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Post by spooch63 on Mar 19, 2022 23:37:55 GMT 1
Put a thread on recently regarding taper lock bushes, unfortunately I haven't been able to resolve the problem. So then, the flywheel on my rotovator is held on with a taper lock bush. Not something I've come across before but after some investigating I'm now familiar with the concept and how they work. The problem is this, the shaft diameter is 18.50mm, in metric the sizes go up in mm's, the 18mm is too small (tried gentle persuasion and it shattered) 19mm is too big and won't nip up. When converted to imperial 18.5mm equates to 23/32, no such size available. I'm now thinking that if I purchased an 18mm could the centre be bored out on a lathe to the size I need. Hence I may if its possible need someone with a lathe to bore out the centre of an 18mm to the size I need. More then happy to pay for your services. I've put the link to the part below so anyone with a lathe and the skill can tell me if this is possible. I've contacted several companies that supply the bushes for advice but none of them had replied. As usual although it's not bike related I'm on here asking for advice and help. www.ebay.co.uk/itm/223387056698?_trkparms=ispr%3D1&hash=item3402e7fa3a:g:umYAAOSwzSlhw1dt&amdata=enc%3AAQAGAAACoPYe5NmHp%252B2JMhMi7yxGiTJkPrKr5t53CooMSQt2orsSvtkx670Z0m Cheers Paul |
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Post by cb250g5 on Mar 20, 2022 0:13:10 GMT 1
That's going to be a fun job.
Things to think about:
Because of the split, it's going to be difficult to bore, as it will just expand out of the way of the cutter or get squished in by the action of the chuck or vice used to hold it. Probably be best to mount it in the pulley (or flywheel or whatever) or make a fixture with the right taper. How big is the flywheel? Does it have straight edges so it could be held in a chuck. It might be easier to mount in a vice on a mill and use a boring head.
If you take some out of the middle, the effective size of the keyway will now be too small. Are you using the keyway? If so you'll either need to broach the keyway out a bit more, or reduce the keys height a bit.
Have you considered using some shim steel and taking up the difference with a shim all the way round, apart from the keyway. I think that would be my first approach to this, but then again the flywheel is probably too big for my lathe, I only have a 3.5" swing.
I've used these on the motors on my lathe & mill, I think they're a clever idea, for mounting pulleys to shafts. Not seen them used for flywheels, or anything other than pulleys.
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lc2
Weekend rider
Posts: 84
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Post by lc2 on Mar 20, 2022 8:28:55 GMT 1
A simple job to do ,I have a lathe but zero free time. Look in your area for anyone involved in model steam engine building and no doubt you will find someone to help out.
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Post by ozzysbikes on Mar 20, 2022 9:21:35 GMT 1
Just a thought, might be easier to do on a milling machine as it's easier to hold by clamping it down and use a fly cutter, I don't think it will open up when machining if it's done right with small cuts but if not it could have a clamp round the outside which would be held down on the taper by the clamps holding the bush in place ?
Alternatively can the shaft that it's going on be machined so that it's a straight fit job in future ?
Just thoughts 🤔
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Post by tony2stroke on Mar 20, 2022 9:35:54 GMT 1
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Post by jon on Mar 20, 2022 10:59:17 GMT 1
That's going to be a fun job. Things to think about: Because of the split, it's going to be difficult to bore, as it will just expand out of the way of the cutter or get squished in by the action of the chuck or vice used to hold it. Probably be best to mount it in the pulley (or flywheel or whatever) or make a fixture with the right taper. How big is the flywheel? Does it have straight edges so it could be held in a chuck. It might be easier to mount in a vice on a mill and use a boring head. If you take some out of the middle, the effective size of the keyway will now be too small. Are you using the keyway? If so you'll either need to broach the keyway out a bit more, or reduce the keys height a bit. Have you considered using some shim steel and taking up the difference with a shim all the way round, apart from the keyway. I think that would be my first approach to this, but then again the flywheel is probably too big for my lathe, I only have a 3.5" swing. I've used these on the motors on my lathe & mill, I think they're a clever idea, for mounting pulleys to shafts. Not seen them used for flywheels, or anything other than pulleys. I would have thought the split would ‘bottom out’ when tightened in a chuck if one of the jaws was on the split? If it did it would be a simple case of finding something to fill the slot before tightening. The key way height too would be minimal with only 0.25mm removed. Only down side is the outside taper holding it in the chuck there would be very little contact. Finest of cuts may be alright? spooch63 if your stuck I’ll give it a go. PM me if interested. Jon |
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Post by cb250g5 on Mar 20, 2022 11:58:02 GMT 1
I may be overthinking this, especially for a rotovator, not sure how high they rev, or how precision they are, but if you squeeze the bush fully closed, and bore it to 18.5mm then there's no split left to grab the crank. If you bore it a bit less, then it won't be quite round when squeezed down to 18.5. Probably not enough to matter in this application.
