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Cheap linear rails idea for CNC machines
Posted by Robotics Guy,
in
CNC
14 July 2011
·
1,450 views
CNC
I’ve been trying to come up with a better method then skate bearings, which my current CNC machine uses, and I think I might be on to something..
One problem with my first CNC machine is that accuracy isn’t that great, which is caused, in part at least, by the way the axis slide back and forth. Another issue is the z-axis not being supported well enough, causing it to vibrate, but that’s just a problem with the machine design – something that will be fixed in my next build.
Having read that using some sort of plastic sleeve bearing on drill rod works really well, I started investigating using drill rod as an alternative to the aluminum trim channel on my first machine. The problem is that if unsupported, the drill rod needs to be a large diameter so that it doesn’t flex, and the larger the diameter, the more expensive it gets. So, what I’m thinking of is using a small diameter drill rod, say 1/2″ , drilling small pilot holes through it, slightly larger diameter holes about half way through the rod inside the pilot holes, then putting screws in the hole and screwing the rod down into the wood. It seems like this would be really sturdy, because not only can the rod not flex down (since it’s sitting on wood for support), but it also would not be able to flex from side to side.
The drill rod is pretty cheap. A 36″ length, 1/2″ diameter drill rod is available from Enco for $4.73. The sleeve bearings cost about $0.80 cents each. This would probably cost a bit more than the skate-bearings and aluminum angle method, but seems like it would provide much smoother motion.
Here are some concept drawings for the linear rails idea:
This is how the two holes would be drilled (one inside the other), so that a screw can be put in to secure the rod:
This would be done a few times along the length of the rod, like this:
This way the rod would not be able to flex in any direction, allowing one to get away with using a small diameter for the drill rod, like 1/2″, instead of an inch or more diameter rod, which is significantly more expensive.
The bottoms of the plastic sleeve bearings would be cut off (just a very small amount) to allow them to slide on the rod (since the rod is sitting on the wood). A hole would be drilled at the edge of the gantry support for the bearing to slip in and be glued in:
I would have the wood go a little further down than in the picture, though, that way since the wood wraps around it, the bearing will not be able to flex at all. (otherwise, since the bearing is cut at the bottom, it might be able to flex a little).
This is just a rough idea of what the machine might look like:
Let me know what you think!
One problem with my first CNC machine is that accuracy isn’t that great, which is caused, in part at least, by the way the axis slide back and forth. Another issue is the z-axis not being supported well enough, causing it to vibrate, but that’s just a problem with the machine design – something that will be fixed in my next build.
Having read that using some sort of plastic sleeve bearing on drill rod works really well, I started investigating using drill rod as an alternative to the aluminum trim channel on my first machine. The problem is that if unsupported, the drill rod needs to be a large diameter so that it doesn’t flex, and the larger the diameter, the more expensive it gets. So, what I’m thinking of is using a small diameter drill rod, say 1/2″ , drilling small pilot holes through it, slightly larger diameter holes about half way through the rod inside the pilot holes, then putting screws in the hole and screwing the rod down into the wood. It seems like this would be really sturdy, because not only can the rod not flex down (since it’s sitting on wood for support), but it also would not be able to flex from side to side.
The drill rod is pretty cheap. A 36″ length, 1/2″ diameter drill rod is available from Enco for $4.73. The sleeve bearings cost about $0.80 cents each. This would probably cost a bit more than the skate-bearings and aluminum angle method, but seems like it would provide much smoother motion.
Here are some concept drawings for the linear rails idea:
This is how the two holes would be drilled (one inside the other), so that a screw can be put in to secure the rod:
This would be done a few times along the length of the rod, like this:
This way the rod would not be able to flex in any direction, allowing one to get away with using a small diameter for the drill rod, like 1/2″, instead of an inch or more diameter rod, which is significantly more expensive.
The bottoms of the plastic sleeve bearings would be cut off (just a very small amount) to allow them to slide on the rod (since the rod is sitting on the wood). A hole would be drilled at the edge of the gantry support for the bearing to slip in and be glued in:
I would have the wood go a little further down than in the picture, though, that way since the wood wraps around it, the bearing will not be able to flex at all. (otherwise, since the bearing is cut at the bottom, it might be able to flex a little).
This is just a rough idea of what the machine might look like:
Let me know what you think!
