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

has anyone heard of or used HIWIN rails and blocks?

I did. Are they the best in the world? I don't have a clue. But how good does your system need to be? Are you going for hobbyists quality or NASA quality? I'm far from an expert but I doubt any linear rails and blocks are better than some of the alternatives like roller-skate wheels. And I'm not knocking those systems. I think they're great. If I build another system I'll probably go straight to automation4less.com and just buy new retail rather than wasting time with eBay. Of course, if I can find them on eBay pretty quickly I will.

ProjectCNC.wordpress.com

I have bought -amongst other things- 3m long Hiwin rails for a CNC router from automation-overstock. I did pick up the merchandise in person since I live fairly close. Automation-verstock and automation4 less (same outfit) have a huge warehouse full of linear ways, bearings, aluminum extrusions, etc, etc.
I bought new 'old stock' at a very reasonable cost. Also the guys there are extremely helpful and accomodating.

Disclaimer: I am not connected in any way to that business, just a very satified customer.

Cheers,
Bernhard

Two much Want a router with a dead control P.M. me and I will see if I can hook you up It may be gone but for the money the Iron would salvage for the cost about 350 mi from you Kevin

A couple of comments on this topic. First, I am employed by Automation Overstock (www.automation-overstock.com) and Automation 4 Less (www.automation4less.com). The fact that a person would try to make a purchase from our website and not feel like there is a secure connection for entering personal details or CC information is a concern for me. I have just tested our Overstock site personally, and indeed it shows me a lock and indicates a secure, encrypted connection to the server. If there is any question, please feel free to contact me through the website and I'll handle your order via phone. We are a brick and mortar company that's been in business for over 10 years. Feel free to check out what others have said about us in the Vendor Forum of CNC Zone.

Now more directly to your question about longer rails/butting rails. The advice given by Gerry earlier in this string is on-target...stagger joints in parallel rails. It would also be worth noting that the smaller the rail size (say 15 mm) the trickier it can be to get a smooth transition of the bearing block going across the break. Conversely, the larger the rail size (say 45 mm) the easier it is to deal with this issue. In general, we advise people NOT to piece together rail sections if they don't have to. In our stocks, we have full-stick rails that range from 2000mm in the 15mm sizes out to 4000mm in wider rail widths. It may cost a few $$ more, but it saves a lot of aggravation to simply purchase the rail length needed (whether from us or someone else) from the get-go.

We have a downloadable technical catalog for the AG and LG Hiwin products on our website at this location: http://www.automation-overstock.com/pdfs/linearguideway.pdf It's 79 pages and 1.37 MB. Page 14 has information that Hiwin publishes about dealing with butt joints. With Hiwin rail, there is the recommendation that the "marked" reference side of rail pieces all face the same direction. Heck, if you want to know just about anything about traditional type linear bearings & rail, this PDF is a good primer.

As for the quality of Hiwin products, I can state that we've sold them since we went into business, and we believe them to be an excellent combination of quality and value. There are thousands of OEMs out there who have included Hiwin linear bearings and rails in their machines. What we have on our Automation Overstock site is the previous generation product lines (AG medium duty and LG heavy duty) that feature a TWO-ROW bearing design. Hiwin has now gone to a four-row bearing design...as have many other mfrs. That being said, we sold the AG and LG for years on www.automation4less.com with virtually no problems, and our decision to buy out what remained of Hiwin's USA stocks of the AG & LG was predicated largely by almost daily inquiries we were getting from folks who wanted them.