Morse Taper Error
Let me preface my question by thanking Frank Ford for his wonderful site, frets.com, which has provided me (a novice) a wealth of inspiration and a lot of great accessories and devices.
Frank has posted a project he made or using a sine bar to quickly set the compound to cut tapers:
In making the simple device, there is always cumulative error installed, which leads to the question, what is maximum allowable error (in degrees) in producing an acceptable morse taper??
The female taper should be 0.0005" to 0.0003 large on the should be +/- 0.0002 on the big end regardless of size. At least that's the way I make them when the occasion arises. I don't know what the commercial tolerance are nor do I have a reference.
What that works out to in angular error depends on the taper length. A #1 Morse would have more taper error than a #5 following my rule of thumb.
Go ahead and set the taper attachment from the sine bar. You will change it slightly to correct the inescapable error anyway. Lathes seldom follow their taper attachments perfectly. I usually stoned the fit under power to refine it after I got pretty close. Blue a new ground sleeve for a female gage. For a male gage use a like new lathe center. When a light coat of blue hits full length you're good enough.
Last edited by Forrest Addy; 06-29-2008 at 10:16 PM.
I seem to recall the JTiers had some figures on that.
I tried "Google" but in terms of figures for tolerance/allowances it seems that reference to the ANSI (or the UK or DIN/ISO) standards might be best.
Actually it was nothing simpler than 1/4" in 10"- and then some fool couldn't measure- and the error became a standard
Actually, Morse tapers are 5/8" per foot nominal taper not 1/4"" per foot - which is the standard for taper pins and machine tool gibs.
Steven Morse who designed the taper system and produced the first gages in 1864. He did a hell of a job striving for 5/8" per foot considering the lack of measuring equipment and standards of his day. The tapers today duplicate the features of the original gages. The orginal gages were amazingly round and conical and fit each other precicely even after 150 years. The original Morse taper gages are one oif the few international standards dependent on the original artifacts as a master reference.
It helped that Morse also invented the present form of the twist drill (furnished with Morse taper shanks) and made them so well and in such numbers that his taper series replaced all other taper systems for general machine spindle use. The Morse taper series became popular so rapidly they eclipsed every other taper system including ones that were technically superior to the Morse such as the Jarno. Morse tapers were the M/S DOS of the day: a defacto standard even before it came into wide use.
If you look at a list of Morse tapers you'll see that his tapers varried as much as .030 per foot. But bear in mind that this was before micrometer dials on machine leadscrews and the micrometer while invented long before that time was not popular until Brown and Sharpe came along later. Fits were made via transferring from inside to outside calipers and referencing scales.
Put yourself in the place of Steven Morse and using the equipment and materials he had available. Then make a set of ring and plug taper gages as accurate as the originals striving for 5/8' per inch actual total taper. Aint easy, is it. Wouldn't hurt to walk a mile in the other fello'ws moccasins before you call him a fool.
Last edited by Forrest Addy; 06-30-2008 at 09:31 AM.
Thanks, Forrest for the history of the MT tapers. I have wondered why each taper is slightly different but have not seen an explanation before.
Actually, I stated 10" not 12" .
10" is the Classic length for doing the sine.
You know the Square on the whatsit is equal to some of the snares on the other two dangles.
Euclid or Pythagoras and we go back to the solution of the squares using the easily divisible 100 rather than 144 using the projection of squares and the solution of them by Euclid's geometry on right angled triangles.
Did it when I was 15 and Euclid was in his prime- numbers of course.
Norm- tripping over his 'guessing stick' to do Naperian logarithims.
You know the logarithim of a number to a given base in the index of the power to which the base must be raised in order to produce the number?
Morse Taper Error
Thank you for taking the time to respond, Forrest. Your answer is much appreciated.
I had a mentor (neighbor) who was a long time machinist and former "chair" of a college occupational (machinist) program, but recently his age and health issues have severely limited his ability to provide information. It's awfully nice to come have a place to ask questions you are unable to locate answers for in traditional sources.
Again, thank you.
For what it is worth, I looked it up, and the error stated in the "Machinery's Handbook" for the "American Standard Self Holding taper" that is identical in gage line dims to a Morse is that the taper must be within 0.002 per foot of the standard.
I didn't see one specifically for Morse in the reference I checked, but I am under the impression that I saw the same tolerance for Morse elsewhere.
I believe I also have seen that the tolerance is such that the fat end must be larger, or the small end smaller, so that it always is tight at the fat end.
Either way, I don't recommend that you rely on that. If you go to the limit, it might work for a mere drill. A drill is wedged in by the drilling force, and shouldn't be relied on for much precision anyhow.
But for a center, or anything else with pretensions of precision, you had better be within a few tenths, or the thing will wiggle like a pen in a pickle barrel.
Forrest Addy and JTiers are probably and evenly certainly quite correct.
If real accuracy is required - as on a cylindrical grinder, the male and female tapers are "made to fit" (either individually or by "selective fit" from a batch). The concentricity of the "point" to or with the taper is not really such an issue as the tail-stock centre was "dead" (ie not moving). The head-stock taper was either "fixed" as well (with the drive/"dogs" rotating about the fixed centre) or else if the head-stock was "live" (ie the HS taper rotated with the spindle) the HS centre "point" (60 arc degree usually) was (re)ground after mounting and before mounting the work-piece on it.
Many HS centres that I used on lathes were "soft" so that they could be re-turned and "trued-up".
On some centres I have used the middle 2/3 or 3/4 of the "male" ("plug") was "relieved" so that the taper only contacted on the ends. This was quite OK as there was no need for the taper to "lock and drive" as it was the "location" that was important.
Any other "errors" can be "tuned out" by adjusting the tail-stock.
Most items that I've seen regarding taper-turning seem to assume that the top/compound slide or the taper turning attachment is not worn and will cut a perfectly straight cone. I would want to do some fairly accurate "proving" before I made that statement or assumption.
"Live" centres are a mixed blessing as it is quite difficult to actually determine where any "run-out" (as detected by a precision dial indicator) really is as there are components of the taper along and across the lathe (bed) longitudinal axis. "Trueing-up" a live centre is not as easy as it might seem either.
The situation may well be worse if using "adaptors" (ie MT4-MT3).
The "0.002" per foot" suggested is 0.002/12 = tan theta = 0.0001666
theta = 0.0095 arc degree = 0.5738 arc minutes = 34.38 arc seconds
"2 thou per foot" is only 1 thou per 6" which is hard enough in itself, but if there are any irregularities in the taper in terms of "straightness" or surface finish, there may well be even more problems.
As usual, Forrest's solution addresses all of these issues ie.
"blue it in" and "paper" it for the required and fit and finish by making one part to suit another.
The "self-locking" feature of a female morse taper in the tail-stock is used on its own without a "tang" for drills and is expected to "hold". If the TS MT is a "precision taper" then it soon will not be if we keep poking those rough drill tapers into the TS MT and especially if we keep "spinning" the drill (or drill chuck, reamer etc.) in the TS MT.
Few would abuse a mill quill taper the way a TS MT is abused but they still expect similar accuracy from both in terms of the quality of the MT (or other) taper/s and of the quills in the bodies of the mill head and tail-stock body. Its one hell of a "Big ask"