Silver soldering zinc-coated steel

Good advice, and something I try always to do.

Bert

I'd never encountered them, thanks.

Bert

They are incredible convenient to use. There is a special tool like a pop-rivet gun to fix them in situ. However I was thinking you wouldn't need that and leave the Rivnut as-is.

I think the result would be quite neat. If increased strength was required you could fit a washer under the top-hat. However Rivnuts are not particularly strong being made of thinnish walled aluminium.

You can get stainless ones, probably couldn't 'set' those properly without the specific tool.

I wasn't aware of that, thanks.

You can make some skirting out of L-cross section steel and if the piece is big enough, it can hide some full sized nuts, plus be fastened to the work itself.

|Hanger| |______| +----------------------- | XXX Platform +----------------------- ------- Skirt | NUT <=== Need to leave room so a \--> | NUT socket driver can tighten the nut |

Instead of an L-shaped piece of metal, you could also use square tubular steel, and then you need to drill a hole in the bottom of the tubular steel, big enough, to fit the socket driver for the nut.

You could even weld up a square of tubular steel, with four large holes drilled in it, for recessed hidden nuts. The tubular steel ring then fastened to the bottom of the platform, with whatever hanger scheme you have meeting the platform.

Paul

Paul, many thanks for all those suggestions but they strike me as being a tad overkill to solve a problem which can also be overcome by using something other than dome nuts.

My current favourite thought is to use carriage-type bolts, possibly with the heads flattened a little, to nearer thick-washer appearance. The only tricky bit would be cutting the recesses to accommodate the square shanks on the bolts.

You could go to a machine shop, and have something turned in steel, with a flat profile head on it. Sorta like your own carriage bolt.

But I don't know what the budget for this project is.

I agree that carriage bolt heads, were never designed to be hidden :-) It is likely the case, that we haven't properly applied carriage bolts in projects, for decades. I've always abused those, and put them places they don't belong.

These have a fairly nice looking head, but they're still hard to hide. The table I'm sitting at, uses eight of these, but it also needed some other mechanical support. And the table is strong enough to stand on.

And what those show, is that it is possible to get a fastener that isn't as ungainly as a carriage bolt. If the female of that would fit a threaded steel rod, you could use those on either end of the threaded steel rod.

But the heads on those iems, I'd still want a fender washer to spread the load. If the heads had a larger diameter, then I wouldn't need a fender washer. It all depends on how "soft" the shelf material is, as to whether it needs reinforcement.

Paul

Roofing bolts are similar to carriage bolts but without the square part of the shaft. However they have a cross slotted head which you may not like.

If trying to disguise the head of a bolt you can get chrome bolt head covers BUT you have to use a bolt with a hex (allen key) type drive.

Three easy options on that...

2) Make the hole opening square with a chisel.

See also

I'm sure using a washer and a nut the square part could be pulled into the shelf. Perhaps finished off with a small wood chisel.

My neighbour used make small car trailers using zinc coated water pipes, v cheap. I often passed his workshop at night, he would be welding with zinc fumes rising past him. He died of cancer after. Good Guy, good neighbour.

That's very interesting; thanks.

I decided to try something similar, grinding down the head of a carriage bolt to leave a largely flat head 2mm thick.

My shelf is 18mm MDF, and with the recess drilled out to sink the bolt head the remaining thickness is 15mm. There's also a further internal step to accommodate the square shank (which I wanted to remove, partially at least, but couldn't because my belt grinder wasn't feeling co-operative).

A couple of pictures:

I would have first tried to insert the coach bolt without that internal step. I would think that the MDF can be compressed enough to take up the square end. On some scrap drill the clearance hole for the bolt, insert the bolt and add a large washer or equivalent to spread the load and a nut. Tighten down the nut until the bolt pulls through so that the bottom of the bolt head is flush with the surface. The bolt will have formed its own square section in the MDF.

I did in fact try that, and found that I could compress the MDF enough to accommodate about half of the shank but no more.

Do you think I've compromised the strength of the assembly too much by drilling out the extra step? I'm still in two minds about it.