Help with thread repair Recoil and HeilCoil

"Richard Hall" wrote: (clip) For a thread depth of over 5/8 inch in cast iron, should I use an insert longer than 0.38 inch. ^^^^^^^^^^^^^^^^ I am not familiar with the Alcoa system, but I believe you should be able to insert two Helicoils end-to-end. You would tap the full depth--then drive in a Helicoil with the insertion tool, all the way to the bottom. Then break of the tang with a punch. Now insert another Helicoil until it meets the top of the first, and then break off the tang.

According to Richard Hall :

Hmm ... "Alcoa" suggests that this is designed for repairing threads in aluminum -- which *may* mean that the materials are a poor choice for your presumed cast iron.

This, I don't know, because I have never experienced those. But presuming that it is similar to the Helicoils, the thread pitch of the oversized tap must be the same as that of the original thread, and I would think that they would make them to use the same size tap.

Hmm ... I *think* that you only need as much thread engagement as the diameter of the screw -- so 5/8" is way overkill. It may have used so much length to reduce the chances of stripping out the threads from the cast iron, which is weaker in tension than steel. The 0.38" long insert should be plenty for your 10-24 screws.

Besides -- how much of that 5/8" screw length actually enages threads in the hole? Since it is bearing preload, some of that length may simply be to allow a wider range of adjustment.

Good Luck, DoN.

RECOIL and HELI-COIL are interchangeable. They conform to a thread standard for Screw Thread Inserts (STI). If you look on the taps they will, or at least should have, STI printed on them. Machinery's Handbook (MH) has the data on these threads. I think the minimum thread engagement is also in MH, not just the physical dimensions of the taps and drills. ERS

From what I have found, I believe it is a fastener company acquired by Alcoa. They offer a wide range of inserts for different materials. The inserts in the kit I bought did not say for aluminum.

I finally found their web site and down loaded an application manual. From my interpretation the 0.38" insert should work.

The plate is fully tightened to the spindle housing, springs are used for the preload.

Thanks for the reply.

After thinking about it today, if the tap is the same size for both RECOIL and HeliCoil then the inserts should be interchangeable. Every time I turn around I risk learning more than I expected. May need to spend several days reading about threads.

Thanks for the reply.

I'm not 100% sure, but I think you may have trouble trying to insert one helicoil on top of the other and maintain a continuous thread.... Ken.

I'm ashamed to say that I used a 1/4" UNC recoil insert the other day to repair a 1/4" Whitworth hole. Same Dia, same tpi, but 60 degrees where it ought to have been 55 degrees. It still works a lot better than the original mangled mess and has saved me a couple of days to make a new part.

Mark Rand RTFM

Yup, Leo, you may be right... although I've never tried it. I guess as long as you didn't *force* the second one down on top of the first, it may be fine.... another lesson learned :) Ken.