# Slight taper turning between centers



## brandon428 (Nov 26, 2021)

I don't have any taper when I turn from the headstock of my 9A in a chuck/collet (what I generally do).  Today, I went to turn a 12" long round bar between centers and am getting a slight taper of about .022 over 6-1/2" (on the tailstock end).  Diameter is thicker on the headstock side.  I have an edge alignment test bar, double checked my tailstock is aligned, and when I run a dial indicator along the test bar, it's consistent within a few thousands over the entire length of the bar.  I have about .004" of runout on the tailstock side with my live center.

I don't think it's being caused by tailstock runout, and given the consistent measurements across the test bar, I don't think it's bed wear. Ideas on what else to check? My gib screws and carriage bolt screws/lock are backed out just shy of causing drag. I have ~0.025" backlash in my cross feed, but everything else feels tight.

I'm not aware of any way to lock the cross feed or compound rest...


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## Ulma Doctor (Nov 26, 2021)

the tailstock may be offset
try to adjust the TS offset with a dial indicator .010" and retest
you will be sending the TS away from you while adjusting


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## SLK001 (Nov 26, 2021)

That's a lot of taper.  You will probably find that your problem is indeed the tailstock offset.


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## woodchucker (Nov 26, 2021)

The edge is meant to test 2 points, *using centers*. the head end, and the ts end. you put the indicator at both and they should read the same... right?  Your indicator is mounted in holder somehow....

if you are reading the same, it should be no taper.... should be.

Like Mike says adjust the ts away from you by half the amount...

Does edge say the middle of the test bar is usable?


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## brandon428 (Nov 26, 2021)

woodchucker said:


> The edge is meant to test 2 points, *using centers*. the head end, and the ts end. you put the indicator at both and they should read the same... right?  Your indicator is mounted in holder somehow....
> 
> if you are reading the same, it should be no taper.... should be.
> 
> ...



I normally only test the ends.  I center the head test point at 0, pull back the dial, slide the carriage to the tail, and the test point on the dial shows 0, which is what I call centered.  If instead of pulling back the dial I remove the bar, slide the carriage, and put the bar back, I can be a few thousands off, but I believe that's due to the runout.

The reason I ran it _*across* _the test bar was a one off to see if bed wear could have been causing the taper.  My thoughts was that if the dial stayed around 0, it tells me that when there's no pressure on the bit (cutting), there's no inherent taper.


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## brandon428 (Nov 26, 2021)

Mike, I tried moving the tailstock 0.010" away from me, and the 1st 5" is tapered smaller diameter on the tailstock as before, but the last 1-2" is now tapered the opposite way (smaller diameter on the headstock side).  Something really funky is going on here.


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## pdentrem (Nov 26, 2021)

How tight are you on center? Properly greased? As the shaft is cut the forces can move things around a fair bit. The shaft will also change length as it heats from the cutting forces.
Are the center holes correct so the points are not touching the bottoms of the center holes? If they touch the bottoms, the shaft will float.
Is your tool below center line? Thinking that the tool is grabbing the shaft and pulling it towards the you and thus cutting deeper in the center area vs the two ends that are properly supported.
Pierre


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## Ulma Doctor (Nov 26, 2021)

brandon428 said:


> Mike, I tried moving the tailstock 0.010" away from me, and the 1st 5" is tapered smaller diameter on the tailstock as before, but the last 1-2" is now tapered the opposite way (smaller diameter on the headstock side).  Something really funky is going on here.


i would concur , something is funny
do you have access to a dead center?


