Chuck Arbor

On the assumption that most on here are pretty savvy, apart from cleaning both the socket and the arbor do any of you do anything special apart from assembling the two and giving the arbor a smart tap with a copper or dead blow hammer? It’s all I’ve ever done and not had one come apart. I ask though as I’m assembling a bigger 20mm capacity Jacobs chuck this time.

Over the pond some folks reckon they freeze the arbor or even heat up the drill chuck in the oven to 350°F!

If everything is clean, and the tapers match, there should be no need for any fancy tricks.

MichaelG.

With a Jacobs type chuck I follow the advice of Ian Bradley and drill and tap the arbor for a securing crew; the chuck body is also threaded for a jack off screw.

I did an article in MEW on this very topic a couple of years ago. Two good firm taps with a copper hammer is all it takes. My test example for the article was a 13mm chuck on an MT1 arbor, so quite a small taper the chuck mounted on. I tested it in the lathe with a 1" drill bit with the shank turned down to 1/2". Tried everything drilling a hole in steel and could not get that taper to let go. You would shear the key in the tailstock or slip the belts first I reckon.

One tip I learned from old time Harley-Davidson racers when assembling their flywheels with tapered crank pins is to wash the tapers with distilled water before assembly. The factory race team always reckoned that degreasers leave a film and solvents including alcohol leave traces of salts on the tapers that can interfere with the fit. Seems to work for me.

And of course you must go over both tapers first and remove any burrs. The ends of the taper on the arbor always seems to need a little bit of a clean up with a fine file.

1" drill mounted on MT1 taper in action:

Edited By Hopper on 15/10/2022 02:31:59

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A serious question, if I may, Hopper [and please resist the temptation to play that old ‘Angels on the head of a pin’ record]

Were those water-washed tapers meticulously dried immediately before actual assembly, or were they [intentionally, or otherwise] left slightly damp ?

The case against the other fluids is good, but I’m intrigued by the use of distilled water

It would be interesting, and perhaps informative, to study an old assembly and look for microscopic rusting.

It would of course be nice to think that the surfaces would wring together like Jo Blocks, but I doubt that … it seems more likely that rust [at a barely detectable level] would be acting rather like a Loctite Retainer does.

MichaelG.

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Pedantic Note: __ other brands of ‘anaerobic’ retainers are available, but I referenced Loctite specifically to avoid using the word [which refers to the curing mechanism rather than the retaining mechanism]

The people who used the radial drills where I used to work put the drill chuck in the socket and then brought it down onto the drill table or vice to secure it. They never had a problem getting the chuck and arbor out of the drill using drifts but if the arbor got damaged they were well and truly wedged into the chuck. I resorted to cutting off a number of them and drilling out the core that remained. This usually reduced the pressure on the taper enough to get the remains out with little effort. The point is that over time the chuck is being pushed further onto the arbor by both the forces of fitting the chuck into the drill (impetus due to momentum or direct pressure) and the pressure on the drill bit in use and together these usually work towards keeping the two parts together.

Martin C

Over the pond some folks reckon they freeze the arbor or even heat up the drill chuck in the oven to 350°F!

Shrink fitting is not required. I would only use that if I wanted a permanent joint! As a last resort - if the components were otherwise destined for the scrap bin.

They are dried with clean air or lint-free cloth before assembly.

Chances of rust developing in the hot oil-filled crankcase of a racing motorcycle engine that is rebuilt between each meeting are zero to none.

The tapered crankpins are drawn into the tapered holes in the crankshaft flywheels by large nuts on very fine threads outboard of the small end of the taper. So no wringing, just wedging action.

Some Harley engines with hundreds of horsepower in nitro drag racing bikes still use tapered crank pins. They are regarded by many as superior to pressed together cranks.

Later model production Harleys that changed over to pressed-in parallel crankpins as a cost saving measure suffer from crankshaft "creep" as they do not grip as well as the old tapered pins. For performance work, the parallel pins have to be TIG welded in position to stop them moving. That is even with a 6 thou interference "crush" fit that takes a 100 ton press to assemble.

Edited By Hopper on 15/10/2022 10:15:50

I was once told by an old-time car mechanic that it was common to clean propshaft bolts and then wet them before assembly, so the resultant rust stopped them coming loose. That would have been in the pre-Loctite (and possibly pre-Nyloc nut) days, I guess.

Sounds feasible and practical, if not best engineering practice?

Rob

One or two YouTubers recommend using pure Acetone to clean the tapers so I’ll try that. It’s 99.9% pure, not sure what the rest is?!

That would be the trace residue/salts Harley-Davidson did not want on their 100HP crankpin tapers. I think we will be ok with it on our 1HP lathes and drill presses though.

Actually it says on the bottle: PROPAN - 2 - ONE, DIMETHYL KETONE. I also made an error, it’s only 99.5%. It’s been suggested the rest is probably water, most likely from the atmosphere?

My new 20mm Jacobs chuck appears to be unused. It has a small hole drilled right through it. I was gifted a rather nice Jacobs chuck many years ago, firmly affixed to a damaged arbor. The owner had tried heating, cooling and wedges etc to no avail. I was told “if you can get it apart you can keep it!” The Chuck didn’t have a hole through it but I read online the easiest way to remove the arbor was to drill a hole in the chuck and knock out the arbor with a drift, which was exactly what I did. Easy when you know how.

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Thanks, Hopper

Just to be clear … I wasn’t thinking of rust “developing in the hot oil-filled crankcase” but rather a microscopic film of it developing immediately prior to the components mating.

MichaelG.