Member postings for Russell Eberhardt

Not at home at the moment but it works ok on my Android tablet.

Russell.

Professional standard 3D printers are available for under £9k now. Have a look at this video from Denford:

Edited By David Clark 1 on 21/09/2012 21:12:51

Most of the belt conversions I've seen on the web use round plastic belting.

Meadows and Passemore sell it for use on watchmakers lathes. You buy it my the metre and join the ends to make the length you need by welding with a hot knife.

Can't vouch for it though as my X2 came with a timing belt drive.

Russell.

Make one yourself. Turn the taper in situ and it will be spot on, mine (ER32) is better than I can measure, 1/10 thou.

Personally I would avoid the backplate type as there is an aditional interface which can introduce errors.

Russell

O.K. we seem to be arguing over a minor point; what is the definition of efficiency?

In my book the efficiency of any system is the ratio of the energy extracted from the system to that put in. The energy drawn from the system does not include the losses or energy used within that system. So, as Jason said, the efficiency is zero at no load.

Your definition seems to be the efficiency of the conversion from electrical to mechanical energy and includes the friction and cooling fan as output energy. Thus this efficiency will be non zero.

Still we have wandered way off topic. His motor is adequate for the task.

Regards,

Russell.

Steve,

Yes, I did read it.

Perhaps you misunderstood me. A motor that is running with no external mechanical load must have zero efficiency because you are putting power in and getting none out. The power to drive the fan, and the losses in the bearings the iron losses and the losses due to the winding resistance are not part of the output power.

Efficiency is defined as (useful power output)/(total power input} and thus, if a motor is running lightly loaded such as driving a free running grinding wheel, it's efficiency must be very low.

I know it's now 45 years since I studied electrical machines at university but the principles remain the same.

Regards,

Russell

It's a bit more involved than that. LibreOffice and OpenOffice are now developed separately.

See **LINK**

Russell.

1 micron!! That's a 25th of a thou in old money. I can only dream of working to such accuracy

Russell.

Or there is LibreOffice available free for Windows, Mac, and Linux.

Russell.

Glad to hear you have it sorted.

Russell.

Steve,

That formula is correct but the efficiency of an unloaded motor must, by definition be zero as it provides no output power.

His motor is loaded but only very lightly so the efficiency will be much lower than 0.9. What exactly it is we cannot know.

Russell.

Have a look at this piece of free software: **LINK**

It allows you to put in the list of gears you have available and the leadscrew pitch or tpi and will then calculate the best combinations of gears. It will do metric pitches on an imperial lathe and v.v

Russell.

P.S.  It works in Windows and, under Wine, in Linux.

Edited By Russell Eberhardt on 15/09/2012 19:19:55

Agreed. A good inverter will maintain constant torque while reducing the speed so if for example you reduce the speed to half using the vfd the torque will stay the same but the power available will be halved. Halving the speed with the belts will double the torque and maintain constant power.

Like Len I just made a circular scale for the speed control knob. That is more than adequate.

I found the biggest improvement was in surface finish as a result of the smoother torque vs. angle characteristic of a three phase motor.

Russell.

Agreed. With the measured 1% slip an error of 0.5% in the measured speed would give a 50% error in the torque or power calculations!

With an ordinary multimeter the current measurement is likely to be within about 5% but the input power is not given by I x V. Power factor must be taken into account, which is likely to be quite low at such low loading.

I think the only valid conclusion from all the above posts is that the motor is adequate for the job but there is a problem with the converter.

Russell.

Both the torque and the current are directly proportional to the slip up to normal working levels. Motors under 5 hp or so are designed for a slip rating of about 4% at their designed output power. Bigger motors have a lower slip rating. Without slip there is no torque developed. As I said you can load the motor until it's speed drops to about 2880 rpm and get the rated power output.

I do however suspect that his input power measurement is a little off. The bottom line however is that he is currently running at a slip of only 1% so is running at about 1/4 rated power. The motor is more than adequate for the use it is put to.

I must agree with you that an electronic inverter drive is the way to go. My lathe and mill are both fitted with them.

Russell.

As Michael suggested just moving an ordinary hollow ground endmill slightly off axis will acheive the desired result. A bit tricky to calculate the required offset but you can make the cut on axis as you have done then move the cutter back a little at a time until you get a flat section.

Russell.

If it's running at 2970 rpm it is very lightly loaded indeed. Nominal no load speed will be 3000 rpm and fully loaded speed is 2880 rpm. For small degrees of slip ( the speed drop) slip is proportional to load power. Thus if you are taking about 1 hp at the moment you can take nearly 4 hp from it before the speed drops below 2880 rpm (provide of course that it doesn't overheat which would be unlikely for ittermittent loading). More than adequate for your grinder I should think!

Russell

There's one just down the road from me but it might be a bit far for you

Russell

The only real way to measure the power is to power it up and load it with a brake until the speed drops to its rated speed, usually 1440 rpm., then measure the output power. Dificult unless you have or can improvise a dynamometer. Instead you could measure the electrical power input which will be perhaps 10% higher. Again that's difficult without a power meter, amps times volts doesn't work.

I really think your best approach is to see if it will do the job. If it runs slow or overheats it's not powerful enough.

Russell

Good idea Wolfie. That was my first model engineering project:

Link to picture.

Dont know what's happening here.  Tried to insert image into the message as usual but it came up with the wrong aspect ratio whatever I tried so I've added the link instead.

Russell.

Edited By Russell Eberhardt on 09/09/2012 16:42:38

Edited By Russell Eberhardt on 09/09/2012 16:44:43