After having problems using my hardware store HeliCoil tool with plastics and soft metal, I discovered HeliCoil makes a MUCH better tool. Most people are probably fine with the cheap plastic insertion tool, but if you are putting a lot of inserts into plastics or soft metals, I did a short video on helicoil's better tool.....
Helicoil prewinders
- Thread starter tom86951
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vanapplebomb
Well-known member
I have found these are required for any light alloys and plastics. If you don’t use a prewinder on Auminum, Magnesium, Copper Alloys, etc… odds of failure are much greater.
The inexpensive one piece installation tools are fine for steels, cast iron, or other strong alloys because the base material doesn’t wear out when the coil is stretched as it is installed.
If you use the inexpensive one piece tools on soft alloys and plastics, the Helicoil wears out the top few threads as it is stretched, causing the STI tapped hole to become slightly tapered. This results in poor thread engagement, and pullout strength is greatly reduced.
Using the prewinder tools eliminates this issue because the prewinder stretches the helicoil before it passes into the base material. This preserves the integrity of the STI tapped threads so the Helicoil fits properly. Makes for a bullet proof reinforcement.
I have done pull out testing, and it makes a surprisingly large difference what tool you use to install Helicoils into light alloys. Steel and iron really didn’t show any noticeable difference between tools.
Also, I have tested other STI tapped hole inserts in 6061 T6 Aluminum with a hydraulic stress test machine, I did a head to head of M8 and M10 Helicoils, Keenserts, and Timeserts. Keenserts and Timeserts are very similar solid wall inserts, differing only in the way they lock into the hole. Keenserts have a keys then get pressed into the base material, and Timeserts have the bottom threads sweged into the base material. Both failed in the exact same way. The top 1/3 of the insert cracked and separated from the bottom 2/3. Then the remaining bottom 2/3 pulled out. You could watch it on the graph. Stress would rise, then you hear a pop and the stress instantly dropped off a bit, then rose again until it pulled. Interestingly enough the Helicoil inserts pulled all in one go, however, at a higher stress than Keenserts and Timeserts. Helicoils were the strongest, about 5-10 % higher across the board. Keenserts were the next strongest, followed closely by Timeserts.
Funny, because so many sing the praises of Timeserts and condemn the Helicoils. I suspect this is largely due to not selecting the proper installation tools for the base material. For those that have no luck with Helicoils in Aluminum, I bet they are using the one piece Helicoil installation tools, and not a prewinder.
The reason why the solid wall Keenserts and Timeserts fail the way they do is because most the load is taken up by the first few threads, same as if it were a normal tapped hole. This means the strain (inches/inch, or MM/Meter) Is higher at the top than the bottom. In other words, the top stretches more than the bottom, so it reaches ultimate yield before the bottom. Helicoils, due to their flexibility, distribute the stress in the fastener much farther down from the surface, so the strain is relatively consistent from top to bottom, so no single spot is taking up the majority of the load. In other words, you can put much more tension on a bolt with a Helicoils before the any individual thread reaches ultimate yield.
I use Helicoils all the time. I design and build some machines, jigs, fixtures, etc with Helicoils in every aluminum tapped hole. Particularly in cast tool and jig plate, or where fasteners may be removed and retorqued. It makes a darn near bullet proof joint. Far superior to a regular tapped hole. Recently I have been dabbling with Helicoils for every stud/bolt on built engines with Aluminum heads. So far, the biggest benefit seems to be on the exhaust studs. Much stronger.
The inexpensive one piece installation tools are fine for steels, cast iron, or other strong alloys because the base material doesn’t wear out when the coil is stretched as it is installed.
If you use the inexpensive one piece tools on soft alloys and plastics, the Helicoil wears out the top few threads as it is stretched, causing the STI tapped hole to become slightly tapered. This results in poor thread engagement, and pullout strength is greatly reduced.
Using the prewinder tools eliminates this issue because the prewinder stretches the helicoil before it passes into the base material. This preserves the integrity of the STI tapped threads so the Helicoil fits properly. Makes for a bullet proof reinforcement.
I have done pull out testing, and it makes a surprisingly large difference what tool you use to install Helicoils into light alloys. Steel and iron really didn’t show any noticeable difference between tools.
Also, I have tested other STI tapped hole inserts in 6061 T6 Aluminum with a hydraulic stress test machine, I did a head to head of M8 and M10 Helicoils, Keenserts, and Timeserts. Keenserts and Timeserts are very similar solid wall inserts, differing only in the way they lock into the hole. Keenserts have a keys then get pressed into the base material, and Timeserts have the bottom threads sweged into the base material. Both failed in the exact same way. The top 1/3 of the insert cracked and separated from the bottom 2/3. Then the remaining bottom 2/3 pulled out. You could watch it on the graph. Stress would rise, then you hear a pop and the stress instantly dropped off a bit, then rose again until it pulled. Interestingly enough the Helicoil inserts pulled all in one go, however, at a higher stress than Keenserts and Timeserts. Helicoils were the strongest, about 5-10 % higher across the board. Keenserts were the next strongest, followed closely by Timeserts.
