The fit of tapers

[HOWARDTParticipant @howardt]

I have used bearings with a tapered inner race in the past for high load situations.

[Martin ConnellyParticipant @martinconnelly55370]

I have designed tooling for fitting items as described by Nick. The drive shaft hub in the tooling is about 250mm diameter for an idea of scale.

The light blue is the shaft, the dark blue is the hub and there is a hollow pancake jack (the brown item with a nominal coupling sticking out the side) to push the hub on to the shaft. Pressure was applied to the jack to bed the taper then oil was pumped down the centre of the shaft to oilways on the taper while the pancake jack kept pressure on the hub. We had to measure how far up the shaft the hub moved after bedding in to be sure it was on far enough. We used CEJN couplings to handle the pressures that went up to 28000psi.

When the hub was removed there had to be a restraint system in place as the hub would otherwise shoot off at very high speed.

The bottom right inset has an alignment hub (purple) shown that was fitted to align the machine then removed for the coupling hub to be fitted later. It was made by a company called Bibbys.

The shaft taper was 1:20

Martin C

[Martin ConnellyParticipant @martinconnelly55370]

Found a photo of a hub similar to the one above being fitted or removed.

Martin C

Edited By Martin Connelly on 29/06/2020 15:20:33

[SillyOldDufferModerator @sillyoldduffer]

Posted by Kiwi Bloke on 29/06/2020 07:36:21:

I suppose the rather unhelpful answer is that the axial positioning repeatability is as consistent as all the variables relevant to the fitting-up procedure. I would think that those (eg torque applied to draw-bar or equivalent, lubrication, etc) would swamp inconsistencies attributable to joint characteristics, material distortion, etc.. This assumes the mating parts are well-made, of course.

Experiment seems to confirm this.

I cleaned my MT2 collet chuck tapers and pushed it hard enough into the spindle socket to take it's own weight plus drawbar. Tightened the drawbar with mild finger pressure and zeroed a DTI before using spanners to apply about another 3/4 quarter turn, at which point definite effort was needed, though I could have gone further. (I avoid overtightening tapers because getting them out becomes violent.)

Tightening the drawbar with spanners lifted the ER32 collect chuck 0.35mm. So linear reset of a taper isn't particularly good because more or less pressure on the drawbar effects it by tenths of a millimetre. I suspect reset would be better if the tapers were consistently cleaned and a torque wrench used. Unfortunately I don't have one.

Dave

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Martin C, thanks for showing your graphics and the method of fitting the hub. Never actually seen it done, but in my old job we had a machine that needed new bearings behind a pair of helical gears that were fitted in this way, we didn't have the gear to do it and it was cheaper to have it farm out to a specialist company than buy such for a one of and hey it was down to them not to mess up to boot, as it was a pricey bit of kit..

Regards Nick.

P.S. couldn't remember the oil inject pressure, but 28000psi may have been a little on the shy side for the gears involved

Edited By Nicholas Farr on 29/06/2020 17:44:25

[Martin ConnellyParticipant @martinconnelly55370]

The couplings went up to 28000psi, the pressure to fit the hub was about 20000psi. There had to be a bit left above fitting pressure in order to remove them when necessary.

Martin C

Edited By Martin Connelly on 29/06/2020 18:06:01

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Martin C, thanks for putting me straight on that. As I say I can't remember the exact injection pressure but 30 something thousand seems to ring a bell and the gears were solid, large and heavy, probably 40 to 50 Kg. each.

Regards Nick.

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