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Mini Lathe

Turning True

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David Watson 303/03/2020 16:37:45
44 forum posts

I hope I am note repeating anything already covered. Having more time in the workshop recently I have found a problem with the Warco Mini Lathe I inherited a few years ago from my late father. I know its only a Mini Lathe but it has a lot of plus points compared to my old ML2/4.

I have always struggled to turn material true. Today I turned a piece of mild steel 1.5" long in the three jaw chuck and supported with a centre in the tail stock..The cut was plus 8 thou at the chuck end.

Could this error be adjusted out by re-aligning the tail stock.

Neil Wyatt03/03/2020 17:20:01
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Posted by David Watson 3 on 03/03/2020 16:37:45:

I hope I am note repeating anything already covered. Having more time in the workshop recently I have found a problem with the Warco Mini Lathe I inherited a few years ago from my late father. I know its only a Mini Lathe but it has a lot of plus points compared to my old ML2/4.

I have always struggled to turn material true. Today I turned a piece of mild steel 1.5" long in the three jaw chuck and supported with a centre in the tail stock..The cut was plus 8 thou at the chuck end.

Could this error be adjusted out by re-aligning the tail stock.

Hi David,

Yes, the tailstock is adjustable and it's best to assume it isn't set accurately as supplied, as it may well have shifted during transit. It's fairly easy to get it pretty much spot on.

I posted this in another thread some time ago:

There are two screws, one at the back of the headstock and one underneath. The tailstock clamp screw also locks the arrangement, so it is a bit of a fiddle. I made a brass gib for mine (Clarke CL300M) to make it easier to get free adjustment, but for now I suggest you go with loosening both screws then retightening to get as near to smooth but shake-free movement as you can get. Make sure no paint has wicked onto the sliding surfaces. Lock the tailstock barrel in place using normal force.

A basic alignment is just to have a centre in head and tailtock and align them using short sight or a loupe magnifier. If both centres are sharp and accurate this gets you surprisingly close.

Interposing a steel rule will highlight any misalignment very well.

A practical test is simply if turning between centres gives you a bar of constant diameter - you can turn away a lot of bar chasing (and overshooting) the last fraction of a thou this way.

Best practice is a dial test indicator held in a chuck and used on the tailstock outside surface to check it reads the same at both sides (and hopefully up and down).

The 'practical' route, as used by LBSC and others is a long 'test bar' between centres with the centre turned down by 50 thou or so to give you a long 'cotton reel' with flanges at the ends. Turn the 'cotton reel', and then skim the tailstock flange lightly, reverse the bar and skim the other end at exactly at the same setting. Use an indicator held in the toolpost to take readings from the flanges and when they both indicate the same the bar is parallel.

Keep the bar safe for future use.

.

Neil

Howard Lewis03/03/2020 17:31:34
6104 forum posts
14 photos

Since you were using the Tailstock, it is possible that the Tailstock is 0.004" off centre, away from the Toolpost.

Or the centre in the bar was off centre! If you drilled it in the 3 jaw, it might be!

The best way to check this is:

Take a piece of bar, as long as possible to fit betwen centres, and pass through the mandrel.

If possible, use the 4 jaw chuck and set to run true as closely as possible.

Face the end, and centre drill it

Reverse the bar and face and centre drill

Remove the Chuck

Fit a soft centre.

Offset the Toolpost by 30 degrees

Skim the centre to true it up

Remove, and if the other centre is soft, repeat. If the other centre is hard, fit it to the Tailstock

Mount a DTI on the Toolpost, and set to centre height..

Mount the bar between the centres.

WITHOUT rotating the bar, at any time.:

With the Saddle at the Headstock end, set the DTI to Zero.

Traverse the saddle to the Tailstock end, and note the reading.

Based on what you have said, so far, the DTI is likely to read - 0.004".

Adjust the tailstock until the DTI reads Zero at both ends.

Take a test cut, and hopefully, the diameter will be the same at both ends.

Do tell us how you get on

HTH

NEIL beat me to it!

Howard

Edited By Howard Lewis on 03/03/2020 17:33:29

Howard Lewis03/03/2020 17:42:10
6104 forum posts
14 photos

Take a look at another Thread on here "Beginners Guide to Tailstock Alignment"

Aligning the Tailstock will be time very well spent!

Howardl

not done it yet03/03/2020 19:00:36
6809 forum posts
20 photos

My first thought would be to try a shallow cut on a rigid bar of easily machined material with a very sharp cutter over a similar distance without the tailstock support. The lathe should cut parallel.

