MYOG Titanium/Carbon Fiber Ice Axe

[Ryan Jordan]

Companion forum thread to:

MYOG Titanium/Carbon Fiber Ice Axe

[Roger Caffin]

> You could very well be correct about the CF insert being the key to better performance. I really should try it out before knocking it.
Yeah, I would REALLY like to see this experiment done. I am quite sure myself it would add greatly to the strength of the head connection, to the point that the shaft might then be adequate. I would recommend that the insert be 1.5 times the length of the current ferrule and a fairly tight fit.

> Looking at it from the another view, if we increased the diameter of the shaft, we could shorten the ferrule
Won't work! Check it on the FEA by all means, but shortening the length of the ferrule will ALWAYS reduce the strength of the joint severely. You could probably taper the ferrule wall thickness down significantly though – but keep that length!!!

Cheers

[Derek Goffin]

I agree with Roger about the length of insert. Theoretically the insert should start about 0.3-0.4 ferrule insert length from the end of the tube. In other words not flush with the end, but a bit further in. To continue the bike analogy tapering the ferrule walls or cutting a notch/s in the end of the Ti ferrule would spread stress.edit having said that machining costs money I would go for the insert without machining.
Roger obviously it is best to have high quality TI alloy if economical.It is certainly worth searching for the best alloy tube but no user until now has mentioned wear on the Aluminium spike of the Potty trowel as a problem. All talk has been of the blunting of the adze. Any Ti I would expect to be tougher and more wear resistant than Aluminium, is it that important? I for one carry a shortish axe and dont need to stabilize myself on rocks, only snow and ice.

[FM C]

Besides adding strength, adding a thin cf insert inside the ferrule extending a couple inches out would spread the stress on the shaft over a larger area. CF will flex quite a bit and when bending, a large amount of force is applied to the hard edge at the end of the ferrule.

When you look at the end of a power cable the usually have a ribbed area to allow the cord to bend at the plug rather terminating at a hard corner. Same idea.

[Steven Evans]

Nia,
Unfortunatley. I think you will need more then one axe to cover all those scenarios. The T and B rated axes are quite different – as they should be. You would be hard pressed to do any serious waterfall climbing with the camp corsa. And you would have a tough time using a T rated axe designed for waterfall climbing during general mountaineering (cane).
For what I use my axe for, a camp corsa (or any rated axe) is overkill, so I will gladly cut the weight in half and bring my Ti/Carbon axe.

"I'd like to see Steve shave an oz or so off his axe at the expense of some strength."

Playing around with the design this weekend, the lightest I think I could get this axe to is about 3.5 oz. That would mean using 0.08" thick sheet instead of the 0.125" and cutting some material away from the head ferrule and spike. Is it worth it?

[Steven Evans]

Hi Chris – good questions.

(1) Current shaft legnth at 19" = 45.2 grams

(2) I calculated early on that the max stress to be 122,000, but after testing found that it is almost exaclty half that at ~61000psi.

(3) A shaft with the same wall thickness as the original shaft having a I.D. of 0.875" and an O.D. of 0.9575" would weigh 57 grams.

Assuming the larger shaft was built the same and had the same properties, it would hold about 80lbs before breaking. This would add 12 grams to the weight of the axe.

Comparing a few more numbers, to get at the 135 lb UIAA requirement, we would need to find out how to increase the 61000 psi number. The numbers just aren't working out as we would need to have a huge (and heavy) shaft.

[Steven Evans]

Regarding the insert. I am going to contact Kevin to see if he can supply something like that. The only problem I see, from discussing with Kevin, is that the carbon tube dimensions are based on the inner diameter dimension and number of wraps. I'm not sure if he can supply an insert with an outer diameter within the tolerances required to fit the shaft without a second operation. For instance, the upper 1.4" of the current shaft (where the ferrule is placed over) is ground accurate to +/-0.001".
I'll let you guys know what he says.

[Steven Evans]

The Ti on the axe spike was actually made from 3Al-2.5V for ease, but when I sent out for quotes, no one could source a tube with the required dimensions…and I mean not one. They all came back stating a material change of 6Al-4V. I know I can get the stuff from Ti Joe, but the problem is that he isn't a reliable source for material because he deals with scrap. Therefore, sometimes he has the stuff, and sometimes he doesn't. For a short production run, I could get away with it, but most places just wanted to order one piece of .875 bar stock, put it in the machine and come back later when all the parts are done…it was very difficult to even get guys to quote the stuff. Other then Ti Joe, I couldn't source the stuff from any of my suppliers. Even now, I'm getting the stuff shipped in from California.

[Sam Haraldson]

There, I finally got around to reading this one. It's been haunting me at work where I've been too busy to take a few moments for it. So now, sitting outside on my back porch sipping a bottle of beer I was able to enjoy your work, Steve and Roger.

Another fine article I can show to my nerdy, math friends who think my backpacking habit is just another one of my tree-hugging, hippie habits.

[Derek Goffin]

"I'm not sure if he can supply an insert with an outer diameter within the tolerances required to fit the shaft without a second operation. For instance, the upper 1.4" of the current shaft (where the ferrule is placed over) is ground accurate to +/-0.001".

