"Spehro Pefhany" wrote in message
...
On Tue, 10 Jun 2008 16:53:01 -0400, "Ed Huntress"
wrote:


"Spehro Pefhany" wrote in message
. ..
On Tue, 10 Jun 2008 14:43:26 -0500, Ignoramus13673
wrote:

This lathe is advertised as 20 HP:

http://cgi.ebay.com/ws/eBayISAPI.dll...m=300231171003

I do not doubt that the ad is true, but I have to wonder why any lathe
would need a 20 HP motor. I have hard times imagining how even a
fraction of that could be expended cutting metal with a single point
lathe bit.

Material removal rate-- there are various tables, and, as always, it
depends on various factors, but by one rule of thumb 20HP would remove
about 30 in^3 per minute of steel or maybe 100 in^3 of aluminum.

If you want to turn something 12" in diameter down to 3" over an 8"
length, that's um.. around 850 in^3 if I did the math right, so it
would take almost half an hour for steel and 10 minutes for aluminum
if HP was the limiting factor.

Which reminds me of a cartoon we ran in _American Machinist_ in the
mid-'70s. The caption was, "Why productivity is so low in the Soviet
Union."

So, what did the cartoon show?
Best regards,
Spehro Pefhany

A lathe operator turning a piece of stock around 12" diameter down to maybe
3" diameter, over an 8" length. Then he held the part up with pride. g

--
Ed Huntress