The Shop > Tools

New (to me) Lathe - Smart & Brown 1024

<< < (3/3)

hopefuldave:
Evening Charles, apologies for the delay - had a few late nights at work :(

I kept the three-speed switch as I wanted to have best-possible torque at low speeds (and the full Holbrook Experience) - the 4-6-8 pole motor gives more torque and usable power (twice as much, at least) in the low-speed (8pole) config' than running the VFD at a low frequency (although I can and do run down as low as 5Hz/2.2 spindle RPM for "jog" and a few special applications), its inductance in 8-pole chokes off the winding current at high frequencies (I go as high as 83 Hz to get the spindle up to 2500 RPM for short periods rather than the original 1500 max.). The Holbrook also has a bit of an inconveniently big gap between the two top speeds, a VFD allows a bit of fine-tuning and some clever stuff like near-constant surface speed for facing and parting (like the Big Boys have on their CNC machines), dynamic braking etc.
I use a configurable relay in the VFD to switch *off* an external fan mounted on the end of the motor when the VFD output gets *above* 30Hz to ensure it gets enough cooling airflow (and it cools it between runs - plus it reminds me I've left the power on!)

As for star points... the Holbrook's motor uses a Dahlander pole-switching setup for the 4 and 8 pole settings (which switches power to the middle of each phase winding of what would otherwise be a delta-winding and connects the "corners" into a "star" point versus just powering the corners) and a separate delta winding for 6-pole use - which is probably why its motor's getting on for the size of a dustbin while only making 3 HP! It takes some thought to get your head around (or mine, at least...)

The RPC is currently coming together (slowly, waiting on the proverbial Slow Boat from...), built on a budget:

5.5 KW (7.5HP) 3-phase 415v 4-pole motor off EvilBay for £70;
Oxford 180A oil-cooled welder (ancient, 240 and 415 tapped primary, 6.5 KVA *continuous* rating, peak 11 KVA - should do the job!) £19 off EvilBay;
32A type-C MCB for 240v input, assorted contactors, 9-13A motor overload (plugs into motor contactor),16A 3-phase MCB, 40A 3-phase RCD (EvilBay) between £5 and £15 each;
Handful of "RUN" rated capacitors for the motor start circuit (50, 100, 200, 300 uF 460 acv - to mix and match) £5-£8 each on EvilBay;
3 off on/off/lamp pushbuttons £1.99 each on EvilBay;
24v control transformer (for contactors and lamps) from my junk pile;
pair of 16A 3-phase sockets (junk pile);
small electrical cabinet with the door cut out and replaced with some Alupanel to take meters, sockets, switches etc., 2.5mm/4mm SY braid-covered cabling to hook bits up, all skip-dived at work :);
lily-gilding: 3 off 500vac meters for phase-to-phase; 3 off 20Aac meters for the phases and a 50Aac meter for the input, £5 - £8 each, guess where; 24v panel lamps for fault indication £1.29 each....

Soooo - a couple of hundred quid, with careful shopping?

The motor and transformer are both a little bigger than I was expecting so they'll be living outside in a kennel built from some leftover Dexion shelves and angle!

The RPC is probably needlessly complicated, but not a patch on the VFD implementation on the lathe...

Dave H. (the other one)
(previously an electrical / electronics engineer by trade, in case you hadn't guessed, now moved on to photons, bits and picoseconds)

hopefuldave:
Not the final wiring diagram, I keep revising it, but a starting point:

Charles:
Wow,

thanks very much for the detailed post :nrocks:

I presume that the S&B motor is the same configuration as the Holbrook one, I wasn't aware that the lower speeds would give better torque, but it makes sense. I would say that's a very good reason to go to the trouble you describe!

I shall have to investigate the condition of the wiring and switch gear before I make a decision on which way to go with this...

Charles:
So, after much delay, the lathe rebuild is inching forwards again.

New house, new workshop, new baby, and my wife suffering from some health problems have pushed this to the back of the pile. but it's now in the new workshop, with the help of a crane over the house as it is too wide for the alleyway  :doh:

 

Once into the workshop, it was lifted off the trolley with a chain hoist & truck on the steel beam in the roof. slid across the steel beam, and then stuck - cheap Chineseium chain hoist refused to lower! Lifted the lathe of the hoist with a precarious arrangement of jacks, stands, and wooden blocks.

 

Strip and rebuild the hoist, lower the lathe about a foot and the hoist jammed again. so, the lathe is now on blocks, about 200mm off the floor waiting for this weekend and a game of workshop Tetris so that I can get the engine crane behind it and finally move it into place...

Meanwhile, I have managed to make a new glass fibre sump - I counted 18 separate holes in the steel one from 50p size down to pinprick. Much as I need the welding practice, I think I would have spent a very long time getting those watertight.

 
Old corroded tray, biggest hole top left, others scattered evenly about the place.
 
Melamine faced chipboard mold, e-glass / epoxy prepreg, under vacuum and ready for cure
 
finished tray, ill add the baffles and motor mount later when I've decided on which coolant pump to use.

Navigation

[0] Message Index

[*] Previous page