I have been using my homemade CNC machine for almost a year now and I would like to make some minor modifications to improve its performance. When I originally built the machine, I was on a very limited (college) budget. I ended up opting for 5/8" drill rod (cheap O1 series from Enco) with plastic flanged sleeve bearings for the linear motion. Enco's website appears to be down at the moment, but the flanged sleeve bearings I am using are here (Enco - Guaranteed Lowest Prices on Machinery, Tools and Shop Supplies). The sleeve bearings are 5/8" ID and 3/4" OD with ~1" in length. While the machine works extremely well for light materials, I quickly notice the sloppy tolerances when I try to machine any harder materials such as aluminum. I feel that the cheap sleeve bearings are the culprit for this poor tolerance.
Can anyone suggest some good upgrades for the cheap sleeve bearings I linked to above? I have been looking at some oilite bronze sleeve bearings that seemed promising, but I have limited experience in this area. It would be HUGELY beneficial for me if the OD stayed at 3/4" so I do not have to bore out the 12 holes I have to replace with larger sleeve bearings.
Oh and if you want to see any other details about the machine, this picture was from early on in the build process, but you should get the general idea
http://3.bp.blogspot.com/_UYb96Pphti...0/IMG_2113.JPG
Thanks!
Bronze bearings on hardened shafts should be much more rigid, but be aware that they're very intolerant of even the slightest misalignment, and will bind if not aligned perfectly.
The unsupported shafts might be a bigger culprit. If they are 5/8", then I'd imagine you can get quite a bit of flex from them.
Gerry
Mach3 2010 Screenset
http://home.comcast.net/~cncwoodworker/2010.html
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
Just a little FYI
Are the bearings press fit? When I went from the plastic to bronze bushings. After pressing the bonze into place....guess what..... the shaft no longer fit. So out with a BRAKE cylinder hone and started opening them up. When you get the shaft to go thru each of the bushings by itself, it still will not go thur them both. Keep honing until its tight and smooth.
Not that bronze wouldn't give you a bit more stiffness if you can get them to work.
The problem is this, just how well built are these slides assemblies. The shafts have to be parallel to within a few microns to allow for the close shaft fit that you need to actually improve the machine. Further on machines using round ways there is often provision for adjusting the fit up of the metal bearings. Even linear ball bearings for round shafts have provision for fit adjustment.
Beyond that, as has already been pointed out, the shafts may simply be undersized for Aluminum. Length is a factor here, but the shafts will flex and bounce.
In any event you have few options beyond bronze if you want to kept the current arrangement. One possibility would be Rulon bushings or Rulon lined steel bushings.
While more expensive your best bet would be to look at rebuilding the machine weakest axis first. This would keep your costs down and can be done incrementally. The unfortunate reality is that there is a small jump in machine requirements when going from plastics and wood to Aluminum. I just suspect that you have a shaft size problem on some or all of your axis. The good point here is that bronze bushings are relatively cheap, you may get buy with only needing the major axis rebuilt and the rest rebushed.
Originally Posted by webtek23
You can order the bronze flanged bushes at McMaster.com, but as mentioned, that may not be the solution to your issue...
CAD, CAM, Scanning, Modelling, Machining and more. http://www.mcpii.com/3dservices.html
Posting Permissions
LinkBack URL
About LinkBacks
