Turning tapers on lathe using tail stock offset method

[churchjw]

Excellent video and made making tapers simple. I do have one question about the process.
In making your offset on the tailstock you mention that where you make the measurement is a reference point. Would taking that measurement from the live center not actually increase your L in your equation? In effect making your measurement length of part plus live center nose length? This causing your offset to actually be less than needed? I know the difference would be minimal but if someone is using a long live center it could easily add more than an inch to the equation.

Please don't take this as splitting hairs as I know I certainly have picked up a TON of knowledge from this forum and many others. I am just trying to get the whole process in my head. I think it will be cool to make my own center drill that fits in my tailstock and to be able to understand how to make other parts as needed.

Thanks, Chris.

Hi Chris

The question is a good one. I remember having the same one when I first tried this. The trick to remember is that the entire tail stock moves perpendicular to the ways of the lathe. This means the pivot point is the face of stock. Other wise the length of the tail stock would have to be in the formula and the same reason that the depth of the center drill does not affect the angle. So it does not matter where on the tail stock you measure the movement as long as its a stable location.

Hope that helps,
Jeff

 

[churchjw]

Hi Jeff,
Just wondering what method did you use to "blue" the steel?

Cheers Phil

Its just a chemical tool black. The one I use is by BIRCHWOOD CASEY® called presto black. I don't think they sell that product any more but they have a newer product that I think works about the same. I got a huge amount of it free when a friend had to do his MSDS listing and it was easier to give away than do the paper work on an old chemical. I use it on everything I make. It just looks cool. :biggrin:

Jeff

 

[cjsamples]

Thanks, that did clear it up for me. It does make sense now.

Ok, now a video on taper attachments????

Chris.

 

[British Steel]

Excellent tutorial! I'm blessed with a taper adaptor, but the tailstock offset method still comes in useful for long tapers (my adaptor only covers 12" of carriage movement).

Only one little (hopefully constructive) criticism - I've found it essential, whatever method, to have the tool dead on centre height to produce an accurate taper, otherwise relative to the work the cut isn't a straight line giving a cone, it's a parabola (I think?) and gives a slight ogive that will rock in a Morse taper socket... guess it'd be a good way to machine large projectiles, though!

Dave H. (The other one)

 

[churchjw]

Excellent tutorial! I'm blessed with a taper adaptor, but the tailstock offset method still comes in useful for long tapers (my adaptor only covers 12" of carriage movement).

Only one little (hopefully constructive) criticism - I've found it essential, whatever method, to have the tool dead on centre height to produce an accurate taper, otherwise relative to the work the cut isn't a straight line giving a cone, it's a parabola (I think?) and gives a slight ogive that will rock in a Morse taper socket... guess it'd be a good way to machine large projectiles, though!

Dave H. (The other one)

Hi Dave good point. I always "assume" the tool is on center but that is not a good thing to assume. I can see where if the tool is low it would want to ride up on the tool and cut strange shapes. On that thought if the tool is to high it may push the work out and you get a curved cone.

Thanks for pointing that out it could help others trying to follow this.

Jeff

 

[churchjw]

Hi,

Paddy, I don't know about his Jet model, but I used to do tapers on a late 50's early 60's LeBlond that the sub-base of the tailstock held the clamp mechanism. And to off-set the top half, you loosened 2 clamp bolts that held the top ad bottom of the tailstock together. I could quite easily move the top portion without having to loosen the bottom. This was important when the shafts I was tapering could weigh up to 100lbs.

dalee

Dalee got it. I have never done this on a really big lathe so I'm not sure how they work. On this one with the tail stock clamped "and all the ones I have used, all tool room size or smaller" with the tail stock locked it moved easy. Would love to see pictures or video of how a really big lathe works.

Thanks for bring alliterative setup problems up.

Jeff

 

[British Steel]

Hi Dave good point. I always "assume" the tool is on center but that is not a good thing to assume. I can see where if the tool is low it would want to ride up on the tool and cut strange shapes. On that thought if the tool is to high it may push the work out and you get a curved cone.

Thanks for pointing that out it could help others trying to follow this.

Jeff

Jeff, it's not a simple matter of the work riding up on the tool etc., a bit of trig' will maybe show what I mean?

Lets assume a taper of 1" per foot over a 6" length, and that the big end's 2" diameter, so we want 1-1/2" at the small end... So we set our tailstock or taper adaptor over 0.250" (half the taper/foot times the number of feet of work length)

Assume that the tool's hideously off centre - 1/8" high *or* low relative to the work (even my old deflicted eyes would spot that!) - high or low will make no difference if we're cutting on the "front" side of the work.

We turn a short stub down to 1.500" diameter measured with a micrometer at the small end, knowing that's what we're aiming for: *if* the tool was on centre height, that'd put the cutting edge 0.750" horizontally (i.e. .750" of cross-slide travel) from the work axis - great, but that's *not* what we've got - the .750" is made up of 0.125" of vertical misalignment and .739" of horizontal travel out from the work axis (vector maths - root of the sum of the squares).

We now turn the taper, knowing our tailstock (or adaptor) offset is the desired 0.250", for the full 6" length

We now have 1/8" of vertical misalignment, all the way along and, taking the small end first, 0.000" (relative) y travel, then at the mid point, 0.125" y travel, at the big end 0.250" y travel - our diameters are now 1.5" to match the stub turned at the beginning, 1.746" half-way along and 1.994 at the large end...

Those paying attention will notice that the error's proportionately larger in the middle - so we end up with a curved "ogive" surface instead of a flat-sided cone

Admittedly, most of us would see that the tool is well below centre, but if we're striving for accuracy (and in the home shop we can take time to!) a smaller error in tool height will still cause an error, although once we're close to (+/- a few thou") centre height it gets "vanishingly small"

P.S. - "Grammaw, that ain't how to do it, egg in the left hand, straw in the right..."

Dave H.

P.P.S. - I think I got the maths right... a lot easier to just make sure it's on centre height!

 

[churchjw]

WOW Dave H That makes since and I never thought about it that way. :thinking: Math is not my strong suit but I can follow your explanation.

Thanks,
Jeff

 

[GK1918]

Although this I have never done, because my large machine has plenty of compound travel and always use that
method. My only question on this is because I am a hardened math dumbell. Usual MTs is TPF so your stock is
4.220" so thats 4.220 X .6024 (MT3) divided by 24 that comes to .106 off set I got that, but, my question is
how does the formula know that 4.220 is inches and not 4.220 feet or is it .4220 X .6024? My method for years
is to sweep a known MT with the DI till it reads -0-. Reason being I do boat shafts like 8' X 1"or 2 and these have
to be shoved into the head stock and I got a roller jig from the floor for whip, then cut keyway then thread it. sam

 

[churchjw]

Although this I have never done, because my large machine has plenty of compound travel and always use that
method. My only question on this is because I am a hardened math dumbell. Usual MTs is TPF so your stock is
4.220" so thats 4.220 X .6024 (MT3) divided by 24 that comes to .106 off set I got that, but, my question is
how does the formula know that 4.220 is inches and not 4.220 feet or is it .4220 X .6024? My method for years
is to sweep a known MT with the DI till it reads -0-. Reason being I do boat shafts like 8' X 1"or 2 and these have
to be shoved into the head stock and I got a roller jig from the floor for whip, then cut keyway then thread it. sam

I don't have a good answer for this other than the value L in the formula is in inches. If anyone here is good at math they can probably figure out how the units cancel out.

Jeff