Quote:
Originally Posted by Dirt Dog  Good post Aaron.
And I have to add (if I missed it and someone already said this)...........
for any given size it will be stronger than the original. (way more so on softer metals like alum.) |
Yup, the Heli-coil grabs MUCH MORE of the aluminum than any bolt could, so you really get a much STRONGER anchor for the fastener.
Spreads the load out a TON more, and gives you a concentrated STEEL contact area for the fastener to pull on!
You can't build anything strong without a good foundation,
And Heli-coils give you a strong foundation to do just that!
I have epoxied in Heli-coils also, but heat and a lot of epoxies don't get along, so using epoxy in aluminum heads for header bolts is a bad idea,
But for stuff like outboard motor 'Lower Drives' and motorcycle head bolts and case bolts, Epoxy works great...
You DO have to use a 'Dummy Bolt' with an Epoxy release agent on it to keep the epoxy out of the threads while the epoxy is curing, but you would be surprised how well they hold!
Epoxy, like JB Weld, will give you so much more anchoring power to the coil, along with strengthening the coil by backing it up and filling in gaps, crevices, ect. it's not funny.
Heat up the coil and it's surrounding material, and Epoxy like JB Weld will FLOW into the areas,
And you get a REALLY GOOD anchor! Doesn't take much heat either! Just warm to the touch, and as the parts cool down, it will SUCK the epoxy into the cracks and crevices!
Making for an anchor you will break the bolt off before you pull the threads again!
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One thing I forgot to mention is,
Tapping aluminum is VERY Dependant on room temprature!
Aluminum expands and contracts two to three times the rate of steel or cast iron,
So tapping something in cold weather might mean the hole is actually too big when it gets heated up.
Try and keep the temp between 70° & 85°F when tapping...
You also need to know that a tap will JAM IN A BLIND HOLE very easily when you bottom out!
When you feel excess pressure on the tap (and the only way to learn is with trial and broken taps!) BACK OUT!
Square nose ('Bull Nose') taps are particularly ornery about sticking in the holes and breaking off...
One way to keep your tap from bottoming out and jamming in the hole is by dropping a ball bearing in the hole.
The drill left a 'V' shaped bottom, and something as simple as a BB or ball bearing (depending on hole size) will keep you from bottoming the tap out and jamming it up or breaking it off...
Through holes don't jam the tap nearly as often as 'Blind' or holes with distinct bottoms!
But you might not want to tap all the way through to keep the coil from walking out the other side!
Something old machinists know that general 'Mechanics' don't know is...
Stay away from high speed steel taps and keep to carbon steel taps when you are learning.
They both break about the same, snap off with no warning,
But a broken carbon steel tap can be shattered with a sharp chisel if you heat/harden the end,
You can't do that with a HSS tap! It simply won't shatter!
If you break a tap off and need to get it out,
Heat the workpiece so it expands,
Then turn a can of the computer 'Compressed Air' up side down so you get liquid,
And spray the tap so it contracts, then try to back it out.
The 'Freeze Off' bolt loosener works pretty good also for freezing the tap, but don't go overboard and contract the workpiece on the tap or you will never get it out!
If chisels and heat/cold don't do it,
You are down to burning the tap out with an EDM (Electronic Discharge Machining) Machine...
I've made several from common parts and used the welder as a power source for burning the tap away,
But if you only have one piece, it's always more economical to find a machine shop to do it for you.
Usually only costs a few bucks, and will save your Part/Work Piece...
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