Thread: The Real Speed

Hi issatree,
You can waste a lot of time worrying about speeds, but now that you have variable speed, you might try what I do with mine. Start slow with a new bowl blank/spindle blank, wind it up till it looks about what you would normally turn at, take a cut and keep adjusting for optimum cutting, and then slow it back for sanding. I never look at the pot, except to wind it back to slow to start with.
Will be interested how you get on,
rgds,
Crocy

Originally Posted by issatree

Hi All,
Not that this really worries me, but it would be nice to know Precisely what the Correct Speed wood be.
I bought a S E W Eurodrive Inverter for my Tough Lathe to make it Variable, but I suppose I was a bit Stingy in not getting the next Model up ( an extra $200. ) that had the Speed Read Out. Mine reads out in Hertz.
I know, that 50.00 wood probably be 3000 RPM.
So for eg. say my Lathe was doing 21.7 Hz, what would my Lathe Speed be.
Just not too good on Maths.

If you have a 4 pole motor (1440 RPM) on your lathe at 50Hz you motor shaft speed will be about 1450 RPM then your lathe spindle speed will depend on your pulley ratio, I have an inverter on my Tough and have the belt set on the middle pulley and rely on the Hz readout and intuition to judge my speed, I just adjust the speed until it feels right, I haven't moved the belt since I put the inverter on and that was about 10 years ago.

If you had spent the extra for the speed read out you will most likely only have the motor shaft speed not the lathe spindle speed.

Hi Crocy, Phil,
Crocy, I only do small stuff, so therefore I don't have to slowly turn the Speed up.
I just thought, it would be nice to know, that's all.
Phil, My Tough's Belt is on the Top, so I'm almost sure that it would be around 3000 RPM.
I do use it slower for some jobs. I also haven't moved my belt for at least 4 + years.
Being a 1HP. Motor, Should have been 2HP. I kind of need the Speed, or that's what I tell myself, anyway. I'm reasonably sure it is 1440 RPM.
One is a bit silly as I thought a bit later, that 25Hz. would be about 1500RPM. then halve that again.
I find that for 1 job I do quite often, I sit it on 23.5Hz. So that would be approx. 700RPM. ???.
Thank you Both for your input.

Originally Posted by issatree

Hi Crocy, Phil,
Crocy, I only do small stuff, so therefore I don't have to slowly turn the Speed up.
I just thought, it would be nice to know, that's all.
Phil, My Tough's Belt is on the Top, so I'm almost sure that it would be around 3000 RPM.
I do use it slower for some jobs. I also haven't moved my belt for at least 4 + years.
Being a 1HP. Motor, Should have been 2HP. I kind of need the Speed, or that's what I tell myself, anyway. I'm reasonably sure it is 1440 RPM.
One is a bit silly as I thought a bit later, that 25Hz. would be about 1500RPM. then halve that again.
I find that for 1 job I do quite often, I sit it on 23.5Hz. So that would be approx. 700RPM. ???.
Thank you Both for your input.

Some things to keep in mind:

• If you have the belt on the top speed with a 4 pole motor (1440RPM) running at max hertz your head stock spindle sped may be as high as 10,000RPM mine is any way (calculated out) this will bugger your bearings in the head stock
• Torque is what you are looking for as your speed increases available torque drops off that is why a bigger motor is needed, I up sized to a 11/2HP motor and I have never run out of torque
• It is possible to calculate your head stock spindle speed, you will have to make some assumptions, if you have a 4 pole motor assume its 50Hz speed is 1440RPM, 25Hz will be half that 720 RPM and 100Hz will be 2880 RPM these are motor shaft speeds allowing for losses (friction,efficiency and windage from the cooling fan etc..) then you will have to use the formulas to calculate your headstock spindle speeds for each belt configuration at each frequency (Hz) setting.
• The other thing to keep in mind is if a motor is run for any length of time at less than half its rated speed (25Hz) you may need to provide some auxiliary cooling for the motor, usually this is achieved by having an auxiliary fan with its own supply so it runs at a fixed speed mounted inside the fan cowl so a constant volume of air can be blown over the motor to cool it otherwise your motor can overheat and eventually burn out, a pancake cubicle fan from an electronics shop is ideal for this, the other way and what I did is to put a larger frame motor in (more iron in the motor to dissipate the heat) that is another reason to increase the motor size from 1HP to 11/2HP

I have turned lots of small spindles with my Tough lathe set up this way with no issues, I used-to sell industrial motors and inverters and any woodworker who had the miss-fortune to ask me got the above advice.

If you really want to know the shaft speed this would do it

Digital Tachometer - Jaycar Electronics

If you have the belt on the top speed with a 4 pole motor (1440RPM) running at max hertz your head stock spindle sped may be as high as 10,000RPM mine is any way (calculated out) this will bugger your bearings in the head stock

You sure on that Phil? That is close to 7:1 ratio.

The tough has if I remember correctly a 4.5" motor pulley (big) driving into about a 2" pulley on the headstock. By my calculations that is 3240RPM.

Originally Posted by

You sure on that Phil? That is close to 7:1 ratio.

