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Turning titanium?

Old 04-28-22, 05:56 PM
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smd4
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Turning titanium?

I’ve got some aftermarket titanium self-extracting crank bolts. The “shoulder” of the bolts is just a little too big in diameter (so the “dust caps” don’t screw all the way in).

Does anyone have any suggestions on how to turn the shoulders down to the original DA 7700 spec? Something I could do at home without a lathe? Should I try and find a machine shop who can do the work? Thanks!
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Old 04-28-22, 06:06 PM
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File?
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Old 04-28-22, 06:08 PM
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Originally Posted by Bill Kapaun
File?
Thought about that, but how long would that take, though?
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Old 04-28-22, 06:19 PM
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Chuck the bolt in an electric drill
Clamp the drill in a vise..
Use a decent quality file. You may have to experiment with different cuts.
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Old 04-28-22, 06:24 PM
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Originally Posted by Bill Kapaun
Chuck the bolt in an electric drill
Clamp the drill in a vise..
Use a decent quality file. You may have to experiment with different cuts.
It’s an M15 size bolt, so won’t fit in my drill, but my 8mm socket fits. I may give it a try. Have to remove 1.4 mm total diameter.
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Old 04-28-22, 06:28 PM
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1.4mm means 0.7mkm "all the way around.
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Old 04-28-22, 07:16 PM
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Originally Posted by Bill Kapaun
1.4mm means 0.7mkm "all the way around.
I know. That’s still a lot of titanium to remove with a file. Hence my reluctance. But if I can do it for the price of a good file...
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Old 04-28-22, 07:34 PM
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If I understand you correctly…. The bolts fit the threaded diameter of the crank, and are not to big to fasten the crank completely to the BB; no issues with properly attaching the crank.

But the shoulder diameter of the bolt, that holds the crank on the BB, is to large a diameter for the dust covers to completely thread onto the crank arm.

And the solution is to remove some of the material from the bolt that is holding the crank on.

Just wanted to understand the situation.

John
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Old 04-28-22, 07:37 PM
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Originally Posted by 70sSanO
If I understand you correctly…. The bolts fit the threaded diameter of the crank, and are not to big to fasten the crank completely to the BB; no issues with properly attaching the crank.

But the shoulder diameter of the bolt, that holds the crank on the BB, is to large a diameter for the dust covers to completely thread onto the crank arm.

And the solution is to remove some of the material from the bolt that is holding the crank on.

Just wanted to understand the situation.

John
Exactly. The shoulders, to work properly, should fit inside the dust caps.(At this level, they’re not really dust caps. They’re part of the crank extraction system).

Last edited by smd4; 04-28-22 at 07:48 PM.
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Old 04-28-22, 09:17 PM
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Originally Posted by smd4
Exactly. The shoulders, to work properly, should fit inside the dust caps.(At this level, they’re not really dust caps. They’re part of the crank extraction system).
I'm familiar with crank extraction devices that thread in and then removing the bolt pulls the crank.

I've just never used them. I remove them, use a Park crank puller, and then thread the extractors back in as dust (thread) covers.

My question was whether reducing the shoulder on the bolt holding the crank, just to use the extractors, is a good idea. I could be wrong, but to get a nice look, I would reduce the extractor depth and use a crank puller to remove the crank when necessary; which probably isn't very often.

John
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Old 04-29-22, 06:10 AM
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My question is why you want Titanium crank arm extractors? Titanium, in general, is a poor material for fastening type applications though though overall the Titanium 64 alloy has good strength. Certainly, any weight savings is inconsequential. Just my opinion.
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Old 04-29-22, 06:36 AM
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Originally Posted by 70sSanO
I'm familiar with crank extraction devices that thread in and then removing the bolt pulls the crank.

I've just never used them. I remove them, use a Park crank puller, and then thread the extractors back in as dust (thread) covers.

My question was whether reducing the shoulder on the bolt holding the crank, just to use the extractors, is a good idea. I could be wrong, but to get a nice look, I would reduce the extractor depth and use a crank puller to remove the crank when necessary; which probably isn't very often.

John
Doesn't sound like you understand self-extracting crankarm bolts and how they work. I don't even think you can use a standard crank arm puller (why would I even try? By design it's unnecessary). It's a completely different design.

But, you are wrong. Reducing the shoulder diameter to the DESIGN SPEC of the original bolts won't be a problem.

Last edited by smd4; 04-29-22 at 06:51 AM.
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Old 04-29-22, 06:38 AM
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Originally Posted by Steelman54
My question is why you want Titanium crank arm extractors? Titanium, in general, is a poor material for fastening type applications though though overall the Titanium 64 alloy has good strength. Certainly, any weight savings is inconsequential. Just my opinion.
Yes, weight savings. A gram saved is a gram earned. I would go aluminum if I could find any. The stress imposed upon the crank arm bolts is minimal. Thanks for your opinion.

Last edited by smd4; 04-29-22 at 07:08 AM.
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Old 04-29-22, 07:01 AM
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Originally Posted by smd4
Doesn't sound like you understand self-extracting crankarm bolts and how they work. I don't even think you can use a standard crank arm puller (why would I even try? By design it's unnecessary). It's a completely different design.

But, you are wrong. Reducing the shoulder diameter to the DESIGN SPEC of the original bolts won't be a problem.
I have cranks with self extracting bolts. Pretty simple design.

