Tail Stock Adjustment and Steady Rest

[pgk pgkParticipant @pgkpgk17461]

Creating Harold Halls test bar

[pgk pgkParticipant @pgkpgk17461]

Sorry if this is going to be a bit long winded.

I recognised my Crusader Lathe was turning tapers so time to readjust. I've done the two-collar method and got that under 0.01mm over 15inches and then decided to have a go at following Harold Hall's method of making a test bar to adjust the tailstock.

To make the pilot centre drill holes i set my raw 300mm long 1" bar clamped vertically in the angle of a 6" angle plate on edge on the mill.. used an electronic edge finder to find the centres and drilled.. so chould be close.

Mr Hall's article uses the 3-jaw to hold one end with tailstock support.. face as close to centre as possible and turn a 12mm length to 22mm, flip and repeat then set a steady rest at tailstock end and redrill a larger centre.

What worries me is that flipping and using the 3-jaw doesn't guarantee that the two machined sections are concentric and that one has to grip the bar in the turned section so there is no clean diameter at the chuck for setting the steady fingers and the other methods of setting a steady that I've come across: using the tailstock, using a DIY tailstock 4-jaw support or even a mag base DTI on the chuck all (seem to me) to depends on a clean bar round surface or an aligned tailstock?

I guess I'm missing something?

The only way i can see of achieving concentricity along the bar length would be to use the 4-jaw, skim say 1.5" of an inch diameter bar , set the steady then keep extending the bar towards the tailstock with repeat indications and skimming to the same setting until it's length is achieved. At least each section should be concentric with every other and the steady would be set correctly? Even then whatever method one uses to centre drill cannot guarantee to be in the centre if the tailstock is misaligned except if one depends on the drill being pulled to centre by the bar?

Perhaps one should try to set a centre drill in the toolpost and eyeball it to the bar centre as would would a turning tool or even drill a greater angle than a centres 60deg to try and have a point fixing each end as opposed to seating the centres within conventional centre holes?…perhaps a small centre ground stub drill on centre for the pilot would be better?

Advice needed….please.

[john carruthersParticipant @johncarruthers46255]

maybe a sacrificial centre held in the chuck would be more accurate? A bit of hex stock turned to a point and a driver on the work piece?

[Neil WyattModerator @neilwyatt]

The approach relies of the fact that if the collar is turned on a long bar very close to the tailstock then it will be very accurately concentric with the holes, even if alignment is slightly out.

It doesn't matter if the hole isn't perfectly central, as long as it can sit squarely on the centre as you will then turn the collar concentric to the centre, not the other way round.

The council of perfection would be to turn both ends between centres.

When I made mine I took a final skim at each end with the lathe at the same setting, using a dead centre in the tailstock.

Anyone fool enough to trust me measuring to tenths will no doubt feel 0.0003" is an excessive error

Neil

[pgk pgkParticipant @pgkpgk17461]

..thinking about this it shouldn't matter where the end centre holes are so long as the bar starts as a large enough diameter and those centre holes are at a 'greater-enough' angle than the fixed centres such that the bar is held at two tiny points then turned between centres with tailstock adjustment untilt the bar is turned parallel along it's length. Once the tailstock is aligned those centre holes could be redrilled if necessary.

My need is for a length of such bar rather than 2 collars to use it to also accuratly set a compound angle later as part of my project.

As i see it theoretically 60deg centres in 60deg holes could 'S' a bar if the holes aren't concentric?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 22/09/2015 08:34:54:

The council of perfection would be to turn both ends between centres.

 

[dead centres]

… as discussed on a previous thread.

MichaelG.

 

Edited By Michael Gilligan on 22/09/2015 09:05:49

[Michael GilliganParticipant @michaelgilligan61133]

Posted by pgk pgk on 22/09/2015 08:45:24:

As i see it theoretically 60deg centres in 60deg holes could 'S' a bar if the holes aren't concentric?

.

So you may want to consider using spherical-ended centres

But … Beware: That may be the road to madness

MichaelG.

[HopperParticipant @hopper]

So what is the runout of the chuck going to be? Probably a couple of thou max. Over a 12" length, the angular difference in the way the centre sits in the hole is going to be some infinitesimally small amount. , something like .00955 of a degree according t'internet. I doubt your centredrill would be manufactured to that close a tolerance, nor the chuck you held it in, nor the centre you insert in it. Follow Harold's procedure and carry on.

[pgk pgkParticipant @pgkpgk17461]

I'm not trying to be deliberately difficult but Harold's procedure (as i read it) has one newly turned section in the chuck and the other end held in the fixed steady for secondary centre drilling.

In my original query I asked how one sets the steady in that situation – I don't see an accurate method. A longer machined section now at the chuck end would allow that.. then relax one steady finger only before moving the steady to the tail could work?

[Neil WyattModerator @neilwyatt]

> My need is for a length of such bar rather than 2 collars to use it to also accuratly set a compound angle later as part of my project.

In that case I would turn the two collars, adjust the lathe so that it is perfectly aligned between centres using a DTI fitted to the toolpost on the collars. I would then fit a driving dog to the test bar and skim the register between the collars to be your reference surface for setting angles. Best of both worlds.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by pgk pgk on 22/09/2015 13:15:07:

I'm not trying to be deliberately difficult but Harold's procedure (as i read it) has one newly turned section in the chuck and the other end held in the fixed steady for secondary centre drilling.

In my original query I asked how one sets the steady in that situation – I don't see an accurate method. A longer machined section now at the chuck end would allow that.. then relax one steady finger only before moving the steady to the tail could work?

.

You are not being difficult … simply stating the [small] facts.

The only way that I know, of placing a centre hole accurately in line with the axis of rotation of the headstock spindle, is to 'catch' it with a hand-lheld graver. … But note: This will not guarantee to put the hole in the centre of the material.

MichaelG.

[David Clark 13Participant @davidclark13]

Looks like you are all trying to make a mountain out of a molehill. Hold the material in the three jaw chuck and tailstock centre. Waist the bar down leaving two collars. True up the collars by moving the tailstock making sure the collars are the same size. Set the fixed steady to the collar on the tailstock end. Reverse the bar in the chuck. Face off the bit of bar that was held in the chuck and centre drill. All should now be true. Finally check between centres.

[pgk pgkParticipant @pgkpgk17461]

Posted by David Clark 1 on 22/09/2015 14:49:58:

Looks like you are all trying to make a mountain out of a molehill. Hold the material in the three jaw chuck and tailstock centre. Waist the bar down leaving two collars. True up the collars by moving the tailstock making sure the collars are the same size. Set the fixed steady to the collar on the tailstock end. Reverse the bar in the chuck. Face off the bit of bar that was held in the chuck and centre drill. All should now be true. Finally check between centres.

Indeed.. and little like the article I was following. As it goes i had intuitively reset my tailstock angle that way after the two collar method for levelling the lathe last week..just not gone further to confirm between centres.

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