Small rigid router - Design advise needed

[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.?. . . .

[mitchejc]

Thanks for the input Jazz. I totally agree with the proven L shape being stronger per $. I'm not too worried about setting it up as the whole thing can be bolted together and adjusted before welding BUT I only have ARC. A bit of bowing of those tubes is not going to be the end of the world but if I get twist its going to be a throwaway so I'm seriously reconsidering my options. I can't get any square tube with walls thicker than than 3.5mm at my local steel shop so that's another curve ball I have to try and dodge with whichever design I'm going.

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

Yes, but I also want it gentle enough to cut little harts on pink mash mellows and then maybe the odd piece of brass in between :-)

[JAZZCNC]

A bit of bowing of those tubes is not going to be the end of the world but if I get twist its going to be a throwaway so I'm seriously reconsidering my options.

Any movement of those tubes is bad news that will affect accurecy and take plenty of work to correct. This is the problem with such ridged design and complex setup that as limited scope to adjust out any build error.!!

Cutting marsh mellow can be harder than you realise..

[mitchejc]

Jazz I think if I use old bra straps to hold down those marsh mellows they are not going to be that difficult to cut ;-)

I'm pondering my choices here wrt to the gantry... my heart says go with the ribs and my mind says listen to these experienced gents :-) Blackrat on here got me into contact with a local supplier of the right epoxy for leveling so that will make things a little easier whichever way I go.