Funny, because so many sing the praises of Timeserts and condemn the Helicoils. I suspect this is largely due to not selecting the proper installation tools for the base material. For those that have no luck with Helicoils in Aluminum, I bet they are using the one piece Helicoil installation tools, and not a prewinder.
The reason why the solid wall Keenserts and Timeserts fail the way they do is because most the load is taken up by the first few threads, same as if it were a normal tapped hole. This means the strain (inches/inch, or MM/Meter) Is higher at the top than the bottom. In other words, the top stretches more than the bottom, so it reaches ultimate yield before the bottom. Helicoils, due to their flexibility, distribute the stress in the fastener much farther down from the surface, so the strain is relatively consistent from top to bottom, so no single spot is taking up the majority of the load. In other words, you can put much more tension on a bolt with a Helicoils before the any individual thread reaches ultimate yield.
I use Helicoils all the time. I design and build some machines, jigs, fixtures, etc with Helicoils in every aluminum tapped hole. Particularly in cast tool and jig plate, or where fasteners may be removed and retorqued. It makes a darn near bullet proof joint. Far superior to a regular tapped hole. Recently I have been dabbling with Helicoils for every stud/bolt on built engines with Aluminum heads. So far, the biggest benefit seems to be on the exhaust studs. Much stronger.
The original Armstrong Helicoil inserters have an aluminium barrel body with a steel threaded nose. Since their patents expired numerous names have appeared on the scene.
2ndGearRubber
Well-known member
I guess I'm a little confused, so please humor me.
My typical uses are m6x1, m8x1.25, and m10x1.25/1.5, and I typically use the fork-style tool above. The only issue I ever have is irregular coil path into the threads, which I can fix by popping the coil down a thread when I feel it. It's typically only on the top one or two threads this is ever an issue, although I only work with aluminum of ferrous metals.
The tool looks pretty cool although it would likely be precluded from a lot of my work due to size.
My typical uses are m6x1, m8x1.25, and m10x1.25/1.5, and I typically use the fork-style tool above. The only issue I ever have is irregular coil path into the threads, which I can fix by popping the coil down a thread when I feel it. It's typically only on the top one or two threads this is ever an issue, although I only work with aluminum of ferrous metals.
The tool looks pretty cool although it would likely be precluded from a lot of my work due to size.
vanapplebomb
Well-known member
Those kind of one piece “forked tools” as you call them are the kind that screw up soft alloys like aluminum. Fine for steel or cast iron, but invest in a prewinder for aluminum, particularly for high stress environments, or ones that heat cycle a lot.
The reason you have trouble with the top two threads with that kind of tool is because the threads get worn out from stretching the Helicoil during insertion. Because the Helicoil is larger than the tapped hole, it literally grinds out and enlarges the diameter of the top two threads as it is pulled into the hole. It doesn’t take much. A few thousandths on an inch ruins the class of fit required for proper thread engagement.
Prewinders prevent this by stretching the Helicoil, shrinking its diameter before threading into the base material, keeping the top couple threads the proper class fit.
I know that prewinders are expensive, but they are worth every penny if you depend on a properly reinforced thread, or want a lasting repair.
I can’t stress that enough. The correct insertion tool for the correct alloy is important. The resulting pull out strength decreases significantly by using the one piece tools in aluminum/magnesium.
The reason you have trouble with the top two threads with that kind of tool is because the threads get worn out from stretching the Helicoil during insertion. Because the Helicoil is larger than the tapped hole, it literally grinds out and enlarges the diameter of the top two threads as it is pulled into the hole. It doesn’t take much. A few thousandths on an inch ruins the class of fit required for proper thread engagement.
Prewinders prevent this by stretching the Helicoil, shrinking its diameter before threading into the base material, keeping the top couple threads the proper class fit.
I know that prewinders are expensive, but they are worth every penny if you depend on a properly reinforced thread, or want a lasting repair.
I can’t stress that enough. The correct insertion tool for the correct alloy is important. The resulting pull out strength decreases significantly by using the one piece tools in aluminum/magnesium.
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2ndGearRubber
Well-known member
Thanks for the explanation, I didn't know if aluminum was in the soft category or not. Most of my aluminum work is in locations too tight to use a prewinder, but I think M6x1 would be a worthwhile idea.
I thought I'd share my video where I use this pre-winder on a real project. The 3D printed drill fixture is unique to the motor I'm working on (Porsche 944) but the concept can be applied to just about any bolt you need to drill and helicoil. 
And, it's not everyday you see a comedy tool video.
And, it's not everyday you see a comedy tool video. txvwnut
Well-known member
The drill guide idea was slick as hell.
vanapplebomb
Well-known member
There you go. Proper tool for the job. The next VW Type 4 engine I am building is going to have a lot of Helicoils in it from the get-go. , particularly “SrewLock”Helicoils for studs. I have been doing Helicoils more and more with anything aluminum. They are just so much better than raw tapped holes in aluminum.