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Useful Speed Ranges

sublime to ridiculous, variable speed for a dinosaur.

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russell12/11/2009 03:13:23
142 forum posts
G'day all
 
I have an ancient (1915) drummond 'B' type lathe, originally treadle driven, now motorised using a non-descript induction motor and poorly matched step pulleys.
 
On the weekend i picked up a complete treadmill (AUD20!). This includes a fairly standard 180v motor, 4300rpm (allegedly 1.2HP).  I am intending to transplant this to my lathe.
 
My question is, what sort of speed range should i aim to achieve? A quick survey of cutting speeds suggests a range of 25RPM (tough steel, 8" diameter) to 4000RPM (Al, 1/8" diameter) (assuming HSS).
 
Instinct tells me 4000 rpm is not reasonable for a plain bearing lathe, especially mine!.  But what is a reasonable top speed? 
 
Does anyone have an opinion on  the benefit (if any) of using a countershaft compared to a single belt? 
Should I implement a stepped pulley to give a mechanical range as well as variable?
 The lathe has back gear, so i ex[ect that the 'low' speeds will be achieved that way, so the loss of power at low speeds is perhaps not a concern.
 
Finally, i propose reusing the speed control from the treadmill. it also incorporates a speed display, which i hope i can also transplant.
 
all comments welcome...
 
russell
 
Ian S C12/11/2009 10:59:47
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7468 forum posts
230 photos
Is the motor AC orDC,the only one I'v seen was DC,but if you have the power supply that goes with it thats good.Proberbly pay to keep the motor revs up,but the lathe maximum would not be more than 700-800rpm,and most of your work will proberbly be half that.You would be best to use a counter-shaft to drop the speed,the counter-shaft driven by a 1450rpm motor is about 4-500rpm,so you'v got a lot of revs to loose.IAN S C
russell12/11/2009 11:25:13
142 forum posts
thanks Ian, thats the info i need. Any other opinions?

The motor is DC, with i assume some sort of PCM controller. There is a 3:1 reduction pulley set as part of the treadmill.  I could simply replace the current  motor and keep the existing countershaft and pulley- which would probably give 4 or 5 to 1, plus the second counter-shaft to lathe reduction.  

Next difficulty is to put a sensor onto the mandrel so the speed readout will be directly proportional regardless of gearing, then somehow calibrate...

regards

russell


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