thook

Hello all,
I bought a fork for my '85 super le tour and it's drilled for nutted brakes. I'd like to run recessed, though, since I have some really nice ones. The stay bridge is already equipped for it, but the hole is stepped (proper term?) so that the nut face is flush/counter sunk. I want the fork to be the same. What bit/s would I need to do this? I have a very nice drill press for proper centering/alignment, and I know there's a proper type of bit for the job. Just can't remember the term, so I'm at a loss to find the right bit for it

Thanks!

bulgie 

Counterbore.

Get one with a pilot the size of the existing hole, to keep the counterbore on-center. That can be the existing 6 mm hole, or the 8 mm hole you will drill it out to.

On some, the pilot is ground from the same chunk o' steel, where others have a hollow that lets you insert different pilots, which is more versatile. Mine is the former type, made by Silva for bike frame builders, but I got it ~30 years ago and I don't know if they're even still in business.

The through-hole (where the pilot goes) is nominal 8 mm, the head of the nut is nominal 10 mm.

If you have trouble sourcing one with metric dimensions, you can get by with fractional-inch as follows:
pilot 5/16" (7.9 mm)
bore 13/32" (10.3 mm)

For using a 5/16" pilot, I would drill the hole 5/16" also, so the pilot fits snug in the hole, reducing chatter. If the 8 mm nut then is too snug a fit, you can open up the hole a little after counterboring. You probably won't need to though; a nominal 8 mm nut will usually go in a 5/16" hole no problem.

The 13/32" bore, being a little large, may not look quite like how they do it in Milan, but it'll be 100% functional, and the extra clearance can even help on holes that get painted (or PC) after drilling, i.e. most any bike that comes with recessed-nut brakes.

I think once you see the prices on good counterbores (roughly the same as what an '85 Super LeTour usually sells for), you may start looking for cheaper alternatives. A normal 13/32" twist drill (preferably the short-length variety for rigidity) will do a half-assed job if it, but I've seen worse. It will leave a conical bottom instead of the prefferred flat-bottom hole, but it'll hold your brake to the fork anyway, and no one will ever know the hole was made by a drill. The drill can also be hand-ground to a flat-bottom pilotless counterbore, which will work OK if you can clamp the fork accurately on-center. Best used only to flatten the bottom of the hole after drilling it to 13/32" with a regular drill. But that's a lot of work just to turn that little bit of conical shelf into a flat-bottom shelf. The shelf, (bottom of a 10 mm bore with an 8 mm hole through it) is only 1 mm wide, so the difference between flat and conical is trivial.

Mark B

duanedr 

It really depends on the fork. If the combined wall thickness of the crown/steerer are thick enough and if you want the head of the recessed nut to be flush, you'll drill the backside hole to 5/16" and then use a counterbore with 7/16" large section and 5/16" pilot. You'll go in about 1/8" or the depth of the head on the recessed nut. I'd chuck a 3-4" rod of 1/4" material in the drill chuck then use that to align the front and rear holes in the axis of your drilling. Then lock it down and go slowly. If you had a mill a 7/16" end mill would also work for the counterbore operation. It won't in a drill press.

Andrew R Stewart 

After looking at the cost of a counter bore bit you might be able to be happy with the lip of the recessed nut standing proud, and not be recessed Andy

unterhausen

I thought there were cheap counterbores on amazon/ebay, but I'm not finding one right now. I have one, and I know I wouldn't have spent $50 on it.

TiHabanero

Andy is spot on with his assessment as I have done this operation several times. Simply bore the backside hole in the fork crown to the same diameter of the shank of the flush mount keeper ("nut") and let the head butt up against the fork crown. Sure, it won't be recessed, but is effective and very straight forward to do, plus no one will be wise to it. Fortunately, I have a large drill bit collection and am able to make the hole only very slightly larger diameter than the shank of the keeper and it fits super nice without excessive tightness, just enough to let the thing turn when tightening.

JohnDThompson 

An 8mm hole will accept the shaft of the Allen nut, leaving the flange standing about a millimeter proud of the crown. Not so bad. Otherwise, a 10mm counterbore with an 8mm pilot can create the recess to make everything flush.

thook

Well, this is a one time deal. IOW's, it's the only frame/fork I have that even uses road calipers. Everything else I have is canti'd. So, if I can find a counter bore bit cheaply enough, even if only stays sharp enough to do this one job, I'll be satisfied. I'm seeing some piloted bits on ebay for not much money. But, I'll see if Harbor Freight or Northern Tools also has something. There again, hmmm...I may have to buy a set...which would be pointless.
Failing that, chopping the end off a normal bit may be worth exploring. Cut it off with a dremel tool and cutting disc. And, go slow on the fork...like you said.
I've done the regular drill out of a fork crown before leaving the nut head exposed on another frame I had years ago. Meh...looked fine and it's not like trying to get the full recessed effect is direly important this time around. Just thought it'd be nice since I'm going to blast the old paint and nominal rust off and repainting the entire frame/fork. You know....get the nice detail of matching front and rear brake holes to top it off.
BTW, do you think some 3 in 1 oil would work for cutting oil? Is that even important?

thook

Maybe an outrageous request, but I don't suppose you'd let me borrow that, would you?

