Joe Perez

iTrader: (8)

Question: Does not this presuppose a mold created by a traditional toolmaker? Would not a mold produced via SLS be satisfactory for the relatively low-volume production of bicycle frames (as opposed to, say, plastic forks)?

Leafy

iTrader: (1)

Probably joe. But I was thinking make the tooling in china and crank out a few thousand of various sizes. And sell them with the bottom end name brand components for the $500 range.

Joe Perez

iTrader: (8)

Hmm. I was thinking more of a small artisan shop, with "Made in the USA" stamped on it, sold for maybe 1/2 of what a comparable CF bike would cost.


Also, I am considering making this my next purchase: 2013 Schwinn Sierra 2 Comfort Bike - Bikes & Frames



This would be the bike which gets parked overnight in Manhattan (corner of 23rd & 6th) every night, and used for the crosstown leg of my commute 23 & 6 <-> 42 & 2.) Remember, I have to use the PATH subway train to get from Hoboken into Manhattan, and carrying a bike on that train is impractical. So there's really no choice but to leave it parked overnight in the bicycle-theft capitol of the world.

Thus, the criteria are:

1: Cheap.
2: Inconspicuous.
3: Comfy.
4: Does not contain high-end components which will attract strippers.
5: Won't break my heart when it's stolen outright.
6: Must survive being ridden on roads which have recently been cluster-bombed.


Opinions?

vehicular

iTrader: (3)

Imo, spending even $100 on a bike that you'll leave outside over night in the bike theft capital of the universe is tantamount to throwing money out your bed room window. Buy $20 bikes on CL, put good tires on them and keep a spare in your laundry room.

Joe Perez

iTrader: (8)

Laundry room? Haha. No such thing here, my friend. The housing situation in this neck of the woods is a bit different from what you're probably accustomed to.

I've been searching Craigslist quite exhaustively, and there just aren't any $20 bikes around here. The absolute bottom-end of the price scale is about the same as what I'm posting here.

Were it not for the fact that I'm 6'2" and wear size 14 boots, I'd buy a $99 bike from Walmart. But having the ability to specify the frame size is important to me, and that's another thing that you're not gonna get on CL. When I ride a "normal sized" MTB, my feet hit the front wheel when I am turning.

And, to be perfectly honest, I just don't want to deal with people on Craigslist.

dcamp2

iTrader: (4)

not familiar with SLS- what is that? I'm just thinking to get plastic to flow into thin-walled long tubes it would have to be pushed by high pressures and the mold would be hot so the plastic doesn't cure halfway through- therefore needing a metal mold.


CF bike molds are low-volume, yet still made of steel... not sure why they can't get away with aluminum or something cheaper/softer but they can't/don't. (i work for one of the big bike companies)





I think we will see 3-d printed bike frames before anything else- no need for expensive molds or skilled welders, just one machine that can print any size frame you want.

dcamp2

iTrader: (4)

buy it, and hit it with brown spray paint (no masking allowed) so it looks like absolute **** and no one will steal it.

Leafy

iTrader: (1)

Round tubes are a limitation set by metal frames, not a requirement. An IM frame would use a variable profile, probably an I beam. With metal inserts left in each molding for the head tube and crank.

SLS is a type of metal 3d printing.

Full_Tilt_Boogie

iTrader: (1)

Buy $100 bike, spend $20 creating a faux rusty pile of **** finish, maybe it wont get stolen.

Leafy

iTrader: (1)

I'd make it look gross too, like putting fake **** on the seat so someone wouldnt even steal it just to ride somewhere else and ditch.

Joe Perez

iTrader: (8)

Selective laser sintering. It's basically the same as SLA, but for metal. You use a laser to melt and solidify a very fine metal power one layer at a time, enabling you to print out extremely complex shapes. It does not leave a perfect surface-finish, but you can fix that in post.

The basic idea is that you don't need to pay a tool-and-die maker to painstakingly hog out a negative from solid blocks of metal, you just design the part in Solidworks and then the let the computer print it out while you pop into Chipotle to watch Braineack fume about how incompetent the employees are.


You're sort of describing the blow-molding process, though I'm not sure how applicable that is to things shaped like bicycle frames.





If someone can tell me where to buy a $100 bike that fits me well (eg: 31" standover, 21" seat tube, > 42" wheelbase) I would be most appreciative.

There is a reason why I haven't already purchased another $99 Huffy for this, and that's because most bikes in that price range are built to accommodate someone 5 and a half feet tall with small feet.

dcamp2

iTrader: (4)

Got it- I have seen that, just didn't know the abbreviation. Probably could make molds with that method, just don't know if they can make SLS parts that big? And i'm not sure if it would be a whole lot cheaper than cutting at that point...



yeah i think it would be like blow molding- Leafy suggested one could make very affordable bike frames that way with some reinforced plastic or something. I'm not convinced.

Leafy

iTrader: (1)

But I dont want blow molding, I dont need hollow parts or tubes. Those shapes work well for bikes make from metals or composites, because its easy for the materials to be made in that shape. But when you open up profiles that are more realistically made with molding you can make the bike stiffer with less material. We're starting to see the departure from round tubes with composite and some aluminum bikes. But obviously according to hustler thats not socially acceptable.

The other alternative to cheap light bikes is aluminum joiners with pre-made CF tubes bonded to it. Cast or machine the joiners for fairly cheap and use Chinese cf tubes, should be able to make low run (like less than 10 per size/geometry) bikes that ride like cf frames with slightly more weight for ~$700 frame including american machining and labor. And be able to change geometry and frame size at the drop of the hat for one bike with more or less no increase in cost.

Joe Perez

iTrader: (8)

I'm not really sure what the true cost to beat is. I mean, you said a traditional mold is $100k, but is that all going into the toolmaker's pocket, or does that count designing the mold, buying all the fiddly bits to load it into the machine, etc?

Another option would be to sand-cast the mold based on an SLA-generated resin positive.

In the end, I'm curious as to what material would actually be used to make the finished product, though. I'm hearing talk of reinforced plastic polymers, not sure what that means. Reinforced with what? (eg: when can you squeeze through an injection or blow-molding process that works as a reinforcing material?)

Leafy

iTrader: (1)

Reinforced with fibers, think unwoven short strands of CF, kevlar, or FG. Think Glock trigger frame.

hustler

iTrader: (6)

Joe Perez

iTrader: (8)

When I think of that, I think of fiberglass sprayed via a chopper-type applicator. Generally, these produce parts regarded as heavier, thicker, and less strong than their traditionally-laid counterparts.

If you're gonna go that way, why not just do actual CF / CK?

Leafy

iTrader: (1)

Because you're injection molding it, not spraying it with a chopper gun.

There's also forged composite which is a similar process to injection molding with a fiber reinforced plastic but using a thermoset rather than a thermoplastic and it uses a higher amount of the fabric material.

Joe Perez

iTrader: (8)

What I'm saying is- at the point where you're using actual CF and resin of the type which we might associate with chopper-gun application, could it be applied in something like a roto-casting process, wherein you could forego the cost and complexity of injection molding, huge and expensive tooling, etc?

Best yet, the resultant frame can still be called "carbon fiber."

Leafy

iTrader: (1)

I guess, but you can get different beam profiles and less labor per part this way. Lamborghini and Calloway kind of pioneered the carbon composite forging, but fiber reinforced plastic has been going on for a while because it can get the strength of steel parts with the lightness of plastic and slightly more money than non-reinforced plastic.