Strength of helicoils

I have just been modifying a piece of equipment that is housed in 'furnace board', which is a thermal fibre re-inforced cement product for high temperature applications. The fixings are 6 mm helicoils about 9mm long, and the originals are set to be flush with the outer surface (ie the side from which the strain is coming).

Having to put in some more helicoils into a 25mm thick board I came to the conclusion that for maximum strength they should be set in from the outer face to allow a larger 'cone' of this rather brittle material to take the stress, so I set them back a further 6 mm. Was I deluding myself or do you reckon it'll help?

AWEM

Reply to
Andrew Mawson
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Would it be worh getting some longer helicoils (if available)? or putting two in?

Tim

Reply to
Tim Leech

Do the holes go all the way through? I would think inserting them from the back, so only the bolt clearence hole is in the front face might help a little, giving a 15mm ridge to help hold the lot in. As to delusions, weather you'd notice the difference kind of depends on if you think a helicoil thread is better at gripping the furnace board than a 'regular' thread. (apart from the larger diameter giving more surface area I doubt it...). If the material is freiable (? spalls in a sort of delaminating effect) then setting in from the front face ought to help a litle, but you will end up with a bigger mess if it does fail...

Dave

Reply to
dave sanderson

product

outer

I've only been able to track down 1.5 x thread size helicoils, ie 9mm for a 6 mm diameter, but I suppose two in one hole would work

AWEM

Reply to
Andrew Mawson

product

giving

It's more to aid dissassembly I think, as a cross thread in cement must be quite easy ! These holes actually do go all the way through, but there is no access to the inside or I would have fixed a steel plate inside to thread into rather than use the helicoils.

AWEM

Reply to
Andrew Mawson

That aren't helicoils. Are you talking about these "Rampa"-nuts:

or about these plaster-board (drywall) dowels:

I'd suggest using the later ones. They work like a charm! They are self-cutting (just screw them in with a cordless) and have a bore for metal screws.

Nick

Reply to
Nick Mueller

Sorry. For the non-German-speaking ones among you: ;-)

Nick

Reply to
Nick Mueller

product

No Nick I am talking about HELICOILS - a spring of stainless steel wire made in a trapizoidal shape wound into a previously threaded hole with a special tool that slightly winds up the coil as it goes in.

AWEM

Reply to
Andrew Mawson

Nope - these ones :

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Radyne, the original manufacturer (who must be the design authority for this equipment) specified those, so that's what I used !

AWEM

Reply to
Andrew Mawson

OK. But they don't hold in your boards. That's why I asked. Couldn't believe you tried them. :-)

Nick

Reply to
Nick Mueller

OK, if you *insist* using the wrong stuff! ;-) Helicoil is for metal and needs cutting a thread. But you knew that.

Nick

Reply to
Nick Mueller

authority

And indeed these are put into a threaded hole !

AWEM

Reply to
Andrew Mawson

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have them upto 3D.

And I'd advise against trying to put two into the same hole. Last time I tried it, it ended in disaster, as the second insert wound it's way inside the first insert, clamping down solid onto the insertion tool, which meant it got stuck, and took quite a bit of brute force to get it back out. And we still had the problem of the second insert being stuck inside the first.

Reply to
moray

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