Spindle Speed Measurement using Variable Speed Motor Drive
|1008 forum posts|
Passion for exact speed?
Possibly because a lot of people don't have the confidence to know by look and feel how fast is actually right. So they want to refer to charts and speeds and feeds.
But those who do go off appearance and feel, and can adjust feeds to match speeds to give a balanced result should remember that perhaps at one stage they did not have that facility, and they too looked at their charts and feeds and speeds?
Edited By meyrick griffith-jones on 05/02/2010 18:18:12
|chris stephens||05/02/2010 18:30:21|
|1045 forum posts|
As one has come to expect, a reasoned and informative posting from the said West country gentleman.
I hope no one ever says you have to have DROs or VFDs, but if you have them, they do make work a little more pleasant and less fraught with mishaps.
|1198 forum posts|
Aye, cynical with good reason pet. Many years ago I worked in the Textile machinery design trade and three customers making the same end product , each had exactly the same machinery but running at within 10's of revs to each other to achieve cotton wool with NO discernable difference but all adament that THEIRS was the correct speed.
My own lathe has eight speeds and my miller has four. Plenty to pick from, so if the new guys have a problem with such a limited range how the devil are they supposed to cope with zero to whatever??
Regards, the cynic
|1008 forum posts|
Circlip _ I'm all for a bit of cynicism.
I used to stalk deer commercially, and if ever (beyond fishing) there was an occupation where the latest gadget was king - of which there was the most fantastic quantity, almost all imported from the US-- and almost all completely useless and serving no purpose other than to lighten the pocket (of the inexperienced and enthusiastic) and make a simple thing complicated - then I never saw it..
So no, I wouldn't change a cartridge, or bullet, or borrow a knife or bother to look through the latest binos with the greatest laser whatnot and GPS pre installed. I just stuck to very good quality simple kit which really worked. The test was only this. Was it useful? Would it actually make life easier? If it was then I never worried how much I had to pay for it. If it didn't then I wouldn't carry it even if it were given free.
And so it is with a DRO. It passes the test - lathe or mill.
As for spindle speeds, personally I like geared or belt driven heads, because you get an increase of torque at low speeds. IOW, I don't like my sine waves chipped. So I have levers on gearboxes which tell me my speeds. Thats fine. As you say, the odd extra or fewer revs will make no difference at all. But less torque is a crime. So IMO, varispeeds serve little useful purpose. But if someone comes up with a torque increasing controller at reasonable cost, then I'll look at it.
(And for all those who have the latest and greatest controllers which amplify everything - I know. My MSc was to a great degree in control engineering. So we wont go down that route, because as we all know the basic principle of stiffness holds with high amplification. As you increase amplification to overcome the gaps, the more difficult it it to retain smoothness of transmission. (So says the Nyquist diagram or Bode plot for almost all feedback loops unless you resort to some quite clever and expensive programming) OTOH it is one of those little things a Victorian gearbox does rather well. )
Edited By meyrick griffith-jones on 05/02/2010 20:58:06
|1504 forum posts|
And to think that all this started out as a question about measuring spindle speeds!
For that purpose I use, when deemed necessary, a hand-held tachometer got via Ebay from the USA, no doubt made in China. It works a treat. Once a speed has been checked, it can be remembered by the noise the machine makes (near enough).
|Ian S C||05/02/2010 21:36:48|
7468 forum posts
|Theres still people using foot powered lathes-would'nt have a motor, not enough control! Ian S C ps Thats not me.|
|1198 forum posts|
Well, after the latest triadibe and swarf slinging, just seen on another foureye that a car type rev counter with a "Hyundi" cam position indicator was used to look at the shaft speed.
Just as an aside, if you're listening to the "Noise" Robbo, save the cost of an electronic Tacho.
|1008 forum posts|
Well come on - measuring a spindle speed isn't a 2 page problem.
You buy/make a proper unit as Les Jones suggested, or you buy a hand held tacho - optical or vibro - of which there are many. End of discussion really?
Or you can put your finger on it and see how hot it gets in how long, to get an answer like slow, fast and sh..ugar.
|3309 forum posts|
|Do you think this one has been "spun" out for long enough? [and I have VFD and DROs on four machines!!]|
|Steve Garnett||06/02/2010 16:21:36|
|837 forum posts|
I don't care what the absolute speed is, either on a mill or a lathe. But in the past, in a noisy environment with several machines running, knowing that a mill has slowed down slightly under load when you can't hear it clearly has been useful information - and to find this out effectively means that firstly, you need to know pretty accurately what speed it's actually running at, in order to resolve the differences, and secondly that this speed indication should be independent of the driving system - so using the analogue output from an inverter won't do. Also, I don't particularly want to do this with a hand-held tacho either - I've tried that before and whilst it might be okay for some, it's not for me.