Basically you are using an allen/hex head crank bolt with a wide shoulder. Torque the bolt and then thread in the dust/extractor cover “all” the way in with a pin spanner. The cover allows access to the crank bolt. When you want to remove the crank, loosen the crank bolt and the force against the extractor cover as the crank bolt is threaded out pulls the crank.

John
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Old 04-29-22, 07:05 AM
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Originally Posted by 70sSanO
I have cranks with self extracting bolts. Pretty simple design.

Basically you are using an allen/hex head crank bolt with a wide shoulder. Torque the bolt and then thread in the dust/extractor cover “all” the way in with a pin spanner. The cover allows access to the crank bolt. When you want to remove the crank, loosen the crank bolt and the force against the extractor cover as the crank bolt is threaded out pulls the crank.

John
Exactly. Then why do you think reducing the bolt shoulder diameter to fit inside the extractor cover--as designed--would be a problem?
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Old 04-29-22, 07:16 AM
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Originally Posted by smd4
Exactly. Then why do you think reducing the bolt shoulder diameter to fit inside the extractor cover, as designed, would be a problem?
As long as the bolt shoulder is the correct diameter and can be torqued flush against the crank, not too large in diameter to fit, you are removing material that was hopefully designed to hold the crank onto the bottom bracket. While the bolt shoulder is designed to pull the crank, its main function is to hold the crank in place.

I have no clue if reducing the diameter will have any impact or not; and I don’t really care. Self extracting systems are a convenience for an occasional removal, chainring or BB replacement, and removing the cover and the crank bolt and pulling the crank with a Park tool is a minor inconvenience.

Occasionally there are problems where the cover doesn’t hold when pulling the crank and it becomes more of a pain than it is worth, so I just take that out of the equation.

John
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Old 04-29-22, 07:43 AM
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Originally Posted by 70sSanO
As long as the bolt shoulder is the correct diameter...
That's the problem--it isn't the correct diameter. Hence my wanting to turn them down.

Originally Posted by 70sSanO
...and can be torqued flush against the crank, not too large in diameter to fit, you are removing material that was hopefully designed to hold the crank onto the bottom bracket. While the bolt shoulder is designed to pull the crank, its main function is to hold the crank in place.
The crank bolt in this particular system has TWO "main functions." If the shoulder surface is even just 1 mm wider than the hole in the crank arm, it will be enough to do what it needs to do. There is very little if any outward force on the crank arm.

I don't think I would ever consider using a crank removal tool--Park or otherwise. Wouldn't want to booger up the BB spindle--which was not designed to have a crank arm puller forced against it.

Last edited by smd4; 04-29-22 at 08:35 AM.
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Old 04-29-22, 08:02 AM
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Originally Posted by smd4
I don't think I would ever consider using a crank removal tool--Park or otherwise. Wouldn't want to booger up the BB spindle--which was not designed to have a crank arm puller forced against it.
For the 7700 Octalink crank, yeah, usually the self-extractor works but sometimes you need a puller tool. Park makes a special tool for Octalink/Isis cranks that won't ruin the BB. CCP-44 Crank Puller — Octalink®/ISIS Drive™ | Park Tool And also the CWP-7 that does both Octalink and square taper BB's CWP-7 Compact Universal Crank Puller | Park Tool
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Old 04-29-22, 08:05 AM
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Thanks Cranky! I'll check these out. Prices aren't bad at all.

EDIT: Just bought the CCP-44 new from Ebay for $16 bucks.

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Old 04-29-22, 01:16 PM
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Originally Posted by smd4
Yes, weight savings. A gram saved is a gram earned. I would go aluminum if I could find any. The stress imposed upon the crank arm bolts is minimal. Thanks for your opinion.
Crank arms are supposed to be torqued at arround 35 to 40 nm, which is not insubstantial, my guess is that is why you don't find aluminum crank bolts
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Old 04-29-22, 01:43 PM
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Originally Posted by squirtdad
Crank arms are supposed to be torqued at arround 35 to 40 nm, which is not insubstantial, my guess is that is why you don't find aluminum crank bolts
Oh, they're out there. The style I want is just sold out, near as I can tell. Truvativ made them.
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Old 04-29-22, 02:23 PM
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Titanium is extremely difficult to grind, file or sand. I will be interested to see if you have any success with a file.
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Old 04-29-22, 03:44 PM
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Originally Posted by Rdmonster69
Titanium is extremely difficult to grind, file or sand. I will be interested to see if you have any success with a file.
You and me both! I'll see what I can do this weekend.
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Old 04-29-22, 06:31 PM
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Originally Posted by squirtdad
Crank arms are supposed to be torqued at around 35 to 40 nm, which is not insubstantial, my guess is that is why you don't find aluminum crank bolts
There were aluminum crank bolts, as smd4 noted. The general recommendation was to use steel bolts to apply full torque and then substitute the aluminum bolts as replacement. More than one aluminum bolt was broken by not following this procedure.
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Old 04-29-22, 06:33 PM
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Originally Posted by HillRider
There were aluminum crank bolts, as smd4 noted. The general recommendation was to use steel bolts to apply full torque and then substitute the aluminum bolts as replacement. More than one aluminum bolt was broken by not following this procedure.
Great advice.
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