DC Motor Question

[Windy Miller]

Why not just get a bigger AC motor and let the gearbox do the speed control?

I like the idea of having the ability to vary the speed by just twisting a knob. Changing the belts is no massive hardship, but it's handy to be able to slow things right down when cutting up to a shoulder for example.

It's one of those jobs where I'd like to spend a bit of extra time farting about with stuff, and then end up with something that I'm really pleased with in the end!

 

[rikrobson]

The power will reduce with speed with a DC motor. You could just stall the motor instead of making a slower cut. a VFD and AC motor would be better if thats what you want to do. The speed is controlled via the frequency not the voltage, therefore should give you better slow speed power, but the VFD will need to have the correct lower speed.

 

[Windy Miller]

The power will reduce with speed with a DC motor. You could just stall the motor instead of making a slower cut. a VFD and AC motor would be better if thats what you want to do. The speed is controlled via the frequency not the voltage, therefore should give you better slow speed power, but the VFD will need to have the correct lower speed.

I had wondered about that, but according to this http://bedair.org/Tmotor/Tmotor2.html it seems to be OK

 

[rikrobson]

with PWM you are turning on full voltage for a % of the cycle. Therefore at 10% over the whole cycle you are only putting in 10% of the power as the other 90% the motor is off. If the base frequency is high enough it will make a smoother run, but still be only 10% power input.

 

[Windy Miller]

Well I'd be happy to fit a 3 phase AC motor and a VFD if that would work better. The costs (including shipping) of all the parts that DanielW and Pete were suggesting ended up being more than the lathe cost me!

To be honest it's all dong my head in! There is a whole load of information available for modding this type of lathe, and some very good feedback about how the mods have turned out. After reading all the info I can find, I come up with a plan of action, and then I hear that it's not going to be any good. Add that to the exorbitant shipping cost, and I wonder if it's a) worth the hassle, b) worth the expense, and c) any good anyhow. Confusion rules!

It's got the makings of a nice little lathe, and I'd like to get the best out of it. Just wish I could see the wood for the trees!

 

[rikrobson]

I'd use the current motor as a starting point. what make, type, size, power is it?

 

[DanielW]

Well I'd be happy to fit a 3 phase AC motor and a VFD if that would work better. The costs (including shipping) of all the parts that DanielW and Pete were suggesting ended up being more than the lathe cost me!

To be honest it's all dong my head in! There is a whole load of information available for modding this type of lathe, and some very good feedback about how the mods have turned out. After reading all the info I can find, I come up with a plan of action, and then I hear that it's not going to be any good. Add that to the exorbitant shipping cost, and I wonder if it's a) worth the hassle, b) worth the expense, and c) any good anyhow. Confusion rules!

It's got the makings of a nice little lathe, and I'd like to get the best out of it. Just wish I could see the wood for the trees!

Eh! a 3 phsae motor and a VFD cost more than £80+carriage and import duty? so can't see what you're harping on about there.

#post 25

TBH I don't care how I get the job done, as long as I get a more powerful motor

Well you can't throw buttons at it can if ya want the job done.

 

[dannyp]

allways found dc motors take extreeme speed controll better than induction motors

 

[DanielW]

I found a UK supplier for the KB electronics DC motor controllers,was gonna go US import but it works out a few quid more to buy in the uk ie you got the freight and customs duty to consider which amounts to about £45? all in.

At last I can put me treadmill on the mini lathe.

http://www.axiscontrols.co.uk/shop/kbic-range

 

[DanielW]

Laughing.....my mistake its cheaper in the UK...

US £103+£12 carriage plus import from the US

UK £97+£8 carriage.....bit dear for the reverse switch but that just a 240v rating 3 position toggle switch which I can buy for far less than that on the bay but don't need one as their alread one on the mini lathe control panel.

http://www.axiscontrols.co.uk/shop/kbmd-range/9370

 

[Windy Miller]

Good find! I've gone and bought a VFD now, so once I find a 1hp 3ph motor I'll be going down the AC road.

