Run out query

[David S Newman]

I have a Myford Super Seven and a Myford ML10, just made a collet holder for ER collets, really made it for the ML10, both lathes have identical nose thread and registar, I have carefully checked the registar on both. I bored the taper for the collet on the ML10 whilst it was screwed on to the mandrel so on checking obviously zero run out, thought lets see how it is on the Super seven and to my suprise 4 thou total run out of the tapered bore, how can this be ?
Both mandrels are running absolutely true (I checked them) the register in the holder I made is spot on, I'm baffled. David

[philbur]

Is the run-out axis parallel to the spindle axis or angled. I'm not sure what the design looks like but have you tried rotating components one by one and checking how the run-out moves.

Phil

[RB211]

dust, grit, swarf, bent spindle.

[lynnl]

I have a Myford Super Seven and a Myford ML10, just made a collet holder for ER collets, really made it for the ML10, both lathes have identical nose thread and registar, I have carefully checked the registar on both. I bored the taper for the collet on the ML10 whilst it was screwed on to the mandrel so on checking obviously zero run out, thought lets see how it is on the Super seven and to my suprise 4 thou total run out of the tapered bore, how can this be ?
Both mandrels are running absolutely true (I checked them) the register in the holder I made is spot on, I'm baffled. David

Mandrel ??? I assume that's the term used for what we call "spindle" on this side of the pond?

Have you rechecked after removing/reinstalling multiple times on the ML10? ...always get a dead true indicator reading each time?
Likewise, do you consistently get the 4 thou TIR on the other lathe?

If so I'd recheck the registers on each, at different radii from the center.
...then I'd do the same as you, scratch my head, roll my eyes, curse the fates, etc. etc.

I'd think there must be some sort of cumulative error combinations creeping into the mix, but I have no more brilliant thoughts to offer. I'd first suspect the culprits RB211 cited, and then go from there.

[Rich Carlstedt]

The "Register" you refer to has nothing to do with the accuracy of the spindle/mandrel, or chuck. ( The shoulder behind the mandrel threads are sometimes called the register.)
I know this is contrary to what most believe, but it is the truth
A chuck is controlled on the vertical and horizontal axises by the threads
The third axis (L &R) is controlled by the face of the spindle/mandrel
[ the face, is the perpendicular surface behind the threads, and adjacent to the shouder (next to headstock)]
You need 3 axises of control (6 directions) in order to stabilize any component.
Trying to match the "register" to the threads produces nothing but stuck chucks if you have not faced the part with the threading operation

The reason for the runout, is that you did not cut the threads AND the face at the exact same setup.
This introduces error in the chuck and is angular in nature
Fixing a chuck or face plate after having this manufacturing error is very hard to do.
Rich

[philbur]

Is this true for all threaded machine spindles or just Myford.

Phil:9

The "Register" you refer to has nothing to do with the accuracy of the spindle/mandrel, or chuck. ( The shoulder behind the mandrel threads are sometimes called the register.)
I know this is contrary to what most believe, but it is the truth
A chuck is controlled on the vertical and horizontal axises by the threads
The third axis (L &R) is controlled by the face of the spindle/mandrel
[ the face, is the perpendicular surface behind the threads, and adjacent to the shouder (next to headstock)]
You need 3 axises of control (6 directions) in order to stabilize any component.
Trying to match the "register" to the threads produces nothing but stuck chucks if you have not faced the part with the threading operation

The reason for the runout, is that you did not cut the threads AND the face at the exact same setup.
This introduces error in the chuck and is angular in nature
Fixing a chuck or face plate after having this manufacturing error is very hard to do.
Rich

[Rich Carlstedt]

Yes Phil, all spindles.
For example
My Boxford has a 1 1/2"-8 Spindle thread.
I have two Pratt Bernard chucks and a Original 6 Jaw Buck Chuck.
These are some of the most accurate chucks made.
The Pratts came with the Boxford and have about .018 (.5mm)clearance from the shoulder diameter. The Buck came with a .025 (.6mm) clearance. yet each have tremendous repeatability when removed and then replaced on the spindle. my P&B is less than .001 and the buck is dead nuts on.

