# A little manual milling on bike parts...



## Tiresius (Jan 2, 2013)

What do you guys think? Me and my friend were trying to figure out how to shave off weight in our aluminum road bikes without going over to carbon fiber. I got this idea and he doubted me about milling the crank arms. After seeing the results, he wanted his done too. Guess he'll have to wait.

On the meantime, here's the photos with results:






That's actually not me...I painted some kind of white-out on the inside to highlight the design I wanted but then threw it all away and did some ovals:





The upper-view of things. It looks so much cleaner on this angle:


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## gadget_lover (Jan 2, 2013)

It looks like you did a nice job. 

Great care should be taken when lightening parts that are designed to take weight/stress. I imagine that the part will now support less pressure before snapping than it did before the mod. Standing on that pedal while hitting bumps may provide much more force than you'd expect. 

If the piece could be made with less material, wouldn't they make it that way in the first place? On the other hand, if you weigh 155# and the part is designed for a 250# rider, then the shaved piece may just work perfectly for you.


Dan


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## Tiresius (Jan 3, 2013)

That's what I thought too, Dan. But seeing that I am only 130lbs and I bike efficiently instead of hard, the weight reduction is safe to use. My friend, I honestly don't have any idea if it'll work or not. He cranks rather hard.

I've looked into carbon fiber cranks and they have snapped countless times without warning or wear indicators. I thought it was a bad idea as well until my friend pointed out that it's not as bad compared to aluminum cranks that are hollow and milled out. It's much lighter than carbon fiber but actually works. They do snap but they start to bend before the snapping point.


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## StrikerDown (Jan 3, 2013)

Now I am having visions from my youth... foot slipping off pedal and the body parts that impact the frame! :sick2:

Being much closer to that 250lb rider than you are I think I would have fluted (ball end mill) the crank leaving a web, instead of completely opening it up. Not quite as much weight would be removed but the strength would not drop nearly as much.

If you are trying for the ultimate in weight savings you have to live with a greater risk of part failure as is common in racing I guess. 

I agree with Daniel those bumps will be the killer.

PS: Don't forget to put the no fat boy's disclaimer sticker on the bike!


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## Tiresius (Jan 3, 2013)

StrikerDown said:


> PS: Don't forget to put the no fat boy's disclaimer sticker on the bike!



Almost forgot about that sticker


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## tbutter (Jan 3, 2013)

Looks nice, you can do some fat bike Rims for me now


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## Tiresius (Jan 3, 2013)

tbutter said:


> Looks nice, you can do some fat bike Rims for me now



lol...I'll have to pass. I can only do straight objects.


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## will (Jan 4, 2013)

I have often wondered why the crank arms are so heavy. I recently rebuilt an old Schwinn road bike. I had the crank arms off and I was thinking of drilling holes on the back side of the crank arms, not all the way through. I decided to leave them alone. Weight is one thing on a bike, another thing to consider is wind resistance. With the slots, instead of a smooth surface, there is going to be greater wind resistance. I am not an expert in this area, but I would wonder if the gain you achieved by milling the crank arms is offset but the additional wind resistance. 

Another area to lighten the bike is to switch out some of the nuts and bolts with aluminum or titanium.

Nice job on the slots...


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## Overclocker (Jan 4, 2013)

i used to be a weight weenie and practiced alchemy i.e. turned other metals into drillium until i realized that the little grams i saved is minuscule compared to what can be saved at the ENGINE


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## will (Jan 4, 2013)

Overclocker said:


> i used to be a weight weenie and practiced alchemy i.e. turned other metals into drillium until i realized that the little grams i saved is minuscule compared to what can be saved at the ENGINE



Yep +1


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## Tiresius (Jan 4, 2013)

My bike weighs 20lbs. It has a few carbon fiber parts that came along with it from the manufacturer. The little milling on the cranks will drop it down under 20lbs. I plan to shave off some weight by making a pvc seat post to replace that carbon wrapped, aluminum seat post I have on mines.

It's actually a huge noticeable difference with the crank weight removed. They weigh less on the feet when dragging upwards and has less inertia. Road bikes are fun and I try to shave as much weight without going to titanium or carbon fiber.


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## Toaster79 (Jan 4, 2013)

I hope you do realize, what will happen when those crank arms brake. Visit to the hospital with broken part sticking out of your leg.


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## PCC (Jan 6, 2013)

Campy Ultra-Torque. Nice cranks. Are those Centaur? I'd start saving for a replacement set as its just a matter of time before they break...

I've broken aluminum cranks before when I was a feathery 120 lbs. Then again, that was when I was a lot younger and on BMX bikes. On a road bike the place to save weight is on the rotating mass, especially on the wheels. The bike will be more lively, will accelerate snappier. The question you have to ask yourself is: at what point will I have gone too far? Load bearing components (cranks, pedals, frame, rims, spokes) need to be strong enough to stay intact so that you can make it safely home, but, you also want them to be light weight so you do less work propelling yourself and the bike down the road. The factory teams who were running Campy Record would usually run Chorus cranks because the Record cranks are hollow CF while the Chorus cranks are solid CF because the hollow CF cranks have a higher incidence of breakage. 

