Thread: Wow - huge price difference

Originally Posted by nearnexus

You recon your a bit rusty, but your still way ahead of me on this stuff

I just hope the 2 HP DC motor has enough power in comparison to the existing 3/4 HP AC unit - which is ideal.

Rob

I'm not an expert on the comparisons between AC motors and their equivalent in a DC motor but I would have thought that HP is HP is HP and that a 2 HP DC would trump a 3/4 HP AC motor. Can't be too sure though.

Even if DC motors are less efficient and the power rating is the amount they draw and not what they put out, you are still 2.5 times the power of the AC motor.

Simon

Thanks Simon.

Regarding the HP rating difference between AC and DC, the one thing that suggests that power may not be an issue is that the existing AC motor has an RPM of 1450, the new motor has 4300 RPM, a factor of nearly 3X.

As I want the new motor to spin the lathe up to about 2000 RPM (V's the current 1800) it means I will be gearing the new motor down with the pulley system by 3:1.

That should produce a pretty massive torque effect for the same spindle speed.

Throw in the supposed HP difference and things get interesting.

If you get my drift

Rob

Love it when a plan comes together!

I have been looking at the underside of the photo circuit board. It's doing my head in!

I'm not sure what the function of U1 is. Not sure if it's an op amp or something. Some one else may know. the wire configurations seems to be what I said but the photo interrupt is powered directly from the red wire so if you give it 12V then it will receive 12V.

R1 is simply to limit the current in the output
R2 + R4 seem to play a part in setting the input current for the diode
R4 also acts as a clamp or pull down resistor for the signal output

Don't know what U1 does

BTW does you lathe have a gearbox to change speeds? If so, are you planning on bypassing the gearbox and put the pulley on the spindle or still going through the gearbox?

Cheers,

Simon

U1 looks like an op amp, is there a no. On it? If it is an op amp the signal will probably be inverse, not that it really matters.

Had to go get the jewelers eye piece for that one.

U1 looks like LM393 or LM398 - damn near impossible to read.

No gearbox on the lathe, all belt drive, and am using the existing pulley system except for the motor (4 step pulley) where I am using a single step pulley same size as the existing lowest gearing size (but that's fine as it's the one you use the most for the various speed combinations.

BTW my LCD digital hand held tacho arrived this arvo ($12 delivered which started this thread).

It's great. I tried it out on a few things ( lathe spindle, lathe motor, bench grinder) and it's super stable and seems pretty accurate.

I also tried it with a chalk mark rather than the reflective tape and it worked quite OK. You have to move a bit closer with the chalk but it's no big deal.

Also it works right down to just a few millimetres which is much closer than the spec says, so it could be crammed into pretty tight places if you wanted to make it permanent.

A mate made up one of the Jaycar kits years ago that had a very similar function and this is way way better than that. The Jaycar one was very feeble and hopeless in light conditions, and I don't think it used a laser, just a photo cell of some sort.

Nice big LCD display on this one too. It's not worth the price Jaycar are asking, but at $12 it's damn good. Pretty gutsy laser on it.

And I even got a free battery with it - beat that

Rob

It's an op amp/linear comparator. It has 2 inputs, it compares the 2 input voltages and turns on or off depending on which is higher. Basically it is just there to clean up the signal to a true square wave, as what comes out of the sensor may not be clean.

Just to add to that, r2-4 probably make a voltage divider to give the LM393 something to compare the voltage from the sensor to.

Thank Ueee, I'm none the wiser.

This is all way beyond me. So in the Queen's English how do I connect this sensor up?

I really appreciate you and Simon's help on this.

If this is not the best way, let me know. I don't mind spending a few dollars to get the right result.

Rob

Heh - I think the Chinese are reading this thread! I went looking for one of those $12 laser tachos when you started this thread, and managed to get one for about $10. Just clicked on the item description wondering if mine was likely to arrive with a battery, and they're now listed for about $20! Perhaps the 240 odd they've sold with free postage have actually cost them money.

Good to know that chalk lines work, means you don't have to bother digging up reflective tape all the time! It should probably work with a white paint pen too, I suppose..

