Saddle causing .150 taper 3” off chuck no tailstock need help.

[stupoty]

If I could only afford one, I'd buy the larger test bar for the headstock. A sleeve is probably accurate enough but will more than double potential errors (two mating surfaces for grit/burrs/whatever to cause you to pull out your hair).

The tailstock is far less critical IMHO. Drills and reamers will tend to follow their own path anyway (you'll need to use a boring bar regardless for accurate holes) and the tailstock is adjustable for cutting/not-cutting tapers when turning between centers. The spindle taper you want dead nuts aligned to the bed ways in both dimensions (horizontal and vertical, maybe ever so slightly pointing higher toward the tailstock — a few tenths over 12" at most).

A taper test bar isn't a mandatory tool unless you have reason to distrust the accuracy of your lathe (or are planning to rebuild it). It's kind of a one time use tool. (But I own both!).

Yeah , I think you are right about the sleeves, I have had my head stock off before but it does sit on the ways for alignment so I might just use the button on the face plate method fof double checking it and call it good.

Although a shiny test bar ? who could resist that ? I will just keep my eyes peeled on ebay unless I find plenty of spare cash in my pockets for some reason

(although the power hack saw motor rewind is priority for cash injection currently)

Stu

 

[Rex Walters]

You can similarly check TS alignment by mounting a DTI in the lathe chuck & turn it around the OD.

I might be misreading, but whatever you do, do not rotate a test indicator around the horizontal axis such that you perform some readings with that dial facing up and some with it down. Gravity absolutely will affect your indicator reading significantly.

It’s a common mistake but easily proven to be terribly imprecise - Richard King demonstrates this effect at the beginning of all of his classes:

I also still prefer dedicated test bars for headstock/tailstock rather than a single bar and an adapter sleeve. But your process sounds great if you only have one for the tailstock.

 

[petertha]

Good point, I should have clarified I'm measuring tailstock in/out relative to operator which is the typical jackscrew offset adjustment relative to bed axis. So I assume the DTI would be seeing the same gravity forces in those 2 orientations where the face is vertical but pointing either towards or away from operator on either side of test bar centerline. But maybe that cant be trusted either? I'm going to repeat that Richard King test at home. I've read about it but never seen it demo'd live like that. Very interesting.

Actually, full disclosure, I have one of those Edge test bars that I use for TS adjustment. I bought it subsequent to the MT test bar. What can I say, I'm a tool junky LOL. The DTI stays in same position from heatstock ring to tailstock ring so the DTI sag issue isn't there. You can also DTI off the top of the HS ring & then compare to TS ring. My TS is about 0.001" high which I'm told is normal.

 

[darkzero]

Although a shiny test bar ? who could resist that ? I will just keep my eyes peeled on ebay unless I find plenty of spare cash in my pockets for some reason

Those things are pretty cheap on ebay. MT3 bar is like $33 shipped all the way from India. I paid like $60 shipped for my MT5 bar. Been sitting in the tool box for years though but at least it's there.

 

[john.k]

I d be checking that the saddle wasnt fouling some part of the bed ,or gap,and forcing the ways apart as it moves forward..................I checked a similar happening once,and the problem was the small piece of rack attached to the gap was oversize.

 

[petertha]

... whatever you do, do not rotate a test indicator around the horizontal axis such that you perform some readings with that dial facing up and some with it down. Gravity absolutely will affect your indicator reading significantly. It’s a common mistake but easily proven to be terribly imprecise - Richard King demonstrates this effect at the beginning of all of his classes:

Well I finally had to try this for myself. I have 2 new-ish Mitutoyo DTI's. One is 0.0005" the other 0.0001". When I hold them by the body or by the dovetail mounted boss adapter & rotate in by hand, the dial goes nowhere in any rotation. It sits in the exact zero position. Do you think this is a fair comparison to Richards demo or should the needle be loaded?

Seems to me I tested this once upon a time too clocking around an accurate dead center with DTI in chuck & needle on OD. Pulled out the dead center rotate 1/4 turn, rinse & repeat. Same setting looking at the underside measurement with a mirror. I just don't recall the needle moving under gravity but I wasn't really looking for the effect either.

I haven't yet mounted it to a mag holder & plate yet like video, that will be next. But now isn't that introducing potential drift of the indicator holder arms & assembly into the equation vs the DTI in isolation? Sorry if this is off topic. I know this has come up before, just cant find the link.

 

[Rex Walters]

Do you think this is a fair comparison to Richards demo or should the needle be loaded?

I’m don’t know what percentage of the gravity effects are with the indicator itself vs the holder arm assembly. I even asked this very question during the class this week.

I wouldn’t be at all surprised if it isn’t almost entirely with the holding assembly. But since you always need some sort of holder assembly regardless, and there are many better ways to indicate the tailstock in, I’d still avoid rotating an indicator.

Richard said Stefan G. did some testing of this sort with various indicator holders to see which were most rigid with this type of testing, and that (quality) old-school rod and flexture clamp type holders were way more rigid than flexible mounts of any type.

 

[stupoty]

I’m don’t know what percentage of the gravity effects are with the indicator itself vs the holder arm assembly. I even asked this very question during the class this week.

I wouldn’t be at all surprised if it isn’t almost entirely with the holding assembly. But since you always need some sort of holder assembly regardless, and there are many better ways to indicate the tailstock in, I’d still avoid rotating an indicator.

Richard said Stefan G. did some testing of this sort with various indicator holders to see which were most rigid with this type of testing, and that (quality) old-school rod and flexture clamp type holders were way more rigid than flexible mounts of any type.

I was surprised the Noga flexed that much over the relatively short distance, next time I am at a loss I will try this with my rod and clamp type holders and see how flexy they are.

Stu

 

[john.k]

I have found that a lever type gauge solidly mounted on a square bar ,held in a 4 jaw ,has negligable gravity effect,and can be ignored,.........however a dial gauge mounted on two angled rods to a magnetic base attached to the chuck face will have several thou gravity effect............and in one case ,an owner decided his tailstock was 005 high!.......,and had the base surface ground,on the evidence of a dial gauge.

 

[jwmay]

It’s been one month since Uguessedit has replied to this thread. We’ve since gone down quite the rabbit hole with him absent. I wonder what’s happening with the machine in question.