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GRANT LAIDLAW
Grant Laidlaw is currently the owner of the Air Conditioning and Refrigeration Academy ( ACRA ) in Edenvale . He holds a Bachelor of Business Administration and an associate degree in educational administration . He has a National Technical Diploma and completed an apprenticeship with Transnet . He has dual-trades status : refrigeration and electrical . He has been involved with SAIRAC for over two decades and served on the Johannesburg committee as chairman and was also president between 2015 and 2018 . Currently he is the SAIRAC national treasurer .
WORKING WITH A TAPER BUSH
By Grant Laidlaw
I have found that many technicians do not understand how to fit or remove a taper bush .
Andre asks : Grant , Twe have a special problem - when working on units with pulleys or couplings we find that the taper-lock bushes are always broken in half , any idea as to why ? Thanks .
Hi Andre , yes this is an interesting question , In most cases it is not necessary to use a hammer or any excessive force to remove a taper bush . In doing so , one causes the damage which you are referring to . In addition incorrect installation could result in pulleys wobbling , vibration , excessive wear of components , or in fact - a catastrophic failure of the taper bush . necessary . The system is highly reliable ; such failures as may occur are mainly due to misapplication or incorrect procedures . Let us have a look at the concept . The bush which clamps onto the shaft has an external taper of 8 º. This fits into a hole in the hub of the pulley / coupling which has exactly the same 8 º taper . Grub screws are used for fastening and removing the bush fit into holes drilled half in the bush and half in the hub . One half hole is drilled right through , and has a thread tapping . The other half hole is drilled part way , and offers a clearance to the screw .
It is very important to note that the holes used for fastening the bush have their threads in the hub of the play or coupling . Do not use the other holes as this can damage or cause misalignment to the taper bush .
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The taper lock bush , also referred to as a taper bush or taper fit bush , is a locking mechanism commonly used in power transmission drives for locating pulleys , sprockets , and couplings to shafts .
RACA Journal I October 2022
A damaged taper bush .
Pulley with taper bush and grub screws .
The taper lock bush is pre-bored and keyed to match the required shaft and keyway diameters .
This allows tight , concentric clamping of a pulley or coupling onto a shaft , and subsequent relatively easy removal when
Fitment and removal of a taper bush
When fitting a taper bush the allen screws are tightened pushing down on the end of the hole which is not through-drilled , driving the bush deeper into the bore of the hub . As the hub bore is tapered , and as there is a ra dial split with clearance in the bush , this action results in the bore of the bush being squeezed tighter , with very great pressure . According to the size of the bush , there are either two or three holes where this tightening is done . Gradually tightening the grub screws in a sequence ensures that the bush is pulled up uniformly .
The removal procedure involves removal and transferring of the grub screw ( s ) into the removal hole ( s ). When a grub screw is transferred to this hole ( s ), and is tightened , the forces are reversed , instead of pulling the taper bush into the taper the bush is pulled out of the taper . As this happens , the taper bush can expand , loosening the fit around the shaft . The taper bush should slide off the shaft with relative ease .
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