8020 vs pipe for rails?

[DistortedDesign]

I have been working on making a cnc like joes wood version. I am looking at not using pipe but using 8020 and a rail system. I am trying to find a cheaper way other than using the expensive 8020 to do it. ($50 and up per rail on 8020) I will probably be making a 4' x3' cnc. I will be using ahren rail system that he is making. It runs on the end of a 1/4" piece of cold rolled steel with basic bearings on the face and two sides like a C-clamp. Basically attach a piece of 1/4" cold to the 8020 with a 1/2" overhang for the bearing plate to attach to. Here are my questions.

Assuming everything is in 4' legnths.

How much does the y gantry weigh on joes wood machine? Mine would be lighter but larger.

Would bolting the cold rolled steel directly to the 8020 help a lot with deflection?

How much deflection is ok for accuracy? I would mostly be cncing (foam, plexiglas, plastic, and soft wood).

[ahren]

Hey distorted,
Bolting the steel to the 8020 is intended to straighten the system -- the 1/4" thick x 4" steel will probably have an appreciable bow in it over its length. Additionally, bolting the steel to a piece of 1530 or 3030 extrusion puts two bolts spaced 1.5" from each other (in the T-slots) in the width direction -- this reduces the lever arm the bearings are exerting on the steel to a mere 1.25", which produces a VERY stiff rail for a hobby machine. However, there's nothing to say you have to use 8020 with this system. You could just as easily bolt the steel to another backing (a wood torsion box, or a hot rolled steel tube, for that matter).
This makes it more difficult to use the other parts I offer, as they rely on the t-slots, but it's still a workable solution, and could save you considerable cost on your frame.

Ahren
www.cncrouterparts.com

[ahren]

FYI, these parts are now available for sale. See product announcement and pictures in this thread:

http://www.cnczone.com/forums/showth...d=1#post380181

Ahren
www.cncrouterparts.com

[LeeWay]

I attached some steel flat bar to some heavy steel tubing on my first router. I am glad I did. These actually came out very straight. If not though, they would have been very easy to shim. I only used a single drive on the X axis, so there was issues with racking initially. I was able to preload the gantry bearing on each side to make it perfectly square to the X and eliminated all the racking. The only reason I was able to do this was because I used this rail method. It is extremely strong. 2 screws on the X would have worked as well, but at a higher cost. My gantry probably weighs around 150 pounds. The roller skate bearings on steel rails make the weight seem like nothing.
80/20 would have worked, but would not have been as rigid and I would have had to use two screws for the X.
V bearings would have been nice to use. I think they alone might have helped to eliminate some racking. If I make a bigger router in the future, I would likely use those.

http://leestyron.com/cnc/xframe.jpg
http://leestyron.com/cnc/rail1.jpg
http://www.cnczone.com/forums/attach...4&d=1113477495

[DistortedDesign]

Originally Posted by LeeWay I attached some steel flat bar to some heavy steel tubing on my first router. I am glad I did. These actually came out very straight. If not though, they would have been very easy to shim. I only used a single drive on the X axis, so there was issues with racking initially. I was able to preload the gantry bearing on each side to make it perfectly square to the X and eliminated all the racking. The only reason I was able to do this was because I used this rail method. It is extremely strong. 2 screws on the X would have worked as well, but at a higher cost. My gantry probably weighs around 150 pounds. The roller skate bearings on steel rails make the weight seem like nothing. 80/20 would have worked, but would not have been as rigid and I would have had to use two screws for the X. V bearings would have been nice to use. I think they alone might have helped to eliminate some racking. If I make a bigger router in the future, I would likely use those. http://leestyron.com/cnc/xframe.jpg http://leestyron.com/cnc/rail1.jpg http://www.cnczone.com/forums/attach...4&d=1113477495

Thanks that maybe a good option for me. I like the 8020 but it is god awful expensive.