Bicycle Mechanics - Opportunity to CNC derailleur hanger, bad idea?

Okay well my CNC class is starting in school in 2 or 3 weeks plus it turns out i've got a few other sources to use a CNC machine :). Sometimes when you get a derailleur hanger is bent and sometimes they snap if you try and fix it. I know they are supposed to be a sacrificing unit so you dont crap out your derailleur and send it to the grave yard early but honestly ive got more of a road bike anyways, with some MTB components cuz i do hit hte trails sometimes. Im wondering if i should try and CNC a derialleur hanger out of steel. A frind who is taking the class this semester says what i am looking to do is not overly complicated. IS this a bad idea?

If you have access to the equipment, I see no reason not to do it.

I think this is a cool project. I want to mill myself a headlight bracket that actually mounts the way I want it to :)

I have read (from Sheldon Brown I believe) that forging is generally preferring to CNC machining for highly stresses bike parts, because CNC introduces stresses at the surface that weaken parts. I don't think a derailer hanger would matter too much though. Please post photos if you do it.

Well im just thinking instead of having aluminum which sometimes come bent and when i try to straighten it (i just did this yesterday) it broke! Steel is stronger, heavier but you know sometimes i dont care. I posted something like htis a while back and people had some reason to say its a bad idea i just dont know why.

It seems like the worst that could happen is you don't machine it quite right and the shifting sucks or it's brittle and breaks, and then you replace it. I don't see the downside to trying it, plus I'm curious to know how hard it is!

Go for it. CNC is just another way to remove metal - you could cut that simple part on a Bridgeport (manual) machine or even hold a piece of flat stock in a vise and file it to the desired shape - it's all metal removal.

Learning CNC is done best when you know what you want to end up with before you start. All your learning about programming and operating the machine then has a definable goal. It sounds like a great starter project. I wish you well.

Ron
(ps I've been in the CNC machine tool industry for 24 years, including teaching programming and ops).

I'd make the hanger out of aluminum. the whole idea of a replaceable hanger is that it breaks before your derailleur or dropout does. so it should be weaker then the derailleur or dropout. if you make the hanger out of steel, in a crash, you might end up with a perfectly fine $10 scrap of metal( hanger), but a trashed 90 dollar derailleur and a trashed frame that costs even more then that.

Well i know we use auto CAD and master cad so ive heard fun things about that. Im probably going to use aluminum as suggested by phatman. Do i use 7005 or 6061? Im leaning toward 6061 i mean thats aircraft standard.

Hi Victor, do you know if CNC is commonly used in manufacturing commercial bike parts? I would assume it is used for BB shells and hub flanges and things with lots of holes, but how about crankarms and brake calipers and such? My hubs look like they have been climb milled...


Go for it. CNC is just another way to remove metal - you could cut that simple part on a Bridgeport (manual) machine or even hold a piece of flat stock in a vise and file it to the desired shape - it's all metal removal.

Learning CNC is done best when you know what you want to end up with before you start. All your learning about programming and operating the machine then has a definable goal. It sounds like a great starter project. I wish you well.

Ron
(ps I've been in the CNC machine tool industry for 24 years, including teaching programming and ops).

6061-T6 is common and easily obtained as scrap from machine shops. it machines beautifully. it will break before it bends, due to the heat treating. as far as milling and stress-risers are concerned, that's a pretty weak argument. if it is really a problem, parts can be polished or media tumbled. machined aluminum will oxidize unless treated. with a hanger as a cnc school project, cool. make fifty as easily as you could make one. engrave your name or logo. make a hanger that's a bottle opener. only trouble i see is getting the right tap for der threads.

WEll i personally own a rather large array of tap and die so i can work that out. I know the one i have is 6 threads, if i can figure out how many threads/inch i can confirm

cnc is used for everything. forged and cast parts (your cranks) are finished with cnc. nothing is done manually anymore...it's about production, repetition, economy, and an idiot can load a fixture and push the green button after the skilled labor performs setup and tooling.
phantom- i would suggest solidworks. you can use sw to design your part, design specific fixturing, and even use a plug-in to send g-code (or whatever your machine uses) directly to the mill. it's the real deal. save autocad for your architecture class.

yer der will be metric, and i think it's a little fine... nonstandard

autocad and mastercad are what i have in school so thats what i can use.

nothing wrong with doing it the hard way...

WEll i personally own a rather large array of tap and die so i can work that out. I know the one i have is 6 threads, if i can figure out how many threads/inch i can confirm

10 x 1mm.

My guess is that CNC machining is used only where necessary because for high volume production, casting and/or forging is cheaper (and often stronger) per part.

I'd suspect that you'd not find much CNC work in BB shells or hub flanges - I'd imaging they cast NNS (near net shape) and grind to finish size - but that's just a guess.

