taper roller headstock adjustment

This method of running 3 phase motors on single phase is well known, Its described in the MAP publication 'Electric Motors'. I also had a milling machine running on this method for over 20 years and no problems with that.

Read my comment and Ketan's response on this page:

www.model-engineer.co.uk/forums/postings.asp?th=130430&p=2

Basically everything you ever need to know about setting bearing preload.

Neil

Here's a good reason to take the time to make sure your headstock bearings are correctly preloaded. It makes a huge difference to how long the bearing lasts. And on some of the older British industrial lathes they can cost many hundreds of Pounds to replace.Some Colchesters its about 600 quid.

As can be seen, lifespan drops off dramatically if preload is too much. And almost as bad if preload is not enough.

So it really is worth, on larger more expensive machinery, to take the time with the required string around a disc of specified diameter and a spring scale gauge to get exactly the required pounds of force required to turn the bearing as specified in the manual etc. .

Edited By Hopper on 11/05/2020 05:16:08

I did the string wound round the chuck setting some years ago. With the lathe warm if you spin the 4 jaw chuck by hand with the gears all disengaged it turns about 11/4 turns before stopping. The headstock gets barely warm after prolonged use but I use 550 rpm most of the time. Actually I use this speed because it seems to suit nearly everything and it's the quietest! I am going to fit a vfd to reduce the motor noise and vibration, I've ordered one on Amazon last night. Chinese so I won't get it for a while. I've already got a chinese one on my drilling m/c and I'm very impressed with it. I got a 2.2kw one because the motor doesn't have a plate on it so I'm not sure of the HP. I've read through the 1947 letter from Timken, that's the one which says pre-load isn't a good thing which seems to contradict the graph above.

I havent seen the Timken letter from 1947 but I imagine things have moved on since 1947. I've rarely come across taper bearings that did not specify preloading in the factory manual etc. Harley wheel bearings, set cold in the workshop, being the only exception.

Let us know how the VFD goes. I've been thinking bout one for my Myford as its 1hp single phase motor sets up an annoying buzz in the drip tray that does not seem to sit flat on the bench. Might try rubber mounting the motor first though.

Edited By Hopper on 11/05/2020 08:53:22

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Hopper

Thanks for posting that interesting ‘conceptual diagram’ ... but, in the complete absence of X & Y axis scaling, it is only one [uncalibrated] step up from the ‘arm-waving’ explanations that we get from AstroPhysicists.

Do you know of a version with at least some more numbers on it ?

... or even just an indication of whether the sales are linear or logarithmic

MichaelG.

Hi Michael,

Perhaps This link page 6 may help.

Ketan at ARC.

Michael,

Although I have given you the above link, I do think it is quite right for the subject being discussed.

Ketan at ARC.

In automotive applications, preloading leads to premature failure, but in a machine tool application, some preloadi is needed to maintain accurate location. BUT, as the graph shows, excessive preload WILL shorten bearing life, so use the minimum advised by the bearing manufacturer.

The preload for a particular bearing, or set of bearings, may well be expressed in terms of linear measurement.

Even if not stated to be 0.00X" for a particular machine, it may be expressed in terms of a number of degrees of rotation of the adjusting nuts, such as "Zero end float, then tighten by 30 degrees", based upon the pitch of the adjusting thread.

So don't overdo the good work, unless your hobby is changing bearings!

Howard

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Many thanks, Ketan

‘though not quite on this topic, it has numbers, etc  ... which is a great advantage

MichaelG.

Edited By Michael Gilligan on 11/05/2020 19:00:58

Just for information, you can check the bearing preload quite easily.

On the M250 when out of gear it should take 0.9 to 1.1Nm to turn the spindle if the preload is correct.

This can be checked by wrapping a piece of string around the periphery of your chuck and pulling with a spring balance. The load to get the spindle turning gives the torque.

By way of example:-

Torque is force x distance, the distance in this case being the chuck radius. For a 160mm dia chuck, the radius is 80mm or 0.08m.

The force required to give 0.9Nm at this radius will be 0.9/0.08=11.25N. Dividing by 9.81 to get Kg gives us 1.15Kg. Similarly for 1.1Nm we get 1.4kg. So if your spring balance value is between these figures then all is well.

Better than a spring balance is to hang on weights. 1.1kg mass - no go and 1.4kg gets it rolling. Better as long as their is sufficient space, of course.