|
Group: Forum Members
Posts: 16,
Visits: 120
|
Hi all. My name's Jonah, I'm a mechanical engineering major (Junior) at Eastern Washington University, and....I have a dream. This is gonna be pretty much just an information dump but I'll try to at least categorize it. I do some ice climbing. Both mountaineering and vertical waterfall stuff. A while ago I looked into some ice tools and had to sit down when I saw that most quality ones run about $150, and you kinda need two. Carbon Fiber ones are upwards of $250 each. So I got to thinking "How hard could it really be?" and ended up designing an I-beam style one in solidworks out of T6 Aluminum. I ran simulated load tests on them and they held up to something like 5kN if you were to attach it horizontally and hang off the end of the handle. I could live with that. I then finally looked up how much a 24x6x1.25" T6 aluminum billet costed....and had to re-evaluate. Aluminum handle:   It was then that a friend showed me THIS, and I started considering CF for a handle. This happened around February, and I was gone all summer so I never really got around to looking into it any further, but...winter is coming. Where I'm at right now, is I have a basic handle shape that makes sense to me, but I have absolutely zero appreciation for the strength/fabric weight of CF, so I figure I'd ask yall and hopefully save myself some snapped shafts and burned money. What I know/think I know: - The handle should be about 20" long and ~1.125" in diameter, with a slightly oval cross-section.
- If I give it a constant radius curve (or mostly at least) it'll be stronger and less likely to wrinkle than one with tight bends (like my aluminum one has).
- I have a friend who works for a machine shop and I'm trying to see if I can get him to machine me a mold of this thing in two halves, out of pretty much any metal he can find.
- Too much resin is bad
- Too little resin is bad
- CF is strongest along the axis of its fibers. Tensile strength baby!
- Epoxy seems to be the way to go for structural stuff
- Galvanic corrosion applies. Fiberglass where metal touches composite.
- I'll play around with fiberglass (maybe get some woven stuff so it's similar to CF) for a while first.
- A chunk of the garage is going to get covered in plastic sheeting and sealed (Breaking Bad style) for dust and epoxy/styrene fume reasons.
- I'll buy a respirator.
My approximate plan of manufacturing: - A two-part mold that splits along the length of the piece seems to be a good option.
- Provided I use a two-part mold that the fabric would expand inside of to form the piece, the woven CF sleeving seems like it would work very well.
- If I am able to get a metal mold vacuum bagging could be plausible but potentially a titanic headache.
- Regardless of mold material, I was planning on using the same method as the other guy who made CF tools, with the fabric wrapped around a bicycle tube, placed in the mold with the other half bolted over it, then inflated to force the fabric against the mold walls and hopefully force out any extra resin.
- If I made the curve radius of the handle the same as some common bicycle tire radius then I'd pretty much have a bladder that perfectly matched my mold!
- Pre-impregnating the fabric with the correct weight of resin, then putting it in the mold seems like a good method.
What I'd like to know/need help with: - If I were to give it a cross section that was something like this...
 would it be any stronger than just an oval? - Would a two-part acrylic mold work? I haven't looked into prices but if it's cheaper than whatever else I can find...
- I'm not sure what temperature bicycle inner tubes can hold pressure to, but if it's reasonably high I have a kiln (for tiles and pots and whatever). I haven't done much research into temperature curing, and I assume I'd have to pre-heat the steel mold (I don't know if fiberglass would hold?) prior to the layup.
- I know that CF is strongest along its axis, but if I were to just use uni-directional stuff along the length of the tool I assume it would break since there's a curve and I'd be compressing the fibers together when I hung on it. This brings me to one big question: What do I use? I've heard Uni is kind of a pain, and I'm also not sure how well it would work here since I'm expanding it inside the mold I assume the fibers would all spread apart anyways, and I guess the stuff they use to hold it together can get in the way. I dunno though. Something like -30/0/+30 seems like a good option. I assume that ice tools experience rotational forces when the pick is stuck and the handle's twisted, so torsional strength is kinda needed, and they also get side-loaded (though not much). I wish I had access to some measurement devices here but my school's not that cool.
- If I could somehow get some honeycomb stuff inside it it'd be awesome, but that seems to be essentially impossible for a multitude of reasons, so I'll just scrap that idea.
- This thing has to go through a metric f*ck ton of decently extreme temperature cycles, from 0*F for hours at a time to 80*F+ when I get back in the car. How should this effect resin?
- How should I go about attaching the pick? I was planning on making a metal "head" so I could change broken picks out, but I'm unsure what the best way to attach it to the handle is. Bolting it through the width seems like uncreative to say the least, and stupid to be blunt. Using any sort of fasteners seems out of the question since they'd localize the load. I'm aware that aluminum expands/contracts a lot more than CF, so it's out of the question (it wouldn't have really work for other reasons anyways...), and steel has a coef of thermal expansion that's like 3-6x that of CF. I considered that I might be able to use this to my advantage if I were to make a steel head a couple thousandths of an inch larger than the shaft ID, cool it down in liquid N2 or dry ice, then get an interference fit, but I don't know if it'd hold or just pop the CF when it expanded or what. I think right now an expanding head is a decent solution. The other guy who made CF axes just epoxied a steel head in, and that seems kinda dumb to me to not even use some kind of fiber or anything. I'd think after enough thermal cycles it'll pop.