Some CNC work might be done on stems, seatpost brackets, brake arms, crank arms, spindles... Some of these might be done on dedicated non-CNC gear also, like screw machines and other high volume automatics (locknuts, shells) or dedicated mills (brake lever holes, etc.). It's all up to the shop with the contract, what can they produce at what quantity (and quality - these are generally not hard to make parts in the grand scheme of things), and cost.

The higher-grade your part (and higher cost) and lower production volume, the more likely you'll find CNC, IMO.

"I'd make the hanger out of aluminum. the whole idea of a replaceable hanger is that it breaks before your derailleur or dropout does. so it should be weaker then the derailleur or dropout."

I will second this. You want the simplest/cheapest part to give/fail first.
But if you want a steel one and you have the tools go for it.
You only risk trashing your frame/derailleur on the next crash.

I'd make the hanger out of aluminum. the whole idea of a replaceable hanger is that it breaks before your derailleur or dropout does. so it should be weaker then the derailleur or dropout. if you make the hanger out of steel, in a crash, you might end up with a perfectly fine $10 scrap of metal( hanger), but a trashed 90 dollar derailleur and a trashed frame that costs even more then that.

Actually, I think the reason for the replaceable aluminum dropout is because aluminum does not take to repeated bending like steel. If you bend a non-replaceable dropout on an aluminum frame, it would become your next fixed gear project. Steel frames do not need replaceable dropouts because if they get bent, you just bend them back.

Aren't some hangers CNC'd to start with?

It seems like the worst that could happen is you don't machine it quite right and the shifting sucks or it's brittle and breaks, and then you replace it. I don't see the downside to trying it, plus I'm curious to know how hard it is!

Going down a hill, you go to shift, bam! thing brakes, gets jammed up in your tires, spokes rip the thing off, gets stuck, you go flying off the side of a cliff at 60mph. SWEET!

Going down a hill, you go to shift, bam! thing brakes, gets jammed up in your tires, spokes rip the thing off, gets stuck, you go flying off the side of a cliff at 60mph. SWEET!

Hehe, fine, that is worse :) But I *was* assuming that the hanger would be tested in more forgiving conditions before being used on a difficult descent. I mean if it's badly aligned you could probably figure that out ahead of time. Brittleness might be a hidden danger, I'll admit.

Oh yes, the derailer hanger is a wonderful project. Save the project and take a copy home. You can find a cnc machine shop and make more when you need them. My personal choices for material would be 6061 aluminum or a mild low-carbon steel which will bend easily and not be likely to mangle your frame.

Doc

CNC a stem or brake calipers. Much more spectacular failures.

I think the whole concept of a frame that needs a d hanger is a bad idea.


If you want to cnc something why not a drop out with a proper d mount.

This whole discussion of steel, aluminum, milled, stamped, forged, should it bend, should it break is ********.

The derailleur should be attached to a dropout with a fastener that is designed to break before the dropout fails. The shift cable should be routed so as to help prevent the severed derailleur from going into the spokes.

16victor-
i worked in a cnc shop that had the contract for fox forks and quickie wheelchairs- including the fancy racing ones- which are basicly bike parts to begin with. just about everything was cnc unless it came off of a screw machine. castings, forgings, and extrusions were all finished in cnc. find a forged part on your bike that does not have a machine process to it. even if it's just a ream, thread, and relief, it's sure as hell not done on a bridgeport. cnc is not reserved for the gods, it is the process of the masses- mass production. even cast pipe fittings are threaded with cnc.

Make a stack of them so if one breaks you have a couple of spares. I wonder how many of these replaceable dropouts are actually available 10 years down the road.
Are there any other bike bits we would like made?
Lamp mountings never seem to be up to the task. I've fabricated a front mount using old cranks and chainrings as raw material, it was all hand cutting and file work.
LOOK do some groovy adjustable stems and seatposts which are used for fitting. The seatpost has a huge range of horizontal adjustment. They are very expensive, so would make a cool project.
http://www.lookcyclesusa.com/pp-ergostem-hsc.htm

Im looking into other little things i could make, might as well have some fun with this. Would i be crazy to make a chain ring? The Truvativ i have is 44teeth, 60% of what i do is road travel, i could use a higher gear ratio. Would it cuase any problems to have a 48 or 50+tooth large chainring and keep the others i already have?

I'm with ya, I know it's not 'reserverd for the gods' but on cheapie mass produced bikes, there's a lot less CNC going on than for the more high-line specialty stuff you worked with when you were a job shopper. Mostly because in China and Taiwan, labor is so cheap and quality can be sacrificed moreso than higher line gear (even if it's Taiwanese). Point is, if making a million or more a year, you want to get from raw material to finished product with the fewest steps required. Machining (including CNC) can be eliminated through increased use of NNS, stamping/welding, and automatic equipment.

