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Turning a precise taper on a manual lathe

Overland

Stainless
Joined
Nov 19, 2017
Location
Greenville, SC
The drawing calls for a taper of 7 deg, 7 mins & 30 seconds.
Length of taper 0.625". (in the sense of the "x" axis).
I've calculated Y axis deflection of 0.078" with this taper over 0.625".

I have a DRO, and taper turning attachment.
So 0.625" in the X axis should give me 0.078" deflection on the tool post, or Y axis, when the angle is correctly set.

It may take several "dry runs" to get the taper right, but does this make sense ?
(I'll need to be careful any backlash is "taken-out")

Thanks
Bob
 
Excellent point, thanks.

Follow up point, how do I measure the taper ?
I'll be turning it "smaller diameter towards headstock".
Seems to me if i calculate the smaller diameter, then turn a straight bore to this diameter. Once I start the taper, if I turn out all the parralell bore with the taper, that should be to size.
That's not really measuring it though.
How would I measure the taper, please ?
Bob
 
Thanks Thermite,
Not sure I fully understand your points.
Yes, a chuck taper, about 5" OD, for scale.
I could set up the taper turn attachment as discussed above.
Then turn a plug gauge using a second chuck as a reference. Maybe so the gauge fits in to be flush with chuck, using dial gauge or straight edge.
Then turn out taper, carefully, until gauge fits flush.
Am I understanding ?
Bob
 
I've set tapers on the taper attachment by using a sine bar. A couple #8 tapped in the side of the T/A lets me mount a small aluminum shelf to hold the sine bar. With the right gauge blocks under one end of the sine bar and the mag base on the bed of the lathe, I just run the carriage back and forth and adjust the taper to zero runout on the indicator.
 
Just doing some more reading....
Read one article that said on D1 mounts, the taper and face must both touch.
I'm thinking that requires an absolute size, with "0" tolerance.
Surely this can't be correct.
Should there be a small clearance on the face when the taper is snug ?
What should this clearance be ?
Thanks
Bob
 
If the best you can do makes a clearance dimension, it should be the diameter, not the face. The face is the larger mounting diameter, therefore it will give you more rigidity. Yes, there is a slight tolerance on the diameter, from a very very slight to a slight press fit in the taper. The cam pins will pull it home.
 
Thanks Thermite.
I found this from a few years back.

I could make a gauge off a spare chuck and use that to turn the taper.
Some very precise work required.
I did my apprenticeship back in the early seventies, then got "promoted". Spent my career in the Supply Chain and Application Engineering in the tire industry. Now I'm retired I'm building up a shop for interest, doing repair work and one-offs.
So much to learn, but it's fun !

D1 Camlock Taper - Dual Contact?
 
The drawing calls for a taper of 7 deg, 7 mins & 30 seconds.
Length of taper 0.625". (in the sense of the "x" axis).
I've calculated Y axis deflection of 0.078" with this taper over 0.625".

I have a DRO, and taper turning attachment.
So 0.625" in the X axis should give me 0.078" deflection on the tool post, or Y axis, when the angle is correctly set.

It may take several "dry runs" to get the taper right, but does this make sense ?
(I'll need to be careful any backlash is "taken-out")

Thanks
Bob

I'm not sure if someone here is pulling someone's leg here ;-) or not ?


Ok.

My math can sometimes get a bit 'Wobbly" but there's no stated accuracy or precision or tolerance band or + this or - that.

________________________


As a kid I was sent to school where by the age of nine you had to be able to tell military-time and was taught 'math" by a retired RAF Major - "Major Gick's" and his "bendy friend" in the closet if we didn't behave - said "Bendy friend" being a small thin cane that would be revealed from time to time for the express purpose of being shown the instrument with which one would be beaten with if one did not behave. ~ This was at a time when teachers could still smoke in the classroom, cigarettes or pipe either or and there was no actual limit on how much or how loud you could scream at a child (regardless of age). But honestly no-one ever f*cked around and the "Bendy friend" was never used. Pure fear of the imagined consequences seemed to suffice ... But he had incredibly detailed models of steam engines (that he built himself) and displayed in the classroom in a glass case as well as amazing origami-like models of super complex three dimensional shapes hanging from the ceiling ~ which may explain how or why I got into 3d computer graphics and VR systems. + things engineering related / "Machining" related.

