lathe toolholder rotation

How much rotation ability is required or useful in a toolholder on a lathe?
Here are my thoughts so far; please let me know what I have gotten
wrong or have neglected.
Small rotation can be used to line up a thread tool or other form tool accurately.
Small rotation can be used to adjust side cutting angle.
There are a few exotic screw-cutting bits that require a 30 degree (counter-clockwise from above) rotation.
Fairly large rotation might be needed to get some kinds of bit into the corner of a shoulder cut.
There should be no need for rotation much beyond 45 degrees since the same thing can be accomplished with less than 45 degree rotation from the other side of the holder.
Large rotation counter-clockwise from above will bring a corner of the holder toward the work, and will bring the cutting bit further from the work, so a large bit extension might be required. A special holder with an angled mount for the tool might be better. Large rotation clockwise from above will bring a back corner of the holder toward the chuck, where it might get hit.
Bob
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No limit, Bob. An Aloris-style toolholder rotates freely. It allows quick and easy alignment of the tool anywhere you need it.
Since full rotation is actually easier to provide than some sort of "stopped' rotation, why would you want anything less than that?
LLoyd
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On Sat, 29 Mar 2014 15:06:16 -0500, Lloyd E. Sponenburgh wrote:

Well I admit that the question may seem a bit abstract.
Some types of holder systems are mostly intended to stay in one position, like the Aloris. Yes, it can be rotated, but then you need to re-align it if you want it square.
Some types of holder systems rotate in fixed amounts, like the Multifix mentioned in another reply.
Some types of holder systems rotate completely freely, like any of the DIY round-post systems.
I can certainly imagine ways to make a holder system that provides only limited rotation, and it is possible that such a system might offer some advantage in construction simplicity for example.
So I was curious about what is actually needed and useful, rather than about specific systems.
Bob
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On Sun, 30 Mar 2014 15:01:13 -0400, Bob S

If you use the old "Standard Tool Post", to use one term, you could rotate it to any position while, if I am not mistaken, the original "Quick Change" tool posts rotated in 90 degree steps. This meant that, using the standard tool post, the angle you ground on your tool bit were far less critical as the tool holder could be rocked, to raise or lower, the cutting edge and rotated for any cutting angle. The 90 degree "quick change" tool posts required the tool bit to be ground much more accurately as the tool post lacked the degree of movement that was inherent to the standard tool post.
While it seems common for small lathes to now use Quick Change tool posts some years ago the Standard tool post was the most common. I remember as an apprentice turning a piece of 12 inch line shafting from an old woolen mill into a 4 inch cutting head for a planer (we did it because there had a lot of that line shaft donated to the school) on a 24 inch lathe and making 5/8" cuts using a standard tool post. Granted it was slow - we spent about 4 hour a day in the shop and you could never start and finish a cut in that period - but it did the job :-)
So, to answer your question, if you can grind your tool bits very accurately you can get away with the 90 degree quick change but some movement will give you more flexibility in tool setting.
--
Cheers,

John B.
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With an Aloris-style toolpost, re-aligning it is as easy as "kissing" the front face of your chuck with the empty toolpost, and tightening the capture nut. Quick, easy.
LLoyd
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    [ ... ]

    Agreed. As long as the chuck is not occupied by something too large.

    My lathes are a bit too far apart in size to do that, and while the 12x24" Clausing has an Aloris style system (really a Dorian for the toolpost, and a mix of new and used Aloris and some Phase-II holders, the Compact-5/CNC has a toolpost patterned after the Dickson ones, but smaller than any I have seen. That is a little 5" swing machine. So, there is little point to trying to keep the same style of toolpost on both machines, since swapping between them is pretty useless anyway. The Aloris knurling head on the Clausing is bigger than the cross-slide on the Compact-5. :-)
    Enjoy,         DoN.
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I've used a Compact-5 on only aluminum, to learn G code. Is it actually capable of good accuracy on hard metals like drill rod or stainless? jsw
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Which is it, Jim? Hard, or stainless? <G>
Lloyd
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in message

All of them are easy for you, right?
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No, but stainless is what I'd call "tough", not "hard", unless you mistakenly work-harden it.
Lloyd
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in message

Compared to aluminum??
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"Hard" carries certain connotations not associated with aluminum or stainless steel. Aluminum is SOFT, SS not so, but 'hardly hard'.
(unless you make it so)
Lloyd
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    [ ... ]

    [ ... ]

