Quseton on machining bike triples

[mrcodewiz]

At some point I am going to make a triple tree for a bike conversion I am doing. My question is about how to make the pinch bolt section. Here is a picture of a pretty standard upper triple for reference:




My broad plan is:

1) mill the stem and fork tube holes
2) mill out the profile
3) drill and tap the pinch bolt holes
4) cut the slot with a slitting saw

My question is about 3 and 4 and whether that is the best order to do them in. Should I cut the slot, then drill and tap. Should I drill, cut the slot, then tap, etc, etc.

I don't know what you call this setup where you have a slot with pinch bolts - I'm sure there is a common name for it and it has many applications other than motorcycle triples so I was hoping for some feedback before I dive into this.

[Boots]

Your method is correct. You will want to drill and tap before you slit. The slit will have to be where your thread starts so the hole on the upper part of the bolt is bigger for clearence. If you slit it first before you dirll and tap your hole may not be at a 90 deg. angle to the bore which is critical for a clamp. Make sure your hole is the same size as your tube you are clamping to.

[mrcodewiz]

Great, thank you! Is the fork tube hole generally the exact same size or a few thousandths larger than the fork?

[Boots]

I would make it the same exact size so the Radii match. This will ensure you have clamping all the way around your tube and not just a pinch. Also if the bore is larger (even a few thou. ) it will distort when you clamp. When you slit it, it will spring apart slightly so you can easily slide the tube in and not scratch it all up.

[mrcodewiz]

Great, thanks for you help!

[HPbyGD]

When I made mine I honed the tube bore to exact size. My reason for honing it was to get a better finish on the bore and thus more contact area on the tube when the pinch bolts where tightened .
Gary

[mrcodewiz]

Originally Posted by HPbyGD When I made mine I honed the tube bore to exact size. My reason for honing it was to get a better finish on the bore and thus more contact area on the tube when the pinch bolts where tightened . Gary

Hmmm... I have never honed anything before. Did you use a dedicated honing machine for that? I was originally planning on just milling the fork tubes out (CNC) but maybe a boring head (or honing?) would be better?

[Fastest1]

I would think boring the holes for the tubes would be the preferred way. Seems like pocketing still has some out of round issues due to axis changing. Probably useable but better if bored.

[rowbare]

Unless your machine can interpolate a perfect circle, you would be better off using a boring head for the fork holes since you are sure your hole will be round. As Gary mentioned, you want as much contact as possible. You might want to bore a touch undersize and then use a hone to bring it to size. A hand held brake cylinder hone would probably suffice.

If you are going to anodize the tree, you might have to be a bit oversize to compensate for the thickness of the surface layer. With the effect Boots described this might not be necessary.

bob

[HPbyGD]

Actually I used the wrong term as I actually used a lap. I think that is what it is called. I turned a piece of tubing down to fit inside the bore and put some lapping compound on it . Then I just kept measuring the ID until I had the exact ID that I wanted.

Gary

[mrcodewiz]

A bunch of great ideas! I think the plan (as of now at least) will be to first pocket the stem and fork tube holes way undersize, then use a boring head to bring them to the exact size. I am planning on anodizing it but I think I will probably just mask off the mating surface. If that doesn't come at good enough, I will go undersize and try the hone.

Thanks again for all the suggestions!

[fpworks]

Come on guys...this is ridiculous. This is not a precision interface...nobody needs to be throwing around techniques used to achieve .0001" when pinch bolts are involved.

Think about how the tube is being made before you go overboard on matching the bore. You don't need to hone or bore the holes for the tubes. Simply interpolate it OVERSIZE by at least .010" so the tubes slide in AND out without getting scarred.

Did you think about the accuracy of your alignment will respect to the lower clamps? You MUST have some clearance, or you'll be smacking everything together with a hammer...and have fun taking that apart.

As for the clamping, the TUBE is fricken hollow...the triple clamps AND the tube will deform when you tighten the pinch bolts. (on something that sized)

...and quit using the words "perfect" and "exact" when referring to machining anything.