________________________


7 degrees , 7 mins, 30 arc seconds ---> 7° 7' 30"

7 degrees ---> 7.0000 degrees.

7 arc minutes ---> [60 mins in a degree of arc ∴ 7/60 = 0.11666666 or 0.1166(reoccurring)*

30 arc seconds ---> [3600 arc seconds in a degree of arc or 60 seconds in an arc minute ] ∴ 30/3600 = 0.008333333 or

0.0083(reoccurring)*


so,


0.16666667(rounded up for calculator people) + 0.0083333 = 0.125 (when taking into account recursion ).

0.125 is an 1/8th of a degree.

So the taper being asked for here is.

7.125 degrees,

7.125°

or 7 and one 1/8th of a degree.


Still wondering about included and non included angles etc. so is it really 14.25° (full included angle) ? 1/2 angle 7.125° - which rings a bell.

Will re-read thread and re-check "Math".

Depending on type of taper attachment - taper per foot ?

Maybe using log tables or your tan function (in deg mode not "rad" mode) on your calculator, or "Machinery's Handbook"

That's

1.5" over a foot.

1.5" over 12".



1.5 inches over a foot,

one and half inches over a foot just so inches and arc seconds do not get mixed up.

1.5000 inches per foot (for example) is not a reliable indication of the actual tolerances required. Actual tolerances are required or even statements of "tapericity " - but in this case sounds like 1 1/2" over a foot taper = 7 degrees, 7 arc minutes , "And" 30 arc seconds.

1.5" over a foot (taper) = 7°, 7', 30" (exactly).

(I haven't checked to see where or IF any divergence occurs at a much higher number of decimal places (obviously not really practical or actionable to 25 decimal places anyway or achievable in a practical fashion especially in this context of tools used. but hey... whatever. ).


1 arc second is 1 degree divided by 3600 = 0.00027°(reoccurring).

The intent of 30 arc seconds (in the context of ( 7° 7' 30") is unknown or unknowable as an indicator of precision in this case with the information thus far provided.



Maybe @DrCielo is right... Machinists CAD Tool - Looking for ideas


_________________________________________________________________________________________________


* For some reason I can't use any of the superscript notations for reoccurring decimals on this site / forum ?

Repeating decimal - Wikipedia

^^^ Such as these ... to use "R" or brackets would be confusing - (sorry !)
 
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Camerman,
Thanks for your input.
I used Exel (Excell or whatever)

It likes radians, so
7 deg = 0.122173
7 min = 0.002036
30 sec = 0.000145
Total = 0.124355
Work the trig from there using Excel imbedded functions, I got:
0.625" in X axis gives 0.078125" in Y.

By the way, that's half included angle, as pointed out earlier.
I think I'm correct... but when I try to make the gauge I guess I'll find out.

But the really interesting part is the accuracy required, and understanding of the principles, to make this work. A very interesting challenge for an old guy on an old lathe...
Bob
 
Camerman,
Thanks for your input.
I used Exel (Excell or whatever)

It likes radians, so
7 deg = 0.122173
7 min = 0.002036
30 sec = 0.000145
Total = 0.124355
Work the trig from there using Excel imbedded functions, I got:
0.625" in X axis gives 0.078125" in Y.

By the way, that's half included angle, as pointed out earlier.
I think I'm correct... but when I try to make the gauge I guess I'll find out.

But the really interesting part is the accuracy required, and understanding of the principles, to make this work. A very interesting challenge for an old guy on an old lathe...
Bob

You didn't read the rest of what I wrote, (as I was still "adding" stuff).

That's 1.5" over a foot.
"taper"


- it's OK to set your "computational device" to degrees and use the tan function on a calculator. Slide rule would work, log tables, machinery's handbook, those little tables and books that machinists carry around or have stuffed into their tool boxes variously. There's a scientific calculator on your i-phone and android phone. if you turn the calculator on your i-phone sideways it turns into a scientific calculator. Not as fancy as a Texas instruments graphing calculator but with pencil/pen & paper you can get pretty far :)

@Overland you're funny :D

That should be compatible with some of the most ancient taper attachments on the planet, no fine mic adjustments or straining eyes to figure out Vernier scales.

Taper and tracer attachments can do some incredible things.

