Delrin tenon failure avoidance

[UnderShade]

I’ve probably dropped 3-4K in the last year. None of that equipment/tooling has made me a better pipe maker, but it definitely has helped me learn faster and given me more consistent results. So far, the metal lathe has been the most worthwhile investment... and the most expensive.

[LatakiaLover]

More consistent results = better pipe maker

[DocAitch]

To get back to the original post, I want to go out on a limb a bit.
I see the beautifully spaced depressions, cuts, and even lathe turned rings on the Delrin and I have questions about the materials strength of the epoxy (I use G Flex).
Does the shear strength (resistance to lateral forces) of the epoxy lend itself to fewer projections which are deeper or will multiple random oriented scratches be more suitable?

My intuition and limited physics background says this pattern, produced with 60 grit paper is a better way to go.
The force is only applied at the interface oF the materials, so depth is meaningless, and the more border length to the prep defects the better.
DocAitch

[LatakiaLover]

The unquantifiable complexity of the mechanics involved in variable scratch depth, varying materials, and varying adhesives make the "textbook" solution (for lack of a better term) irrelevant in practical terms.

The desired end result is zero failures.

I've repaired hundreds of pulled-out tenons. All had been "scuffed" before gluing.

Of those I've repaired using the type of divots shown, none have failed.

Is it an execution/implementation thing? Probably. But why risk it? There's obviously a threshold BELOW which scuffing is inadequate. The shop-level problem is knowing where it is for every combination of the aforementioned scratch depth, materials, and adhesive. Variables that don't matter when divots are used.

[caskwith]

Of course the best method is to thread your tenons

[Ratimus]

I wonder if anybody's ever used Dunhill-style "through dots" as clevis pins to mechanically secure a tenon.

[LatakiaLover]

Of course the best method is to thread your tenons

Do you cut matching threads in the receiving hole so they screw in?

[caskwith]

Of course the best method is to thread your tenons

Do you cut matching threads in the receiving hole so they screw in?

I certainly do.

[LatakiaLover]

I thought you probably did, but wanted to be sure.

I've got drawers full of those pre-threaded Delrin tenons in different sizes. Nifty widgets. Save time AND increase reliability to 100% seems like a no-brainer. Why every pipe maker (who prefers Delrin) doesn't use them is a mystery.

[seamonster]

] pre-threaded Delrin tenons in different sizes. Nifty widgets. Save time AND increase reliability to 100% seems like a no-brainer. Why every pipe maker (who prefers Delrin) doesn't use them is a mystery.

Hmmm.... where, these days, does an interested party procure such pre-threaded delrin tenons?????????????????

[n80]

What do you cut the threads in the shank with? I have a tap and die set and considered making a threaded deer horn shank extension just for kicks.....but over tighten something like that once and the shank is toast.

[LatakiaLover]

Hmmm.... where, these days, does an interested party procure such pre-threaded delrin tenons?????????????????

Tim West stocks five diameters. (The larger three and smaller two are different thread sizes)

Send him this pic and he'll know exactly what you want:

[caskwith]

What do you cut the threads in the shank with? I have a tap and die set and considered making a threaded deer horn shank extension just for kicks.....but over tighten something like that once and the shank is toast.

Tap for the stem and die for the tenon.

[LatakiaLover]

What do you cut the threads in the shank with? I have a tap and die set and considered making a threaded deer horn shank extension just for kicks.....but over tighten something like that once and the shank is toast.

???

Threads in the shank?

You mean how to cut threads in the "receiving hole" in the stem?

If so, yes, just a hardware store tap. Starting taps dead-straight can be tricky, though, I strongly recommend making or buying a jig designed for the purpose.

[LatakiaLover]

I wonder if anybody's ever used Dunhill-style "through dots" as clevis pins to mechanically secure a tenon.

The same way they attach bamboo?

It would be like walking west around the world to get to the east side of a street. Theoretically possible, but pointlessly difficult to execute. (And not terribly stable/durable if you managed it --- "stake-able" metal is soft. The repeated twisting and pulling of stem removal would almost certainly bend it)

[n80]

LL, I meant stem, not shank.

[Sasquatch]

If only we could just somehow cut the tenon from the same material as the stem....

[Ratimus]

The same way they attach bamboo?

No, I'm thinking drill from outside the stem and into the delrin a couple places, then glue in a tiny rod of ebonite or whatever. I guess more like a keyed motor shaft than like a clevis pin.

The reason I'm thinking along these lines is that it's pretty easy to cut some grooves around the circumference of the tenon to prevent it from pulling out along the axis, but much trickier to prevent it from breaking free and rotating about the axis while still trapped in those grooves.

Seems like a pin or two would be less work than threading, but I agree that the shearing action might cause problems. Plus, not everybody wants dots on their stems.

[caskwith]

If only we could just somehow cut the tenon from the same material as the stem....

What a stooopid idea

[UnderShade]

Yeah Sas... that’s like makin’ a pipe outta wood or somethin’!