Obviously I recognise that this generally wouldn't apply in a home workshop, where generally only one machine at a time is running, and you can hear what's going on. But that still leaves the 'anal' reason for wanting to know, of course...
As for DRO's - well, what Meyrick said, as far as I'm concerned. But my DRO is definitely in a case!
|Stub Mandrel||06/02/2010 22:14:26|
4311 forum posts
I built a tachometer, largely because I wanted to get into AVR microcontrollers and it looked like a good starting place. It does have one really good use, that I haven't seen mentioned elsewhere.
With a fairly small, low powered machine (mini lathe), one can keep an eye to how much the revs drop when you put on a cut. It's surprising how much you can increase the depth of cut/feedrate before the revs drop more than a few percent, and it's a much kinder approach than waiting for it to stall, start labouring or popping fuses.
FWIW I also replace the fuse with a circuit breaker.
|Steve Garnett||07/02/2010 11:26:47|
|837 forum posts|
So you didn't read the post previous to yours, then?
|Ian S C||07/02/2010 12:13:50|
7468 forum posts
|It would give you a comparison between sharp and blunt tooling,and also the effect of cutting oil.Once you'v checked the rpm against the speed control and perhaps noted the speed/ possition you will rarely need the tacho on the machine. Ian S C|
|Bill Davies 2||24/09/2020 19:01:08|
|197 forum posts|
Found this on our website:
Go down the page.
|Bill Davies 2||24/09/2020 19:03:00|
|197 forum posts|
Ooops, added to the earlier thread; go up the page!
|Peter G. Shaw||24/09/2020 21:40:24|
1170 forum posts
The easiest method is to use a cheap & cheerful bicycle speed computer. These devices have to be set to match the wheel diameter, and on the one I bought, this can be adjusted down to about 100mm diameter or thereabouts. It is necessary to then experiment to see what the display shows - I used my lathe which has 9 fixed speeds.
If you can find them, try ME page 432 dated 11 Apr 97 where Ron Wallman describes the idea and in issue dated 04 Jul 97, DAG Brown recommends the Sigma Sport BC500. Also, MEW178 (Jul 2011) where Michael Cox describes a cycle computer with a RPM range.
Peter G. Shaw
|Pete Rimmer||25/09/2020 19:09:40|
|781 forum posts|
Many good lathes fitted with variable speed have also been fitted with a tacho or speed readout.
Rivett 1020, Smart & Brown 1024, Holbrook minor, Monarch 10EE - all top-bracket machines. If those manufacturers saw fit to fit them then it's perfectly reasonable for a machine being retro-fitted with variable speed to also have one fitted.
|241 forum posts|
Pete says "Many good lathes fitted with variable speed have also been fitted with a tacho or speed readout." mine is only mediocre and has one fitted. Mill and Drilling machine share at the flick of a switch.
Variable speed power feed is also a good option. An Amp meter fitted to the main motor leads will help keep from overload when using a heavy cut.
|ANDY CAWLEY||26/09/2020 08:23:42|
|172 forum posts|
I checked the spindle speeds of my Chinese import lathe some yeas ago using the sweep hand on my wrist watch, a length of all thread, a nut and a felt tip marker pen. All of these items were in my shed so I didn’t have to spend any money.
I put two marks on the rod as far apart as possible. Whilst holding the nut by hand I ran the lathe at various speeds and timed its travel between the two marks. Having measured the distance between the marks and knowing the pitch of the thread it was simple enough to calculate the rpm. I made sure the free end of the rod was inside the tail stock to guard against the possibility of flailing should the rod get out of hand. I was very conscious of this possibility however things never really showed any signs of running amok.
The speed control on the machine was a simple rotary knob so I put marks on the machine casing using the marker pen and wrote speeds against the marks.
I make no claims about the precision of this method but it was good enough and dead easy to do and it got me going with the lathe. The further apart the marks are the more accurate the results.
|Ron Laden||26/09/2020 09:04:44|
2010 forum posts
I added one of these to both the mill and lathe, cheap as chips reliable and accurate. Comes with a 4 digit display and easy to fit, there is always a place somewhere on the mill and lathe where it can go.
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