Guesstimating required thickness

[londonsean69]

OK, so I will soon have a snazzy new toy, and have been thinking about projects for it.

Question is, how do people go about designing what thickness to use on stuff?

For example, on a paddock stand for a motorbike, what wall thickness tube would you use?
And the framework for a welding bench, or cart?

Does it come down to experience, proper structural calcs, or what is lying around?

Nothing I am doing is life support equipment, although obviously if a paddock stand collapses it's gonna hurt (especially the pocket)

Cheers

Sean

PS examples of what has worked for you in the past would be welcome.

The reason I ask is because there is quite a choice at the stockholders, from 1.6mm wall through to really thick stuff in the bigger sizes.

 

[fingers99]

Most of the time -- for us mortals -- I suspect it's a mix of what's available and experience. The software is around for doing the calculations, but the important thing is to know what are the likely loads to be put through it. Not easy, by any means.

For a paddock stand it'll depend how heavy the bike is -- you'd expect a Harley (unless Buell have had a hand in it) to need a much more substantial stand than a TZ250, for example.

And remember that OD and process is just as important as wall thickness.

I'd be inclined to look at what works -- if the paddock stand has been welded chances are that there's a drilling in it through which you can insert the end of a paper clip, which will give you a fair measure of wall thickness.

 

[peterd51]

Hi,

in my case it's generally what I have laying around and I re-design it slightly to add extra supports if it doesn't look thick enough.

Like you I generally don't do 'structural' work, but I also tend to over-engineer...it's much stronger than it really needs to be.

Regards
Peter

 

[londonsean69]

I guess I'll just copy what's out there to an extent, similar OD and wall thickness, then maybe add a few gussets.

Then test it by loading it with a soft heavy weight (my little brother) and getting the fat oik to bounce up and down on it....

1 of the 2 projects uppermost in my mind (as well as finishing the exhaust) are a paddock stand.
In theory, nice and simple, but my bike now has a single sided swingarm, so lots of extra bracing, although I might work something out that clamps onto the swingarm pivot, like the ABBA stands.
I do have a crappy clarke tube crusher I want to use (after mullering some 2" stainless exhaust tube with it) so will probably look at 38mm OD with a 3mm wall.

The second is a bead breaker, like the ABBA one (has been a very slow day at work, so I drew one up)

I am guesstimating at using 2.5mm or 3mm RHS for the bead breaker, and then whatever is left over (lots - 6m lengths) can be used for a welding table or cart, or both.

Then again, do people bother with a welding cart for larger migs like the portamig?

Cheers

Sean

 

[English Steve]

You wont need a welding cart for the Portamig - it comes with it's own wheels and handle and carries the bottle on the back.
Material thickness can also be governed by shape - the triangle is very strong and lets you use thinner material if that's all you have. Generally if you sketch the shape out on a piece of paper you can see what thickness everything needs to be - if it looks right it probably is. Your soft weight test should be very useful though

 

[londonsean69]

You wont need a welding cart for the Portamig - it comes with it's own wheels and handle and carries the bottle on the back.

That's what I had kind of assumed mmmm, big chunky welders, rather than dinky disposable using things

I was thinking more of a place to keep the grinders and tools while working. I might construct a little bolt on roof type thing, bit like an awning, with hooks to hang the cables and stuff when not in use

 

[Hitch]

That's what I had kind of assumed mmmm, big chunky welders, rather than dinky disposable using things

I was thinking more of a place to keep the grinders and tools while working. I might construct a little bolt on roof type thing, bit like an awning, with hooks to hang the cables and stuff when not in use

Thats what regulators are for


As for choosing material sizes/thicknesses a fair bit is just experience. 90% of the time i go over the top. Better that way than undersizing it.
If your making something that you could buy, have a look at one first. Often mass produced stuff is thin wall, like 1.5/2mm, but even still, io go for 3mm most of the time as its just easier, it cuts easier, welds easier...

Benches, the heavier the better imo, a fair bit of that is whats laying around though i expect.

Proper calculations just arnt worth the time for a lot of stuff, unless its safety critical or structural, or mass produced parts.

For a bike stand, id say 33mm tube with a 3mm wall, bench, id say a minimum of 40x40x3 for a small bench. A lot depends on what sory of thing your doing on it.

 

[londonsean69]

Thanks for the replies guys.

The sort of answers I was hoping for really

Suck it and see....