leadscrew reverse

I was looking at some pictures of lathes in the catalogues of certain well-known traders. My wife understands this need and only objects
mildly to the time I spend with 'dirty Gerty', my Myford, in the privacy of our garage.
Anyway, a couple of the mid-sized machines have a leadscrew reverse on a knob at the front of the lathe. This does not look like a tumble reverse. Rather, I guess there is some kind of selector fork behind the panel. The Chester DB10 is an example:
http://www.chesteruk.net/store/product_detail_pages/images/db10_v6.jpg
My question is this: What is going on behind the covers? I can't figure out what arrangement of gears would give a leadscrew reverse from this position. Can you tell me or, better yet, point me to a picture or other explanation.
Thanks
Pete
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On Fri, 12 Sep 2008 22:09:30 +0100, Peter Harrison

Normally it will be a simple sliding shaft arrangement. One position drives the gearbox via the sliding shaft and the other position drives via the sliding shaft and an additional idler gear. The shaft itself may be slid by cams, a fork or by a circular rack with a pinion on the control shaft. It Is possible that the shaft will be fixed and the gears will be slid on it, what ever the designer thought was cheapest!
Mark Rand RTFM
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Mark Rand wrote:

Ah, of course. I think I have it now. I must have used up my week's allocation of imagination early. There is only so much of it to go around. A bit like being nice to people. Someimes I run out of that alarmingly early in the day as well.
I will dig out some Lego gears and make myself a little model.
Thanks
Pete
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wrote:

I think some reversing gearboxes use 3 bevel gears arranged in a U shape. The parallel ones are in line with the shafts and the intermediate gear is free to rotate on a fixed shaft. The input is connected to one of the parallel gears and the output shaft is connected to either that same one or the other parallel gear by a sliding dog. It reverses sort of like an auto differential will when you turn one wheel with the driveshaft stationary and the other wheel goes in the reverse direction.
Don Young (USA)
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