3/4" thompson rail and 7" thompson bearing - CNCzone.com-The Largest Machinist Community on the net!

Ed Williams · #1 03-16-2008, 12:12 AM

I was hoping that someone could shed some light on this. I was going to use two 3/4" rods and a 7" dual bearing on each side of my X. I wanted to have them 6' long. My Z&Y weigh about 50lbs. It seems like there is some sagging in the rail at mid point. These are thompson brand rods and bearings. Will they work at this length. Has anyone else did this.
Thanks Ed

ger21 · #2 03-16-2008, 07:08 AM

Even at 3' you'll probably get more sagging and flex than you'd like. If you want good results, you'll really need to support the rail and use open bearings.

LeeWay · #3 03-16-2008, 09:00 AM

I think Gerry is correct. I think unsupported rail would work the best in a very short run. Either a very small machine or on a Z axis only. There is a lot of flex even in solid ground and thick rod.
There can be lots of stress on parts of a machine, especially a cutting machine. You can get away with lighter built machines for plasma, but a cutting machine will stress every axis at some point.

Ed Williams · #4 03-16-2008, 11:05 AM

Thanks guys I thought so.
Ed

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