What did I do wrong?

[Bob Engelhardt]

I made this arbor to go on a 5/16 motor shaft, for a wheel with a 1/2 hole:



I used a piece of 1" mysterium in a 4-jaw, more or less centered,
-drilled a hole 1/64 shy of 5/16 (drill chuck in tailstock),
-used an adjustable reamer to open it to fit the shaft closely (a thou or 2 under 5/16), (reamer held in tailstock chuck & probably 4 passes or so to remove .015)
-turned the shaft to 1/2" & parted off (it was threaded with a die later).
Once the raw stock was chucked, it was not moved.

With it on the motor I was getting a lot of vibration, so I measured the concentricity on the lathe. The shaft has .006 TIR relative to the bore.

What happened?

[Doozer]

No mention of a boring bar operation.
You can't get axial concentric threads with a die.

-D

[Gary Reif]

I wouldn't blame the threads for the R/O, probably should have used a boring bar to finish the 5/16 diameter. My guess is that the reamer did not hold a perfect center.

[754]

Thread not important.
turn OD and finish bore by boring ..without removing..

[redlee]

If you want a concentric hole you must bore before reaming. Spot Drill - Drill - Bore - Ream
Doozer is correct , Die will not cut a concentric thread.

[chipmaker4130]

Don't even consider the thread. It doesn't matter anyway if all it does is hold a retaining nut. Its obvious that the drilled hole was off, and a reamer always follows the hole. As mentioned, boring is the only way to get it right outside of fancy hones, etc.

[Doozer]

Ummm......
If the nut is crooked against the wheel....
Shlt not going to run true,
no matter how good the rest
of the features are.

-D

[BCRider]

Ummm......
If the nut is crooked against the wheel....
Shlt not going to run true,
no matter how good the rest
of the features are.

-D

Afraid Doozer has it right here. An off kilter thread can put more pressure on one side and due to the paper faces on the stones the stone will run off kilter. Also if you used a regular nut then the end faces of the nut may not be all that square to the thread's center axis.

For the mandrel I also have to agree that a drill can wander. I would have drilled 1/32 under, bored to true it up and get close to the 5/16 then clean it up with the reamer which would follow the proper bored axis of the hole. Then turn the 1/2" portion and single point the thread from there.

For the nut if you don't want to turn and internally thread your own nut I'd run two nuts onto the thread with an O ring between them. LIGHTLY skim the face of the end of the second nut which sticks out past the end of the threaded portion. Why the O ring you ask. So hopefully the nut you are skimming rests as best it can against the thread of the shaft and the skimming you do produces an end face which is dead square to the thread axis. The other end I'd dress with an angle or other feature so you don't confuse which way the nut goes after that.

[dian]

or just use a rubber washer.

[rjs44032]

Rule of thumb I was taught: drill, then bore, then ream.

Best Regards,
Bob

[Doozer]

Why ream after you bore ? ?
Does your lathe cut crooked ?

-Doozer

[754]

Why ream after you bore ? ?
Does your lathe cut crooked ?

-Doozer

If hole has any run out, you bore the entry part, gives the reamer a fighting chance to fix the sins..... in my experience I have done so.

[J Tiers]

Why ream after you bore ? ?
Does your lathe cut crooked ?

-Doozer

Depends how smooth you get it boring. Reamer can smooth the surface. Probably better to drill, bore, grind. But you may not have that good a grinder. Lapping is a substitute that is more akin to reaming.

[754]

Depends how deep the hole is as well , I can ream a 1/4 hole 2.5 inches deep, but am lucky to bore it maybe 1.25 deep..

[BCRider]

Why ream after you bore ? ?
Does your lathe cut crooked ?

-Doozer

I do the same if I've got the proper size reamer. The reaming is for size and finish. Size being quick to achieve with the reamer and the finish giving a greater degree of contact area that won't "wear loose".

Where I want the very best fit and supportive finish that won't "wear loose" and don't have a reamer then I'll do my darndest to bore to a snug "twist tight" fit and then hone or polish for the final fit.. grinding would be a nicer way to go but I don't have an ID grinder... yet....

The way I see it the cutter will generally leave a "hill and valley" finish where the shaft will ride against the crest ridges of the "hills". Going more for a twisty tight finish then honing, lapping or even just fine abrasive polishing with fine grit paper on a suitable mandrel will cut those crests down to flatter shaped plateaus for that final "half a thou" finish where the shaft slips in like it grew there and where the flatter plateaus on the ridges will provide more contact area for a more durable long term fit.

Is this a fussy and time consuming way? For sure it is. But it's given me parts fits that are more consistent over the long term.