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Drilling and tapping fender and rack eyelets in steel rear forkends.

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Drilling and tapping fender and rack eyelets in steel rear forkends.

Old 06-23-13, 03:54 PM
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Jaywalk3r
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Drilling and tapping fender and rack eyelets in steel rear forkends.

I have a 2008 Redline Monocog. The frame is 4130 steel, but I don't know if that is just the tubing or the entire frame. I asked my LBS if they would drill and tap fender and rack eyelets in my rear forkends, but they were not interested in the job. So, I am left to do it myself. Before I proceed, I want to make sure I'm not overlooking something that would make this a really bad idea. I don't like the idea of P-clamps, but they are certainly preferable to failure of the forkend.

Is there any reason the forkends should not be drilled? They appear to me to be substantial enough that they could each handle a couple small holes without structurally failing, but I know little about frames from an engineering perspective.

If there is no reason not to drill and tap the frame, what size hole should I drill, and what size tap do I need?

I'm not particularly concerned with preserving the ability to mount a rear disk brake.





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Old 06-23-13, 04:33 PM
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Bandera 
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Originally Posted by Jaywalk3r View Post
I asked my LBS if they would drill and tap fender and rack eyelets in my rear forkends, but they were not interested in the job.

Is there any reason the forkends should not be drilled?
Any reason other than catastrophic failure?

Your LBS was also not interested in litigating w/ your executors post mortem.

Get some P-clamps and install the mudguards/racks of your choice, it is highly unlikely that the aesthetics police will intervene.

PS

Dropout material is quite hard, drill-press hard not 9.5V Ryobi hard, don't waste your time/bits to install scratches/stress risers.

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Old 06-23-13, 04:47 PM
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Bandera, that raises another question. What precautions are taken with forkends that are fitted with drilled eyelets new to prevent catastrophic failure?
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Old 06-23-13, 05:03 PM
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I don't see any reason not to do it from a structural viewpoint. Bikeshops really aren't equipped to do jobs like this
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Old 06-23-13, 05:19 PM
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Originally Posted by Jaywalk3r View Post
Bandera, that raises another question. What precautions are taken with forkends that are fitted with drilled eyelets new to prevent catastrophic failure?
Rear dropouts & forkends are designed for the application and fitted w/ proper mounts for mudguards & racks when manufactured.

These ( or a plethora of others ) might meet your requirements if a lightly loaded rack is needed:

http://store.velo-orange.com/index.p...ttachment.html

A good machine shop ( few and far between these days ) might retro fit drilled & tapped for your dropouts but it would be very $( fresh frame $), and still perhaps a bit dicey.

P-clamp away and keep this need in mind when you move to new bikes. I purchased a new (to me) frameset recently w/ fender clearance & mounts F&R as a requirement, nice to have in a "not race bike".

-Bandera
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Last edited by Bandera; 06-23-13 at 05:27 PM.
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Old 06-23-13, 07:10 PM
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Look at the amount of metal in those drops compared to something like a Campy 1010b. There's no way a small hole will cause failure. Use a sharp bit, start small and work up if you need to. Use cutting oil and a slow drill speed. Drilling a hole in a flat plate like that will be no harder than drilling a brake hole through a fork crown and steerer.
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Old 06-23-13, 07:37 PM
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only thing I see to take into consideration is proper edge distance. 2x the diameter is considered minimal edge distance for an application like this. Tapped holes would probably suggest more.
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Old 06-23-13, 09:21 PM
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Another reason the LBS avoided this was that it would mean making a nonreversible change to the frame. If something went wrong during their work the frame might not be "made whole" again. I wonder if they were able to charge the replacement cost for the frame if they would have done differently. (And therefore covered themselves for the worst case). Andy.
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Old 06-24-13, 07:04 AM
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I agree with posts 6 & 7. It can be done safely with a hand drill. 4130 is easy to cut and the dropouts are likely of a lower allow.
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Old 06-25-13, 01:10 PM
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Thank you, everybody, for the input. It sounds like I can safely drill eyelets in the forkends with the proper precautions.
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Old 06-25-13, 02:21 PM
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There's a crapload of material in that DO. One tapped hole 5 or 6mm won't reduce it's strength- especially when you tighten a fastener in there. I'd be surprised if that drop is 4130 like the tubes. My guess would be 1018 or 1020 steel. Doesn't matter though. 4130 is easy to work, and you can barely tell the difference between it and mild steel when machining.

Personally I'd file a divot on the DO edge and braze on a threaded eyelet. But drilling and tapping the hole is another good option if you don't have welding capabilities. Or, you could drill a plain hole and use a screw and nut. I'd place it 3/8 to 1/2" from the edge and slightly chamfer the hole. Use sharp tools and you CAN do it with your Ryobi.
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Old 06-25-13, 02:25 PM
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And, don't forget to scribe and center punch your hole FIRST!
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