40/50mm aluminium bar, over a distance of 100mm, might be a good starting point?

Little point in setting the tailstock centre if the lathe bed is twisted?

David Watson 303/03/2020 19:05:27
44 forum posts

Thanks folks. I centre drilled the end of the stock before I started turning and it appeared to be in the centre. I always thought there was a problem with the tailstock . At the back of the tailstock there is a label with lines on it and a mark on the tailstock. These show the tailstock being about 1/2" out of line. with any of the marks. I always thought the markings.were wrong, it cant be that far out I hope.

The lathe has had a lot of moves before I took it over and there are signs of it may have been dropped or something dropped on to it. I will take the tailstock off tomorrow and give it a good clean before I start. The screws at the back of the tailstock stock are covered in paint. To make life easier I may swap these to cap headed bolts.

I will update with a progress report after a day of tinkering tomorrow.

David Watson 304/03/2020 13:04:40
44 forum posts

After a morning of sorting the tailstock I found some strange things. The screws at the back of the head were well painted in,not helped by being deeply recessed and slotted. There was no locking bolt underneath and there was a bush in the hole for the main clamp bolt preventing any side ways movement.

I removed the bush and replaced the lock bolt. The two screws at the back had to go back in untill I get some better screws. To get enough movement to move the tailstock side ways I milled out the hole for the main clamp bolt.

After reading the advice I realised I dont have a centre for the headstock, I have a MT2 live and rotating centre but no MT3 for the headstock. I made a live centre in the three jaw chuck to mount a bar between centres and ran a gauge along the bar. I found an error of five thou at the tailstock end.This accounts for the error I had.After lunch I will try turning between centres again.

After adjusting the tailstock the marks on the back are nearer but not quite in line. I wounder if the tailstock has been messed with when my father owned the lathe or is this the way it was delivered. I dont think it had been used much, I saw it in three workshops before I inherited it.

I still find the Mini Lathe meets all my needs. They cant be all bad considering how many there are out there. As I said my last lathe was a cross between an ML 2/4 and very worn out.

Martin of Wick04/03/2020 15:10:36
249 forum posts
5 photos

I wouldn't fret about it, you have done pretty well.

From new, my mini lathe tailstock came offset in the Y axis and not parallel to the bed with respect to Z AND with a bloody great burr in the MT2 taper AND with the barrel clamping bolt stripped.

So you can see why they have the reputation they have, but once you have taken a bit of time to sort the minor niggles out they are perfectly satisfactory machines for most small jobs.

Edited By Martin of Wick on 04/03/2020 15:12:12

David Caunt04/03/2020 18:14:34
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99 forum posts
38 photos

If the lathe has been moved a lot surely, the first thing to check is that the lathe is mounted firmly and not twisted.

Try Harold,s page at:- www.homews.co.uk/page309.html

not done it yet04/03/2020 19:20:43
6809 forum posts
20 photos
Posted by David Caunt on 04/03/2020 18:14:34:

If the lathe has been moved a lot surely, the first thing to check is that the lathe is mounted firmly and not twisted.

Try Harold,s page at:- www.homews.co.uk/page309.html

Eggzackerly! See my earlier post - at least two of us are on the same wavelength!

Howard Lewis04/03/2020 21:43:36
6104 forum posts
14 photos

If you do not have a soft centre, you can make one.

As a "Quick and Nasty" just grip a bit of bar in the 3 jaw; offset the Topslide by 30 degrees and turn a centre. You now have a centre for the headstock., so that con check the bar between centres (Assuming that the centres in it are spot on ) .

As a longer tem measure, if you do not buy a centre, one can be made by sacrificing an old MT drill. You might be able to scrounge a dud from a local Engineering shop? The shank will be fairly soft, so hacksaw off the flutes.

Having made sure that the taper is clean and free from bruises, it can go into the Headstock and be turned to make a centre.

You just have to keep going round in circles, eliminating, or reducing, errors until you get the result that you want.

Never give up!

Howard

Hopper04/03/2020 22:42:43
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6393 forum posts
334 photos
Posted by David Watson 3 on 04/03/2020 13:04:40:

After adjusting the tailstock the marks on the back are nearer but not quite in line. I wounder if the tailstock has been messed with when my father owned the lathe or is this the way it was delivered.

Disregard the lines on the tailstock. They are only a rough guide, not absolute. When you get it set dead right, add your own scriber mark across the two surfaces.

Howard Lewis05/03/2020 11:44:10
6104 forum posts
14 photos

Quite right Hopper!

Better to believe what your DTI tells you,rather than the graduations on the Tailstock

Howard

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