2" shaft mounting Pt 16: Tollok locking bushes.

*

The arrival of my Tollok TLK110 50/65 locking bushes has at last provided me with a firm mounting for the large saddle.

RS.dk accepted my order but the items were sent over [freight free!] from GB overnight via DHL Express. Tuesday delivery is excellent service for items ordered online on Sunday afternoon in Denmark! Full marks to both companies.

By tightening the multiple M8x21mm, socket head screws the two conical components are drawn tightly together. Since the outer, split component, with flange, cannot expand due to the slip ring [or fitted component] the inner cone must shrink. In doing so it grips very firmly onto the shaft without the need for key-ways, split pins, adhesive or grub screws. A fitted component would enjoy a matching degree of expansion inside its stepped bore. The machining quality and finish for what is an industrial component is really first class. Probably from tumbling in a gravel filled vibrator after CNC machining.

I could carefully mark out the 15 screw positions on the saddle by spotting through the larger flange. Carefully ensuring the correct orientation because the screw holes appear slightly different in spacing viewed from front to back. Though this may well be an illusion caused by the slit. Then I'd use the fixing screws to mount the saddle firmly to the shaft. The band should ensure sufficient retention but I ought to seriously consider turning a sleeve to share the load evenly along the shaft and the bush.

My original idea of trapping the saddle between the flanges via a large hole might be the best theoretical arrangement for stiffness. The flanges would provide even support from both sides. But might easily cause flange lock up before the cones were fully tightened together. Or, the flanges might not meet tightly enough to ensure a proper grip. I'd still need to drill all fifteen screw holes into the bargain. Preferably with slightly oversized holes to avoid circumferential tension as the two component parts shrink and expand differentially as they tighten together. After careful thought I think the best way to use one of these bushes to hold the saddle is to use slightly longer M8 25mm screws with large washers through holes drilled in the saddle. Though I could turn a ring to match the larger flange to 'sandwich' the saddle's channel material. This would avoid any risk of compromising the opposed taper action of the bush or a loose saddle. Tens crews[with washers] spread over such large area is probably as good as it needs to be.

 Here I have separated the components to show the apparently simple, dual tapered mechanism involved. No doubt a great deal of careful research went into optimizing the very large range of sizes in each model.They are available from the dinkiest of sizes right up to the absolutely huge!

The five empty, threaded screw holes are for separation of the cones for easy removal of the bush or its supported component after tightening. The fixing screws are loosened or removed and then five of these same screws are driven through the threaded holes to push the cones apart.

General view showing the split components and the deliberately loose, outer expansion/compression band.

The bore is 50mm in this case with a 65mm outside diameter. While the flange is a very handy 92mm in diameter to provide a firm base for a connected plate or component. The retaining ring is usually removed and the bush used to expand inside the stepped bore of a carefully dimensioned component, usually a pulley or sprocket but not exclusively. Bearings can also be mounted.

A perfect fit on my 50mm stainless steel shafts! No welding, grub screws or Loctite required. Just a hex key to obtain a firm and self centering grip on the shaft simply by tightening the screws alternately to a torque of 41nM or 30.2 lbs/ft. [NB: This torque figure is ONLY for the TLK110 50/65. Other sizes and models have their own torque requirements! Do not use any information here to employ a locking bush for any purpose. Do your own homework using the manufacturer's own literature or direct contact with them.]

The bush should be lightly oiled before use and the screws should be tightened evenly in a criss-cross pattern: 9-3-12-6-2-8-4-10-1-7-11-5, etc. If repeated removal of the bush is expected then the screws can also be oiled.

Tollok's English language catalogue: Catalogo TOLLOK inglese.pdf

The TLK110 details are on page 6. Note that the bore dimensions of the component to be fitted to the bush is vitally important to its designed grip.

The supplied expansion band would normally be replaced by a pulley or sprocket. Since the saddle channel is only 3mm [or 1/8"] thick I had better not try expanding inside that. Though a thicker collar could be turned to fit over the bush to supply the necessary resistance and even give a larger fixing plate for the saddle. A simple tube used in unison with the supplied band/ring would also work in my intended method of fixing.

Longer M8 screws are easily obtained if I decided to use these for holding the saddle with load-spreading washers. This would give the lowest profile fit for the saddle without visible protrusion on the upper face where the tube rings will sit. Since the bush does not move axially [along] the shaft during tightening there is really no need for the mounting shaft to protrude right through the saddle surface. Except as a visual check for monitoring the shaft's precise location. A smaller sight hole would do. Better than having the telescope tube [OTA] suddenly detach without warning having sneaked along the shaft unseen! However unlikely as this might occur in practice. This will depend on the exact details and care taken during fixing.

These locking collars might look relatively compact but a YouTube video shows some really hefty chain sprockets being attached with them! Which means they can cope with some seriously heavy torque and axial thrust.

Click on any image for an enlargement.

*