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I have a few questions that I hope this forum will help me understand.
1)Why is it that the majority of designs I see out there have tall gantry legs as opposed to a "tall rigid wall" with the rails mounted on top? I would think that it would be easier to build a rigid wall as opposed to adding extra corner bracing??
2)With the rigid wall design, why would you not mount the rail(Cold rolled steel plate with roller bearing carriages) vertically(on edge) as opposed to horizontally?
1) Adding a 'wall' would be more rigid, but at the expense of travel distance.Quote:
Originally Posted by Flyn Hawaiian
2) not sure I follow.. It's horizontal because the axis travels horizontally, only Z is vertical.
* Edit:
i read it again And on 1) There would not be much benefit in adding two huge walls on each side & attach the rails on top. (Ok maybe would be better protected from chips & dust) It would also be more expensive.
The "Tall rigid wall" method makes loading and unloading difficult, especially on larger machines. That's the main reason it's not used much.
There are machines here that use that approach, though.
My machine is a hybrid, with the walls being in the air, allowing the work to be slid underneath if required. But Gerry's point is exactly right : it is a pain to be reaching over the rails to get to the table, and losing 8-10 inches of Y travel is unpleasant. This may not be an issue if the machine is wide enough that you are always working from the front of the table, but then the width becomes a source of weakness. My next build will have low sides.
CarveOne has side mounted CRS rails, but he has high gantry sides. It seems that if you have the high rail sides, then it is natural to have the gantry carriages running on them and directly supporting the gantry rail.
[I don't think it makes much difference, really.]Quote:
Originally Posted by Flyn Hawaiian
Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software
1) It's probably more about using structural tubing instead of thick plate material due to lower cost and they are going to use the tubing for the framework anyway. On my original effort to build a larger machine I found that the tubing I used was much more flexible as far as racking of the gantry than I would have expected. Two tries at building a better gantry didn't work well, so I scrapped the whole idea and ordered the new (at that time) R&P drives from cncrouterparts and built a whole new machine that ended up about 5' x 12' in overall size.Quote:
Originally Posted by Flyn Hawaiian
2) Ahren used the horizontal rails for his prototype machine and later for his kits. I tried the vertical rails and a solid 5/8" thick by 9" wide by 20" long vertical plate of cold rolled steel plate to support the gantry. There is a drawback to the vertical rails and bearing carriages in that the lower bearing plate is just a guide, and is not supporting any of the now 185 pounds of rolling weight. The upper bearing block is supporting all that weight on two bearings each side of the gantry. It is working very well though. I connected the upper and lower bearing carriages with the vertical plate and the R&P drives are mounted into the plates.
If I add triangulation plates at the intersection of the gantry beam and the vertical plates it would limit the Y axis travel more than I liked, and a piece of angle iron would not help much with the flexing of the beam to plate junction. I decided to make the end of the gantry detachable by welding a 5/8" thick x 6" high x 9" wide plate to the end of the gantry beam (which is cut to fit over the end of the beam) and bolt it all together with 1/2" button head bolts. If I want to redesign the beam (what, again?) I can do that and still use the same vertical plates. The plates are outside the machine's rails where it allows me to shield the rails and get more Y axis travel in a little smaller footprint. Replacing an upper carriage's bearings is not very much work at all. I have not needed to do so yet, but I have removed them a few times for other reasons, like readjust the bearing preload. In the lower end of the vertical plates are set screws that I use to snug the lower bearing carriage against the lower edge of the rail. No C clamps are needed. The lower carriages mostly act as guides and prevent lifting of the gantry during fast plunges into materials.
I haven't seen anyone else using this approach but I haven't been looking for them very much. It makes a simpler looking machine in some respects but it comes with a lot of milling work. My only regret is that I should have used larger box tubing for the frame of the machine. There is some vibrations in the frame during cutting that is not due to resonances. Feedrate and acceleration has to be allowed for with harder materials.
Look for the CarveOne's Worktable build log in the woodworking machine build log forum.
I also have a smaller machine that uses the vertical rails idea and ACME lead screws. CarveOne's Steel Channel rebuild.
See if either of these machines will give you any additional ideas. Use anything you may find useful.
CarveOne
Guys, thanks for the comments.
the Meckmate MechMate CNC Router - Build your own with our detailed plans
Has the design that I am questioning.
The X axis flat plate linear rail is mounted "flat" on top of the wall as opposed to having this plate mounted on the side of the wall (on edge).
I would think that keeping this "flat" surface clean of debris could cause issue with smoothe travel of the linear bearing carriages???
CarveOne,
Your "steel channel rebuild" seems to be right on track with both my questions.
I will need to re-read the entire thread for all of the great insight you provide there.
My current needs are only for a small CNC of 2' x 3' so the 5 start acme lead screws I believe you used in this rebuild is also in line with what I want.
Thank you.
The MechMate has a steel right angle sitting on top of a "C" channel. The right angle rail's vertical edge has an inverted V edge ground into it. V shaped ball bearings roll along the edge of the rail. Anything that falls on the V edge will either fall off of it or will get squeezed off when the V bearings roll over it. The MechMate gantry is 250+ pounds. Two of my local friends built a 5' x 10' version and it is a smooth working system.
A good dust collector and dust shoe will keep the machine very clean. If the project can't be cut with a dust shoe in the way then you will stay busy vacuuming the machine as it works.
CarveOne
I kinda wish I had made the long axis (X) longer than it is. Using the Mach3 DROs yesterday to get a better measurement, it is 28-1/4 x 35-1/2". 48" would be nice to have. As it is, it should make most of my future router mounts and motor plate needs plus cut wood and MDF parts. This one may be cutting some more Rhoacell and carbon fiber parts for a UAV model soon.
CarveOne