Mounting into aluminum

[bio-smear]

I have reason to drive some binding screws into solid 6061-T6 aluminum (you guessed it...P14's into some Primo platform pedals... ) I need some specs on the standard binding mounting screw that comes with Axial 140's. With my calipers it looks like 5mm posidrive coarse thread sheet metal/woodscrew with .5 threads/mm. Normally they would be self tapping for wood or even a thin layer of steel/titanium, but I don't want to work too hard on driving these into the aluminum(which is about 8mm thick) so I think I'll have to pre-tap.

Confirm specs on the screw and the designation of the tap?

Thanks.

[flip]

Use socket head machine screws, not normal binding screws. Solves your problem and will hold much better in the aluminum. You can get pozidrive screws from Tognar, or just use Allen key screws from your local machine shop or McMaster-Carr.

[Lok]

You should doublecheck this, but I think screws for mounting alpine bindings are ANSI #12 AB (AB is the part that means they are self tapping).

[bio-smear]

Use socket head machine screws, not normal binding screws. Solves your problem and will hold much better in the aluminum.

You sure about this? The threads on normal binding screws are pretty deep, deeper than a machine screw. Wouldn't more bite be better for axial loads on the screw(albeit less threads/cm)? I agree this would make tapping easier, but more thread profile seems more bomber. Plus, I've already got the screws that came with my bindings.

[El Chupacabra]

You sure about this? The threads on normal binding screws are pretty deep, deeper than a machine screw. Wouldn't more bite be better for axial loads on the screw(albeit less threads/cm)? I agree this would make tapping easier, but more thread profile seems more bomber. Plus, I've already got the screws that came with my bindings.

You can get metric screws for bicycle parts in a lot of different lengths; would think that a 5mm or 6mm screw would be about the right size for a binding's countersunk hole. Lowe's has a pretty good selection of metric screws. Use Loctite.

Quick google -- pic is worth a 1000 words -- this shows the countersunk hole I'm talking about, and the shape of the kind of machine screw I'm talking about:

[bio-smear]

I'm familiar with countersunk flathead machine screws, still wondering about the designation of the tap for standard binding mounting screws. ANSI #12? Aren't all ANSI measurements in inches? Isn't all ski hardware metric?

Found this document, but even the metric coarse thread taps in 5.5mm only show a thread pitch of .9mm, and I measure 1.6mm between threads on the standard binding screws.

El Chup, what do you use if you're going to tap a metal layer under the topsheet when mounting?

I'm starting to think using metric machine screws will just be easier.

[El Chupacabra]

El Chup, what do you use if you're going to tap a metal layer under the topsheet when mounting?

A bigger screwdriver.

I have a set of metric and SAE taps & dies, but haven't used any of them on skis. The topsheets I've screwed with (ha!) haven't been that thick. Haven't drilled any Volants though.

For that binding plate contraption, I'd tap it like you would any other hole that needed tapping .

[/gratuitous use of FM]

[bio-smear]

Yeah I've decided to use 5mm machine screws. Daddy is a machinist and has the full compliment of metric taps...should be cleaner.

[EstoBum]

I was looking at this today as well, with my Mechanical Engineering Refernece Book (and although old 80's version) and looking at the binding screws they seem to be more of a "Type B thread forming (formerly Type Z)". The difference is that AB have a sharp point while B has a tapered, but blunt end. This is refere ncing a British Standard (BS 4714)

Although flipping through the Rossi Shop Manual, the screws are metric (M8x whatever length). This and the fact that nearly all equipment involved in skiing is in metric makes me assume that they are actually a similar but ISO standard.

As for mounting into aluminum, It would make sense to tap a UNC or UNF thread into the hole and have the machine screws. The standard binding screws are thread forming, which are supposed to cut threads into a softer (wood/fiberglass) material. With a stronger base material (6061 Plate) the threads on the machine screws don't need to be as big to get the same strength.

I'm actually looking at building my own binding plates so I will be lookinging into this later this week. Maybe I can find a newer metric reference book to check this out.

Anyone also notice the teeth cut into the back of the heads of the binding screws? Seems like a elegant way to have them dig into the binding like a lock washer.

[EstoBum]

I'm familiar with countersunk flathead machine screws, still wondering about the designation of the tap for standard binding mounting screws. ANSI #12? Aren't all ANSI measurements in inches? Isn't all ski hardware metric?

You're probably not going to find a tap for this type of screw since its a thread forming screw does the tapping itself

[bio-smear]

which are supposed to cut threads into a softer (wood/fiberglass) material. With a stronger base material (6061 Plate) the threads on the machine screws don't need to be as big to get the same strength.

I came to this conclusion too, and figured that self tapping a harder material would leave me with a chunky mess.

Anyone also notice the teeth cut into the back of the heads of the binding screws? Seems like a elegant way to have them dig into the binding like a lock washer.

Yeah, an extra lil bit of tensioned friction to keep them from backing out. Is there any designation for that feature?