Small rigid router - Design advise needed

[mitchejc]

Thanks for the advice so far. Muchappreciated! Plan is still to build a base with aflat top and then bolt my machine on top of that. I'm basically done building the base and I'll post a few pics soon so its now time to start focusing on the actual machine.


I really had a hard time deciding onthe gantry design. I know the box section designs are proven and works verygreat but if possible I would like to try something a little different with a welded structure made from round tubes, angle section and flat cross supports. Tubes will be sand filled. I'm hoping to get away without epoxy leveling so the idea is to have the X and Y rails sit on 10mm thick ally plates bolted on top of the steel that I can hopefully machine flat and parallel. If that fails I'll go the epoxy route.


Below is what I have in mind. Pleaselet me know if you spot any fundamental issues or things I canimprove. Steel parts are blue and alu parts are grey



The core of the gantry looks like this consisting of 76mmx5mm round section, 50mmx5mm angle section , 100mmx10mm flat bar and several 10mm and 6mm thick braces

[Boyan Silyavski]

What are these 3 small diameter bars along the sides? mounting threaded bars with nuts to hold all together when welding?

What do you want to hear that may be you don't know-beautiful to look at but a waste of material with no further benefit, even worsening some strength points. Unnecessary heavy/plates/ where not needed / table structure/ but nevertheless pleasing to the eye .

What about the orange material, what is it made from? The sides are weaker than box section so if this is weak all will creep.

Basically the "fundamental" issue i see is this:
Instead of strong all supported rails supported by strong all supported steel box structure, supported by itself and gravity on a not so strong table, you are trying to do exactly the opposite- make very strong table, weaker structure and even its weaker semi supported just below the rails themselves. And that for at least 2 times the weight /$$$/ of the material needed.

That is why when i design something i design it like this- bench top, even if its 3x2m steel cnc. Why? Because that's the main structure that will do the job. All else is secondary-serves to lift it to some level or to put something between the floor and the "real structure".

So why not forget all and design a good strong benchtop CNC and then design separate table for it...


When i finished the yellow machine from my first build i said to my self one thing- on the next one i will do all possible to avoid laser cutting and massive laser cut part list and i see here lasercut steel that weights a lot and $$$ to cut.


Plus actually similar sized steel tubes are not stronger or more ridgid than box section:

100x100x4 moment of inertia 236cm4 , torsion inertia 353cm4 Shear modulus/rigidity 36.86cm3
100x4 tube 139cm4 278cm4 55.33cm3


Your mistake here is that yes, 200mm x4 steel tube is much more stronger and rigid than 2 x 100x100x4, but imitating it with 3 tubes and a lot of steel ribs does not do the same job . The questions with 200x4 tube is how to fix the rails and how to deal with overhang/the bulge of the tube/ mantaining at the same time the spread between the rails.



So, box profile structure beats all in simplicity and strength, especially if made stair like with short pieces in perpendicular direction. Sides and gantry.

Please excuse me about the colors,but it helps me better express my thoughts and organize them. I tried not to make all in red and bold