Drill with synchromesh????

See:-
http://www.tool-net.co.uk/data/index.php?ToolID15811
The drill supposedly has a "three speed synchromesh gearbox"! :-)
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Chris Green

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snipped-for-privacy@isbd.co.uk wrote:

If you do a google search for this drill (Metabo Bst 12) lots of the descriptions claim it has a "three speed synchromesh gearbox". Curiouser and curiouser.
More to the point none of the sites seem to agree on its torque or the battery capacity.
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It presumably means you can change gear while the motor is running .. if you want to.
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I went and took a look at the Metabo site and they describe it as "3-level planetary gear" which makes a bit more sense.
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Yes. A planetary gear may be changed under full power with no distress - car autos have been doing this for years.
A car type synchromesh system wouldn't last five minutes without the clutch.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Really? Do you mean you need a 'crash' gearbox to be able to do clutchless gearchanges like you can on a motorbike? I'd assumed that a synchromesh gearbox would make it even easier, but then I have no idea how synchromesh works. (I do know about epicyclic gear boxes.)
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Jan

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If you want to make a habit of it.

Easier, yes. But it doesn't help reliability.

There's a bronze ring with a cone clutch on it and tapered lead-ins for the splines on the sliding member.. When you try to engage the dogs, the ring gets there first. Once the cone has spun to the matching speed, it allows the dog splines to slide freely.
Do too much of it, you wear the nose off the dogs. then the blunt nose jams in the socket, locks solid, there's a bang and the ring breaks into fragments. You're now left with a rather sloppy crash box. On some gearboxes, the exploding clutch can get caught in the works on the way out and do more damage.
Porsche's gearbox design is different and doesn't use the same sort of bronze cone. They're more robust for being used clutchless. OTOH, I believe that if they break, they always lose that ratio.
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A crash box and a motorcycle type aren't the same. On a crash box the gears actually slide into mesh. A motorcycle box is constant mesh with dog clutches to engage them.

Synchromesh uses a friction clutch to 'spin' the gears to the correct speed to engage silently. But it's only designed to work on a box with the drive disengaged. To handle the engine's power, they'd be vast in size, and require considerable effort from the driver.
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Dave Plowman (News) wrote:
But it's only designed to work on a box with the

Do you mean drive disengaged, or just not while under power (ie with the throttle pedal backed off)? We have advanced driver training at work and the ex-police instructors (especially the older ones) often change gear without using the clutch. I do it myself when the mood takes me, and the higher gear changes seem effortless. Changing down is a bit more awkward (matching revs) but it's a potentially useful skill in case the clutch cable breaks.
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wrote:

That would be because "advanced drivers" are all too much a smartarse hazard for everyone else _ESPECIALLY_ older police drivers.
Why would you change gear in a modern gearbox without using the clutch? What advantage does this convey ? Make a habit of it on a V6 Carlton or some of the more powerful but weaker-boxed Sierras and you were just asking for trouble (and look at the scrap pile round the back of a police garage)
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If you match the gear speeds through careful use of the throttle etc, there's no need for any form of synchronizer. This was the basis of double declutching - needed with crash boxes.
However, if the speed isn't exactly matched, the synchromesh cones, which are a form of friction clutch - will try and do this, and if under load will either not succeed or be subjected to loads they're not designed for.
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On Tue, 26 Oct 2004 23:22:10 +0100, "Dave Plowman (News)"

Just how old are you ? 8-)
There are plenty of "crash boxes" with dogs - pretty much anything post war. They're not sliding-gear boxes, they're not synchro boxes, but in the absence of a better term we call them crash boxes just the same.
Motorbikes have the advantage of a sequential shift too - they can shift from one ratio to the other with a lot less faffing about than a wobbling joystick.
What was the last crash box in production ? Landies ? bottom cog in Heralds ?
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On which car? I'm not familiar with commercial vehicle practice and was only referring to cars.
Rover for one made a constant mesh box with dog clutch engagement - pre WW2 - but it was hardly a common arrangement with cars. And it was mated to a freewheel which makes down shifts less of a problem.
All the cars I can think of - made up until the advent of all synchro boxes round about '70 - had a 'crash' first gear, where the gear teeth were normally out of engagement. And this practice continued much later with reverse gears.
There were a few earlier all synchro boxes on some cars, but these were usually three speed. Or not actually - commonly a four speed with first blanked off. Early Austin Healey and some Triumph models for example.

But they don't have synchromesh. A slight - or even not so slight - 'click' on engagement might well be acceptable on a bike, but not in a quiet car. There's also the question of feedback of this action through the lever.

Pure genuine crash box with no synchromesh at at all on any gear in a car? Something dating back to the early '30s, before Vauxhall introduced synchromesh in the UK.
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wrote:

yup, you can drive cars clutchless in dire necessaity but you do have to get the revs dead on.
NT
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On 27 Oct 2004 snipped-for-privacy@meeow.co.uk (N. Thornton) wrote:

I used to drive my parents' Mini like that. It was a '59 Austin Se7en with the original 3-synchro magic wand box, not the later all-synchro baulk ring type. I found it was easier if I pressed the dipswitch with my left foot in order to get the timing right (not at night of course:-).
The synchromesh on those boxes didn't last long anyway, so I had to double de-clutch on my driving test. That was nothing to do with me driving clutchless of course (my mum had previously learnt to drive on that car - say no more).
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The early boxes were cone synchromesh but soon replaced with baulk ring. The all synchro boxes were very much later.
I don't know why it took so long for BMC to introduce baulk ring synchro to the A Series box - the B Series one had it in the early '50s.
The Mini probably made the problem worse - the extra inertia of the transfer gears.

It's probably easier to change gear without the clutch with no or poor synchro anyway - it tells you if the revs are wrong much sooner. ;-)
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Good box - internals were used in the Cooper Climax F1 car as well I believe.
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I very much doubt it. It was barely up to handling the torque of the original Mini. Later ones were beefed up.
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wrote:

That was the old 1.5 litre F1 and it only had to last 3 hours. I expect the parts were selected and heat treated though.
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Right. Of course you could completely replace the internals. IIRC Knight made a 5 speed conversion with straight cut gears. Sounded wonderful.;-)
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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