I need to know what the dia of a un-supported shaft needs to be for a span of 48" These shafts will be supporting my gantry for a laser cnc machine design. I really don't what to use a support shaft if I don't have to.

I'd like to use somthing like this-

I'm thinking 3/4" too 1" would work, mind you their is no up and down forces and no real weight on the gantry from the head.

Here is my new laser-

Yes, anything from 1/2inch up in diameter will work. You'll be using 2 of them.

Even 1" will sag a little at 4 ft, but it probably won't affect the cutting, I wouldn't think.
If you can double up the end mounting clamps, it gets quite a bit stiffer.

Where can I find this, I have looked un and down the internet

Well darn...did some calculations...here they are for Thomson 60 shafts.

Unsupported Length = 48 inches
Weight of Load = 100 lbs
Deflection at the center of the unsupported length (24 inches) is:
1/2 inch dia. shaft ~= 2.493 inches
5/8 inch dia. shaft ~= 1.00 inches
3/4 inch dia. shaft ~= 0.49 inches
1 inch dia. shaft ~= 0.1536 inches

For a load of 10 lbs the deflection for the 1/2 inch shaft is 0.2493 inches. You can guess what the others are.

Paul

Where can I find this, I have looked un and down the internet
If you want to use the T-rail then you should buy shafting that is pre-drilled. Thompson has it....anyone that sells shafting has T-rail.....the one you picture looks like a home made one...but I'm not for certain.

:boxing:

CNCAdmin

interesting project. Keep us up to date on how it goes.

How much load do these rails have to support?

The linear rails in post #6 are Igus Drylin S supported shaft part AWUM - metric only. They're hard anodized Aluminum for open plastic bearings only.

Pacific bearing do something similar too..

thank you this is what I was looking for- http://igus.bdol.com/drylins.asp

cool laser, is that the co2 set-up from amazing-1?

No, I got it from a ebay seller, It's a RF co2 laser.