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## Ulma Doctor (Nov 26, 2021)

you can easily make a dead center in the headstock, the tailstock needs one to rule out alignment issues
your spindle bearings may be loose
to check, mount a dial indicator on top of the spindle- insert a suitable rod larger than 5/8" and about 20" long into the spindle
give a pull up and give a push down- observe the dial indicator readings and record


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## graham-xrf (Nov 27, 2021)

brandon428 said:


> I don't have any taper when I turn from the headstock of my 9A in a chuck/collet (what I generally do).  Today, I went to turn a 12" long round bar between centers and am getting a slight taper of about .022 over 6-1/2" (on the tailstock end).  Diameter is thicker on the headstock side.  I have an edge alignment test bar, double checked my tailstock is aligned, and when I run a dial indicator along the test bar, it's consistent within a few thousands over the entire length of the bar.  I have about .004" of runout on the tailstock side with my live center.
> 
> I don't think it's being caused by tailstock runout, and given the consistent measurements across the test bar, I don't think it's bed wear. Ideas on what else to check? My gib screws and carriage bolt screws/lock are backed out just shy of causing drag. I have ~0.025" backlash in my cross feed, but everything else feels tight.
> 
> I'm not aware of any way to lock the cross feed or compound rest...


As much as 0.004", (in my world more than 0.1mm) before you even start, is too much. A good live centre, in a tailstock that is locked gives a fixed point that cannot contribute to taper if it is lined up to the spindle centre. The uncompromising hardball way is use dead centres, and be sure they fit the centre spot holes in the test bar without bottoming on their points.

Next is the headstock. Discover if it has runout. Even if it has some, the error effect it makes is more about cyclic surface finish than taper. A whole 0.022" is because the tail centre is about 0.010" nearer to the tool. Absolutely do as @Ulma Doctor suggests. Get to know everything about the spindle play.

Turn between dead centres to discover the tail alignment. Sure - folks like to run a dial indicator along the shaft while moving the carriage, but the definitive way is to very carefully use a test bar you make cuts on, and directly measure them. The final cut should be very light, low force kind. Make it up yourself for a test area near the headstock, and another at the tail end, with the space between relieved just deep enough so you can move from the cut at one end to continue the cut at the other end without moving the cross slide out at all. If you can't lock it, then just don't touch it. Leave it at the setting where the tool was cutting with backlash taken up.

Finally, measure the test diameters _with a micrometer_! If the taper is still there, adjust the tailstock Y-axis screws.

There can be messed up taper effects if the tail point is not on the correct centre height. Check with the indicator it stays on the line, right up to the tail. At this stage, if there still is a problem, you will have gamed it to the point where your own senses will be giving you clues to the cause.

You want to know the whole deal, like if maybe if your the whole carriage is moving out of a worn area as it approaches the tail, or if there is a bed twist that needs leveling out. I don't say this is what is happening, but I do think you can zero in on the cause.


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## Technical Ted (Nov 27, 2021)

How level is your lathe? What did you use to level it?

Ted


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## Alcap (Nov 27, 2021)

Is it possible that the live center with .004 runout cause issues if it didn’t rotate constantly with the shaft ? Maybe mark the shaft  and center to verify it’s not slipping.


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## tq60 (Nov 27, 2021)

Start fresh.

Get some round stock, 2 inch or so diameter, a few inches long.

Maybe another, 1 inch diameter a foot long.

Short piece 1/2 inch diameter.

Long one needs to fit through spindle so whatever size that is.

Start by facing the ends of everything but the short 1/2 round.

Make a good center drill in each end. De-burr after drilling.

Place the large round I chuck and support with tail and remove material from center leaving maybe an inch or 1/2 inch at each end.

Reduce center by about a third, not critical, just make it look good.

You now have a "spool"

Place short in chuck and turn a center.

Place center in tail

Put spool between centers, no dog needed.

With a marker paint the part as it spins.

Take very light cuts, prefered with power feed on finest setting.

Only cut enough to remove the ink on both ends.

Measure both ends and now you see offset in difference in diameter.

Place dial indicator so you can measure tail shift and move it 1/2 the difference.

When it gets close often just tightening one side is enough, if it moves it was loose...

Repeat until both ends same.

Ts now aligned.

New tool made. 

Now you do same but use dial indicator in tool post

Put long round in and make a cut at the ends.

Position cutter just past end and insert stock between centers, make cut then remove stock and move tool to opposite end and repeat.

