I found some NOS idler gears for my Rockwell 11's quick change on ebay. One fits pretty sweet, the bore on the other's a little small. Dave Gingery describes a way of making reamers that sounds doable - make an acute bevel cut across a piece of drill rod or crs.
I only need it for one bronze bushing - think it'll work? Anybody made/used such a tool?
A "whistle reamer" as they used to be known.
They give a good finish, but they need a reasonable lead in and have a minimum hole length of a couple of diameters, if they're not to make the hole bell-mouthed.
Lose the reamer idea. That's what boring bars are made for. A bushing should be dead concentric with the OD, which you would insure by boring and turning in the same setup. No real reason to go to the trouble to make a reamer that would be used for one purpose, with less then perfect results, when you can make the bushing in less time by my suggestion. If, by chance, the entire gear has to be turned, the same thing still applies. You can make the necessary setup by various means, then bore the bushing after it's pressed in the gear. A reamer would be a poor choice, for various reasons.
Harold
Yes, they work. They were used a century ago for reaming the holes in master watch plates and so on -- then the highest-quality toolmaking work done anywhere.
I used to make them a lot, when I was doing a lot of hobby machining. I also made plain D-bit reamers and drills; they work, too. Worn-out or broken drill bits make good stock for these things, but be aware that the butt-ends of drill bits aren't hardened much, if at all. And the butt-ends are undersize.
-- Ed Huntress
Do it the easy way.
Assuming you don't have a sunnen hone, see if your brake cylinder hone will go small enough. If not cut a slot in a steel rod that will go in the bore and but a strip of emory paper in the slot. Hold the rod in the drill press and work the gear up and down. Easy to take out a few thousandths and/or slick up/debur the bore by using correct grit paper.
Uncle George
No doubt it works, but it's a bitch to avoid bell mouth, or to control size. I do not support a brake cylinder hone when size or configuration is critical. They have the potential to destroy an accurate bore.
Harold
And how is this a problem with idler gears? For grins measure up some well used but still functional change or idler gears and see how the bores measure. It all depends if you want to machine perfection or cut metal .... i.e. when is 'good enough' good enough.
Uncle George
It also depends on if you'd like to establish concentricity and perpindicularity, or can live with runout. Not a great idea with gears. The point is there's better ways to do a job like that, with less effort and better results. There's no such thing as "good enough" when it gets down to gears meshing. They're right, or they aren't. Well used gears that have excessive wear, idlers, or not, are called "worn out".
Harold
I could imagine one time a reamer might be appropriate for a job like this - if a) the original bore of the gear were only several thou undersized, and also not bored concentric with the OD. And the person involved did not have a four jaw chuck.
But for any other case, simply indicating the bore of the gear in, and using a boring bar to skim a few thou seems like a real cheap shot to do the job fast and right. Nothing to make, nothing to heat treat, etc.
Jim
Funny, that's how I see it, too. *Especially* if there's a keyway involved.
Harold
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