Lockdown is getting to Ed
Bob
The only thing lock-down has prevented is coming up to Surrey to whoop your **** to find that bell-housingLockdown is getting to Ed
Bob
Ah but he's not the real one - I was taught by the real one.but prof green is a DJ, a good one
They ain't cheap anymore - mainly because they're mostly just metal and therefore expensive. It's basically just a transformer so beautifully simple. RS have some - you might want to look for an alternative though...How much is a variance and where from?
the torque of a universal motor will be next to nowt at that sort of speed
I understand that perfectly (Despite the rather condescending overtones), but what that graph is showing is the breakdown of torque due to loading of the motor - not reducing voltage which is what we are talking about in this case.
I understand that there was a lot of maths but what part of torque is inversely proportional to speed don't people get? It's less the faster you go!
Here ya go, a picture.
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Lack of cooling I agree is an issue
The main problem I can see with doing something like this is the speed which you will need to run an angle grinder at for polishing.
Polishers typically run at a max speed of around 3000 rpm, and angle grinder will likely have a no load speed of ~12,000 rpm - so you are going to have to run it at a max of 1/4 speed - the torque of a universal motor will be next to nowt at that sort of speed however you decide to do it (Variac, PWM whatever...a fancy pants speed sensing system that compensates as speed drops off from setpoint might give you more of a chance, but your not going to knock one of those up in 5 mins), so as you put more pressure on it (Polishing requires a fair bit of pressure) the motor will just stall. Added to the lack of cooling at that speed, and increased amps I reckon you will cook an angle grinder in short order, esp given that polishing will likely involve prolonged operation - not just a quick blast.
If you wanted to try something then my first suggestion would be an Aldi or Lidl 5" grinder with variable speed, which are usually to be had for £20 or less - they have a rear handle and 1200W motor - but even so when you dial the speed down you can noticeably feel the torque dropping off (I use mine with a wire brush). But really, I would think you might be better taking the plunge and looking for a cheap dedicated polisher (which will achieve the speed reduction through gearing - instantly giving you a torque advantage.) on Gumtree/ Facebook free sites etc
You might get more joy using it on a jigsaw, which probably isn't as torque demanding as polishing, but I picked up a variable speed jigsaw from Aldi for £7 (Albeit quite a few years ago now...) which is still going strong - I don't think I would risk cobbling something together if I had a decent jigsaw.
And what I was saying is that the effect you are seeing is an effect of the power supply not the motor. It is not delivering the current required to sustain the torque requirements demanded by the motor.I understand that perfectly (Despite the rather condescending overtones), but what that graph is showing is the breakdown of torque due to loading of the motor - not reducing voltage which is what we are talking about in this case.
If you reduce the voltage the shape of that curve will be broadly the same but shifted considerably to the left. So, reducing the voltage in order to reduce the speed does reduce the torque available. I can demonstrate this by stopping the spindle of my angle grinder by hand at it's lowest speed setting (The speed controller is just a crude voltage regulator)- if I increase the speed setting to it's maximum I wouldn't have a hand left if I tried to grab hold of it from a standstill. Or perhaps everyone else's experience of torque dropping off is also incorrect .
@Parm How about a slow-start grinder with variable speed control? That way you could have some control over the important things in the project.
I bought one which was very cheap [Amazon, eBay....can't recall now but Iirc it was sub £20] - it must have been for me to lash out to make it my 6th angry grinder..... I'll check make [def won't be Milwaukee ] in the afternoon.
EDIT: No time like the present, it was an online Aldi special offer a wee while back
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