators at each side. Yes, cutting area is quite reduced, but it represents a price to pay for a far more rigid and stable method of CNC cutting, within a viable Hobby cost. There will always be room for both types of CNC, because they both have different benefits, and failings, to offer, and both are easily within the financial reach of just about everybody. I guess the whole point of this Forum is just that,........ to point out the Advantages and Disadvantages of all machines built on this Forum, and for all of us to learn and move on to the Next Best CNC. I'll get off my box now and quietly walk away Gray
That's what I'm working on. Didn't start out as the plan. In one of the openbuilds videos Mark commented some build a little one and use ithe to make parts for a bigger more custom build. After a few weeks of reading, planning, pricing out plates I saw that video a second time. Then saw the little c beam plate maker bundle at the parts store. This time it made more sense. Between that and a friend who's got some interest in a machine of his own I ordered parts for a slightly revised c beam machine. Soon after I'll be using it to make custom plates for a larger OX style machine.
Thanks for all the replies I thought it would be good to get these things out in the open . I think the best thing is to build both and then I still need to build a printer
LOL, I started with a simple diy 3d printer. Thought it would be a good simple way to get started. $170 anet a8. It's been a fun and have learned alot. I will eventually do one openbuild style but have two projects to finish first!
