Taig Lathe Runout

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I would say this.For a small lathe there is a limit to how accurate you can get it
Forget bed twist and head misalignment etc.If you already within a couple of thou then just try improvement with what you can.Be happy with what you can get.A couple of thou is ok don't think of getting within tenths.If its a small lathe it is possibly just sitting on a bench not bolted down to a solid/flat surface
Make a test piece if possible gripping in a collet and skimming down between centres,max length poss for your lathe.I made one from 1"dia bar x 12" lg
and took light skims with a sharp tool,adjusting the tailstock and bedding it in
If I remember I got the tailstock to +2thou and the test piece to 1 thou taper
Good enough for me.If you want greater accuracy then polish down with emery OR buy a new lathe.Did a thread on it you mind find useful under Bazmak diary of a benchlathe Regards barry
 
I guess it could have a bend, but I think there would be other larger problems that caused this.
 
benster said:
I did try adjusting my tailstock and it was a little out "left to right" I adjusted it to about .0005. However, it's off by .001-.002 vertically, is there some way to shim the Taig tailstock? The way its built I can't think of a way. Also, I've tried adjusting the carriage gibs but they're just at the point where any tighter and it won't slide.
Click to expand...

Been there, done that, on my Taig the solution was to shim the headstock up.

Gerrit
 
I am afraid that despite the well meaning advice, the vertical adjustment of the tailstock or spindle height is 'a Red Herring' or a waste of time to those whose English may be a second language. The concept written by the experts in machine tool design and restoration suggest that come out in favour of what 'Taig' did- and every other machine tool manufacturer In other words, leave well alone and concentrate on what is either worn or badly adjusted.
Benster's remark about 'being half a thous out in lateral adjustment' should be addressed. It reflects a full thous in diameter although a half thous in radius. It may be more or less or it may be less but that is the 'measuured' figure which he alone can provide.
In a small workpiece, this is a substantial matter and needs addressing.

What also needs attention is this 'lapping' thing. I have tackled many machine tool problems and 'lapping' is an expedient to be avoided. I doubt that few here can achieve 25 spots or points of contact by lapping but it can by scraping and bluing- against a known 'reference'.

I'm using 'machine tool' phraseology as in Connolly who still is a standard of good practice. Using a stone to break the crests of the spots is acceptable and expected.

What must be remembered is that a Taig( like ant other lathe) has very little points of contacts on the bearing surfaces and as such it becomes imperative to try get 100% bearing surfaces or a minimum of 25 spots per square inch. If one doesn't get to this state , saddles and shims and whatever will 'rock' A small amount of rock may be allowed in a bigger lathe but certainly not in something so small.

So I can only apologise yet again for what appears to be a 'lecture' but I have actually restored a number of lathes for myself and for friends.
As Barry rightly summarises, you may have to accept lower standards of accuracy than envisaged or if you are unwilling to follow what the experts( not me) have decreed, one buys a better lathe.

Not my words, I am simply trying to put into a very small précis, what runs into hundreds of pages which- I have to remark- have been cited quite recently by other contributors.

Therefore, I wish you greater success in future.


Norman Atkinson
 
I am afraid that despite the well meaning advice, the vertical adjustment of the tailstock or spindle height is 'a Red Herring' or a waste of time to those whose English may be a second language. The concept written by the experts in machine tool design and restoration suggest that come out in favour of what 'Taig' did- and every other machine tool manufacturer In other words, leave well alone and concentrate on what is either worn or badly adjusted.
Click to expand...
Except when you try using a very small centre drill and your tailstock/headstock is misaligned. Snap goes the tip. Sherline made their tailstock chuck adapter adjustable for a reason.

As an expert watchmaker on another forum indicated, for machining Taig, Sherline and the like you need to think differently from 'the big stuff', ala Sieg and up.
 
goldstar31 said:
I am afraid that despite the well meaning advice, the vertical adjustment of the tailstock or spindle height is 'a Red Herring' or a waste of time to those whose English may be a second language. The concept written by the experts in machine tool design and restoration suggest that come out in favour of what 'Taig' did- and every other machine tool manufacturer In other words, leave well alone and concentrate on what is either worn or badly adjusted.
Benster's remark about 'being half a thous out in lateral adjustment' should be addressed. It reflects a full thous in diameter although a half thous in radius. It may be more or less or it may be less but that is the 'measuured' figure which he alone can provide.
In a small workpiece, this is a substantial matter and needs addressing.

What also needs attention is this 'lapping' thing. I have tackled many machine tool problems and 'lapping' is an expedient to be avoided. I doubt that few here can achieve 25 spots or points of contact by lapping but it can by scraping and bluing- against a known 'reference'.

I'm using 'machine tool' phraseology as in Connolly who still is a standard of good practice. Using a stone to break the crests of the spots is acceptable and expected.

What must be remembered is that a Taig( like ant other lathe) has very little points of contacts on the bearing surfaces and as such it becomes imperative to try get 100% bearing surfaces or a minimum of 25 spots per square inch. If one doesn't get to this state , saddles and shims and whatever will 'rock' A small amount of rock may be allowed in a bigger lathe but certainly not in something so small.