If I had a derailluer hanger contract - bound to be high volume - I'd be stamping those beetches and trying to come up with a non CNC way to cut the threads.

you dont need CNC to cut out threads though, if you wanted a non cnc way to cut the threads just make the hole accordingly and use a powerthreader or tap and die kit

16v- roger that.
if i were to do a cnc project, i would try to make a linear-pull hub (pulstar, ksyrium, crossmax, etc.) for fixed gear use. it would take several steps, some more advanced fixturing and an index setup, but man would it be cool to knock out a bunch of those puppies. there is a small niche market for something like that.

A sprocket would be a cool project. You could use some cool CNC features like rotation, or just do that in your CAD system. Flat plate is all you'd have to start with - just watch your clamping. Toe clamp in 5-6 places onto a sacrificial piece of aluminum or even plastic - under the whole ring. You don't want to be re-indexing this once you've started cutting, just do 20-30 degrees, program a retract and an M0, then remove your next clamp and move it to the area you've just completed. If you index and aren't dead perfect, you could screw up your teeth shape in at least two spots, not to mention your radius could vary.

(side note, did you see American Chopper where the CNC shop did that front wheel for the Spider bike? The idiots indexed the wheel - one mistake and their balance is screwed for good).

The only thing I'd be really careful of on this part is getting the tooth profile right and making the bevel on either side. I'd try to get a new sprocket onto a comparator to get some valid real-world dimensions for the tooth profile.

This should be a very fun project.

HTH

16V

I may buy a cheaper chainring that would fit for a more common cassette that has 50+ teeth and base it off that, but im wondering if it will cause any shiftng problems. going from 22 34 and suddenly 52

i used to run a 56 as a big ring, no shifting problems there.
you can use a program called geartrax to calculate a sprocket. takes the brainwork out of it entirely. i highly doubt mountain sprockets are indexed. many are stamped if you look closely. or maybe EDM would be a good way to do it. i have a 10mm thick sprocket on my bmx that's cnc all the way, though. bmx sprockets by design are ideal to be cut on an indexer setup, because of the hole in the center and single (or double, triple, or quad) alignment pin instead of arms. but my SR chainrings and stock bmx chainring is stamped for sure.

I think someone has thought about it before, see for yourself:
http://stores.ebay.com/CNC-Machined-Bicycle-Parts

A giant chainring would be cool. Single speed would be easier, for sure, because you wouldn't have to worry about twisted teeth, pins or ramps. Just circular beds, and slightly angled teeth. Its actually possible to make perfectly functional chainrings using only a drill press and a hand file, its just a slow process. ;)

I've got a few sprockets knocked up in various CAD programs, if you want a dxf let me know.

peace,
sam

CNC is most appropriate for repeated small batch production, because the set-up times are low.

Der mount thread is 10mmx1.0mm (same as the axle thread). This is a standard thread on the fine side. Steve

Well its getting closer to when i might do it. I could use the ones at school, but first I want to make a QCTP. Next up on the "to buy" list is a mill (still paying off the lathe right now).

I think this is a cool project. I want to mill myself a headlight bracket that actually mounts the way I want it to :)

I have read (from Sheldon Brown I believe) that forging is generally preferring to CNC machining for highly stresses bike parts, because CNC introduces stresses at the surface that weaken parts. I don't think a derailer hanger would matter too much though. Please post photos if you do it.

CNC doesn't introduce stress, it leaves small tool marks that can act as stress risers (places where a fracture can start). Proper surface finishing (like bead blasting) after machining will eliminate this.

CNC doesn't introduce stress, it leaves small tool marks that can act as stress risers (places where a fracture can start). Proper surface finishing (like bead blasting) after machining will eliminate this.
Gotcha. Does it matter whether you climb mill or standard mill on the last pass?

Gotcha. Does it matter whether you climb mill or standard mill on the last pass?

I'm not sure I understand the question; in a CNC rig the stock will be clamped and the cutter will work itself around the part according to the program. I always thought climb milling was when the stock was fed into the machine with the rotation of the cutter rather than against it; usually done in woodworking.

I'm not sure I understand the question; in a CNC rig the stock will be clamped and the cutter will work itself around the part according to the program. I always thought climb milling was when the stock was fed into the machine with the rotation of the cutter rather than against it; usually done in woodworking.
Well, I learned how to operate a manual (not CNC) metalworking mill so I could make some equipment for physics research.

The instructor taught us to climb mill parts on the last pass, as it leaves a finer surface finish when done correctly, which is important for some vacuum applications in particular (so that that surface can form a good seal against a gasket). I am wondering if that finer surface finish also results in fewer stress risers...

Well, I learned how to operate a manual (not CNC) metalworking mill so I could make some equipment for physics research.

The instructor taught us to climb mill parts on the last pass, as it leaves a finer surface finish when done correctly, which is important for some vacuum applications in particular (so that that surface can form a good seal against a gasket). I am wondering if that finer surface finish also results in fewer stress risers...

I guess it would, since climb milling suppossedly causes less tool chatter.

Bead blasting does more than just remove surface marks; it actually peens the surface on a microscopic level so it "heals" the stress risers as well as sightly work-hardening the material.