Help with angle iron calculation

[NOTTNICK]

I have constructed this unit for my son's recording equipment.
Unfortunately the 38mm base isn't strong enough to support the weight and it is sagging.
I think the solution is to attach a piece of angle iron across the bottom (underneath).
Hopefully this will give the extra strength for support.
What I don't know is what dimensions I'll need.
I am also not certain if angle iron is the best solution, would a box section be stronger for instance?
The width of the unit is 980mm. I guess the weight it is supporting is in the region of 50kg (Not all in the middle).
There is also strength/support in the nature of the way the equipment is mounted.

Is anyone able to give me an idea of what steelwork I'll need to get?

Thanks a lot.

Nick, Nottingham UK

[Kelly_Bramble]

Yes, an angle iron running across (left to right as shown in the picture) would help. I think a piece across the front and back and to be sure you could put another castor in the middle of the case front and back..

Looking at standard angle iron available in the UK, I would recommend nothing less than 40mm x 40mm x 5mm to be sure.

Your can estimate deflection if you know how to calculate the moment of inertia (angle iron) and determine various the angle iron characteristics here --->

http://www.engineersedge.com/beam_be...m_bending1.htm

The website I'm looking at wants (L)35 for 3 metres excluding VAT... L=pounds, sorry...

After modification pictures would be nice.... Good luck!

[NOTTNICK]

I just lost my reply, so if this is repeated, sorry.
Thanks for this Kelly.

Unfortunately I'll have to use the angle iron in the middle. The turning circumference of the casters means that I can't put the reinforcement at the font or back.
I suppose I could use two pieces back to back. That would fit. There is the potential problem of distortion in the other plane of course, but I don't know what I can do about that. It'll be about 170mm to the front so hopefully the 38mm of chipboard frame will be strong enough over this distance.

I considered an extra caster initially, but I can't guarantee a flat floor so it could well result in a wobble. That would be the easiest of course as the vertical pressure is only in the very middle and at the edges, the temporary support I have put there does the job fine at the moment, but I can't move the unit of course. I wonder if there is a solution here that I am missing - lateral thinking......

[PinkertonD]

Just make the angle length long enough to clear the rotating caster. The angle does not have to go right to the ends of the cabinet. Just get it as close as you can. Have the down blade of the angle at the front, maybe even half inch towards you, forming a ledge to the front for more clearance on the caster. Do the same at the back.

Bolt through the wood beam at the bottom. Join with another piece of angle front to back using hole 3, or even two pieces of angle if you like using hole 2 and 4.

[NOTTNICK]

That's a good thought and it's helped me with an idea....
What I might do is cut a 5mm wide 40mm deep slot on the front edge (about 3mm below the bottom shelf).
I can then recess the angle iron so it only overlaps below by about 5 or 6 mm. If I'm lucky, the castors will have clearance, if not I could grind a few mm off the edges where the casters hit it. As long as I paint the iron first it should look neat. Won't need screws either, just a bit of glue as it will be held in place by the slot.
There's no pressure at all in the very middle, it's all on the front edge so I reckon I'll get away without the cross strengthener, although I suppose it'd be easy to put one across anyway.
I must just make sure I am neat with my work as I don't want to spoil a good piece of furniture.

[PinkertonD]

Hmmmm, if I understand what you are contemplating, it is doomed to failure. Care to do a little sketch and post a pic of what you have in mind before spoiling a good piece of furniture?

You could always tip the left-to-right angle up the other way with the blade up and against that bottom rail. Then it could go all the way across and be bolted to the bottom rail. Not a fan of screws in this situation, but they might be OK.

[NOTTNICK]

You're quite right, thanks.
What you suggest doesn't work as the shelf is solid (no lip) but it has made me think - all I need to do is wrap it around the front and rear edges. I'll only need to screw it underneath. It will show, but if I paint it black (like the other panels etc.) it should blend in OK.
I really appreciate time and help. I'll definitely post a picture when I have done it.
I guess that the 40mm dimension of angle iron is the outside dimension (the shelf is 38mm deep) so it should work. (if I'm wrong, please tell me).
Nick

[PinkertonD]

Happy to help, that's what we are all here for. It does look like some nice woodworking too.

Yup, that 40mm is the outside dimension. You will need to radius or chamfer the bottom corner as steel angle has a fillet radius in the inner corner.

[RWOLFEJR]

Hope you have some fans in the back of the cabinet or the backside is open...? Looks like a lot of heat there.

[Kelly_Bramble]

Hope you have some fans in the back of the cabinet or the backside is open...? Looks like a lot of heat there.

I was thinking the same - looks like a NASA control center...

[NOTTNICK]

I was thinking the same - looks like a NASA control center...

It's amazing what these recording engineers use. You should see the wiring at the back!!!
It's all open - stays cool.
Got 2 metres of 6mm thick angle iron for £13. All spray painted black and drilled ready.
Just need my son to take all the equipment out so I can turn it upside down to fit it.
I'll post an 'after' pic when it's done.
Nick