Expanding bolt example:  I have more stuff but I have to go to Chem right now! I know some more stuff and have some more questions but hopefully I've been slightly entertaining thus far. Thanks in advance everyone! Ahhhh I just realized I didn't even mention how strong it needs to be!! Here's an article on strengths, I'm going for CEB-T!
|
|
Group: Forum Members
Posts: 16,
Visits: 120
|
For me I would increase the number of layers in the area where the head will attach, giving a tapered wall thickness along its length. To try and disperse any point loadings. You could add some E-Glass or similar to improve impact resistance if required. I would be concentrating more on how to attach the head to the shaft reliably.
Just like how bicycle frame tubes are butted!
I never even thought of it that way! I was planning on doing a layer or two of uni, and finish with a layer of fiberglass for galvanic protection, but completely spaced on how making them butted will make them stronger too. I have a tendency to overthink things and miss obvious details 
I would like to recommend very strongly that you use at least one layer of kevlar/twaron mix fabric in there... What you're building is a tool for "hammering" some measure of impact resistance seems vital to me .. I was still planning on this, but earlier today I was thinking about it and realized the following: If i incorporate a layer of Kevlar that runs the length of the shaft, and the shaft were to break while it was already stuck in the ice, the loading would change to something like this:  In which case the tool would probably slip off anyways. That being said, I'd still like to throw a layer of CF/kevlar weave in there in case I lend it to my roommate and he smashes it on a rock and cuts through the CF somehow. Bottom line: a layer of CF/Kevlar doesn't weigh that much, doesn't seem like it will be hard to include, and won't make things worse. And as long as I'm not making things worse I'm doing okay! Running kevlar tows between the ends seems like a good idea, but I'm not sure how I would get the tows between the two inserts not only taught, but tied off none the less. I considered placing an eyelet on each insert, attach the two with a piece of spectra/dyneema or even basic nylon webbing, epoxy the head in, then twist the bottom insert until it was against the bottom of the shaft, and epoxy it in place. The webbing would still have enough give to let one insert pop out though, thus negating most of the benefits. If I could come up with a way of attaching the inserts so that they're tight inside the shaft I'd feel pretty comfortable climbing on them, since even if the epoxy bond were to fail the inserts would remain inside the shaft and since it's an oval they'd be unable to twist. Currently I feel as though there's two ways that this design can fail that are far more likely than any others: 1.) The CF fails at one of the pressure points on the head. 2.) After enough thermal cycles, vibrations, and impacts, the epoxy bond between the head and shaft fail, resulting the head pulling out from the shaft. I think that with Warren's idea to make the tubes butted, with extra uni and E-glass, the shaft failing is becoming considerably less of a hazard. This leaves the issue of the head pulling out (oh man...), but thanks in part to Brian I think I've got something to help out with that too.  So Brian came up with cutting horizontal slots in the head insert. (Everything you're about to read could actually be a terrible idea, and I just don't know it. It's a good deal of speculation.) I was originally planning on hollowing it out, but this is a lot less labor-intensive and I believe is quite a bit stronger as well. I realized that I could run CF tows through these holes prior to epoxying it into the shaft, wet them down, and epoxy it in. Ideally the fibers would be running DOWN instead of UP, but ya can't have everything. Depending on how many tows I use I assume I'd have to taper the insert a little bit to accommodate their width while still holding 0.01" gap around the edges for optimal adhesion, but I thought I'd pitch the idea and see what everyone thinks. This could pose an issue with galvanic corrosion, so I'll do some research into how well spectra/dyneema bonds with CF and how well it handles compression in a matrix, but I thought it was an interesting idea; kind of like Dravis' idea of tying the two together with kevlar, but...reversed. Shaft flex is something that's been of slight concern. My old roommate plays hockey, and I remember him telling me how the CF hockey sticks he has actually bend when he hits the puck with them. As he swings, the blade lags behind the shaft, then snaps forwards at just the right moment to hit the puck, meaning you have the kinetic energy of the stick, plus the kinetic energy of the blade snapping forwards. Cool stuff! I'm not sure how to factor this into my picks though, it seems like the only way to figure it out is trial and error; keep trying different layups until it feels right. I think I have a decent margin for error though, since most of the ice climbing I do you don't swing your picks like you're driving framing nails with a hammer, but more like you're driving finishing nails. Two or three relatively light taps to chip away a little ice is all it takes; a couple millimeters of ice will support your bodyweight pretty easily. I have a chemistry lab report due in an hour and a half (We weighed water  ...) so I'd better get to work on that. Thanks for the help everyone! Slowly the idea progresses to eventual fruition!
|