Od should come out same.

Wear in bed pay cause some difference, this is same as first tool but not wasting the material and a different part of the bed.

Ours looks like this.
	

	
	
		
		

		
			








Sent from my SM-G781V using Tapatalk


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## ddickey (Nov 27, 2021)

Flip your piece around and take a spring pass. The result may be interesting.


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## Lo-Fi (Nov 27, 2021)

A live centre is not the tool to use for accurate work unless you've got some serious faith in its lack of runout and repeatability. If it's got 4 thou runout unloaded, I'd not be surprised if it's rocking over under tool pressure, which explains your success measuring with the test bar but not with a cut. 
I learned this the hard way making a precision spindle recently and ended up going old school with a dead centre.


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## pdentrem (Nov 27, 2021)

I do cylindrical grinding on a Landis machine and always between dead centers. When trying to hold sub 0.0003” it is the only way. 
As for live center, there are accurate ones and as the accuracy increases so does the price. Even a cheap one holds better than .004”. Many can be serviced. The back cap is either screwed in or pressed on. Under the the cap is often a nut and spring with the support bearing. A little servicing may reduce the looseness.
Pierre


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## Janderso (Nov 27, 2021)

Tail stock- bed wear?


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## Beckerkumm (Nov 27, 2021)

I've been messing with the same issues and this is what I believe happens.  The tailstock is usually sitting on the part of the ways with the least wear as is the stock nearest the chuck.  As you move the tailstock for different lengths, it is moving up or down relative to the chuck center.  The the cutter moves from less to more wear, the tool tip moves down and away as the wear increases and closer and higher as it approaches less wear.  That movement also changes where the tip hits the bar.  As it moves down and away, it moves off center and takes less DOC ( assuming you start at center or below ), opposite as it moves to less wear.  You can adjust taper by moving the tailstock or even with slight adjustments of the tooling up or down.  The problem is it is a pain if moving from 6" to 12" as you have to readjust the tailstock and seldom want to mess much with cutter height.  I do set up a dial and zero it against my cutter tip that works best for non tailstock turning and know that a couple thou adjustment works better when the live center is out a certain length.  Some of this isn't necessary most of the time but I do a lot of experimenting with a machine to learn its quirks or give it a chance to learn mine.

I've also had poor luck with cheap live centers, and by cheap I mean 100+.  I have a NOS Bison with a short nose and a Royal long nose that have run out less than .001 but have a new center that came .002 out of the box and the seller ignored my attempts to return.  In fairness I let it sit untested for a few months so test them immediately as even the $125 ones can be crummy.  Dave


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## graham-xrf (Nov 27, 2021)

Janderso said:


> Tail stock- bed wear?


There is a considerable psychological resistance to ruthless discovery and acknowledgement of this possibility. The good thing to know is that if you know it's there, you can work around it, compensating for it when you happen to need to work on a long piece. I dislike it so much that I suppose it's the one thing that would have me either scrape it out, or seek to change the whole machine!


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## graham-xrf (Nov 27, 2021)

Beckerkumm said:


> I've also had poor luck with cheap live centers, and by cheap I mean 100+.  I have a NOS Bison with a short nose and a Royal long nose that have run out less than .001 but have a new center that came .002 out of the box and the seller ignored my attempts to return.  In fairness I let it sit untested for a few months so test them immediately as even the $125 ones can be crummy.  Dave


Dave - I so agree about the not-so-good new stuff that has a three digit+ price. Though I have not yet tried it myself, I am tempted by the Joe Pieczynski video. Making your own is not such a bad idea. He used cheap bearings, and did not turn a 60 degree point, but if one wants to just expand the idea a bit, then using other bearing types, or making a taper back end, whatever, seems reasonably possible.

Need a Live Center For your Lathe?? Lets Make one !


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## brandon428 (Nov 27, 2021)

Only had 20 minutes today, but I think it may be bed/tailstock wear.