Doug Fattic 

You can buy the right one from MSC for $37.25. MSC Part # 08862161. Another option is MSC Part # 45403334 for $44.34. Then you can loan yours to other amateur builders. You will never miss or regret spending the money. If however you just drill it out with a 5/16" or 8mm bit only without countersinking, it will bother you always. I speak with confidence about your future mental state because my college major was in psychology and my graduate studies in counseling (so I could be a high school counselor). When I was apprenticing in England, I got guff for downgrading my social standing by learning a manual skill. I couldn't have cared less about their opinion just like your joy of making your frame look just like you want it will allow you to ignore all those that think you could have spent your money more wisely (on what I ask?) by just drilling but not countersinking your fork.

MSC is a bit of a nuisance to order from. You have to establish an account first. Neither are they the cheapest to buy from. One of their biggest warehouses is local to me so I order from them all the time. They have those annoying promotion offers because usually it requires a $ minimum.

I should add that you can use a 13/32" end mill. However at a minimum the fork needs to be held securely in a drill press but more preferably in a vertical mill. And you somehow have to make sure the bit is in dead center and the fork won't/can't move. Using a drill bit is a bad idea because the bit will flex under load.

thook

Thank you, Doug. I do appreciate your sentiments and validation. It's not others or their opinions (I asked for) I have to live with. Just my wife who might find it unreasonable...haha! And, it's true....I have been spending a fair amount on bike stuff lately. I do have to balance the budget with other aspects of life. My dad just gave me his 2000 Dodge Ram 2WD and I just spend $400 on a locker for the rear differential. And, likely in the spring I'll need to get two new tires. That's another $400-$500 right there. And, that's on top of what I've spent already and what I still need on suspension parts for my little CRV. It adds up and keeping harmony in the household has not been my strongsuit lately.
Also, I do not have or have access to a vertical mill. And, forgive my ignorance, but why would an end mill not work in a drill press? And, why would a short hardened drill bit not be sufficient? I get that counterbores and end mill are made of higher grade steel and I get there's more flex in a regular bit. But, I've got some pretty hard drill bits for heavy steel. They're black in color and a lot more rigid than the gold cheapies in my DeWalt/Ryobi kits

Andrew R Stewart 

Drill presses (or at least the usually found ones) are not very stiff along their axis. Tool end deflection is very common. Using an end mill bit in a drill press is quite doable, centering (or keeping it centered while cutting) it might be more of a challenge w/o the pilot a counter bore has. A flattened drill bit might work too with some detailed grinding of the new cutting face, however a drill bit is even more flexible than an end mill. Do know that the cut surface "quality" can often be a result of tooling and fixturing. My choice would be to do a clean job with a drill for the nut to fit but not recess for the lip. A well done basic job can look nicer than a hacked and poor fancy one. Andy

unterhausen

I thought my drill press was pretty good, but I'm positive an end mill would remove the chuck. I suppose I should buy a chuck cleaner. It's not scarred up, yet

thook

I suppose I'll call around see if there's a machine shop that can do it for less than what I'd pay for a piloted counterbore. I really don't know first hand how much forces are encountered doing something like this and maybe my little press up to the job. OTOH, would a piloted counterbore mitigate any of those forces over an end mill? Being that it has the pilot and all

thook

Web image of the press I have. What do ya'll think? Up to the task?

thook

And, would a counterbore like these work??

https://www.msdiscounttool.com/catal...1137&filter_65[]=2539440960

Doug Fattic 

Yes the counterbores in your picture is exactly the bit you need. If I were you, I'd secure the little bench press to the bench top somehow so it can't move. Probably with a C or any other kind of clamp so the drill press stays put. I'd also make a special effort to secure the fork to the drill press too. You can position the fork before clamping it down somehow by putting the pilot of the counterbore in the enlarged brake hole first. When everything is very secure you can drill the counterbore.

Does your drill press have a stop on the downfeed? You need to make sure you don't drill too far. That look is terrible. Somehow you have to make sure to drill it far enough but not too far. If you don't have a stop, you can put tape on the counterbore so show you how far to drill. Remember that before you remove the clamped fork, to drill the piloted hole out to 8 mm (which is almost exactly 5/16").

thook

It does not have a stop, but I am aware of the bit stops and the tape trick. Thanks!
I'm sure I can get everything clamped and secure to do the drilling. Get it centered with a rod all the way through from the chuck, through the fork, and a board the fork's secured to that's secure to the press. Use coated two hole straps to secure the fork to the board at the blades and steerer column

thook

Oh, yeah....found a metric bore, too

https://www.rshughes.com/p/Dormer-G1...%20-%200107607

thook

https://www.msdiscounttool.com/catal...ducts_id=98798

geckocycles

Just use a 13/32" bit and be careful not to counteresink it too much. Best to set a stop on your press. THe slight taper on the bottom of the counterbore is no big deal.

Fredo76

I didn't think anything of it at the time, but 45 years later, I wonder if participating in my high school's 'Professional Internship Program' by apprenticing with Colin Lang building bicycle frames instead of with some lawyer or doctor is what kept me out of Brown University in the '70s.

I have zero regrets, however!