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
Reply to
Bob S
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Bob S fired this volley in news: snipped-for-privacy@4ax.com:
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
Reply to
Lloyd E. Sponenburgh
I have a Multifix tool post which rotates 360 degrees in 40 steps of 9 degrees.
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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
Reply to
Jim Wilkins
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 -----------------

Reply to
Pete S
The tools which I use benefit from having one face of a quick-change toolpost (e.g. Aloris) parallel to the face of the chuck, and the other parallel to the axis of the workpiece.
This assures that the insert tooling for threading is in the proper position, and that turning and facing tools (e.g. the Aloris BXA-16N) have their working edge almost at right angles to the direction of travel during the cut. For turning, the tip very slightly leads the rest of the side, so when you halt at a given location and switch to cross-feed from lateral feed, you get a nice finish cut on the face left by the previous cuts.
Also, the knurling tool is sensitive to angle, and is best used with the faces of the knurls parallel to the axis of the workpiece.
This also means that a boring bar holder will have the boring bar parallel to the axis, so if the tool tip is touching to cut, the rest of the boring bar will clear the workpiece -- assuming that it is not too large for the hole in question.
I have, in addition to this, two holders which hold the inserts at about 60 degrees, so they look like an oversized threading tool. These are useful for breaking (beveling) corners after the main work is done -- without ever needing to shift the toolpost itself.
The only time I need to shift the toolpost (other than when it has been removed to replace it with a toolpost grinder or something else) is when I shift the compound angle from 29.5 degrees (normally 60-degree V threads) to something else, such as 14 degrees for Acme threading, or other angles for weird threads, e.g. the 55 degree Whitworth threads.) So -- when I shift the compound angle, I reset the toolpost to again be parallel to the chuck face and the workpiece axis.
Selected by the bit and the holder, not by rotating the toolpost. Aloris has some insert holders in which the insert part can be set in 15 degree increments to produce a reasonable tool angle for whatever you want to do. Again -- without having to move the toolpost.
Agreed -- assuming that you need the rotation at all. I find that I prefer the tool holder to stay in the same position. If it were not for the occasional adjustment for the weird threads, I would drill the compound and the toolpost for a dowel pin, so it would always go back on at the same angle.
So -- look at the Aloris holders which have the adjustable insert holders -- and (almost) never touch the toolpost itself.
Just my own preference here.
I think that the habit of rotating the toolpost comes from the old days of the Lantern style toolposts -- where every time you changed a tool, you had to re-adjust all the angles prior to clamping it down again.
Enjoy, DoN.
Reply to
DoN. Nichols
While I also use an Aloris style, and I keep it locked down with one dovetail parallel to the chuck face, and the other parallel to the workpiece axis.
If you are putting two tools in a single holder (I don't, as this usually requires re-adjusting the tool height when you swap between ends), put one turning tool and one facing tool in the holder, so when you switch from the side dovetail to the front dovetail the tool is already at the proper angle -- no need to shift the toolpost. And shifting it defeats the indexable tools idea, where you always have the tool at the same projection from the post. If you use one tool to do something, and zero the dial with that tool, then shift to another which does not require you to re-zero the dial (e.g. facing the workpiece), if you have not shifted the toolpost, when you go back to the first holder the dial is still correct for the next part to be turned to the same diameter. If you have shifted the toolpost, you will have to re-establish the zero for that tool when you come back to it.
As I mentioned in an earlier (slightly earlier) followup in this thread, the only time I loosen the toolpost is when I'm resetting the compound for threading at other than 60 degree threads -- or when putting the toolpost back on after using something like a toolpost grinder.
Different ways for different people. :-)
Enjoy, DoN.
Reply to
DoN. Nichols
Interesting. I always thought that a knurling tool was used at a very slight angle to the work piece so that the teeth gradually cut in as you advanced the Z axis feed.

