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Taper-Lock Bushes - tolerances

Limits and fits for taper lock bush

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Simon Williams 329/12/2020 16:40:55
652 forum posts
82 photos

Good afternoon and season's greetings all.

I've been looking for a definitive statement for the shaft size limits for standard taperlock bushes. I have a 3020 bush on a nominal 48 mm shaft which measures 48.01 mm and it seems awful tight to get on.

I want to fit a flywheel to the other end of this shaft, which would involve a 2012 bush, and 48 mm is at the very top of the range of sizes for a 2012 bush. This end of the shaft is presently 48.04 mm dia. Do I need to get nearer to the nominal 48 mm dia?

I've found a passing reference in the Fenner catalogue indicating that (quote) "accommodates shaft limits of +0.051/ - 0.127 mm". My shaft sizes fall inside these limits, but this gives no indication that the shaft tolerance might change with shaft size as I would have expected.

As ever, my thanks for the expertise.

Any ideas?

PS (edit)  It always helps to know the application.  I'm making a simple stone crusher, as I have a large pile of useless stone and several boggy gateways.  And I want to clear the stone but am too tight fisted to pay someone to haul it away.  So I thought the last lockdown would be usefully invested in making a gadget.  

I'll add a link to a Youtube video of its very first outing to a separate post,

Edited By Simon Williams 3 on 29/12/2020 16:51:32

Simon Williams 329/12/2020 16:57:54
652 forum posts
82 photos

Further to my original post reference limits and fits on taper lock bushings, here is a link to the gadget. Yes I know it needs some guards...

PTO Driven stone crusher

The top shaft (crankshaft) is a 60 mm dia piece of EN32, with a throw of 9.5 mm. This lets me use 50 mm self aligning bearings as the main bearings. The outboard ends are turned to 48 mm for the main drive pulley (fitted)l and the flywheel (not yet fitted).

Many thanks


David Jupp29/12/2020 17:16:52
822 forum posts
17 photos

Those values given by Fenner contradict their own statement that the bushes work effectively on shaft with h9 tolerance. The tables I looked at show max size limit for h9 as dead 'on size' (+0 micron).

oldvelo29/12/2020 17:18:41
294 forum posts
56 photos

Hi Simon

One method used when assembling 'Taper Lock Bushes' is insert a 'Fox Wedge' or a flat blade screwdriver in the slot of the bush to open up the diameter slightly.

Then fit it into the pulley-flywheel with the retaining screws done up finger tight only to keep it secured the it will slide easily on the lightly greased shaft. NO grease on the tapers or retaining screws.


old mart29/12/2020 19:28:07
3720 forum posts
233 photos

You could just make it a sliding fit, after all, it is designed tighten up as the tapers are pulled together.

Paul Lousick29/12/2020 21:49:04
2013 forum posts
711 photos

If Fenner state that they "accommodate shaft limits of +0.051/ - 0.127 mm" and your shaft is withing these limits and it won't fit, then the taperlock bush is outside of these limits.

Take it back for a replacement of the correct size.


Clive Foster29/12/2020 22:00:37
3104 forum posts
107 photos

Design tolerance call out is for h9 shaft but they will work, as will clamp down and grip, over +0.051 / -0.127 mm range. But any shaft oversize makes them tight to slide on.

But power transmission and stability may be reduced.

I've seen considerable marking under taper lock bushes fitted to shafts whose precision was clearly less than h9 standards. In retrospect I should have measured things rather than just gone by appearances.


Hopper30/12/2020 00:38:13
6197 forum posts
321 photos

Bang a screwdriver in the slot in the taper bushing and slide it on the shaft to where you want it. Remove screwdriver. Fit rest of pulley. Carry on.

That's what the slot is for: so the bushing can adapt to the exact size of the shaft.

Agonising over 0.01mm (.0002" ) at one end and 0.04mm (.0015" ) at the other is over thinking by far.

If it really bothers you that much, a one-minute polish back and forth with a long strip of emery tape wrapped 180 degrees around the shaft will remove that much metal and bring it to within a micron of perfection.