Long story short, I went to re-check the run-out of the live center before swapping in the dead center (I do have one), but my carriage wouldn't clear my tailstock to check run-out on the live center.  The 0.004" of runout I measured the other day was on the _collar of the test bar_.  I normally have the ram ~1/2" out from the tailstock, so to get clearance to check the center itself, I backed up the tailstock so the ram was out 1-5/8", and the tailstock was now back 1-1/8" on the bed from where it was before.

In the new position I saw < 0.001" of run-out on both the live center itself and the tailstock side collar of the alignment bar, and the tailstock was ~0.005" offset towards me.  I re-adjusted the tailstock alignment, and now have < 0.001" of run-out on the live center and tailstock collar of the alignment bar, zero (or not measurable) run-out on the headstock collar of the alignment bar, and what looks like an aligned tailstock.

Bed wear or tailstock/ram wear?

I'll try taking some cuts as well as throwing my dial indicator on the headstock as Mike suggested in the morning...


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## brandon428 (Nov 27, 2021)

Technical Ted said:


> How level is your lathe? What did you use to level it?
> 
> Ted


My lathe is _close_ to level with a machinists level.  I say close because the bench is level, and while I did level the lathe before, my bench is made of wood, and the level can change based on how hard I tighten it down.

I thought this is more of an issue with newer lathes?


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## ddickey (Nov 27, 2021)

All lathes must have no twist aka level.


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## Beckerkumm (Nov 27, 2021)

I had a thread on tailstock adjustment on the Richard King forum here a few days ago.  Might be of some help.  Dave


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## SLK001 (Nov 28, 2021)

Your 0.022" is far outside what a bed twist would give you.  You might be suffering from tailstock spindle droop, a common SB problem.


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## ddickey (Nov 28, 2021)

Plus if it was twist it would be over the entire length.
If it was a low TS the piece would be larger on the TS end not the HS end I think.


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## Technical Ted (Nov 28, 2021)

brandon428 said:


> My lathe is _close_ to level with a machinists level.  I say close because the bench is level, and while I did level the lathe before, my bench is made of wood, and the level can change based on how hard I tighten it down.
> 
> I thought this is more of an issue with newer lathes?


The only reason you level lathes is to remove bed twist. A level does not need to be level to cut true.... but, there must be no bed twist. Bed twist, depending on how it is twisted, can cause all kinds of tapers. See if this South Bend document helps.



			http://vintagemachinery.org/pubs/1617/3532.pdf
		


Ted


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## brandon428 (Nov 28, 2021)

SLK001 said:


> Your 0.022" is far outside what a bed twist would give you.  You might be suffering from tailstock spindle droop, a common SB problem.


How is that remedied?


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## pdentrem (Nov 28, 2021)

Have to confirm first. With both dead centers in, bring the tailstock up to the spindle snug the hold down and see whether the two tips touch correctly in the vertical. Next start extending the ram and see whether the tips still touch. The worst should be a maximum extension. Also tighten the lock for the ram and see what happens then. Many times the ram will shift as the lock is tightened. 
Once we have the data, we can figure out what to do. The usual fix is to bore the first inch or so, to fit a bushing to support the ram. Once the bushing is in place here comes the slightly hard part, ream that bushing to fit the ram and inline with the spindle. Milling machine and reamer with proper fixture.
Or attempt to find a better tailstock, $$$$ and they not commonly found anymore.
Pierre


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## brandon428 (Nov 28, 2021)

Ulma Doctor said:


> you can easily make a dead center in the headstock, the tailstock needs one to rule out alignment issues
> your spindle bearings may be loose
> to check, mount a dial indicator on top of the spindle- insert a suitable rod larger than 5/8" and about 20" long into the spindle
> give a pull up and give a push down- observe the dial indicator readings and record


I get .001” of vertical play.  Is that considered loose?


