Thread: What metal do I need

Here is what we want to do I hope i sent this diagram correctly. The plastic buffer is to cushen the wire when it is moved. The wire gets replased when it snaps.

thanks
miles

Originally Posted by miles and jules

Hi ...Yeah we tried alluminim today(are there different grades of aluminium?)...but we need to tap it and put a screw in it and it just threads when we tighten it. So we are really after any mild steel-like tube that we can tap easily that doesnt rust and isnt copper.

It would be really great if we could get tube in this same zinc stuff we have in the sheeting.

These guys look like they have small sizes in stainless http://www.spec-net.com.au/links/link141.htm

Try aluminium rivits rather than screws gives a better result drill straight through the tube and wire but double the wire first or tripple it whatever the tube size will hold
Rivits are easy to remove and replace simply drill out the head

Rgds

Hi
We need to use a screw as the wire needs to be replaced often. The screw needs to be tightened to lock the wire in position. Then loosened once the wire has snapped then replaced and retightened.

Thanks
Miles

Miles,
what about using the aluminium tube and putting a helicoil thread insert in to make the thread last? See here for an overview of the procedure.

Mick

How about pinching the tube from outside? Should be enough elastic rebound to allow removal of the wire.

Joe

Hi Mick
I like ths sound of that ....where would I get one of these inserts small enough though. Maybe a hobby shop?

Hi
Actually a similar technique could be to use a t-nut inside the aluminium tube if i could get one small enough. then epoxie it into position with the t on the inside..... then when i tighten the screw against the wire the t wont be able to pull through the aluminium. i guess this will depend if they make them this small. If they dont I could always tap a small sliver of the zinc/steel then insert that in the tube.

What do you recon?

Noticed you are from Brisbane. You could try some of the Aerospace fastening systems available, ie RIVNUTS. They work by simply drilling a suitable hole in the tube or whatever and inserting a rivnut into the hole and actioning off like a rivet. The tail expands and secures itself like a rivet, however the centre is theaded allowing the insertion of a compatable screw- very easy process, only thing is you require the tooling to action the fastener off.

There are a number of Aerospace repair facilities around Brisbane- Archerfield and Brisbane Airport to name a few.

Anthony, I never thought of using rivnuts. You can alos get them from truck bodybuilders. I know that they are used to mount external fairings etc.

Have you thought about automotive fuel or brake line (steel not rubber)

If you are worried about it rusting - remember galvanic corrosion!

If you end up making it out of a heap of dissimilar materials, you may end up with something that corrodes faster than plain old steel.

Stainless steel only likes to be with stainless; zinc coated (zincalume) metals dont like copper, lead, stainless and chromeplate.

Do it in mild steel and paint it. Easy to get in most sizes, thick wall so you can tap it with confidence, and cheap. Yeah, it can rust - you can probably make half a dozen of them for the price of one fancy stainless one and consider them consumable.

Or remove the idea of tapping it for repeated removal - put the screw all the way through, bend the wire as a loop before you push the wire down the tube, catch the screw with your wire loop, and twist the end of the wire to make it secure. Repeat as the wire breaks (although that sounds like a weak point if it is breaking!)

Hi guys...thanks for all the info!
Wow RIVNUTS sound perfect....that way i can keep the aluminium tube(so its light weight) Do you know any shops that carry them in bris? I'll google them.

The galvonic corrosion sounds like a bit of a worry....These armatures that we are building probably only need to stay strong for a couple of years...do you think that will effect if we used RIVNUTS with aluminium tube...i guess it would depend on what the rivnuts were made from)

thanks again'
Miles

I wonder how small you can get the rivnuts...... we wanted to use 3mm alan key screws to hold the wire in place.

Maybe we could just tap a stainless/aluminium rivet .......aslong as it still had enough thickness in the rivet on either side.