Personal feeling is that they're nifty enough to be worth the price:-
) Locally, most auto parts stores have single size Helicoil kits in
the 1/4" to 1/2" range (& corresponding metric sizes) for a fairly
reasonable price. For the smaller sizes, you still have to go to an
industrial distributor. FWIW, the aviation industry routinely uses
fine threads for everything to maximize fastener strength (greater
root diameter.)
A few years ago, Sears tried some dedicated hardware stores - nifty
places, apparently didn't sell enough to stay open. Locally, the
only reliable retail source of NF stuff is the "Do It Best" hardware
store with the aisle filled with drawers of hardware assortments.
Mercifully, the industrial hardware place actively encourages retail
sales; unfortunately they're halfway across the next town over.
Roy
--- In 7x12minilathe@..., <trainguy_347@...> wrote:
Hi, Roy. That is a good point. I had thought of recommending
Helicoils, but the expense of the special taps and insertion tools
seemed somewhat prohibitive at our level. Used many a Helicoil myself
to get a million dollar light bulb-making machine going again. Not as
impressive as saving a 10 million dollar jet fighter, but they do
work great, if you have enough depth to use them. I have cut them off
to use in shallower holes, but I was getting paid to do that, not
playing on my own time. They are a wonderful tool to have in reserve
when just nothing else will work.
Rance, don't be afraid of using steel for making things; it
machines nicely, and is pretty darn common in junk and salvage yards.
Don't be seduced by stainless steel for making parts, unless really
needed. It sounds superior, but for a novice it can be a nightmare,
mainly because of it's "stringy" toughness when machining. Wait a bit
until you see how other materials cut, then practice on some
stainless to see the difference. All part of the learning curve,
Babe!
BTW, remember to use coarser threads in soft materials, and finer
threads for harder ones. For example, 1/4-20 for aluminum, 1/4-28 for
mild steel. That's why the different thread sizes are there, not just
for marketing purposes, as it sometimes seems.
Which brings up another point: when did hardware store like Sears
stop selling fine thread fasteners? It seems like everything is now
the coarse thread (NC as opposed to NF). At least thats the way it is
at my local Sears.
Ron.
---- roylowenthal <roylowenthal@...> wrote:
A common method of making strong threaded holes in aluminum is
with
Helicoils. If you're not familiar with them, they're spring
looking
objects, wound from trapezoidal wire, usually stainless steel.
In
practice, the hole is tapped oversize with a special "STI" (Screw
Thread Insert) tap, the insert is screwed in, its driving tang is
broken off & the job is done. In addition to being common in the
aviation industry they're also widely used to repair damaged
threaded
holes.
Roy
