No, I plan to support 50 mm bars every 600 mm more or less. I'm attaching some pictures of the design I'm working on
If you really want to go with this I would second Chris' suggestion of using HDPE or UHMW. You are still gonna wear those shafts out pretty quick unless you use chromed shafts. Hydraulic rod is hard chromed and accurate diameter. I don't know if you can get 50mm hydraulic rod in those lengths but if you can it would still be pretty costly. The bushes will be service items so make plenty of spares!
I also thought about reducing the 3000 max RPM with the worm and gear to 100 RPM on the shaft
Don't use a worm or planetary gearbox. They have backlash (especially worm boxes) and don't like repeated drive reversal. Harmonic drives work well but don't have enough advantages to offset the cost in this application. You are looking for an overall 10:1 ratio so that can be done by two belt reductions. Say 3.2:1 from the motor to the shaft then another 3.2:1 from the shaft to the pinions. Cheap, simple and reliable.
I uploaded the pictures because the list doesn't allow me to attach them. Here's the link: https://imgur.com/a/7kLUWsq
I'd like to see some triangulation in that frame. Try to make sure the screw/rack/whatever is well below the top of the table. You want to be able to easily slide sheets on and off the table without fear of damaging anything.
In my opinion screws are out unless you use high pitch screws, say at least 25mm pitch, 30+ mm diameter. Even with rotating nuts there are limits to how fast you can spin the nut before the balls start jamming in their guides. I have used endless belts with a fixed motor, as Roland suggested, on a couple of machines. One was a 2.5m x 1.5m table machine and I had problems with the long belts flapping around, especially when changing direction. This was a plasma cutter so there wasn't much load. The other machine was a 3.5m long feeder which only needed to push accurately in one direction before retracting. I didn't have any problems with the belt flapping but stretch under load was a significant issue. On the plus side, that machine has been running every day for 10+ years with no noticeable wear in the drive system. Using a belt that is fixed at both ends and looped over the pulley is more than twice as rigid as an endless belt and it won't suffer from the flapping issues. For a machine your size I'd use two 30mm wide belts on X with lots of tension. I really like the servo belt idea and am thinking of using it on a machine I am planning on building. Keeping dirt out could be an issue. I have serviced a lot of commercial CNC routers and generally they either use high pitch screws or rack.
Todd suggested a minimum of 5KW for the spindle. It does depend a lot on what you are doing. You can do a lot with a 1/2" cutter which will work fine on a 3KW spindle. If you want to go bigger you will need more power. Don't forget about extraction. You'll be generating a LOT of dust. Making a good extraction hood isn't nearly as easy as you would first think. If you need multiple tools for each job you might want to allow for a tool changer. If you can't have a tool changer at least have a tool setter. Tool setters are easy enough to make and save a lot of time. Just make sure it is well protected so you can't damage it when loading/unloading sheets.
If indeed its that critical, one would need a dynamic distance detection method of some sort riding the work pretty close to the tool...
Whoa Gene, before you get too esoteric the solution is actually really cheap and simple. Make the top of the table out of something that is easy to machine, say MDF or plastic. After building and leveling the machine skim the whole table using the router. The distance from Z to the table will be pretty darn accurate over the whole area. As long as the machine is built reasonably accurately the table will be pretty close to flat. Remember this is a wood router, probably cutting large sheets. If the machine has a slight bow the sheets will bend enough to sit flat on the table, especially if it is a vacuum table.
This brings up another point. How do you intend to hold the work down? The simplest solution is to have a MDF bed and screw your work down but that can get old fast if you are working with big sheets, especially if you are cutting lots of different parts. You only need one miss placed screw to wreck a cutter and probably the job as well. Vacuum works well. There are two options. The first is a pod system. You have a number of vacuum pods like these <http://vacuumpods.com/>. They use a high vacuum and hold well but are best suited to production work on pre-cut blanks where you can set up and run hundreds or thousands of parts. A matrix bed pulls a vacuum through the whole bed. They rely on high flow and a lower vacuum. They are best for sheet work, especially if you run lots of different parts. You need to make sure unused areas of the bed are sealed off.
For that size machine you are looking at a vac pump rated at 10kw at the very minimum for a matrix bed, maybe 5-7kw for pods. My 8'x4' Rye router with a matrix bed has 2x 4kw vane pumps and they are barely enough. Another 8'x4' machine I use occasionally has 2x 3kw side channel blowers and they are also only just enough. I have been investigating using multiple vacuum cleaner motors (say 5 or 6 of them). They are relatively efficient and should generate enough vacuum for a matrix bed. They are much cheaper than proper vacuum pumps though in this application they would need to be replaced at fairly regular intervals.
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