Turning down OD of a tapered roller bearing race.. Timken cup

[MattiJ]

Thanks for all the advice ,and useful discussion.
I have no doubt the lower hole was NOT finish bored.
I have no doubt I can re machine it, but this one a bit tricky to hold.
but in the interest of building momentum, and keeping my kid keen on this, the quicker we get it on wheels and keep working on it.. the less chance of stalling out on a new project, so temporary fix is fine till it needs paint and will be ridden.

I have not yet reached out to manufacturer. The only thing I hope to get from them is maybe paperwork.. certificate of origin.
shipping a frame back to the U.S. is notnreally an option, cost be near what we have in the frame. If we run into any problems 're the frame origin or numbering, we can always make a new neck..and a local guy has a frame fixture, has built many frames.

As to the bearings, The races are cheap should be 10 bux or less, so I care not if I use up one or two trying something , if I can turn and grind them.
And someone said don't mod a bearing to fit the frame.. it goes on every day. It is a thing. The olderJapan bikes used loose balls in grease with hardened upper and lower race and cone. On Honda this is two different sizes, smaller up top. . Because tapered roller are preferable, there are many conversion kits..and guess what.. custom ground outer races ! Why, because loose ball bearing races OD are not standard bearing cups OD. They must do a crapload at a time because they are cheap. . Like 25 to 40 bux for 2 cones and 2 cups and often dust seals.

So I will sort it out , but for now not having my mill and big lathe wired, it limits my immediate options.

How about ”line boring” the bearing seats instead of trying to wrangle the frame to the mill?

[754]

Thanks for all the advice ,and useful discussion.
I have no doubt the lower hole was NOT finish bored.
I have no doubt I can re machine it, but this one a bit tricky to hold.
but in the interest of building momentum, and keeping my kid keen on this, the quicker we get it on wheels and keep working on it.. the less chance of stalling out on a new project, so temporary fix is fine till it needs paint and will be ridden.

I have not yet reached out to manufacturer. The only thing I hope to get from them is maybe paperwork.. certificate of origin.
shipping a frame back to the U.S. is notnreally an option, cost be near what we have in the frame. If we run into any problems 're the frame origin or numbering, we can always make a new neck..and a local guy has a frame fixture, has built many frames.

As to the bearings, The races are cheap should be 10 bux or less, so I care not if I use up one or two trying something , if I can turn and grind them.
And someone said don't mod a bearing to fit the frame.. it goes on every day. It is a thing. The olderJapan bikes used loose balls in grease with hardened upper and lower race and cone. On Honda this is two different sizes, smaller up top. . Because tapered roller are preferable, there are many conversion kits..and guess what.. custom ground outer races ! Why, because loose ball bearing races OD are not standard bearing cups OD. They must do a crapload at a time because they are cheap. . Like 25 to 40 bux for 2 cones and 2 cups and often dust seals.

So I will sort it out , but for now not having my mill and big lathe wired, it limits my immediate options.

[old mart]

That's a fresh outlook on it. Perhaps the frame manufacturer forgot to finish bore the lower bearing housing. I trust the op has talked to the frame builder about this. Ten years ago, I bought a full suspension bicycle frame from one of the biggest bike retailers in the UK. It arrived in their standard cardboard box and after examining it thoroughly, I noticed that there was a flat in the front of the lower steering head. The frame was aluminium, 7075, possibly, and it was not likely to be salvageable without messing the paintwork, and annealing the area before forcing it back to shape, and even then it would very likely need a strengthening ring. The dealer was very helpful after seeing the photos of the damage and I got an immediate replacement. It had been dropped on to a hard surface at the only possible angle which could possibly cause damage. The guy I talked to at the company said they had shipped thousands of frames in similar boxes, and mine was the first one with that damage, so they wouldn't bother to revise the packaging. I still have the bike I built around the replacement frame, and can now ride it with both knees replaced, but it's hard to lift a leg up high enough to get on it.

[Doozer]

I came across the website of a custom frame builder. He says he welds the frame up with the headstock bearing seats undersized as they distort during welding. Once fully welded, he puts the frame into a milling machine and finishes the bores with a boring head. https://www.instructables.com/id/Mak...cycle-Chassis/ If this is a brand new frame, could it be that the seats still need to be finish bored? Ian

This sounds most plausible, for sure.

