calipers and forks

[creighton]

Being my first post here.. I feel like I should know this stuff.. but I do not.. sorry.. I am really trying to figure it out myself before I ask.


However, I am having a real problem with fork lengths as they pertain to calipers, short reach. I am at an impasse.

I am working on and on and on with road running commuters for folks that ride... myself being the primary test bunny. This means +/- fenders, 25c tire mainly sometimes up to 32c ( bit of flat trail going on as well). larger tire clearance is easier for I can spec. long reach.. its the short that is the issue.


There are many crowns with many brake hole locations..

I JUST CANT GET THE BLADE LENGTH NAILED!!!! especially for short reach jobs. I have a fork garden growing in the shop. This pains me for they are well made and beautiful but.. wrong. I feel I am thinking too much.. but is there a base number from tip to hole? Is that number from hole along steering axis/ right angle intersect of tip/axle line.. or a direct point to point from hole to tip?

I mentioned different crowns.. some brake holes are higher, some lower.

I like Issmo crowns.. SEXY! The hole works out to be high as compared. So do I scallop for tire clearance or go with long and let it fall? I enjoy tight stuff that pleases the eye.. trying to get it right.

Thank you for your time and apologies for the simple question stuff, Just having a difficult time wrapping my brain around this...

C

[e-RICHIE]

it's the only spec i use that's imperial rather than metric, but 14 1/8" from the brake hole to an axle placed
in the dropouts, measured from the front of the crown, along the centreline of the fork, to said axle, should
get you there atmo. i spelled centreline the same way prince charles would if he were replying.

[creighton]

And I almost said 'tyre'... but I dont know yer shoes Yo! Thanks!

[Craig Ryan]

I've got quite a garden growing on the wall myself! I feel for you...

[steve garro]

i had a "fork corner" growing behind my "magic box" but i gave them to someone for an art project.........oh, the $$$$........oh, the learning curve.........Steve.

[Curt Goodrich]

Rim radius + desired brake reach + distance between brake hole and crown race seat = fork length. Set it up in your fork jig and measure. Don't overthink this.

Regarding the Sachs crown hole location, I typically fill it and drill it a little below center but I'm funny that way.

[creighton]

Thanks all.. Yeah Curt, I can think too much at times.

CW

[Eric Estlund]

14 1/8" from the brake hole to an axle

What he said-


And just to re-state Curt's method: 311mm + brake reach (usually centered in the range, though subject to circumstance) = axle to drill spot.

I dry fit everything, measure with the full length legs, then subtract the above number. This gives me the cut off length on the leg. This way I can take all my measurements externally. AC, A to Brake and cut off length. I don't need to measure the crown shoulder, brake hole offest, actual fork blade length, etc. Slightly different approach, same result.

[Dazza]

your data sheet/folder for quick reference next time.
include the fork blade cut length for the particular crown used

[cement shoes]

dazza,

do you also use that device to check offset? slick tool.

-Tom

[Dazza]

dazza,

do you also use that device to check offset? slick tool.

-Tom

Yes.
It gives me blade cut lengths
for straight forks , 0mm
and all the rakes with the sliding dropout thingie

A lathe and a mill/drill, beautiful things

[lighthousecycles]

I've always used 14.1 in. from the center of the axle to the center of the front brake hole for short reach and it works fine. funny I've always used the emperial measurement for this one too.

[creighton]

Rim radius + desired brake reach + distance between brake hole and crown race seat = fork length. Set it up in your fork jig and measure. Don't overthink this.

Regarding the Sachs crown hole location, I typically fill it and drill it a little below center but I'm funny that way.

Got it folks! Thank you very much for your time to reply...

A thought and question Curt... You say that you fill and drill to a lower location. I dont know what you use for the 'glue'.. brass or silver?? still though I wonder if the softer material is enough to keep the bit on track as it passes off center through the rather larger balance of tougher steel? Path of least resistance and all....


Hrmmm... Is the through hole made with a long enough short/ridgid split point drill bit or a center cutting end mill bit? I could see a split point wandering off line. that is if its standard length index box jobber variety..however a sharp end mill, not so much. How is this easier than keeping the original as cast hole and mebbe file coping the underside of the crown a bit for tyre clearance. Do you make the counter bore for the brake bolt nut? use a collet block for 180 degree rotation, find center of the through bore and make a recess? Thanks, CW

[Curt Goodrich]

Got it folks! Thank you very much for your time to reply...

A thought and question Curt... You say that you fill and drill to a lower location. I dont know what you use for the 'glue'.. brass or silver?? still though I wonder if the softer material is enough to keep the bit on track as it passes off center through the rather larger balance of tougher steel? Path of least resistance and all....


Hrmmm... Is the through hole made with a long enough short/ridgid split point drill bit or a center cutting end mill bit? I could see a split point wandering off line. that is if its standard length index box jobber variety..however a sharp end mill, not so much. How is this easier than keeping the original as cast hole and mebbe file coping the underside of the crown a bit for tyre clearance. Do you make the counter bore for the brake bolt nut? use a collet block for 180 degree rotation, find center of the through bore and make a recess? Thanks, CW

I use silver. Yes, in theory the bit would wander into the path of least resistance but with a fairly robust drill press or mill if you're into overkill and reasonably sharp center drill bit it's a non-issue. I drill the front hole to 1/4". Don't drill them to 6mm because paint build up makes the hole too small and then you have remove the paint to insert the brake. I flip the fork and drill the back side to 1/4". Then I use a counterbore with a 1/4" pilot to drill the counterbore. After that I drill to accomodate the brake nut. I don't remember the size bit 'cuz I'm doing this from home. Trust me. It works everytime. I do this especially for bikes that may have fenders on them. I prefer the top of the brake arch to be the same height off the tire as the bottom edge of the crown. It's just one of those things I'm picky about.

[Tyler Evans]

i know you said "you got it" but i just need to pass this on, i might not apply to brazed crowns with curved blades, but if you are making straight bladed welded unicrown road forks (which you most likely aren't) then it will.

okay, think about this...

is the brake hole tangent to the wheel or not?

we (IF) drill the brake hole perpendicular to the steerer, yet the blades are mitered at an angle to the steerer (our forks are straight bladed). if you are looking at the fork in profile with the brake mounted on it you will notice that the brake axle is doing a nosedive into the tire (not tangent to wheel), it needs to be higher than the seat stay brake bridge on the frame (which is tangent to the wheel). So if the hole is drilled tangent to the wheel (perpendicular to the straight blades) then it is the same measurement as the rear bridge (for the most part), if it is drilled perpendicular to the steerer then it is variable, depending on the brake and the fork rake. I hope i'm making sense... it's been a long day.

but, as eric said "dry fit everything" and as someone else said "write it all down" (or record it somehow)...

I've got quite the garden as well.....

Tyler.