Joe's 1000x600x200 steel and aluminium router started

[devmonkey]

I've just checked the EM806 datasheet and the fault outputs can be set to normally low impedence, i.e. normally closed. This makes things much simpler as they can just be placed in series with e-stop.

[devmonkey]

My plate has finally arrived. The first piece had a bend in it:


I think it must have been hit by a forklift in the warehouse. Anyway called Smiths and they exchanged it the next day, the new piece is perfect.



I've roughed out some bits for the Z axis on the table saw.


I got a deal on this plate because it was originally an offcut piece, however I have way too much material for this machine. I certainly have enough plate to build the gantry entirely from plate and not bother with the extrusion, has anyone done this or know of any build threads (I have looked)?

From plate I'm guessing I would form a channel 160x80 with the back open, question is would this be sufficiently twist proof?

[Voicecoil]

From plate I'm guessing I would form a channel 160x80 with the back open, question is would this be sufficiently twist proof?

Obviously it depends on how thick your plate is! BUT channels aren't generally that strong torsion (twisting) wise, a box is much stiffer weight for weight.

[devmonkey]

You are right!

I just used the demo version of shape designer, this is 16mm plate.

Torsion constants, for reference the 160x80 ITEM heavy profile 390cm^4

160x80x16mm channel is 39cm^4
160x80x16mm box is 1400cm^4

[Voicecoil]

Something else to think about..... 6" x 3" x 3/8" box section (available off the shelf): Ix = 352, Iy = 1152, torsion constant (J?) = 823 - and about 1/2 the price of Item 160x80, though you obviously have to drill some holes A lot of the slotted structural profiles don't seem to be that amazing torsion-wise, I guess it's because a lot of the metal is a fair way inside the extrusion, whereas in a box section it's all at the outside, where it does most good.

[JAZZCNC]

Something else to think about..... 6" x 3" x 3/8" box section (available off the shelf): Ix = 352, Iy = 1152, torsion constant (J?) = 823 - and about 1/2 the price of Item 160x80, though you obviously have to drill some holes A lot of the slotted structural profiles don't seem to be that amazing torsion-wise, I guess it's because a lot of the metal is a fair way inside the extrusion, whereas in a box section it's all at the outside, where it does most good.

Cheaper yes but it's not better unless it's prepped correctly and even then it's much more resonant. The profile is generally much flatter than box steel which isn't flat in any direction and it's less resonant, it's a lot easier to work with and does the job fine.

Torsion isn't an issue until gantry width gets wide and even then if sized correctly profile works fine for routers.

[devmonkey]

So I just did some maths, if 've got all my units correct, a 100N force on the cutter exerted at 300mm below the centroid of the gantry cross section and half way along the 1000mm Y axis would cause a deflection at the tool of approximately:

160x80x16mm channel is 39cm^4 - deflection 0.22mm
160x80 ITEM heavy profile 390cm^4 - deflection 0.022mm
160x80x16mm box is 1400cm^4 - deflection 0.006mm

I guess that 100N is unrealistic and would break the cutter first.

I'm going to have to drill all the holes anyway, is the bog standard 6" x 3" x 3/8" aluminium extruded box section flat and twist free with parallel sides?

I was looking at the Item profile extrusion since I thought it would give me parallel flat sides without having to process it. My mill table is only 700mm long, not quite enough to surface the entire gantry without re-locating the work which is difficult to do accurately in plane.

I'm also sure I've seem some pictures on here of peoples gantries constructed from plate?

[Voicecoil]

Cheaper yes but it's not better unless it's prepped correctly and even then it's much more resonant. The profile is generally much flatter than box steel which isn't flat in any direction and it's less resonant, it's a lot easier to work with and does the job fine.

Torsion isn't an issue until gantry width gets wide and even then if sized correctly profile works fine for routers.

I was meaning box section aluminium, not steel, I'm aware of the problems with that. The stuff I got was pretty straight, the only error from square was a very slight (0.3mm) but even dip along the middle of the long sides, obviously the die designer didn't get his shrinkage allowance quite right

[Doddy]

<deleted... I need to read to the end of thread, not end of page>

[devmonkey]

I was meaning box section aluminium, not steel, I'm aware of the problems with that. The stuff I got was pretty straight, the only error from square was a very slight (0.3mm) but even dip along the middle of the long sides, obviously the die designer didn't get his shrinkage allowance quite right

That is interesting, if the box is square to its corners then it is much simpler to skim it flat on the mill.I would need to buy a length in order to check it in the mill with a DTI, Aluminium warehouse if out of stock.

I'm still interested in looking into constructing the gantry from all this spare plate I have.