Loctite, Crankdiscs, their part in my Downfall

[Bluechip]

John

Yes, I'm sure you're right re: bespoke adhesives for specific applications in industry. Used some myself.

I too, knurl shafts, not particularly for adhesive clearance, but to get the wretched thing at right angles to the crankdisc. Or very nearly!
The little oscillator I made earlier this year was done in that manner. Which brings me to a modest Rant. ( It's cold, miserable and damp, I feel I owe it to myself).
Rant begins ..

On more than one occasion, in ME and other mags, often while describing a beginners engine crank assembly or the like, something along these lines ....
'Ream the crankdisc 3/8", clean the shaft and disc, assemble with Loctite, and leave to cure for xx.' ..No susequent mention of skimming the disc!
Er, no! Gonads! It doesn't work. Not for me anyway. That disc will not run true. (1) the round bar will be undersize. (2) The reamer will cut oversize.
With a hole some .003/4" larger than the shaft, there is a whole lot of wobble at the disc periphery. Agreed, Loctite will effectively fix the two items together. I doubt if it evens out any error, it's not intended to do so.
What I did, FWIW, is, similar to what John says, to lightly knurl the shaft leaving about 1/2" plain as a guide. The disc will now be a light push fit on the knurled part of the shaft. Clean shaft, apply Loctite, push the disc on, then bring up a bit of 1/2" sq. oak in the toolpost to gently push the disc true. I got about .0012 TIR. Did skim it to remove the stub from the disc centre. I would be pleased to hear of a better method. It is possible to get undersize reamers. Are they the 'professional' answer? Bore the disc, not ream?

Rant Over
Dave BC


 

[bogstandard]

Dave,

I think you have the correct technique, basically the same as mine, except I don't use a reamer, they always seem to give me an oversized hole on small parts. I actually use a drill bit of the correct size, but wack it thru as quick as I can, so there is a slightly rough finish in the hole. Then I will give a fairly deep knurl on to the pin or shaft so that there is plenty of grip, and a dab of loctite is put on the joint to be.

After rough assembly, I actually use the v-groove in my grinding vice to line things up. Tighten the vice up so the shaft is held fairly tightly in the groove, then tap both disc and shaft down until the disc touches the ends of the jaws. If the v-groove is square to the ends, then you should end up with a disc square to the shaft, like mine do. You can do that with both crankpin and shaft.

You can buy over and under reamers, but for the number of times that I would use them, I couldn't justify buying them, as I get perfectly good results by doing it as I do it now.


John

[Stilldrillin]

Dave,

Next time you`re at mine...... Gimme a nudge re undersize reamers. 

Unless 10/ 12/ 14mm is too large....... 

David D