Grabbing that taper in a lathe chuck, getting it square, so the shaft is concentric with the lathe spindle, not at a slight angle is going to be a fun set up job. Hope it doesn't move when boring, the jaws will only be holding the end of the taper.
I'd still start with some 0.25mm shim stock and make a collar for the crank.
The key should be a precision fit, There's a formula for size & length and depth split between shaft & pulley. You don't want it loose. I can't remember the details, but I could probably find them if the OP is bothered, I know the shaft diameter comes into it, and if I remember right you measure depth not from the top of the round, but from where the slot reaches full width in the shaft, IE where the cutter first engages both sides. It'll be ISO something or other. Assuming the manufacturers followed a standard, and with a 18.5mm shaft, maybe not.
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Post by jon on Mar 20, 2022 12:08:50 GMT 1
Sorry didn’t check my wording. I meant to say I wouldn’t have thought the split would bottom out.
But as I said even if it did it would just require a flat piece of metal the same width as the groove to stop the bore reducing and going oval. Tightening the chuck would clamp it.
As for the key way we’re talking key height. 0.25mm will not be enough to affect it.
Jon
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Post by spooch63 on Mar 20, 2022 17:38:49 GMT 1
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Post by spooch63 on Mar 20, 2022 18:20:16 GMT 1
I've managed to upload some photo's of the parts.
First two are of the flywheel although I guess it's a pulley of sorts, It's about 250mm diameter and weighs about 3kg.
Third obviously is the shaft diameter it fits on.
Next is the engine, very common lawnmower/rotovator engine
Next few are of the output shaft on the engine.
This morning I put the 19mm in the vice and made the gap wider on the lock bush with a hack saw just to see what happened. On fitting it back in the flywheel it did nip up nice and tight but on removal it came out in two pieces which didn't surprise me but thought I'd give it a go to see what happened.
The thing that is confusing me is that the engine is a very common engine and so you would have thought that it should be relatively easy to replace the part I need, obviously not.
I've looked at shim steel as suggested, I only need a small piece and can't find a piece small enough on ebay, smallest piece is £18.
So, plan B, I've found an engine in my shed buried under a load of other stuff as you do that I didn't know I had. I've measured the output shaft which is 3/4 inch. Pretty sure I can replace the Briggs and Stratton that is currently fitted with this engine. I'm hoping that if I ordered a 3/4 taper lock bush it will fit without any problems then swap the engines over. If that fails then it's back to square one and a pm to Jon.
This taper lock bush system seems like a very complicated way to do what I would have thought is a simple job.
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Post by cb250g5 on Mar 20, 2022 19:49:45 GMT 1
The advantage of the taper lock is that they only have to produce 1 centre for each size of shaft and 1 pulley of each size and then you can mix & match to your hearts content, much easier than each size of pulley with each possible size of hub. Anyway, 0.25mm is as near as damn it 10 thou www.ebay.co.uk/itm/254033765586Would do the job I reckon. Looking at your pictures, is the bit the flywheel sits on worn compared to the outside bit? It may just be a bit discoloured. |
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Post by steven on Mar 20, 2022 23:32:58 GMT 1
Hi,
Its a Briggs and Stratton, so American, so I would hazzard a guess it will most deffo be imperial.
Steven.
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Post by JonW on Mar 21, 2022 0:06:46 GMT 1
Silly thought? Have you tried some of the US B&S parts suppliers to see if they have the part you need? My thinking is that if the shaft came with the motor then they must have something thats fits it? Else what about NOS parts from the rotorvator company?
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Post by stirling11 on Mar 21, 2022 13:51:15 GMT 1
Not so silly Jon, I was thinking the same thing, beware though that some B&S engines are actually metric
The USA is slowly being dragged kicking and screaming into the 21st century when it comes to fasteners etc, no offence to our US based audience
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Post by spooch63 on Mar 21, 2022 22:40:56 GMT 1
Silly thought? Have you tried some of the US B&S parts suppliers to see if they have the part you need? My thinking is that if the shaft came with the motor then they must have something thats fits it? Else what about NOS parts from the rotorvator company? Rotavator is probably older than most of us on here and the company went out of business many years ago. Tried everywhere to find a NOS part, even the specialists can't help. |
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