To better understand the function of helical threads, take a thread that has a loose nut on it, and push it radially, and note that the nut is not restricted totouching the crest or root and can move. Now add some force with your fingers such as seen when you load the nut in a normal application. As you apply a axial load, the nut will automatically center itself on the thread, and no longer allow radial shifting. You may note that it even resists twisting as well. You may recall that when ever you strip a bolt from overload, it is always a complete concentric failure. You never strip a bolt or screw on one side ?
The helix angle and V thread is extremely effective in centering the nut, and your chuck threads....accurately, every time (no dirt or chips please).
Now as the spindle loads the chuck, the rear face of the chuck meets the face of the spindle. If the chuck face was turned at the same time as the threads were cut, The face will be perpendicular to the load and be in harmony. If the face was cut during another setup, it will not be true as it will touch in one point first,and it then will attemp to cock the chuck, resulting is error and maybe a stuck chuck. If the shoulder clearance ( ie register) is tight, it will jamb the chuck before the "faces" are in total contact

Rich

[philbur]

Hi Rich, then I’m confused as to why DIN 800 has a specific tolerance requirement for the "register" but not for the thread.

http://www.rohm-products.com/uploads/tx_userproducts/us_maschinenspindelkoepfe.pdf

Also the test protocol for my lathe takes great interest in the run-out of the "register" but no interest in the thread. Its clear when I screw the chuck on that the “register” is forcing the chuck to align with the spindle.

What am I missing?

Phil

[Richard Wilson]

I don't agree. What is the purpose of the register then, if it isn't to centre the backplate? My school installed 2 Boxfords new in 1964 (My only ever exposure to new lathes) and on both of them you could feel an increase in resistance when the register started to enter the chuck backplate, so there obviously wasn't significant clearance between the two as supplied by the manufacturer. I have always been taught that the thread is there to hold the chuck in place, the register and the flange face behind the register are there to align the chuck. My Raglan lathe has a square thread nose, which can't be self aligning as described above, and 2 registers, one in the normal position and onother smaller one at the front of the screw. The handbook says 'The spindle nose has two bearing positions for accurately locating backplates, faceplates etc, the function of the square thread being merely for screwing these attachments on and off'

richard

[Black_Moons]

"the function of the square thread being merely for screwing these attachments on and off" Square thread? I thought the previous poster only mentioned V threads. Of course square threads won't locate anything.

[Richard Wilson]

"the function of the square thread being merely for screwing these attachments on and off" Square thread? I thought the previous poster only mentioned V threads. Of course square threads won't locate anything.

Yes he did only mention Vee form threads becasue these are the norm, square threads are unusual, but the point I was trying to make, is that regardless of the thread form, the register and the flange face are there to locate and align the chuck, the thread is only to pull the chuck tight up against the flange face. Whatever clearance the poster has between the backplate and the register of his Boxford now, however many years old it is, my exmaple was that when they were new, straight from Boxford, the register and the backplate were a close fit. My Raglan still has what I beleive to be an original burnerd chuck, which I don't use except for rough work because its well worn, and it has about 0.030" clearance between the registers and the backplate, but evidence points to this having been 'bodged' at some time, and from my quotation of the Raglan handbook, it certainly wasn't what the makers intended.
Bottom line. The register and the flange face align the chuck, the thread is merely to pull it into place, whatever thread form is used. The thread need not be close fitting, but I can't see any harm if it is. Having said that, assuming that the register and the thread were cut during the same set-up, there shouldn't be a conflict between the alignment from the thread and the alignment from the register/flange unless something has been abused/damaged somewhere down the line.

richard

[philbur]

I can’t see how a Vee form thread can be self aligning. If it has some slack (as they all do) surely it will start it’s alignment according to the influence of the applied torque, then frictional forces between adjoining thread flanks will take over, prevent true alignment as it tightens up, if it is not restrained/guided by the register.

Phil:9

[shadoof]

I think the op said he had made one collet chuck completely on his ml10, just for laffs he tried it on the ml7 as they have the same threaded nose.

might need to make two

Lee

[TGTool]

My experience with making ER adapters for threaded spindles, and I've made quite a few of them, is that runout issues are almost always caused by inaccuracies on the 8 degree collet cavity. In spite of dialing in the compound slide angle with angle blocks and an indicator, something has happened to shift the angle only very slightly, but enough to compromise the fit over the length of the collet and allow one end or the other to move introducing eccentricity. I check with bluing to make sure I've got good simultaneous contact on both ends of the collet. In addition I'll use a collet which I can put a dowel pin or ground rod into so that there can be no question of collet spring compromising the contact check.

[lazlo]

dust, grit, swarf, bent spindle.

Myfords have plain bearings -- they should have NO runout