Unfortunately I'm packing stuff up so all my old books on older taper standards and methods where-in are in said boxes + a bunch of much older "Machinist theory" books that go back to the early 1960s, 1950s and 1930s.

Good luck :)

Where's @littlerob1 when you need him ?

If I say littlerob1 backwards three times in a mirror - " 1borelttil, 1borelttil ..." does that work ? Does he appear ? Bettlejuice, bettlejuice

Bye :leaving:

__________________________________________________ ___________________________________

*

Beetlejuice | Even More Top Beetlejuice Scenes | Warner Bros. Entertainment - YouTube


____

Again: Turn your i-phone calculator that comes with the phone - sideways. Don't worry about the fact that the "calculator" is running on what is essentially a 'Super computer" literally in your pocket. ~ and by "Magic" a pretty powerful and numerically rigorous scientific calculator "Appears" .

maybe I got my math wrong and you could double check it.



^^^ Tech Jungle - shows what to press to go into scientific calculator mode from normal calculator mode. so "Tan" function and 2nd for inverse Tan (depending on calculator) . Good argument for clean on line advertising free standard "calculating" interface. - Perhaps like what @drcielo maybe thinking about. Aimed at machinists but also explains how to do these calculations by hand if one wants or needs a deeper dive.

Mainly thinking for education purposes for kids that's can't afford Excel etc. I'm thinking a kid in a local library or community center that's trying to learn this stuff or figure this stuff out and maybe does not have access to a computer at home.(for many reasons)

Not every kid has a "smart" phone or a computer or 'Excel" .
 
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Web 2.0 scientific calculator

Ohhh look an online scientific calculator ^^^ (except it's jamm packed full of distracting advertising all around the edges ... how distracting especially if one is ADD (like me) ) - reminds me of another wedbsite / message board can't quite place it... :scratchchin: Ahhh it will come back to me

@drcielo lol...

Free Online Math Calculator and Converter

^^^ you can get into a lot of trouble here ... I don't think their 'taper" calculator was made by or for machinists (cough cough).

I dunno man I'm wondering where the sticks / monkey / banana guy is ?

Later,

Peace
 
Thermite,
All this started when I was thinking about converting a solid casting L1 chuck to D1-8.
I've not seen an adapter available, and not sure if I could convert one, to screw onto the existing thread.
Just "chasing this rabbit" a little. No decisions made yet.
Thanks, to all, for input.
Bob
 
Thermite, Thanks again for your input.

IMG_3343.jpg


I thought about machining the back face flat, but the boss for the L1 taper is very small. From the back, I have nothing to bolt to, unless I bolt straight through to the front. I guess I could use 8 bolts, one either side of the Tee slots, but there's not much support.
Bob
 
Every taper I turn with the compound is precise, precisely the wrong angle so don’t feel bad!,
Thermite nailed it
Mark
 
Making a male taper between centers easier (IMO) because one can pull the part and bench check it. Making it longer would make checking better to insure better accuracy. If it was made 1 1/2" (or 2") long then it could be checked by pulling a 1" 123 block from the checking station, and easier rough checking on the lathe with a caliper. If a male taper was made it might be used as a lapping device to work in the last .001 or so of the female taper. Yes, checked in a sine plate would be best.

I have never done, so just thinking out loud.

Having a gauge/lapping device like this one could put a center in a drill or mill and set that center in the lapper's big end and so have the out end stabilized dead over center.

At the very least just use the male taper for a gauge with not any lapping with it.
 
Thanks for all the input.
Just to recap, I'm thinking of converting a big 4 jaw with an L1 taper, to go on a D1-8 spindle using an adapter.
If you look at the photo above of the back of the chuck, there's not enough material in the original casting to remove the L1 taper, and start with a flat back.
Hence the notion of making an adapter that would screw onto the L1, then machine that to the D1-8 taper, and add locking pins.
One point that has me concerned is how I would center the adapter on the L1 threads.
It would be quite difficult to turn the L1 threads.
It would also be quite, maybe very, difficult to turn the D1 taper, in conjunction with the mating D1-8 face.
Overall a very difficult project.
I have just picked up me a "new to me" lathe, and it includes a 15" 4 jaw, as well as a 12" 6 jaw. (D1-8).
So I will stick with this for now, and maybe try to sell my Italian 18" 4 jaw (L1), in very good condition.
Thanks again for all the excellent input.
Bob

My new lathe:
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