Helicoils in Cell Terminals

[ArthurEld]

That’s what I did, and all the way until the tapered tap bottomed,

I then switched to using the near-bottoming tap but there was not enough thread established to guide it.

I’ll see if the tap guide allows me to salvage the thread that’s been started, but the fragility of the aluminum terminal in the face of the hard steel of the tap has caught me by surprise.

I feel like I’m working with wet clay...

Just put the bottom tap in the drill press chuck and start the tap by hand. Forget about those other threads. If there's not enough thread to start the bottom tap, then there isn't enough material removed to worry about.

 

[ArthurEld]

Yes, that’s how I drilled the hole and started the tap. I had no idea the top of the press could rotate like that, so thanks for the tip.


Yeah, Helicoils to spare.

I’ve done some work with aluminum before and have a sense of how the entire process would feel in typical aluminum. These terminals are far softer than any aluminum I’ve experienced before, so I’m not sure how much learning there is to be had in practicing on harder aluminum...

I almost feel like I should practice in wet clay or wax.

If you did it in scrap, you'd know the bottom tap wouldn't follow the other taps threads. I still think you should get a piece of aluminum to practice with

 

[ArthurEld]

You have to remember that your hole was smaller than 1/4" I assume the bottom of the 7 thread taper tap is smaller than 1/4"
So it cut threads but they are in material that isn't supposed to be there.

 

[fafrd]

If you did it in scrap, you'd know the bottom tap wouldn't follow the other taps threads. I still think you should get a piece of aluminum to practice with

Well, the tap guide doesn’t get here ‘til Monday, so I’ll probably follow your advice...

 

[fafrd]

You have to remember that your hole was smaller than 1/4" I assume the bottom of the 7 thread taper tap is smaller than 1/4"
So it cut threads but they are in material that isn't supposed to be there.

Good point.

After what I experienced today, I’m just much more aware of how important it is to keep the tap straight once tapping by hand.

 

[ArthurEld]

You should try to duplicate the process but using scrap aluminum.
Then you can perfect the flat bottom drill part of the process that you skipped.

 

[fafrd]

I just repaired one of my stripped threads and documented the process of drilling/tapping/helicoil'ing them in a video:

It's *so* tempting to do this to all my cells and just be done with this 6mm-in-aluminum nonsense.

Just watched your video again. Looks like you used the 6th-biggest thread guide for the tapered bit, which should correspond to 19/64” or 7.54mm.

My tapered bit won’t fit into my 7.5mm hole so I guess I’d need a standard tapping guide for that.

On the other hand, I’m pretty much touching the bottom with the tapered tap so I think I’m past the point where that will help.

Pretty sure I’ve cross-threaded the top two partial threads that are left, and the bottoming bit inserts a full two tapered threads before hitting, so I think my best bet may be to use the bottoming bit on the 7.5mm hole and hope is stays straight enough to get a thread started.

I did forget to use tapping fluid when I tapped the tapered bit, so not sure whether that may have resulted in the snafu I’m dealing with now, but I just did not get ~2 threads nicely formed after using the tapered bit (by hand using the drill press in my case).

I’ll get some aluminum and practice with the tapping guide as you demonstrate so I hopefully get some sense of what things should feel like once a thread has been properly started.

Whether I can salvage the thread I (mis)-started in the stripped cell or not remains an open question, but at least I should be less of a neophyte for next time...

 

[fafrd]

By wrapping 2 wraps of masking tape around the tap (above the 7 threads I’ll need), I’ve gotten the tap to be sufficiently snug in the 7.5mm hole.

But now I am worried about keeping the tapping guide stable on the terminal - it’s barely overlapping the edges of the round aluminum terminal and feels very unstable.

I suppose I can build up a support on either side to increase stability, but thought I would ask if anyone has any better idea before going to that trouble...

It’s going to be near-impossible to assure any support structure is co-planar with the surface of the terminal.

 

[cinergi]

By wrapping 2 wraps of masking tape around the tap (above the 7 threads I’ll need), I’ve gotten the tap to be sufficiently snug in the 7.5mm hole.

But now I am worried about keeping the tapping guide stable on the terminal - it’s barely overlapping the edges of the round aluminum terminal and feels very unstable.

I suppose I can build up a support on either side to increase stability, but thought I would ask if anyone has any better idea before going to that trouble...

It’s going to be near-impossible to assure any support structure is co-planar with the surface of the terminal.

?‍ I found it relatively easy -- you can feel when it becomes perpendicular and just hold the pressure as close to the center as possible so it doesn't wobble.

 

[ArthurEld]

I've never tried a tap guide.
If I didn't have a drill press I wouldn't have a choice.
I'll have to try one out next time I'm working with helicoils.