    "Good accuracy" is asking a lot of a machine whose diameter turning varies in steps of either 0.02mm or 0.002" -- and both are approximations based on what the ballscrew can deliver with the step size of the stepper motors. Try to turn a Morse taper with it, and it will be *visibly* stepped.
    Coarse threads are sort of a stairstep wrapped around the shank, too. Limited by the step size, and the number of indicated points for a full rotation of the spindle. I think that it is either 100 or 128 points. And the CPU is an ancient 6502 (the thing which ran old Commodore PETs and Apple-][s among other things. It is seriously strained, and limits the spindle speed to something like 200 RPM or less for coarser threads.)
    And even repeatability is a problem. Especially in inch mode, it tends to gain or lose a step every run or so -- either diameter or Z-axis (along the bed). If you are doing a long series of runs, set up indicators to allow you to verify position at the start of each run, and adjust it before you hit the "start" button.
    But -- it is the easiest way to cut metric threads that I have. I've got a change gear set for the Clausing, but metric threads on an inch leadscrew are a real pain.
    And certain complex things are easier to do on it than on a manual machine.
    Now -- I recently saw one which had been modified by another member of the local metalworking club, with finer and faster stepper motors (with microstepping), and a LinuxCNC controller. That would make it a much nicer machine.
    Some of these days, I plan to retrofit mine with servo motors and encoders instead of the coarse steppers. A *lot* faster, and smoother -- even if the resolution is only 0.001" on radius (and it can be made a lot better during the conversion) the servo operation would make the Morse taper a proper smooth taper instead of a stepped cone.
    Oh yes -- the original has filled plastic wear strips on the underside of the bed, held down by two cap screws, and they tend to wear rather quickly under the heads, and give a lot more play to the carriage. Take some 1/8" aluminum, cut it to the size of the wear strips, counterbore the holes for the screws, and it spreads the force of the screws over a much larger percentage of the wear strips, and causes a lot more operating time between needs to adjust the strips. (Like years instead of months).          Enjoy,         DoN.
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wrote:

Thanks. They show up second-hand sometimes but it sounds like they aren't that useful as-is, or worth the time and expense to upgrade, if you have larger machines that also need attention. I suspected that the training exercises concealed their limitations. jsw
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I have a Multifix tool post which rotates 360 degrees in 40 steps of 9 degrees. http://www.anglo-swiss-tools.co.uk/tool-posts.html
Rotating the holder is useful with hand-ground HSS bits when cutting both a diameter and a shoulder, but I've placed it only square to the work with carbide, or boring bars.
Chinese toolholders fit the Swiss center post fine. jsw
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On Sat, 29 Mar 2014 17:23:41 -0400, Jim Wilkins wrote:

Thank you jsw
I have seen the fascinating Multifix. I assume that like most Swiss things it works extremely smoothly and costs both arms and all legs.
So I guess that you find at least some unspecified amount of rotation to be useful with HSS bits, and like DoN you only need it square for carbide inserts.
Bob
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The toolholder has to be square for parting, knurling, boring and threading too.
If you grind your HSS bit point symmetrically, like a threading bit but at an angle closer to 90, it both turns and faces when set to 45 degrees on the toolpost. Bent Armstrong-style bit holders accomplish the same thing in a standard toolpost.
I paid $50 for the Multifix post plus a cutoff, boring, and two turning toolholders, and special-ordered some import clone toolholders. I had gone looking for an Aloris clone and from my experience using a Dorian on a CNC lathe would have been happy with that style too.
The compound also rotates, steplessly to any angle, and on the Multifix the toolholder can be mounted on the right side of the post and reset square by pressing the toolholder against the tailstock spindle. On my lathe it's more accurate to remove the collet and press the cutoff holder against the face of its adapter jsw
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On Sun, 30 Mar 2014 17:36:59 -0400, Jim Wilkins wrote:

$50!!! Where did you get a deal like that? I thought it was several times that much!
It looks like a nice gadget.
I am not sure that it matters anyway; it looks like the smallest size might just barely fit on the cross slide, but not the top slide, on a Proxxon.
Bob
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http://www.brentwoodmachine.com/ I had to saw off and replace the bent and mushroomed M7 clamping screws.

It's nice, but I didn't claim it's any better than the Aloris / Dorian style, especially if you use carbide bits which already have the correct cutting edge angles.
I can tolerate a lantern or turret toolpost by planning the job carefully and milling custom-height shim blocks, some of which I still use to position small bits under the screws on the Multifix.
I started with a lantern toolpost I made from a bolt, partly by hand, and partly by clamping a tool bit to the top of the compound with a strap and two carriage bolts with heads ground down to fit the slot. jsw
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I'm not sure why you ask, but-----
I use an "aloris style" quick change toolpost/holder. It has dovetails for
lot. I have several tool holders for it that have a bit sticking out both ends, so I have to swing the toolpost around a lot.
Pete Stanaitis -----------------
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