See what Kevin says but Roger's "fairly tight fit" sounds good enough to me. This bond does not have to take tension as great as the ferrule joint after all, it just has to transfer some bending forces. It might not even need such expensive glue. I was hoping that glued in it would add about 8 gram and cost about $5

[Roger Caffin]

> Playing around with the design this weekend, the lightest I think I could get this axe to is about 3.5 oz. That would mean using 0.08" thick sheet instead of the 0.125" and cutting some material away from the head ferrule and spike. Is it worth it?

Doubtful imho.
0.1" would be my limit, but I think even that would be trading off too much. I favour the 0.125" myself.

[Roger Caffin]

> Assuming the larger shaft was built the same and had the same properties, it would hold about 80lbs before breaking. This would add 12 grams to the weight of the axe.

I would buy that increase. I think the wall is a shade too thin at present.

[Roger Caffin]

> "I'm not sure if he can supply an insert with an outer diameter within the tolerances required to fit the shaft without a second operation. For instance, the upper 1.4" of the current shaft (where the ferrule is placed over) is ground accurate to +/-0.001".

The inside of the main tube will be dead accurate: it is made over a mandrill.
Grinding the outer surface of CF tubing to meet spec is quite common. ALL CF arrow shafts have a ground outside surface, to 0.001" or so. It should be no trouble to get some CF tube centerless ground to a very nice snug fit. The thinner the glue line the better. I would think Kevin would have the facilities.

[Steven Evans]

OK, I heard back from Kevin, who happens to be away from work at this moment. He is going to verify that he has the tooling available at his work to manufacture the required insert. He is familiar with the insert technique being used in situations like the one we have with the axe, however, he stated that it is not common practice.
In the meantime, I am going to run some numbers to get an idea of how long it needs to be, how much strength it will give us, and how best to go about the process.

[Roger Caffin]

Hi Steve

> In the meantime, I am going to run some numbers to get an idea of how long it needs to be, how much strength it will give us, and how best to go about the process.

My guesses (others are invited!), based on an insert of the same wall thickness:
1.5 times the length of the existing ferrule
75% extra strength
Tight fit with epoxy or engineering-grade cyano-acrylate

Cheers

[Derek Goffin]

Fun I want to play that game, my guess 50%

edit or 55% if the insert is inserted flush to the end then pushed in another 1/3rd ferrule length. Insert length 1.5 ferrule length

[Derek Goffin]

Fun I want to play that game, my guess 50%

edit or 55% if the insert is inserted flush to the end then pushed in another 1/3rd ferrule length. insert length 1,5 ferrule length.

[Aaron Sorensen]

Hey Steve,
I know this is a fairly new and who knows how expensive, but is it possible to use / get a CF tube that is made with the new Nanotube technology?

The company's that have switched to them have not changed there prices that much with the same product using the Nano.

I would think that since the CF tube is strong and just needs to flex more before breaking, the Nano just may be the trick.

This may be a $10 addition cost to you but you could add it as a $25 option to make up for low cost gain that you have.

[Steven Evans]

…that is a fun game…I'm gonna guess about 35% increase. Nothing would make me happier then being wrong (stronger axe!), I just don't see it adding a substantial amount. However, I'm just waiting for Kevin to get back to me to see if he can make them, and then we'll see. I haven't gotten around to running any numbers yet, soon though.
Aaron, I'm going to look into the Nano – Kevin never mentioned it, so maybe I have to ask. Thanks for the heads up.

[Steven Evans]

Just thought I would give a quick update for those interested. I have all the material for the axes, I'm just waiting to hear from Kevin on the carbon insert. He told me he was away for the next week or so, but was going to let me know if and when he could provide them…he has been very helpful, so I don't want to hound him. :)

I did run some numbers but I believe they were not very conclusive. I am getting about a 10% increase in strength, which would equate to about 4 lbs of additional load capability…hopefully I am wrong. I do realize that we will be relying on the insert to spread the stress over a larger area, and this is very difficult (for me) to calculate, and I can't run it through my software as I don't have all the required material properties…so we may have to wait for the test to see solid numbers.

So we hurry up and wait…

[Paul Tree]

Hi Steve, what about rather than reinforcing the shaft with additional material in the same orientation, and instead making a lengthwise sort of I-beam vertical strut inside like: (|)

or

[Derek Goffin]

Thanks Steve,
I am glad to have the update. We are off to the Pyrenees on the 9th july. It would great to have a just in case axe for then but it sounds as if they wont quite be available by then.

Derek

[Steven Evans]

Paul, another good idea. I do have a concern with a high stress point where the (I) would end. I've contacted Kevin and I'm going to wait for his response before going another route.

[Steven Evans]

Derek, amazingly enough, I just got an email from Kevin stating that he has built the inserts and is shipping them tomorrow. I should have them by the end of the week, but I wouldn't be able to promise anything by the 9th…I'm STILL struggling with getting some of the pieces quoted.
Then again, I'd really like to get one out there for someone to review it in the field. We'll see…

[Paul Tree]

yes, you'd want to have some kind of fillets that not only acted as gluing surface but also to spread the load. So they'd need to be hard and stiff enough to help. In boatbuilding they use microbeads for epoxy fillets… or colloidal silica looks good. There must be some ultralight carbon beads out there..

Tap plastics has Cabosil :
Tap

Microbeads don't seem to have the same adhesive value as silica. More for filling than filleting.
West #406

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