Reply to
Bob La Londe
The problem in all machines, whether it is a mill or a lathe, is that if you have adjustable angle part, it can be off from 90 degrees (or whatever the normal setting). Perhaps it went off last time you took a rough cut? You have to always check it.
In my early days with machinetools I though it is nice to have adjustable things for doing those odd jobs, but I have changed my mind regarding that. A two axis tiltable vice is just never 90 degrees, unless you spend a lot of time adjusting and measuring it. Sure, it is nice when you need to machine the odd angled surface, but all the other time it is a compromise compared to normal vice. Same for bridgeport J head - it could have moved - while a sturdy mill head with fixed angle is always at correct angle (or it is broken). If at all possible, I nowadays have several vices etc. with different degrees of rotation freedom - and use the one with minimum freedom that does the job. Keeps me sane at reasonable cost. :)
My opinion: rotation is nice, but install some mechanism that keeps the holder definitely at 90 degrees, when you don't want to rotate it. (With reasonable accuracy for the job, nothing is precisily 90 degrees).
My quick-change holder has a long pin for that. After rotation (for threading or whatever) install pin back to index it, and then tighten the big-ass M20 nut that holds the quick-change holder body. The pin prevents it from rotating when not wanted. The pin and its hole have good enough fit that it really is quite close to correct angle.
Kristian Ukkonen.
Reply to
Kristian Ukkonen
Thanks DoN for the clear explanation of the "no rotation" approach. It sounds like "small rotation only for unusual threading, and everything else handled by specialized holder". I suppose that if you did the odd-angle threads often enough you could even make or buy a holder for that angle, and never move the toolpost at all.
I can see that the Aloris-style holders and the carbide insert holders seem to have undergone mutual evolution to work well together.
It looks like most of the same things could be done with HSS bits, except for the 15 degree indexing insert holder trick.
Bob
Reply to
Bob S
Yes, I agree; an adjustable angle is likely to be a wrong angle...
A good mechanism for resetting it would be very helpful.
Bob
Reply to
Bob S
Well, I was thinking about the contrast between the Aloris-style square posts which are apparently intended to almost never rotate, and the various round-post designs that apparently consider rotation as a feature. I was wondering how each style worked out in practice and whether people often wanted to rotate the non-rotating style, or never rotated the rotating style.
I was also curious what would happen if there was an in-between style of post that (for whatever reason) only allowed limited rotation; would it be useable. That's why I was asking about the "requirements" rather than the capability.
Certainly the popularity of the square-post style suggests that rotation is not vital as long as the toolholders come in varieties that include popular angles.
Wow, tools out both ends; that's one that I never heard of. I recall reading about people who have tools on all four sides of a rotating turret, and reading that they tend to acquire scars.
Bob
Reply to
Bob S
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
Reply to
Bob S
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
Reply to
Bob S
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
Reply to
Jim Wilkins
Greetings Bob, I've read the other responses and thought I'd contribute, since it is metalworking afterall. I own a machine shop and make my living with it. I have an Aloris tool post on one lathe. It mostly sits square with the X and Z axes. Sometimes I rotate it a bit for one job or another. But even though it is mostly normal to the axes it is almost never square with the compound. The compound gets slewed over to different positions on a regular basis. For example, I might need to use the compound to machine a taper or a large chamfer. It might be set at 29.5 degrees for threading 60 degree threads. And then it will need to be rotated again to cut some Acme threads. And then maybe the next day rotated again for clearance. But no matter what angle the copmound is set at the tool post will still probably be square. So having 360 degree rotation of the tool post is really nice. Eric
Reply to
etpm
$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
Reply to
Bob S
Thank you Eric for pointing out so clearly what I had completely overlooked. Its not just the tool angle. The post system has to be able to rotate enough to compensate for whatever angle the compound slide is at. It might not matter much for turning a slight taper but it would matter a lot for half-angle threading.
Bob
Reply to
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.
Reply to
John B.
[ ... ]
O.K. My knurler (an Aloris scissors style knurler with arms on dovetail slides and a single leadscrew adjusting both symmetrically around the set height), happens to be fitted with knurling rollers with a slight rounded bevel, which handles that part.
And it is often used in the middle of a workpiece (where the knurl happens to be needed) just by positioning it there and either clamping it down at that point, or (if already set for the depth of knurl desired) by using the cross-feed to remove it from the first workpiece and then advance it into the second.
I certainly agree that a bump style knurler would benefit from the slight angle, but I think that a scissors style does not need it.
Enjoy, DoN.
Reply to
DoN. Nichols
Agreed.
[ ... ]
Not all J-heads are adjustable. The Bridgeport used in their early CNC machines had a choice -- rigid ram, or adjustable one. The rigid ram is normally set up *once*, and taper pins used to lock it once you have it right. (Before pinning there is a very small freedom of adjustment if the bolts are lose.) And yes, that machine *did* have a J-head.
Enjoy, DoN.
Reply to
DoN. Nichols

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