Edited By Hopper on 30/12/2020 00:40:59

Nicholas Farr30/12/2020 09:33:26
3312 forum posts
1529 photos

Hi Simon, having fitted taper lock bushes many hundreds of times I would say you shouldn't need to worry too much about it being a little tight going on, as suggested, the gap can be used to slightly open the bush with a slow wedge, but do not force it too much as they are cast iron and will break quite easily. However, you must make sure there is a clearance on the top of any key. If you feel you need to have the bush an exact size, you can skim it out by fitting it into a pulley with a close fitting piece of steel in the gap so that you don't close it up under size when clamping it in, but of course you will need a lathe big enough to swing the pulley although you can get weld in bushes to hold them. Yes they must be clean and free of any oil or grease between the bush and the pulley but put a little oil on the screws that clamp it in.

Regards Nick.

P.S. although the taper lock bushes can break easy, they can still be fitted successfully in two pieces.

Edited By Nicholas Farr on 30/12/2020 09:38:43

S.D.L.30/12/2020 09:45:08
236 forum posts
37 photos

If you don't want to wedge open the the taper-lock the shaft should be h9 giving 47.94 to 48.00 so your shaft is a smidgen oversize.

Turn it down or open out with screwdriver.


Alistair Robertson 130/12/2020 10:16:01
144 forum posts
6 photos

We did work for a local quarry and we fitted 100's of Taper-Locks and I can honestly say we never had any problems with them fitting on to often abused shafts and even after years driving crushers with 120 horse power motors they were far, far better than on-size bore pulleys and gears. They survived even when they cracked at the split, in fact we had one fitter who said that if a shaft was a bit rough that they gripped better when split!

Simon Williams 330/12/2020 10:42:05
652 forum posts
82 photos

My my my, thank you all for your enthusiasm.

I have found a reference in a catalogue for Dunlop taper bushes for shaft and hole to be h8/H8.

That makes the shaft limits 47.961 to 48.00, and the hole 48.00 to 48.039. This data is (are?) quoted for the American style with a flanged bush, but it's the best I can find. As Hopper says, a few (more) minutes with some emery will get me in that range.

I take the point about the bush gripping come what may - and I've driven a screwdriver up the slot many's the time, but I was interested to know what the answer should be (and how far adrift I might be).

Thanks as ever

Happy New Year to all


S.D.L.30/12/2020 11:14:39
236 forum posts
37 photos

The h9 tolerance I quoted is out the Fenner download. either way h9 or h8 top limit is 48.000


Simon Williams 330/12/2020 11:38:15
652 forum posts
82 photos

Steve - many thanks for clarifying that. Looks like I have a little bit of work to do.

However you have satisfied my curiosity to find out what the size limits should be.

Best rgds Simon

Nicholas Farr30/12/2020 12:49:20
3312 forum posts
1529 photos

Hi, in this on page 131 Fenner Shaft Fixings it actually says "Taper Lock bushes work effectively on shaft diameters with h9 tolerance. If in doubt please consult your local Authorised Distributor (Nominally +0.05/-0.125mm)

Therefore it is not contradicting its own statement, i.e. effectively means desired size, nominally means above or below reality of the desired size.

As I have stated that I've fitted many a tight bush to shaft and most of which performed in very harsh, vibrating and heavy conditions and all performed excellently without failing or damage to shaft, bush or pulley and very often 24/7 continuous actual hours between shutdowns. They will also work very well without a key being fitted.

Regards Nick.

Edited By Nicholas Farr on 30/12/2020 12:55:52

Simon Williams 330/12/2020 13:44:48
652 forum posts
82 photos
Posted by Nicholas Farr on 30/12/2020 12:49:20:

Hi, in this on page 131 Fenner Shaft Fixings it actually says "Taper Lock bushes work effectively on shaft diameters with h9 tolerance. If in doubt please consult your local Authorised Distributor (Nominally +0.05/-0.125mm)

Well spotted sir, thank you.

That's the sort of definitive statement I was hoping someone would find. I didn't have a copy of that exact document in my library of design information - and even if I did it's in mighty small print! But it answers my original query very neatly, even if the size range quoted seems to be at odds with h9.

I'm a happy bunny!

Best rgds to everyone.

S.D.L.30/12/2020 15:25:11
236 forum posts
37 photos

h9 is clearly the intended shaft tolerance, I suspect the numerical tolerance is the range over which the taper locks should work

holding the h9 Will probably make removal easier if needed


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