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## Technical Ted (Nov 28, 2021)

If you're still getting a taper between centers, here's a section out of South Bend's "How to Run a Lathe" on doing a two collar test and instructing to align your tail stock if getting a taper. Have you already tried this? You should be able to remove the taper and turn true between centers by properly adjusting your tail stock. At least get it pretty close, not 0.022" off... 

Use mics though, not calipers. 

Ted


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## Kevin T (Nov 28, 2021)

I skimmed all the posts but wanted to pipe up and say I found that my lathe had a worn TS base from all the decades of use. I ended up shimming mine to raise it up on the quill end and make up the gap between worn bed and worn TS. I had also purchased an import MT3 test bar for my TS in this pursuit. This was a good purchase for me since the tool is useful for other things like setting MT3 tapers on the taper attachment!


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## brandon428 (Nov 28, 2021)

Ok, few updates:

When I can put dead centers up against each other at the headstock, the tailstock center has a visible offset both away from me and above the headstock center.

However, when I use the 12” alignment bar, they’re lined up almost perfectly: dead on left to right and tailstock is 001” high.

So Then I tried cranking the offset on the tailstock 020” away from me. I have a 6” cut I’m working on, and with this big offset, I now see a taper larger towards the headstock as I had before for the first 1”, something flat-ish between 1” and 4”, and then a taper in smaller towards the headstock between 4” and 6”.  Shrug...


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## Ulma Doctor (Nov 28, 2021)

brandon428 said:


> I get .001” of vertical play.  Is that considered loose?


No, that’s good
Any tighter may cause undue wear


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## Ulma Doctor (Nov 28, 2021)

brandon428 said:


> Ok, few updates:
> 
> When I can put dead centers up against each other at the headstock, the tailstock center has a visible offset both away from me and above the headstock center.
> 
> ...


It is common to have the tailstock slightly higher than the headstock on new machines 
As the TS wears, it gets closer to the HS height
The difference is intended as far as I was informed


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## Ulma Doctor (Nov 28, 2021)

p.s. a chunk of brass is not a good starting point , the brass is out if round, even in a collet.
You might want to try a piece of drill rod or a center drill or carbide drill to be the indicator to start with


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## brandon428 (Nov 28, 2021)

Ulma Doctor said:


> No, that’s good
> Any tighter may cause undue wear


Great, and I have no discernible runout on the headstock spindle -- so we can at least rule that out.


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## brandon428 (Nov 28, 2021)

Ulma Doctor said:


> It is common to have the tailstock slightly higher than the headstock on new machines
> As the TS wears, it gets closer to the HS height
> The difference is intended as far as I was informed


Yes, and I didn't mention before that I had shimmed the tailstock similar to what Kevin had done when I originally bought this machine.  IIRC, it was ~0.005" low, so I added a 0.006" shim because was also told they should be a thousands or two high when they're new to account for exactly what you said.


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## brandon428 (Nov 28, 2021)

Ulma Doctor said:


> p.s. a chunk of brass is not a good starting point , the brass is out if round, even in a collet.
> You might want to try a piece of drill rod or a center drill or carbide drill to be the indicator to start with


I'm using 12L14 tight tolerance steel rod.


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## Ulma Doctor (Nov 28, 2021)

brandon428 said:


> I'm using 12L14 tight tolerance steel rod.


not good enough, you'll need ground material < .0005" TIR or less              '


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## brandon428 (Nov 28, 2021)

Sorry, not good enough for what?  Do you mean if I make my own test bar?


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## brandon428 (Dec 7, 2021)

Forgot to follow up last week, but following up now for posterity.  Thanks to Mike for talking me through an answer.

The problem turned out to be the diameter.  My bar was 12" long and 3/4" diameter turning down to 1/2", so after adding a steady rest in the middle, the taper effectively disappeared.


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## chatter chatter cut cut (Dec 7, 2021)

sure sounds like bed twist . a rough test is to clamp a 4 ft. straight edge to the bed close to the headstock and another to the tail of the bed . a good carpenters level at the ends will show any twist magnified greatly.when the level shows the same when turned end for end you can know there is no twist.


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