Usually when we talk about swing, it is the diameter of the largest item, so for instance a centre height ot 3.5 inches like my Myford is a swing of 7 inches. It used to be that Americans went by swing and Brits by centre height, presumably so that they could fail to communicate more effectively!

But anyway, while I don't have any experience of either of these machines, my feeling is that these variable speed drives are fine for slowing the machine down for light work, but not so good for serious machining of big items. This is because the maximum torque at low speed is no more than it was at high speed, when for turning large diameter items you really want more torque at the low speed. This is especially true for turning a cast iron flywheel, where you may need a decent cut to get under the hard skin that castings often have. So although my own Myford has a VFD, the pulley steps and the back gear still get a fair bit of use when larger items come up, since you can step the speed down and then take a decent cut. It takes long enough at slow speeds, without having to reduce the cut to a mere skim. Also, if you are having to take light skims, you will probably want to use HSS tooling rather than carbide, the carbides tend to work better if you are removing a decent amount.

It does all depend though…if you are only doing a very few large jobs, you can probably put up with them taking a long time. You can also do things like taking off the hard layer with a grinder before putting it in the lathe, so long as you don't overdo it.

John

Well I was going by the previous post that mentioned a Myford which I doubt will be able to remove as much metal as yours. Maybe a Myford owner could comment on what feeds, speeds and DOC they would use on a 9" flywheel casting particularly with HSS but even if I'm using 1/4 of the DOC that they would be using the fact I'm running at 300rpm rather than 40 means I'm able to take 7.5 cuts in the same amount of time as it won't take them to do one deeper cut.

Actually quite pleased with what Mine is removing in those videos 10.5" dia, 300rpm, 0.025" DOC 0.003"/rev is approx 0.75cu in/min considering it's at 1/3rd power and we know Warco have a habit of quoting input power not what the motor puts out.

As for turning capacity, having has a lathe that could only turn upto 8" diameter for a number of years it was very limiting in the choice of stationary engine models that were available this is mostly due to designs being produced that could be built on a Myford which had a narrow gap bed which was able to accomodate the common 9" flywheels seen on many models. So Mark, if your main interest is in stationaly steam then I would look to something that can swing 9.5 – 10" which puts you into the "240-250" size lathes if looking for new.

I only saw motor power, which did not state output or input. But makes no odds if you need a 125mm centre height lathe.

If you really want torque you must use backgear on a hobby lathe

Quickie jobs are not a big deal but if you need it for any length of time then backgear is the only way

Whoa! Slow down. Wrote a longish post about motor power the other day, but never mind, it was boring and I won't repeat it. Instead, ask yourself the questions: 'How fast do I need to cut metal', and 'does the extra time taken by a 0.75kW rather than a 1.1kW motor matter?'

I wish machine tool adverts quoted both input and output power plus the graph needed to relate input power to torque over a speed range, but alas they rarely do. So, unless it says otherwise, best assume the power advertised is Input and that the motor isn't continuously rated. (Duty cycle is far more important than power rating, because it limits how long a motor will run before overheating. A motor rated at 750W input continuous, is likely 'better' than a 1.5kW output motor, 25% duty cycle.)

Murky waters, but in practice it may not make much difference in a hobby workshop, even though I'm more attracted to vendors quoting honest output power rather than sales speak. For what it's worth, a wattmeter on my 1.5kW hobby lathe, a WM280, shows it's difficult to take cuts deep enough to fully load the motor. Apart from the unpleasant spray of red-hot chips it produces, the lathe isn't quite rigid enough to be worked that hard. Putting a bigger motor on this model would probably be a pointless waste of money. The only valid reason I can think of is to maximise low speed torque, but some sort of back-gear would be a lot more effective if a lot of slow cutting is on the agenda.

Bear in mind a motor rated at 750W out will deliver more power than that in short bursts, which may be 'good enough': just be careful not to overheat the motor and electronics.

There is no perfect lathe, especially when held back by budget and location. Whatever you get will be a compromise, it's just that some will be closer to what you need than others. My advice, don't dismiss options too quickly!

Dave

Edited By SillyOldDuffer on 30/03/2021 10:01:48

Not in my experience of running variable speed mills and lathes for 14years

Overload breaker just trips on my machines, switch off to reset it and good to go again

Never turned the speed down to slowest/zero just leave it where I want it and press the green/red button.