Small rigid router - Design advise needed

[Sven]

I haven't read this thread for some time now and I am surprised at the design of the router as it is now. It looks really nice.

Am I correct in that you will have pieces cut by laser as part of the build?

If so, why not build a steel torsion box from nothing but laser cut sections?
That would save a hUge amount of time, and be stiffer too.

[mitchejc]

Yep Sven, the idea is to have the parts laser cut. Interesting idea. I'm sure what you are suggesting would be possible and EXTREMELY stiff. Its amazing how stiff some of the light torsion box or honeycomb composite structures are like on the photo below

[Sven]

I'm currently in contact with a guy who is building an extreme fixed gantry router. He can calculate this stuff in to extremes.
He suggested to me that a steel torsion box is nearly as stiff as a solid steel one and when designed right wil only need spot welding to keep it together, but can even be glued if you have the right technology available.

[mitchejc]

Ok, now its down to bartering. A friend needed some aluminium house numbers urgently and he had something I wanted, so I cut the numbers Wednesday night and swapped this

for this


Great deal, don't you think? :-)

Back to plan A of using I-beam for the gantry sides. The beam I got was a bit higher (254x148) than I hoped for but I'll make it work. I guess for me DIY CNC is more about what I have/can get/can build rather than building the ultimate design from the best choice of material. I also listened to the advice and went with a slightly more practical approach and used 76x76 square tubing, and some 10mm and 5mm plate and also bolt or weld the X sides directly on the base. Gantry weight is +- 60kg excluding Z. I know Y rails top bottom is the better approach but I'm thinking its going to much easier for me to get them parallel and on the same plane if I put it on the front. I'm hoping the laser cutting is not going to be too expensive otherwise I'll have to go for plan B with the gantry. See pics below.
Again please comment if you see any obvious issues.

[Boyan Silyavski]

Looks awsome. Will need a lot of patience welding.

[mitchejc]

Thanks Silyavski, yep that's going to be many many hours of welding. I'm a bit worried that the two square tubes on the front will bend a little during welding as its only welded on three sides but I'm hoping it will be ok. Maybe I'll only weld them top and bottom and not the back to prevent distortion. Do you think I need some ribs on the inside of the I-beam to prevent flex in the Y direction or is it going to be stiff enough with just the bearing and motor mount plates welded in?

[JAZZCNC]

Your making life much harder and expensive than it needs to be with all those rib plates.!!. .

Two large thick walled pieces of box section arranged in a L shape with a few triangle braces at the rear will easily match your gantry in strength and be much cheaper and simpler to achive. It will be much easier to achive accurecy as well because with that thickness of steel on those square tubes then heat from welding will almost certainly have an affect either pushing or pulling on the boxsection with so many braces to weld, even on just 2 sides.
If you used a Tig welder you may have chance but even then I'd be surprised if it doesn't.! You will certainly have to take it very very slow keeping welds short and leaving plenty of time between to stand any chance.

Your design will be strong but no stronger than more conventional setup and 3 times harder to achive and probably 3 times more expensive.?

Also Please don't tell me this is just for cutting wood with occasional aluminium use.?. . . .