Please review this router gantry idea

[GTJim]

I no expert but all the strength seems to be in the centre of the gantry, yet your rails are top and bottom the weakest points.
I may be wrong though.
Jim

[EddyCurrent]

Yes I see what you mean, there will be end plates so I'm expecting these to resist any twisting, there will also be blocks mounted on the end plates behind the ballscrew to support the horizontal box sections.

[JAZZCNC]

Don't let the ball-screw being slightly further back put you off the L design.!!. . . In reality it makes very little difference it works fine and makes for a very good stiff gantry. It also very neat and keeps screw out of arms way and makes cable management easy.

Your design would be too tall making for a weaker design.

[EddyCurrent]

Jazz, thanks for that, I'd read you mentioned this before and obviously Matt's machine works well.
So before I set off down the L design how about this one ? pipe + 2 bits of channel

I'm also thinking that any hollow material could be filled with builders expanding foam to act as damping as it's very lightweight.

[Jonathan]

Your tube design would be hard to fabricate, particularly when it comes to getting the rail mounting surfaces parallel. However it would be exceptionally strong as a tube is the strongest shape in torsion.

To make it easier to make you could put the rails on the front flat surfaces, as they could be machined or leveled with epoxy. If you did this you'd want to use profile rails to reduce the overhang.

[mekanik]

Looked @ it earlier and liked it but as jonathan says its the manufacturing that's going to be a bit tricky, are you near any Engineering shops with a long bed surface grinder ?
Out of interest where in Cumbria is you @

[EddyCurrent]

In response to Jonathan's comments



mekanik, Cockermouth area

[mekanik]

OK how about this, if you have a lathe that will swing a couple of inches greater than the pipe you intend to use you could manufacture a faceplate mounted fixture that will hold suitable size blocks of steel, preferably machined square on all faces, set up in the fixture and produce the radius to conform to your pipe OD.
Then you want substantial section gauge plate to use as the mounting surface for your profile rails, drill&tap the support blocks rail ect attach the two end blocks to both rail supports & align them on pipe, tack them up and add the remainder of the blocks & tack also,REMOVE mounting rails to prevent twisting ect, finish weld the blocks to pipe, using your support rails and blue marker, file & scrape the blocks so you have a flat datum,fix one rail, measuring from that set to on the opposite side and finish the faces on the other blocks to bring them parallel, rail support beams can now be fine tuned with brass shim.
Does that make any sense ?
That's close enough, Stainton with Adgarley

[JAZZCNC]

Jazz, thanks for that, I'd read you mentioned this before and obviously Matt's machine works well.
So before I set off down the L design how about this one ? pipe + 2 bits of channel

Yes it would work and tube is very stiff. But large tube is expensive and will resonate quite a bit.!! How about something like this.? It will probably be cheaper and stiffer with 2 x 100mm tubes

[EddyCurrent]

Would the two tubes try to rotate about each other ? they would need to be connected somehow, it seems the basic strength of one tube has been lost maybe, but you are right that large tube might be expensive unless of course a scrap yard had something.
That gantry you've drawn would be pretty lightweight I imagine.