Machinist Question

[bikerphil]

This is about drilling out a fork leg (aluminum) that uses a 15mm axle to fit a 17mm axle. First, there is plenty of meat on the leg to embiggen the hole. Problem is, there is a pinch bolt on each leg, so there is a slot in the hole, as in the drawing below. I am guessing that the drill bit would catch on this slot causing difficulty. If I tighten the bolt so the slot is closed, im guessing it should drill fine. The next size down from 17mm would be a 21/32 (16.669mm), and down another size would be 16.5mm, then 41/64 (16.272mm). Anyone have any wisdom they'd wanna share on how to do this?

[Ivan]

Put the whole assembly in a vice on parallels and dial in the center of the hole, then use a boring head to incrementally take it out to size.

You will not get a decent or round hole with a twist drill, especially in a hand drill.

[tarzan]

I agree with Ivan.I would probably put it in a vee block or vise.You definitely need to get the hole prpendicular to the fork, and round.A machine shop will probably charge about an hour or less to do it.That's what we would do.
Shop rate around here is $60 to $80 an hour for general machining.

[petejw]

would this work to find the correct drill bit,
tighten the pinchbolt without the axle,
and measure the inside diameter of the whole,
subtract that from the thickness of the original axle.
then use that figure to subtract from the larger axle
to get the drill bit required,
or does it have to be drilled without the pinch bolt?

[bikerphil]

does it have to be drilled without the pinch bolt?

I'd like to drill it with the pinch bolt in to close up the slot gap, which is only .65 mm.

[tarzan]

You can't close the hole.Because then when you remove the pinch bolt the hole will be too big and you won't be able to clamp on the axle.
If you decide to drill it,you should at least put a wedge in the gap and then tighten the pinch bolt.Then when you drill it and remove the pinch bolt,you can insert the axle and clamp with the pinch bolt.
The problem with drilling it is you will have a hard time getting a decent finish and fitment won't be optimum.as well as keeping accurate hole position.

[bikerphil]

Also, the axle hole is seperated in the center for access to the damper rod bolt. It would be drilling two sections. Photo from side and bottom...





Tarzan, putting a metal wedge in the gap first, tightening, then drilling. I like that idea.

[petejw]

just had a closer look at a spare fork and axle ive got lying around,
Tarzans right in that the pinch bolt needs to be removed,
the axles a snug fit then, so the drill bit u would use would
then have to be the same size of the axle. does that sound right?



btw phil, the bikes coming along well on.

[Silent]

A few well placed pieces of shim stock will fill the gap proper. You do want to use a mill to bore the holes for the best possible quality. If you just clamp down the pinch bolts, the resulting hole will be egg shaped when the pinch bolts are loosened, and that's not going to work so well for your axle. If you fill the slot with shim stock, then bore the hole to .002 to .005 over the axle diameter, when you remove the shim stock you will have the proper clamping force to hold the axle in place.

At least that's what I'd do if I needed to enlarge the axle hole in my fork.

[bikerphil]

Pete, Ray, I like the idea of tightening the pinch bolt with an aluminum shim in the slot flush up with the hole. Then it should drill to 17mm and have enough gap to clamp tight. What say you?

[petejw]

i woundnt have it flush with the hole or
youll be drilling into the shim,
was thinking if u filed a 'v' into the gap
that would also help stop it grabbing.

was also thinking(i kno it hurts) you want the pinch bolt
fitted to stop the bit from chattering, if u put the old axle into
the fork, shim it so when u tighten the pinch bolt the axle is snug in the whole,
that should give u the gap u need. u could use feeler guages if u got a cpl lying around.

are u using a drill press?

[bikerphil]

No drill press, but I'm better than average at drilling a straight hole. If the shim stock was a soft metal, I would think it could just be drilled away with the rest of the metal, no? There would be no gap for the drill bit to catch on then.

[latexeses]

If you drill the hole with the pinch bolt cinched down you will have a distorted hole. You would not have a round hole when you released the pinch bolt, which is what you need to properly grab the shaft.

I would put a .65 spacer, that will not crush, in the slot and put it as close to the hole you wish to drill (use aluminum) and pull the pinch bolt down. Set the tube in a drill press vise but do not tighten, yet.

Take a 15mm rod or a 15 mm drill bit that is turned down to 1/2" or whatever is your chuck size. Chuck the drill in your press and with the drill press off lower the drill through the 15mm hole in the fork to center the tube in the vise.

Lock the table in place while the drill is through the fork and clamp the tube in place in the vise before you raise the quill. Don't move the table up, down or side to side after it is centered in the vise.

Now the shaft is centered in your press. Raise the quill and remove the 15mm bit and replace it with a 17mm bit and drill the hole you need. If you feed the bit slowly you should have no problem with the bit grabbing the gap.

Use come cutting fluid for cutting aluminum. It will help with galling.

Hope this isn't too windy and makes a bit of sense. It might be easier to explain in person but that look unlikely.

[latexeses]

Looks like it took me too long to type this out.
Sorry

Without a drill press I would look for a counterbore to besure you keep the hole straight.

[bikerphil]

Rodger, that is some very good information. If I can get access to a drill press, that's the way to go. Thanks.