tommyd49

Hi guys

Apologies for the fact that I know this topic has been raised many times before, but I want to put a dual pivot brake on the front of my old steel road bike. I've attached a picture of it and I'm concerned because my fork crown is thin. I haven't seen any pcitures of conversions so I was wondering whether people think it'll be OK to enlarge the hole from 6mm to 8mm?

It's not the drilling that scares me per se (even though I've only got a basic 500W electric drill and cheap bits), it's just the fact that my fork crown looks so thin.

Any help would be much appreciated. Thanks!

lostarchitect 

I don't see an issue. I've done it on fork crowns like that--But get a good bit! You could mess it up with a crap bit.

tommyd49

Ah, that's reassuring, although the price of getting good bits for this one job...

I was thinking, although my bits are crap, they go up in .5mm increments, so if I did it incrementally it'd be OK. Maybe not?

Retro Grouch 

So you really don't think that you'll ever use your drill for anything else?

FBinNY 

Actually, sometimes a dull bit is better for a job like this than a new one. Drill bits are designed around the principle that the resistance offered by the center of the hole will be balanced by drilling pressure to control the depth of cut. When simply enlarging a hole by a small amount a sharp drill can grab and feed itself too fast, either jamming, breaking or making a jagged hole.

Use cutting oil and it'll drill out well enough, but be sure to only drill the back, since you need the smaller 6mm hole in front to locate and support the bolt. Also don't forget that you need a concave washer for the front to match the curvature of the crown. You can skip that in the back.

Kimmo 

If the drill's not happening, you can use a rat-tail file of the appropriate size, pushing it into the hole and turning it to unscrew the teeth.

If going recessed on the rear too, you should use the concave aluminum washers, and drill out the back one. You can make it real tidy by filing the back washer to taper from its base to the nut.

If you have a plain tube for a brake bridge, and you have to drill all the way through it, don't sweat it - the washers will spread the load and locate the brake just fine.

If you have a fancier brake bridge, you might want to think twice.

tommyd49

Thanks for all the replies.

I'm only interested in doing the front: I'm upgrading my fixed gear bike (although I'm going to run an old sidepull brake on the back as well - I know - sissy).

I was thinking of reusing the old concave washers, but drilling one to 8mm - but I don't need to even if I don't countersink the hole at the back?

As for supporting everything, I was thinking of setting the headset up too tight (I'll most likely replace the BBs soon so not worried about damage on that front), put the bike in the repair stand and getting someone to hold the handlebars while I drill. Sound reasonable, or like a disaster? BTW I don't have anything sophisticated like a drill press!

Stealthammer

The steerer tube should extend down through the fork crown and it should be quite a bit thicker than the fork crown. Remove the wheel and look up from the bottom and you should see the the fork is actually much thicker than just the thickness of the fork crown itself.

dsbrantjr

"brake on the back as well - I know - sissy"

Not sissy in my book, backup brakes are "smart", hitting stuff is "dumb" and "hurts"

FBinNY 

Nothing wrong with 2 brakes on any fixed bike, bie it isn't necessary.

A decent rider has good control and equal stopping power trough the legs on a fixed gear bike as a rear brake would provide (able to lock wheel). The front brake is a necessity for street use, because stopping distance is too long with a rear brake (any) alone. Once there's a front brake, then the rear brake becomes optional. Having two brakes (fixed gear counts) is also necessary for redundancy because things happen, like chains falling off or cables breaking.

tommyd49

I agree that a rear brake is generally unnecessary on a fixed bike (I've been riding fixed without one for years) but I'm moving to London soon so I am becoming quite safety-conscious - I want a back-up to the back-up (how does that work on a freewheel bike?)

The only thing stopping me drilling now is think how to secure the fork while drilling - I'd be interested to know what others have done.

FBinNY 

Certainly a freewheel bike will need a rear brake, and it won't hurt on a fixed gear other than a few ounces of extra weight.

As for drilling the fork, it depends on what you have. If you have a vise, clamp the steerer lengthwise in the jaws with the fork turned so you're drilling across not down. This way he jaw will support it and you won't need to clamp very tightly. Without a vise lay the forn on a sheet of cardboard on the floor, gently step on the back of the blades with one foot, and drill down.

Either way, use minimum down force on the drill so it doesn't overfeed and seize. It's a 10 second job so you don't need to overthink it.

tommyd49

Thanks for the tips, I drilled the fork out today, I've mounted the brake and the recessed nut is as snug as bug in a rug.

I know I was making a major issue out of a minor job, but I just wanted to make absolute sure I didn't damage my fork!