New Machine Build- Opinion on Base Design

[Mr.Chips]

This is the base that I am planning and want some opinions on the construction. It is made of 2" square tubing, in four sections, each section is welded together then the brown sections are bolted to the gray sections.

I am hoping that by adding a horizontal piece about 6” down it will add enough rigidity, what do you think?

Typically I see a lot of constructions using diagonal bracing forming triangles which makes for a very rigid form. However diagonal bracing makes it very difficult to utilize any of the inner spaces for drawers and storage.

Comments and suggestion appreciated.

[FandZ]

It's hard to put in words, but on the corners, why don't you just have the cross beams connect to one extrusion instead of two? I think that would be stronger, as it is now, it relies on the strengths of the bolts at there weakest point. Grant it, I doubt;t you'll have forces trying to squeeze it from a square shape into a diamond.

If you need me to sketch what I'm saying, let me know.

Originally Posted by Mr.Chips This is the base that I am planning and want some opinions on the construction. It is made of 2" square tubing, in four sections, each section is welded together then the brown sections are bolted to the gray sections. I am hoping that by adding a horizontal piece about 6” down it will add enough rigidity, what do you think? Typically I see a lot of constructions using diagonal bracing forming triangles which makes for a very rigid form. However diagonal bracing makes it very difficult to utilize any of the inner spaces for drawers and storage. Comments and suggestion appreciated.

[Mr.Chips]

Originally Posted by FandZ It's hard to put in words, but on the corners, why don't you just have the cross beams connect to one extrusion instead of two? I think that would be stronger, as it is now, it relies on the strengths of the bolts at there weakest point. Grant it, I doubt;t you'll have forces trying to squeeze it from a square shape into a diamond. If you need me to sketch what I'm saying, let me know.

Yep, a sketch will be worth a thousand words.
Thanks

[jsheerin]

If you support the cross beams at more places or move the legs in to give a shorter unsupported span between them (don't put the legs right at the corners), you'll get less static sag and less deflection under load.

[thaswell]

I have an eight by 12 foot Digital router running on a similar frame but with diagonal braces. It has two 4' x 8' frames made of 2" x 2" steel tubing using one at each end with 2" x 3" tubing running the long dimension. I agree that the diagonals are a pain where you don't need one and would suggest using diagonals on only three sides of each cube and welding all connections. This would leave one side available for storage. I did not build the router I have or it would have been done that way. The 2" x 3" tubes are bolted (Clips) to each cube. Remember to keep one dimension of your cube at or under 31" so that it will fit through a standard door. Sooner or later someone is going to want to move it. I have mine on the second floor of my work shop and if it was one inch bigger we would not have gotten it in.

Have fun .......

TH

[Mike F]

Hi Mr Chips,

Always think triangles when wanting a rigid structure. Any structure built using parallelograms can be made to collapse very easily. If you were to remove your extra rail and use diagonals instead, it would serve two very important purposes. One; it would make the whole structure very rigid indeed and, two; it will add very substantial support halfway along your top rails where the downward force of the whole machine could be acting.

I would go even further and add two more diagonals accross the top from corner to corner. This will stop any movement then, in all directions.

I have attached a very crude sketch showing what I mean but without the additional, top bracing as, without using CAD, it would not be clear.

Hope this helps,

Mike

[Mr.Chips]

OK, how is this compromise.

Three sides cross braced, front side I retained the horizontal brace. But kept the brown wended sides being bolted to the gray welded sides.

[thaswell]

With a 3/4 " plywood shelf and top bolted to your cross members you will have plenty of rigidity in your frame. I cannot help but be curious about your aversion to welding all of the corners together. What am I missing? I sure wish I had the storage space your design will give you!

TH

[Mike F]

Yes, much better

I still feel you will get some flexing of the front, top rail, with nothing supporting the middle. Do I assume correctly, that you want to be able to get into the space below for storage or whatever? If so, another compromise would be to put some diagonal bracing from the ends of the secondary rail to the middle of the upper rail. I know it means you cannot get a drawer or something into that space but structural integrity is probably more important. An alternative would be to make the front rail much more massive and put it edge on, maybe something like 4" x 2". That would give you a lot more bending strength.

I just noticed, you still have your secondary rail at the back also. Is there any particular reason you wish to keep these? They add very little to the strength of the frame - nowhere near the amount the diagonals do. If it is for reasons of storage or access, you still need to find a way of supporting the middle of the top rails.

Just another couple of pence worth.

Mike

[Mr.Chips]

I owe you all an apology, I suddenly realized that I didn't make it clear that this is the table, that will support the CNC and not actually part of the machine it's self. This makes a lot of difference in the design requirements. Sorry I did not make that clear at the onset.

The base will be approximately 4’ X 3’, and even though it will be in the garage I don’t want to eliminate being able to take it apart in the event it is ever moved through a doorway.

[thaswell]

Here is a photo and a sketchUp drawing (excuse the quality of SketchUp) of what I think would be a good design. With a size of 3' x 4' i would use 1 1/2" x 1/8" wall square tubing. I am sure it would handle all the load you will ever put on it especially if you would weld all joints. If you still want to bolt some joints consider filling the tube with a piece of wood to prevent crushing and use at least a grade 5 bolt. Draw them up tight! As for getting through doors remember if you stick to the 31" height I suggested your machine will bring your work surface up at least another 3 to 6 inches.

Have fun....
That is what it is all about.
TH
thaswell@amplex.net

[FandZ]

Thaswell did it best. You could park a Volvo station wagon on that setup.

Originally Posted by thaswell Here is a photo and a sketchUp drawing (excuse the quality of SketchUp) of what I think would be a good design. With a size of 3' x 4' i would use 1 1/2" x 1/8" wall square tubing. I am sure it would handle all the load you will ever put on it especially if you would weld all joints. If you still want to bolt some joints consider filling the tube with a piece of wood to prevent crushing and use at least a grade 5 bolt. Draw them up tight! As for getting through doors remember if you stick to the 31" height I suggested your machine will bring your work surface up at least another 3 to 6 inches. Have fun.... That is what it is all about. TH thaswell@amplex.net