G'Day Fellas,
Just got in after a truly psycho day in the field, here are a couple of quick photos of the sector plate and sensor and rough temporary housing for the display. I need a shower, a feed and a couple of drinks, so see yuz later,
Martin

Originally Posted by Ueee

It's an op amp/linear comparator. It has 2 inputs, it compares the 2 input voltages and turns on or off depending on which is higher. Basically it is just there to clean up the signal to a true square wave, as what comes out of the sensor may not be clean.

Just to add to that, r2-4 probably make a voltage divider to give the LM393 something to compare the voltage from the sensor to.

Give that man a Cigar! Ewan I think you are right on the money with that. Also, do you think Rob should run the photo sensor straight from 12V or bring down the voltage to about 5V?

I think he should be OK to run the green (signal output wire) straight to the signal input of the tacho. With the input impedence of the tacho and the buffered output from the op amp it should be all good. Just don't know about driving it at 12V.

Simon

Originally Posted by toolman49

G'Day Fellas,
Just got in after a truly psycho day in the field, here are a couple of quick photos of the sector plate and sensor and rough temporary housing for the display. I need a shower, a feed and a couple of drinks, so see yuz later,
Martin

Thanks for the pic toolman. I think i will copy your setup when my tacho arrives. If I'm happy with the outcome then I may even lash out and buy another for the mill!

Cheers,

Simon

Originally Posted by nearnexus

BTW my LCD digital hand held tacho arrived this arvo ($12 delivered which started this thread).

It's great. I tried it out on a few things ( lathe spindle, lathe motor, bench grinder) and it's super stable and seems pretty accurate.

I also tried it with a chalk mark rather than the reflective tape and it worked quite OK. You have to move a bit closer with the chalk but it's no big deal.

Also it works right down to just a few millimetres which is much closer than the spec says, so it could be crammed into pretty tight places if you wanted to make it permanent.

Nice big LCD display on this one too. It's not worth the price Jaycar are asking, but at $12 it's damn good. Pretty gutsy laser on it.

And I even got a free battery with it - beat that

Rob

Yep. Once again thanks to another thread a while back I ended up buying one of them too. Very handy indeed and same same about repeatability and stability. My only gripe is that it seems every time I go to use it (once every 3 months or so) the battery is flat! I think I'll store it without the battery in.

Thanks for the info on your lathe. I was just wondering what people did when they convert to variable speed electric motors if they have a gearbox. Ideally I would love to by-pass the gearbox if I put a variable speed motor and have the motor connected by pulley straight to the spindle but I'm not sure if that's wise. This treadmill motor I have ATM runs flat out at 5000 RPM which is 2X what I would possibly ever need!

By-passing the gearbox is probably making the set-up more complex than it needs to be. I just thought it would be nice to remove some of the unnecessary gear noise.

Simon

Simon there is another thread going about which lathe to buy, and one being considered was the TL250V Titan which is variable drive.

It just direct drives to the spindle via one of two spindle ratios.

Titan Machinery - TL250V PIC

But if you have a gearbox you would still need to take the gears out of mesh somehow to stop them freewheeling off the spindle, with the alternative drive system being used.

Gets complicated.

PS regarding the battery going flat on the LCD tacho I did notice that when you put the unit back into it's snazzy little blue carry bag, it can very easily turn itself on in the bag just from light pressure on the switch. Maybe that's what's happened ?

Regarding the optical sensor voltage, I do have a 7 volt DC powerpack - would it be wise to try it off that first ?

Rob

Originally Posted by simonl

Give that man a Cigar! Ewan I think you are right on the money with that. Also, do you think Rob should run the photo sensor straight from 12V or bring down the voltage to about 5V?

Simon

I would go to 5v, not knowing what voltage it should be run off makes it hard. Unless of course Rob you can hook it back up and test the supplied voltage? I would just use a 7805 reg. But that leads to another question, do you buy a reg or just buy a HE sensor? The problem is you still may need an op amp to get a clean signal from the HE, not a problem for me, i have some left over LM335's from from the last analogue thing i made, but it's a bit more of a problem for you Rob. Then of course you need to make voltage divider etc.
If you can hold off till after next week i will be back and should have the sensors and taco and can tell you what you will need to do.
The 7v from your plugpac will not really be 7v, unloaded it will be more like 10 or 12.