--D

[Ian B]

I came across the website of a custom frame builder. He says he welds the frame up with the headstock bearing seats undersized as they distort during welding. Once fully welded, he puts the frame into a milling machine and finishes the bores with a boring head. https://www.instructables.com/id/Mak...cycle-Chassis/ If this is a brand new frame, could it be that the seats still need to be finish bored? Ian

[thaiguzzi]

I've done a bunch of different forks, yokes (triple trees in 'Mercan) and stems in different chassis over the years.
A bunch.
1. Consult a taper roller brg supplier's catalogue and see whats available. Metric and/or imperial, its irrelevant.
2. Measure your ID of your headstock, top and bottom.
3. Measure your steering stem, top and bottom where the brgs sit.
4. Choose either to use an undersize OD brg with a custom machined spacer
or
5. machine and fit a new stem.

Its all relatively straight fwd.
I would not even contemplate modifying an outer TR race.

[old mart]

If you are having difficulties measuring the bore, them making a plug gauge on the lathe is the best option. It can be stepped, or double ended. What you are looking for is a just possible push fit, then if the bearing is the same diameter, Loctite can be used. This would be the best option, as after welding, there is very little chance of the head being exactly round, making conventional measuring difficult.

[Doozer]

Hey man, your shop, your rules.
But I think it is absolutely bat shlt nuts to turn or grind a custom bearing.
Making a non-standard bearing to match some machining f-up is crazy.
Why not fix the head tube or make the guy who messed up the head tube fix it?

-Doozer

[CCWKen]

I haven't read anything about accuracy unless I missed it. (Except for your loose measurements. You must be "spot-on" in getting the sides perpendicular to the base. If you don't, you'll probably feel a binding in the shaft after assembled. I hate to Ass-U-Me but I'm only guessing the frame head was bored straight. As long as this thread has been running, I would have made a new head for the correct bearings. But I have a jigging setup to use.

[jhovel]

Cheap Chinese cermet tips turn bearings without any trouble at all, even very small cuts. I use them frequently on hardened steel and get a great finish. They will NOT tolerate interrupted cuts AT ALL!.

[754]

The start of the thread was asking how hard these races are to turn down. If its 47 thou or 51 thou, wont matter much.

Believe me i spent 1/2 hour looking, since my move a few things are scattered about like my 3 ....1-2 inch mics and my t gauges.. I did measure with a divider set and a caliper. I know where my inside Mic is just not sure if t starts at 1.5 or 2 inch
Whether I am out 2 thou or not matters not till I start the work.

[Arcane]

I get 49mm at 1.929 48.5 mm is 1.909. Any way its around 49 , need to measure with a mike, and be accurate. I have no doubt it's machined wrong unless it has a sleeve, will look closer. Any time a factory has 2 sizes of races, smaller is on top.. this is reversed. Wil get around it, probably do a temporary soft race .

This is what you should have done before you made your first post.

[754]

I get 49mm at 1.929 48.5 mm is 1.909. Any way its around 49 , need to measure with a mike, and be accurate. I have no doubt it's machined wrong unless it has a sleeve, will look closer. Any time a factory has 2 sizes of races, smaller is on top.. this is reversed. Wil get around it, probably do a temporary soft race .

[Mark Rand]

48.5mm head set bearings
1.938" taper rollers


Looks like the frame head was bored wrong. If the upper bore is a good fit, I'd be tempted to use the head set bearing and some Loctite 660 to retain it. It worked in the 'swinging arm' bearings of a peugeot 405 estate car/station wagon for 10 years...

[old mart]

You will have to make something to hold the outer race in the lathe, to machine the entire od in one go. I would try different grades of insert, or look up the most suitable from the makers charts. As I said, the finish is not critical and there is not much to remove anyway. A solid dummy bearing will certainly be ok for continuing the build, just make it easy to remove from the frame when the time comes. Measure the height of the assembled taper roller before making the dummy. I have bought a couple of CBN versions of the common inserts on ebay cheap, one has two edges and the other, an Iscar has four edges, I can't remember the shapes, and I have never needed to use either.