My advice on the seat post idea: don't. The seat post takes a good deal of weight and, if you spin (as you've implied), then you're putting a larger load on the post than you realize. That's why integrated seat masts have become hugely popular these days. They're far stiffer than a conventional frame/seat post combination and weigh less. Now imagine what would happen if that seat post breaks in the middle of a ride? Now imagine that you didn't realize that the saddle fell off and you sat down? Get yourself an American Classic seat post, the older style, preferably in a mountain bike length, then cut it to 10" long overall, which will make it essentially new. Don't worry about the extra one or two inches adding weight to your bike: that post is made from thin wall 7075 and you're saving grams per inch, roughly a half ounce for 2 inches. Hardly enough to worry about. I actually made my previous bike heavier by taking my tried and true AmClassic post off and swapping it with a Campy Chorus carbon post (hey, the price was right, so, why not?).

I can honestly say that I feel no difference at the top of a long climb whether I ride my 16lb carbon wonder-bike compared to my old 21lb Cro-Moly war horse. The time it takes me to get to the top is probably longer, but, that just means that I carried more weight to the top. It's exercise.


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## will (Jan 6, 2013)

Reducing the weight is a nice idea. I ride a road bike here in Florida. I swapped a lot of parts for aluminum, and some other weight saving ideas. Then, Safety had to come into play. 

Added:

Front and Rear wheel reflectors.

Front and Rear lights. These are the type that have a few modes of operation and are also reflectors. Drivers here in Florida just don't see you.

Added a short bicycle pump, attached to the frame. Nothing like a flat 5 miles from home.

Under seat bag. This has a patch kit, a spare tube, a few tools, and a modified first aid kit. I took a fall earlier this year, nothing serious, but I managed to scrape my knee and lower leg. I did not have any thing I could use to stop the bleeding. Now I carry antiseptic wash and betadine, with some gauze pads and some paper towels. 

And - don't forget the water bottles. 

Pretty much any weight I saved, I added back on

( Old Schwinn Cro Moly frame, with all the stuff - 28 pounds )


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## subwoofer (Jan 6, 2013)

I appreciate the desire to optimise design and like metalworking, so do understand your intention, but there are a couple of things I would say:

1. Removing material from a 'designed' component when that material is supposed to be there is not something I would risk, especially not on something like the crank which will be taking a massive loading. When designing a component from scratch you can specifically design in the weight reductions, as long as you make sure the remaining material is strong enough. Efficient, high performance, light weight design is a good thing. 

2. Why is there such an obsession with taking off a few ounces here and there? When you consider that the actual weight you are saving is probably not much more than a mouthful of water and will only make a real difference to the type of rider who can ride the Tour de France. The average rider has far more excess body weight (me included), and it is far better to work on losing this than in weakening a critical component, is it not?


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## KC2IXE (Jan 10, 2013)

PCC said:


> ...snip... The factory teams who were running Campy Record would usually run Chorus cranks because the Record cranks are hollow CF while the Chorus cranks are solid CF because the hollow CF cranks have a higher incidence of breakage.
> 
> ...snip....



In the real old days, a lot of teams ran Novo record bottom brackets with super legari (sp?) pedals vs the Super record Ti stuff, and the Ti stuff had a habit of breaking and was more expensive. In 1983, Laurent Fignon snapped a SR bottom bracket - some great photos out there - I don't remembe which race - memory makes me say the TdF, but I've also read various spring classics


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## tarrow (Mar 8, 2013)

will said:


> Reducing the weight is a nice idea. I ride a road bike here in Florida.


Most of Florida is pretty flat, at least the parts I have ridden. If you want to go faster in Florida it might be better to attend to rider positioning etc then weight (if we are talking about road bikes and races other then crits).


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## 127.0.0.1 (Mar 8, 2013)

good way to kill yourself, dude. I have seen ripped open legs with extreme arterial bleeding
due to cranks breaking and a happenstance meat-grinding event immediately following

stick to leaving cranks as they come from factory. doesn't matter if you pedal 'light'
and 'efficient'...100% of your power (minus what shoes and socks eat) is going into those cranks

save yer coin and get lighter cranks but do not modify them...man o man machining them is a bad idea

anyhow your bike your legs not mine, have at it. 

the risk would too far to great for anyone I know or knew in biking for the past 40 years


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## AnAppleSnail (Mar 8, 2013)

See this page: Click For a few 'proper' drilled out crank arms. Those long forks seem to have about a fifty-fifty chance of being in a great position to stab through your leg on the next crank whenever they break. Smaller holes make smaller wounds.


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## Tiresius (Mar 9, 2013)

Too late, my cranks snapped. I wasn't on the bike when it happened. Bike fell off the hanger in my garrage and onto the floor. The crank cracked off one side and the other side has stress cracks.

My friend's crank is still solid. His cranks aren't milled. I liked the cranks like this but 7071 Aluminum isn't strong enough to handle the stress of 300lbs. There was no problem with riding like this because I never get off my seat to pedal. I'm actually more worried about my bottom bracket failing than the cranks themselves. Oh well. Onto getting a Shimano Ultegra Triple when I get the funds for them.


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## will (Mar 9, 2013)

It is a good thing it broke while you were not on the bike. 


Pretty sure there is a lesson to be learned here......


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