I'm trying to build my cnc router using THK type linear bearings. My problem is that there seems to be a lack of longer length rails available on Ebay, or I'm getting impatient. I know it is possible to match up the ends of two shorter length rails to create one longer one. My question is will there be a problem with the smoothness as the bearing truck rides over the joint? I don't want any problems to appear on the part that I'm trying to cut out because of the joint. Any comments are more than welcome.

If you make a "perfect" joint, it should be ok. Stagger the joints on the two rails, and you should be OK. Have you considered the Bishop Wisecarver Dual Vee rails and wheels? They might even be better for a router, as you don't have to worry about dust getting in them.

I like to scrounge stuff up but I think that I have gotten to the point where parts will need to be bought. I have seen the dual vee rails used on large machines, how do they compare in price per foot to the THK style? Do they come up on Ebay?

Never seen them on Ebay, but they have prices online. http://www.bwc.com

http://www.misumi-europe.com/eucatalogue/04.html

If the THK type rails were not ordered for end to end use, the factory chamfers the ends. Even with perfect alignment, you will have a small hitch in when the bearing passes over the seam - you can feel it during assembly, but I have never really noticed it once the motion platform is assembled and running. It's there, but it's less noticable after assembly.

Scott

I just built a gantry style frame and butted rails together in two places. It works fine, but only after some serious work. It is very hard to align everything and get a smooth ride over the joints, but it can be done. I would avoid it if possible, but if you have to, be prepared for a lot of additional work aligning them correctly. The problem is when you drill the mounting holes and tap them everything must be EXACTLY right, or when you tighten the screws up it will pull the rails allignment out. A real pain in the $*&, but not impossible. As just mentioned, once everything is put together, there is allmost no detection of a ridge or bump, but while putting together you can feel it on some joints. I had to remove the chamfer on my rails before assembling by sanding with a stationary bench disc sander.

Misumi supply rails up to 2Meter in 1mm....is that enough
??????

Hello,
Iam making my own bench top mill and plan on using Linear Rails like the THK.
Question has anyone heard of or used HIWIN rails and blocks?And,ever heard of automation-overstock.com.They have bought out the stock of HIWIN,but not sure if they are safe or not,i dont see any security locks or links on there web site.
Any help and direction to low cost rails would be awesome :)
Thanks
Troy