Does the same thing apply to rotary converters?

I measured my lathe a while back and reported the results in another thread:

'My lathe is a WM-280 fitted with a 1500W 3-phase motor, VFD and two continually running cooling fans. (One on the motor, one on the VFD). How much power does it actually consume in operation I asked myself?

So with belts set to the high-speed range; banjo gears set for fine feed; auto-traverse engaged; and the built-in gearbox set to the finest feed-rate:

• Lathe switched on (ie. with only the fans and electronics running) – 47W
• Motor idling at 150rpm – 210W
• Motor spinning at 1500rpm – 360W

Using 13.7mm o/d steel welded gas pipe as a test piece with carbide inserts and no coolant/lubrication:

• 0.3mm deep cut @ 1500rpm – 542W (A 0.3mm cut removes 0.6mm from the diameter)
• 0.5mm deep cut @ 1500rpm – 540W
• 0.7mm deep cut @ 1500rpm – 565W
• 1.0mm deep cut @ 2400rpm – 960W ( A 1mm deep cut removes about 80 thou from the diameter.)
• Parting off with a 3mm wide carbide blade @ 1000rpm – 600W, lower than expected.

At the finest feed rate (0.07mm per revolution), a 23mm long cut takes about 20 seconds at 1000rpm. I'm too befuddled this morning to calculate how much steel I can remove with 1kWHr's worth of electricity costing me about about 11p.

Taking 2mm off the diameter of a steel rod in one cut is pretty much the hardest I ever drive my lathe in practice. In this test doing so produced a string of smoking blue swarf from the gas-pipe rather than chips. At that rate the lathe pulls less than 1kW, which suggests that I need to drive the lathe significantly harder to stress the motor, and thus have the opportunity to make the carbide inserts work better. On the other hand an unstressed hobby lathe will last longer! (I've no idea what this lathes operational sweet spot is. My car is best if I drive it at a steady 60mph. Lots of stop-start slow speed city motoring is bad for it, as is hammering up and down a motorway at 90.)

Interesting that the belts, banjo and gearbox in fine feed eat a couple of hundred watts before any useful work is done.

Normally I guess I have the lathe burning about 550W during cuts. That's only a couple of amps from a domestic mains socket. I use more electricity lighting the workshop and making tea than I do cutting metal!'

So yes, quite likely a hobby lathe won't use much power.

Fair amount of energy is wasted in my lathes gears. Apart from the screw-cutting banjo there is also a 3-speed gearbox driving the leadscrew or power-traverse. Make sense to disconnect these from the spindle when not needed. The amount of power wasted in the transmission while warming up will be more obvious in a lathe fitted with plain rather than roller bearings. Being a weakling I don't normally use my workshop when it's very hot or very cold and rarely bother to warm my machines up. 'Very cold' in South West England is rarely the same as 'very cold' in Toronto!

Once power has reached the cutter some typical figures for metal removal in Watt-Seconds per cubic mm are:

• Aluminium Alloys – 0.3 to 1.1

• Cast Irons – 1.0 to 6

• Steel – 1.9 to 9

Dave

I was just checking out the warmup chart on the Kitamura CNC at work. It has different warmup schedules depending on how long it's been off. If it's been off for a week, the warmup routine is 4 hours, starting with 20 minutes at 10% max spindle speed! This is as much for lubrication as it is for accuracy due to thermal expansion, I suppose.

I recall trying to kick over an old 45 cu in Harley with straight 30 weight oil at 15°F. I was down to my t-shirt before I got it started.