Woodruff key (slop) ?

[pontiac428]

Loctite sleeve retainer "green" is specified for woodruff keys and will handle a .004 gap. Perfect!

 

[graham-xrf]

Centerpunch the sides of the key in a few places, tap it in...good to go.

Yes - this indeed is apparently what has happened before in the life of the key from the SB-9A. There are two punch marks, and that "stops the wobble". The other key (SB-9C) just wobbles away

I was not sure whether this kind of fix would rank as a "quick and very dirty bodge", or whether it's an excellent re-work idea without much downsides. The "high" points raised by the punch marks are confined to just around the punch marks. The rest of the key still has clearance, but it does make it go in as a "pliers push" fit.

The logic in me says any force transmitted through the key only goes through the punch mark craters, but if the key is inserted with the punch marks facing the toolpost side, then the punched side of the key does not have to deliver the main torque. The dodge may have merit!

My apologies to those who see we are getting into the weeds over Woodruffs here. I may have pictures too , but I might spare you HM folk getting to the deep and grubby limits of what one does with keys. I do know that one gets it wrong, the damage can get ugly!

 

[graham-xrf]

Loctite sleeve retainer "green" is specified for woodruff keys and will handle a .004 gap. Perfect!

My thanks for that! As much as 0.004" does surprise me.

One consideration is that if ever there is a need to disassemble. Green (Loctite 640) is not quite as strong as 628 retainer, but it is still mighty stuff, and it would be a pain to get it out. This is not a big concern. How often does one ever get the spindle out? When I finish reassembly, it will likely run excellently, well beyond the point I am able to care I like things that way - unlike the modern so-called "white goods" that grace our households.

 

[Liljoebrshooter]

Its easy to get apart. Just put some heat on it from a torch for a few seconds and heat up the loctite. It will come out.

Joe

 

[mikey]

If the key doesn't clock something precisely, could you cut a new accurate keyway 90 or 180 from the worn one? A Woodruff key should be an interference fit, with a depth and height above the key that falls within tolerances.

I agree with John; the key should fit well or it will just wear again.

 

[graham-xrf]

If the key doesn't clock something precisely, could you cut a new accurate keyway 90 or 180 from the worn one? A Woodruff key should be an interference fit, with a depth and height above the key that falls within tolerances.

I agree with John; the key should fit well or it will just wear again.

I am definitely with John and yourself on this one. Given I have them all apart, this is the opportunity to put them together right!

The keyways are in standard hardened super-finished South Bend spindles, and are unharmed, still with their machining marks from the key-cutter.
(The spindles, even at their age, are still rather beautiful!)
While cutting new keyseats to better suit somewhat skinny undersized keys is possible, that may be a bit like getting new diamonds to fit the ring better!

The keys are clearly Woodruff 606, that is, 3/16" width x 3/4" long. According to Machinery's Handbook, keys should never be smaller than the 3/16 nominal (0.1875), and can be up to +0.001 oversize (0.1880").

The key seats (maximum) for that size should be up to width 0.1880" which is 5 tenths over-wide, so a exact key might have from 5 tenths "easy slide in", up to 5 tenths interference fit.

The key seats (minimum) can be as tight as 0.1863", which is 0.0012" interference on a perfect key, and as much as 0.0017" interference if it encountered a maximum fat key. The thinking behind this is, I guess, that an over-fat key can rapidly be lapped down to a snug fit, and the worst case loose fit is still a quite well fitting 5 tenths "sloppy".

When it comes to measuring the reality of what we have, the keys are easy enough using micrometer. Mine is a Mitutoyo 0-25mm resolving 0.001mm, which is about 40 millionths inch. Measuring the width of the keyway is a touch awkward. It's hard to get consistent measures with a digital caliper. I tried a 3.1mm gauge block along with three inch type feelers all together. I will have another go soon. However wide the seats are, I will contrive keys to fit. Right now, I am diistracted by the need to fix a problem with the house hot water system, which is just the greatest thing to have at Christmas Eve!

That said - my best wishes for the season to all. Have a great Christmas and New Year!

 

[graham-xrf]

While I was measuring the excess with a feeler gauge, the naughty thought did occur to me.. Hmm.. feeler gauge shim!
Instead of making a nice, firmly fitting key from scratch (and 4140!) , is there anything so very wrong about simply making up the excess space in the slot with a key-shaped shim? It needs 0.05mm (about 0.002"). Clearly the spindle slots are a "South Bend special", sort of.

I know it strays into the "quick-n-dirty fix" territory, and it does offend my sense of wanting a proper fit key in there, but I am still Catch-22 on making one. All it needs is a bar turned to 3/4", parted off to the "fitting" thickness, and the flat milled onto it 1/16" above the centerline. I guess I can do the quick fix on one lathe, then make up 2 (or 3) keys, from 20mm dia 4140 I already have, and install when next I can.

 

[matthewsx]

Loctite sleeve retainer "green" is specified for woodruff keys and will handle a .004 gap. Perfect!

I used the Loctite sleeve retainer for sloppy fitting crank bearings when rebuilding racing kart engines (picture a Briggs & Stratton 6.5hp built up to 21hp).

It’s good stuff that’s more than up to the job you’re describing. I agree that if you can find one that fits perfect it would be ideal but we don’t all live in an ideal world.

Read the technical documentation and see if it will work for your application.

LOCTITE® 680

LOCTITE® 680 is a green, high strength, anaerobic-curing retaining compound for the assembly and attachment of cylindrical fitting parts, particularly where low viscosity is required. The product prevents loosening and leakage from shock and vibration, and provides robust curing performance by...

www.henkel-adhesives.com

I bet it will.

John