Keep us updated on the progress DW - I'll be interested to know how you get on.

Which lathe do you have?

 

[DanielW]

I've got a brand new 1.5 Hp AC brushless motor(induction) that I was going to use but decided to use a treadmill motor.

I'll be selling this and putting it up on the board for £25 as its just gathering dust.

Just got a normal run of the mill minilathe ie Clarke lathe but have made some alterations/mods to it for better reliabilty ie change the chuck for a larger 4 jaw one instead of the puny 3 jaw self centering effort.

 

[DanielW]

Good find! I've gone and bought a VFD now, so once I find a 1hp 3ph motor I'll be going down the AC road.
Keep us updated on the progress DW - I'll be interested to know how you get on.

Got the controller today via 24 hour courier,expensive for what it is but looking at it it well constructed and good electronic components used,no way am I spending £44 for the forward/reverse switch which really only amounts to £7 in reality from farnell or places like that,cannot even begin to justify £44 for a switch.

 

[Windy Miller]

Any progress on this DW?

 

[DanielW]

None at the moment due to me being a little under the weather all last week and a couple of days into this week.

So alls I've done is tested the 180v treadmill motor on the controller and it seems the motor works fine on it,it does have quite a bit of torque so thats good.
I'm just looking for a suitable timing pully now on ebay as the shaft of the motor is 16mm.
I will also doing away with the tray that these lathes are bolted to(not worth a blow on a ragmans trumpet),I will weld together a 25mm box section frame for the lathe to bolt too and rather have the motor at side back, position it within the frame underneath the lathe so that its out of sight covering the frame with aluminium plate.
Built a rev counter from scratch as the motor has an attached sensor and speed encoder wheel.

 

[Windy Miller]

Well that's a bit of progress at least!

My VFD eventually arrived, so now I need to find a 3 phase motor. Going to try a 1hp one, but I've not yet decided on the speed that I need. At the moment I'm leaning towards a 2800rpm one, and retain part of the belt and pulley system so I can still use the clutch mechanism that comes as standard with my lathe.

I need to work out the ratios yet, but if my idea works out ok I should avoid the need to slow the motor more than 50% and risk overheating due to reduced speed/airflow from the fan. I do have some fans from a server rack that I could fit if it does get too warm though.

I'll get the measurements and work it all out later if I can stay awake long enough after dinner!

 

[DanielW]

I think a 3 phase motor on your lathe is an overkill,work a treat mind but I'd seriously consider in changing the headstock bearings for more expensive set as the chinese standard ones leave a lot to be desired.

Changed em on mine for the STK conical roller type,far better and runout is pretty tight.

 

[DanielW]

there's your three phase motor?

https://www.gumtree.com/p/plant-tractors/ingersoll-rand-3-phase-compressor-£50.00/1129154987

 

[Windy Miller]

I think a 3 phase motor on your lathe is an overkill,work a treat mind but I'd seriously consider in changing the headstock bearings for more expensive set as the chinese standard ones leave a lot to be desired.

Changed em on mine for the STK conical roller type,far better and runout is pretty tight.

Lol yeah maybe it is overkill! I have heard so many conflicting opinions and ideas about this. There will always be many different ways to achieve the same thing, each with its own plus and minus points. There's always more than one way to skin a cat! I'm just going to experiment until I'm find a way that suits me. Good shout on the bearings though - I'll check them out.

there's your three phase motor?

https://www.gumtree.com/p/plant-tractors/ingersoll-rand-3-phase-compressor-£50.00/1129154987

If I bought that I'd want to keep the compressor, and I've run into a serious got no room problem, so I'll steer well clear of that one. Cheers anyway though!

 

[DanielW]

If I bought that I'd want to keep the compressor, and I've run into a serious got no room problem, so I'll steer well clear of that one. Cheers anyway though!

Laughs,thats the way it goes but I would think there's a very good chance of getting your money back and walking away with the motor for nowt.