The tough has if I remember correctly a 4.5" motor pulley (big) driving into about a 2" pulley on the headstock. By my calculations that is 3240RPM.

That is assuming if the motor is running at 1440 RPM. The maximum plated speed on my Tough using a 4 pole (1440 RPM) motor is 3400 RPM so double the motor speed and you double the spindle speed.

What if the motor is cranked up to 3000 RPM? that will give 6800 RPM at the spindle or as in the case of my inverter I can crank it up to 150Hz which brings my motor spindle up to around 4500 RPM spindle speed close enough to 10,000 RPM. I have had my Tough clocked at 10,000 RPM with a tacho just to see what it would do. At those speeds (6000 - 10,000 RPM) you will still bugger the bearings or at the least considerably shorten their life.

Every one I sold an inverter and motor to for a lathe I told them to only run the lathe on the two middle pulleys (limiting the headstock to about 3000 RPM) as this would cover all their requirements without compromising loss of torque at the headstock, the other thing is anything coming off the lathe at high speed is dangerous

Thanks for the explanation Phil.

Yeah, I wouldnt be to hooked up on actual revs. The speed for me is all about how stable the job is, vibration etc. Ok its a judgement call and some folks struggle with that, so I tell them to go as slow as they feel safe to do so. In time and with more experience under thier belt they tend up the speed.

Originally Posted by Jonzjob

If you really want to know the shaft speed this would do it

Digital Tachometer - Jaycar Electronics

Jaycar's price is a little high on this tacho $79.95 for one.

eBay has a similar item for a little over $13.00.

Originally Posted by hughie

Yeah, I wouldnt be to hooked up on actual revs. The speed for me is all about how stable the job is, vibration etc. Ok its a judgement call and some folks struggle with that, so I tell them to go as slow as they feel safe to do so. In time and with more experience under thier belt they tend up the speed.

Exactly Hughie, you have hit the nail on the head, I tweak the spindle speed to reduce vibration (on burls especially). If I want a finer finish sanding or polishing an acrylic pen I wind it up a bit, for bowels I usually have the inverter set at 50Hz or less when I start off. Spindle turning usually 60 - 70 Hz if the spindle is the length of the bed and thin I tweak the speed to help eliminate flexing/vibration of the spindle I hardly ever go above 70 Hz.

The reversing feature is handy for a finer finish when sanding, just have to be careful not to unscrew the chuck.

The other thing if a speed readout is included in the inverter it only gives motor speed not the speed of the headstock spindle.

Originally Posted by Phil Spencer

I just adjust the speed until it feels right...

Phil, it seems to me that knowing what feels right comes with experience.

But, how do you get to that stage and safely?

Watching and listening to an experienced turner as they select appropriate speeds for the various sized piece and stages of the turning process is one way. By watching I mean the piece rotating on the lathe not a tachometer. And by listen, I mean not only to what the experienced turner is saying but also to the piece on the lathe. It's as much about sound as sight. Also touch... putting your hand on the headstock to monitor the level of vibration in the lathe. And, of course, all of the above varies between lathes.

If you don't have access to someone to help you develop your own benchmarks of appropriate lathe RPMs then a tachometer and a reference chart would be a very helpful next best option. The eBay tachometer isn't going to bankrupt anyone and is probably as accurate as we need.

I've never had a tachometer myself, so not sure if I would refer to it if I did have one.

But variable speed is another matter, that is one innovation that I wouldn't like to be without. I'm in the habit of turning the dial back to zero every time I stop the lathe and winding it back up to what feels right as I resume turning or start a new piece or process. A good practice for the novice turner, too, as it is more forgiving if we get our initial pulley setting wrong.

Originally Posted by NeilS

Phil, it seems to me that knowing what feels right comes with experience.

But, how do you get to that stage and safely?

Watching and listening to an experienced turner as they select appropriate speeds for the various sized piece and stages of the turning process is one way. By watching I mean the piece rotating on the lathe not a tachometer. And by listen, I mean not only to what the experienced turner is saying but also to the piece on the lathe. It's as much about sound as sight. Also touch... putting your hand on the headstock to monitor the level of vibration in the lathe. And, of course, all of the above varies between lathes.

If you don't have access to someone to help you develop your own benchmarks of appropriate lathe RPMs then a tachometer and a reference chart would be a very helpful next best option. The eBay tachometer isn't going to bankrupt anyone and is probably as accurate as we need.

I've never had a tachometer myself, so not sure if I would refer to it if I did have one.

But variable speed is another matter, that is one innovation that I wouldn't like to be without. I'm in the habit of turning the dial back to zero every time I stop the lathe and winding it back up to what feels right as I resume turning or start a new piece or process. A good practice for the novice turner, too, as it is more forgiving if we get our initial pulley setting wrong.

Here you go I worked out a range of spindle speeds when I fitted the inverter to my Tough, I did however change the bottom pulley because I had to drill it out to match the motor and I did not know if I wanted to revert back at some time in the future. The pulley sizes are approximately the same as the Tough one.
You will see that having the belt on either of the two middle pulleys should cover all your speed needs.

This should give an idea of safe speeds