So I can only apologise yet again for what appears to be a 'lecture' but I have actually restored a number of lathes for myself and for friends.
As Barry rightly summarises, you may have to accept lower standards of accuracy than envisaged or if you are unwilling to follow what the experts( not me) have decreed, one buys a better lathe.

Not my words, I am simply trying to put into a very small précis, what runs into hundreds of pages which- I have to remark- have been cited quite recently by other contributors.

Therefore, I wish you greater success in future.


Norman Atkinson
Click to expand...

The short form here is that lapping together poor fitting parts of a machine tool is simply bad practice. I know a lot of people don't want to hear this but I had the concept drilled into me in my teens working with an extremely talented machine tool rebuilder.
 
The issue started when I tried to build a spindle for a dividing head and had a .005 difference end to end. Until I can purchase a new lathe I'm going to just design my devices to account for wear/runout etc. It adds extra complexity but will allow me to adjust for the issues I've encountered.
 
benster said:
The issue started when I tried to build a spindle for a dividing head and had a .005 difference end to end. Until I can purchase a new lathe I'm going to just design my devices to account for wear/runout etc. It adds extra complexity but will allow me to adjust for the issues I've encountered.[/QUOTE

Probably the taper for your dividing head is solved fairly easily.

As you will appreciate, the spindle on a dividing head is not exactly like it was designed to rotate at Mach1. Well, none of mine do. I would take up the play with a smear of a filled epoxy such as Devon or even metal filled
car body paste and scrape to fit. My spindle on my Myford Super7B is tapered- intentionally.

As for taking up wear on your lathe ( or whatever it actually is) I would suggest that another smear of 'goo' might correct small problems.

What you have remember about gibs is that they should be pinned and have no rock or movement. Mine- and I've got a narrow guide system on my bigger lathe- has both scraped gibs and plastic filler \as recommended here.

Good luck in your new(er) lathe when it arrives.

Norman
Click to expand...
 
Do you use a standard scraper for this or is there a special scraper for cylindrical surfaces?
 
Apologies for delays but being old, I get phone calls from my grown up kids. One of which has invited me for Easter and the other is going to pick my new/old lathe up.
So your problem? Yes, you need or would benefit from a curved scraper rather than a flat one. That doesn't mean that you need to go out and buy one. At a ;pinch, you could use a boring bar end or even a penknife on soft plastic or even softer metals.

My best scraper is the hollow arm from a pair of scrap lawn edging shears with a b it of carbide lathe tool stuck or screwed in. I have no doubt that once you have the idea roughly, you will find an cost free alternative. Maybe you have access to the right size drill or reamer and you can forget the scraper.

PS, I've given you a 'like' because you are now thinking. Good!

Cheers

Norman
 
So with the attached setup I have 1.021" at the dead center and 1.023" at the chuck. I had dialed in the dead center to less than a thou of center horizontally. I used both calipers and micrometers to measure. The work piece is only sticking out about 1.5". I guess I have to live with it.

DSC_0033.jpg
 
Benster, you have to go back a step, with the diameter of the piece and that overhang you shouldn't need to support the end with a centre. Actually, with that much overhang of the centre the work piece will be forcing the centre over. Now, without the tail stock and centre in place, take a light cut over the piece in the chuck. If it is still tapered, then the problem lies with the alignment of the headstock, which will have to be corrected. If it cuts nice and parallel as is, but not with the centre in, then the problem is with the centre / tailstock, which will have to be corrected.

Paul.
 
This is the article regarding the dead center design.

http://www.cartertools.com/dead center.html

Following Dean's example from.

http://www.deansphotographica.com/machining/projects/deadcenter/deadcenter.html

I don't remember what dimensions mine came out to exactly but it does look about an inch too long. Surprisingly enough, after I got the piece closer to final dimensions of .850" diameter, the taper was less than a thou, or within the accuracy of my calipers - with the tailstock in place.

Like I stated previously the taper is such an issue because I'm trying to make shafts and bearings. This piece is going to be the front spindle bearing for my old craftsman 109. Normally a couple thou would be acceptable, just not when I'm trying to create bearing surfaces like this.
 
Benster,is the lathe fastened down,if so it is possible that the bed has a slight twist and by adjusting the hold down bolts to remove this may be the answer.I have done this to get accuracy on my Myford,just a thought.
Frank
 
benster said:
So with the attached setup I have 1.021" at the dead center and 1.023" at the chuck.
Click to expand...

For the setup as shown, you realy shouldn't need support with a Taig. To loose .002 in such a short distance, something is wrong.

The Taig headstock bearings are supported by a two piece design that clamps the bearings and the bed at the same time. Perhaps taking the headstock apart and clean out the chips and or burrs where the bearings rest.

Perhaps the bed is worn with an hourglass shape where the carriage normally runs.

Is the tool height off causing too much pressure on the workpiece? I find with mine if the tool height is off or the tool is dull it puts too much pressure on the work and then causes tapers on long runs.

I'm sure you may already know about these things, just throwing out what I have experienced with my Taig
 
Carter Tools mentioned above is the best Taig resource out there. Nick Carter is very helpful, answers his emails quickly and has a great knowledge of the lathe.mm
 
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