Need opinion from mech engineering types....

I am thinking of having a machine shop lathe an aluminum steerer / crown assembly from 1.125 to 1 inch.

Is this a very bad idea? Shaving approx. 3mm diameter from 1.125 diameter 6mm walled pipe.

Thanks.

 

Why?

 

What are you trying to accomplish?

 

Limited options for 1 inch head tube vintage MTB. I was looking at a fork I had, and 3 mm around doesn't look like too much. Just floating the idea to see if I'm taking too much of a risk.

 

whats the hole diameter on the crown? if you are going to have any kind of a "step" in the steerer tube from 1-1/8" to 1". I would refrain, good place for the tube to fail.

 

Good info, thank you. Yes, there will be a step where the steerer enters the crown.

It's a vintage bike, with V brakes, so I won't be putting modern MTB stresses on it. Am now approaching this with more caution.

 

Hope you have good dental insurance......

So you are basically looking at removing 66% of the material in the 2nd most important part of the bike?

 

I hope your health and dental insurance are good! Oh wait........

 

lol.. that's so messed up

 

How did you get that? I havent done the calculations, but from the back of a napkin estimate, I need to shave .7mm around off a 1.125 (28.575 mm) diameter 6 mm-ish thick tube. 66% is way off.

edit: I think your confusing wall thickness with diameter.

Oh gawd, the "bolt on crowd" is circling over head. This isnt one of those. Hahaha.

For any mech engineers, just need to be pointed in the right direction. Do I look for formulas on shear strength? And how much does a step in the pipe affect strength? Is it a big stress riser?

edit2: phuck it, I did the math. http://www.calculatorsoup.com/calculators/geometry-solids/tube.php Steerer wall thickness is going from

t = 6 mm

to

t = 3.913 mm

I was hoping to shave at the most down to 5mm wall thickness. Not good. End of story.

 

I don't know if I'm part of the "bolt on crowd", what ever that means?? But I am part of the "common sense" crowd.

 

double post.

 

Nobody knows shit until one tries to find out. The question was posed to do just that.

Re: bolt on - where you buy a part and simply bolt it on. this a situation that requires some re-fabrication, re-purposing or whatever it takes to find a solution that is not.... bolt on. I wouldve thought your common sense wouldve caught that

 

Could you press the steer tube out of the fork and press in a tapered 1"?

 

Can't do it. Talked to some industry people. Supposedly, modern fork steerers are glued in. The crown wont take well to a second pressing.

Also had a machine shop look at machining down a headset. No go.

Shaving the head tube is not an option, nor welding a new one on.

Really just want a 1 inch suspension fork that is not elastomer sprung. Dont wanna go rigid as the frame is suspension corrected.

Any 1 inch SIDs there anyone want to sell?

 

1" steerer

The only reason I sold off my Bontrager Race Lite and Road Lite, lack of 1" fork options.

 

You know it. I am restoring a Race Lite right now There is a Taiwan carbon fork on the market. It's getting harder and harder to resist just going that route.

 

I remember a guy did a 1.125 fork into a 1" beach cruiser frame using smaller bearings.
Found it
http://www.socaltrailriders.org/for...ith-1-1-8-quot-steerer-on-an-old-school-frame

 

View attachment 163242

 

It is not really in shear, but if we call it shear lets call it double shear. Anyways, you could always sleeve the inside with a better material. You say it is aluminium, I say what Al Alloy ie: 2024, 6061, 7075? This makes a big difference.
How are you going to finish the bare al aly? anodize? that will take 3 tenths (.0003). Hard anodize? it will add a few tenths. What will you seal it with? Diameter is not quite enough, better work on some tolerances to describe what you want to the machinist. Here you will talk position or concentricity.

You talked about a step, these are called stress risers. give a nice .03 min fillet radius, that will do the trick.

The shear sleeve: it should be something good like phosphor bronze, nickel-chrome, A286 stainless. It will not need to be very thick, the shear modulus on these materials is tits. Go with a light press fit (see ANSI fits table) I would go with a LN1 to 4 if you have the dough or an LT if you are on the cheep. Me I am going with the cold reduced A286

Happy machine design trails, finally somebody is talkin my language