Linear rails, rod which is better for cnc?

[snokid]

I have noticed that a lot of people are using supported linear rod type bearings and a few are using linear rail type bearings.

Is there any reason for your choice in which type you used?

Is on type stronger than the other?

thanks
Bob

[Darren_T]

It was all about cost and availability for me. I purchased all Thomson linear rail(rods), some supported and others not. They were readily available on Ebay and the price was right. I would have loved to go with THK bearings but they were a little less available and cost quite a bit more.

[balsaman]

Mostly it's whatever you can get you hands on

Eric

[Cold Fusion]

How do I determine which thickness rods to use?

[steveald]

Hi,
With the exception of eBay and surplus bargains, THK style bearings are very pricey. They are also very high precision and can carry amazing loads, but require very accurate installation. Looking at some of the machines on this site, you can see it is possible to build a linear slide with simple materials such as angle iron and skate bearings with excellent results. If you have the money to spend on bearings, I would recommend Thomson style round rails, they have ample load capacity and accuracy, and are easily installed and forgiving of installation errors. (I have seen Thomson continuously supported rails Hilti'ed to shop floors) If you have the money to spend on THK style rails, I would recommend putting that extra money into other areas of the machine such as ballscrews rather than threaded rod, servos rather than steppers, etc... You are building a system made up of many parts, and it will only be as accurate as the weakest one, so spread the money around. This is my philosophy anyway
Good luck with your project, it will be worth all the time, trouble and expense when you have cut your first part, friends and family might think you're nuts, but we understand

Steve

[alarants]

Hi,

I am planning to build my second machine. More accurate this time. Can anyboby tell some address where linear guides are online available. Ebay was not the place. I them to be need at least 1200 mm (47') long.

Alar

[steveald]

Hi,
You can try http://www.use-enco.com or http://www.pic-design.com

Steve

[alarants]

Thanks, they look promising.

Alar

[turmite]

You might also try here:
http://www.automation4less.com/linmed3.htm

turmite

[Swede]

THK - type linear rails are just about ideal except for cost, like so many have mentioned. But Ebay is a killer source for these at what can be great prices. The semiconductor industry goes through them like candy for their wafer-processing machines, and since many come out of clean rooms, they are pristine.

For a typical router, you can really get away with what appears to be a dinky little rail and truck, as their load capacity is pretty large, and when you get into the 25mm rail sizes (like THK SHS25) the load capacity per block is a whopping 8,000 lb! I guess I'm pointing that out to show that many surplus rails/blocks are rejected as "too small", when in fact they are phenomenally strong for their apparent size. Of course, you'll need to mount the rails properly to get a load allowance like that.

Sometimes, though, the round LM guides are just too convenient. I guess what it boils down to, is "what's available?" and "what's the cost?"


http://www.thk.com/THKCatalog/THKCat_en/tocf_THK.htm

These guys will sell online if you got the $$.