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

[754]

So we just picked up a chopper frame for Sohc CB 750. It appears lower race is way undersize. Like 1.929 and should be 1.979 or so.
so not having mill set up now, to fix neck bore. It will be easier to turn OD of the cup..outer race.
anyone got an idea how hard they are ?
I will try to cut it with a carbide on a SB 9...if it's too rough I will have to grind to finish size.,
let me know if you have tried it..

[doctor demo]

I seriously doubt that you will be able to turn the o.d. with anything readily available. Grinding might be a better option.

Steve

[epicfail48]

Outer race is probably going to be hardened, somewhere in the 58-61rhc range. Suppose you could turn it if you have CBN on hand, but grindings probably the better option

[Willy]

Sounds like you may have to improvise a tool post grinder setup of sorts.
Leave the OD a little proud, freeze the cup as cold as you can get it and pop it in quick.

[BCRider]

If the frame is from a reputable maker originally chances are good that there's a bearing out there which should fit.

And, I'm guessing a bit here, what is the other end of the neck tube sized at for the bearing? I'd say that normally they should be the same? If the other end is sized correctly then you may have gotten a reject steerer tube that somehow got away? And if that is the case you might want to check the alignment to find out if the bearing seats are actually in line correctly to the frame centerline before you try modifying a bearing to fit. Boring the frame might be the only option if it's not actually centered on the line it should be centered on.

These may be questions that have already occurred to you. But they are what leaps to my mind to start with.

[754]

I would rather get most off with a tool and the last 4 or 5 thou with a grinder.
when I worked in the die shop they used CBN or diamond or something, and did hard turning on punches very often..
I don't mind grinding on my SB 9, but dont want to on my soon to be running nice big lathe..

[nickel-city-fab]

It's definitely in the territory of hard turning with carbide, or grinding. I would definitely want a light feed with either flood cooling, or an air blast on it.

[754]

It's the lower race on this neck, hard to setup in a mill, but I have done it before (dont have mill wired right now).
in the interest of getting mocked up and started on this getting a race in the bottom, would let us get ahead..

[Hopefuldave]

It's possible, I had to hard turn circlip grooves in some outer races as they were replacing flanged outer races (yours for only £800 each bearing, I needed 5, minimum order 100...) - quality carbide insert (neutral rake or negative if your lathe has the guts and rigidity - it will NEED both anyway), about 150 -200 SFM, 0.010 minimum depth and a small feed = lots of orange-glowing ribbons and sparks
It's VITAL that the race is rigidly held - I turned a pot chuck to about a tenth oversize with a lid to clamp (and had to wait for the race to cool to get it out), for your appliction you could turn a mandrel with a matching taper and have a cap to pull the race onto it, bearing against the "thick" end of the outer race.
If you run coolant (I didn't!) it MUST be a continuous stream or thermal shock WILL fracture the carbide insert...

Dave H. (the other one)

Edit: just spotted that you have an SB9 - it may be a bit light for the hard turning - I used a 4400 poound Holbrook toolroom lathe with 3HP and it knew it was taking the cut... You could try though, keep the depth of cut fairly substantial (carbide nose radius to bury) and reduce the feed if its too heavy a cut for it? Or... toolpost grinder (50 thou" willl take a little while if you want a good finish though at a thou" or two per pass)?

[MattiJ]

CBN insert cuts it like butter in a lathe with enough speed, horsepower and stiffness. SB9 has none of those but I would try anyways. Getting any close to correct size is probably the biggest problem..I’d probably sharpen the CBN insert only for this purpose so that it would need slightly less feeding force.

[Mcgyver]

ceramic, i.e. cermet, is commonly used to turn hardened steel.

[Ian B]

1.929" is almost *exactly* 49mm, it almost sounds like it had a metric sized taper roller bearing installed. 49mm doesn't seem to be a standard size, but there is a 25mm bore, 47mm OD available. Could you machine up a thin sleeve? Ian

[Doozer]

All Balls Racing
has those half-millimeter bearings
common in steering necks.

-Doozer

[old mart]

It sounds to me that a mistake was made when the steering head tube was machined. I have never heard of two sizes in one headstock before. If you have an old ball race kicking around, you could try and see whether your carbide would machine it. The finish would not be too critical, a light press fit and Loctite low strength to prevent corrosion caused by water ingress. The bearing cannot fall out.

[754]

Exactly, i think it was machined wrong, trailer bearing kit for 1 inch ID has always worked for Harley stem bearings i know its near 49mm, I only took quick measurement with dividers and caliper, as I did not have a Mic and telescopic gauge handy.
if I can't turn the race on the lathe easily I may just make a bushing to continue with mockup, need to get any slop out of the stem to fork assembly to proceed.