aaarrggghh -- need help with Aloris #8 threading tool

I'm not being very successful using this tool - I think because I don't know if it wants rake or not - should the top (cutting) edge be horizontal,
tilted down (e.g. perpendicular to the back of the HSS bit) or tilted up? should it have any side rake? I know how to thread, that's not the problem, I just don't know how this tool wants to be ground, and the Aloris catalog isn't much help.
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Bill
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Here's a rule of thumb that should help you understand form tools, of which threading tools are one.
Any time you alter the top surface of a tool, such that it no longer is on the centerline at (all of) the point(s) of contact, you change the geometry of the tool. It may not be much, but the change can be significant in that it can effect how the tool performs.
When threading, unless an insert has been designed with rake, the tool should remain flat, parallel with the centerline of the spindle. No rake! To add rake of any description alters the tool's ability to take plunge cuts, which can be VERY useful when taking a thread to size, providing an excellent surface finish.
I am not familiar with the tool in question, so I may be wrong in that particular case.
Harold
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well, you were right - when I got this, it had a fairly significant negative rake and I just couldn't convince myself that it was ground wrong - which in retrospect should have been obvious - anyway, when I reground it so the top surface was level rather than negative, it worked great and I was able to complete the job I was attempting to do.
Another learning experience ---- thanks

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Welcome!
I figured that would be the case.
Harold
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So what's the problem? Chatter, squeal, heat?
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the problem is tearout - the tool is tearing the metal not cutting it. I'm going to regrind the top of the tool and try again, perhaps tonight
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On Tue, 10 Feb 2009 19:51:46 -0800, "Bill Noble"

You are either way below center, or have very little side relief.
Gunner
"If the personal freedoms guaranteed by the Constitution inhibit the government's ability to govern the people, we should look to limit those guarantees."
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If it is what I think it is, it has no side relief.
http://www.use-enco.com/ProductImages/0906120-11.jpg
It *can* be rotated to match the pitch angle of the threads.
Positive side rake and positive top rake should help.
Wes
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wrote:

Wes,
Both should be avoided like the plague. Each effects the tool's ability to generate a correct form, but not in a good way.
When you introduce rake, the tool no longer makes contact at the centerline---- When you introduce side rake, one side is positive, the other is negative, which is an absolute no-no.
Keep threading tools flat and on center for best results. Also, keep them sharp. Very sharp!
Harold
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I stand corrected. I was thinking of a good finish and you pointed out affects on form.

I wonder what the best way is to sharpen that style of threading tool?
Wes
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Send it out.
Gunner
"If the personal freedoms guaranteed by the Constitution inhibit the government's ability to govern the people, we should look to limit those guarantees."
Bill Clinton 1993-08-12
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On Thu, 12 Feb 2009 05:10:34 GMT, "Harold and Susan Vordos"

Good advice. Also, don't buy into the mythological tale that all threading is done with the compound, which is always set at 29.5 degrees. (That was good advice circa 1900 when using stringy hot rolled stock. Certainly, you aren't doing *that* are you??)
Feed straight in with the cross feed, with a tool perfectly on center, and zero rake..... you'll be fine! (12L14 is your friend......)
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wrote:

odd, everything I've read except your post says to use the 29 degree angle to cut the amount of cutter edge in contact with the cut in half. My lathe is only a 12X48 inch Logan/powermatic - I don't know if it is rigid enough to do some of the things a larger lathe does, but I can try it some time
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Keep in mind that the tool pressure is going to go up. Not an issue if part doesn't deflect easily but on long and slender stuff, it matters.
Wes
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wrote:

There's a lot of conflict with chip flow when plunge threading. I do not recommend you do it, although material choices and spindle speeds make a huge difference.
Point pressure on threading tools is extreme due to the narrow tool and depth of cut. Adding chip flow conflicts to the mix is a recipe for tool failure. Stick with the compound for better tool life. Plunge thread for finish passes, which will clean up the back side of the thread. Tool must be VERY sharp, and depth of cut must be shallow, .002" max., with less desirable.
Modern machinery (CNC's) that are capable of extreme spindle speeds tend to have much better results with plunge threading, although I'd avoid doing so even then if I had the option. You'll get much better tool life by feeding at 29 degrees.
Harold
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On Thu, 12 Feb 2009 21:39:50 -0800, "Bill Noble"

Well, now you're going to read another point of view.
I almost always use a 10 degree infeed when cutting a 60 degree thread. Read it many years ago in a Kennametal catalog, and it was recommended as a compromise between the 29 degree, where the trailing edge is dragging and 0 degree where chip flow becomes a problem.
I've been using this for many years, mostly on Logan 12" and 14" lathes and have been very happy. Granted, I am using carbide inserts and high speeds (or at least as high as I can). I don't usually use back gear, except on very large diameter threads, or if I have to thread up to a shoulder. Even then, I've gotten pretty good at stopping and retracting pretty quick, even cutting threads without an undercut and using my eye to retract at the same point.
'Course, it helps to have a LOT of practice/experience!
Even nicer, when I can, to use CNC. Speed is limited by carbide cutting speeds and CPU processor speed (limiting effective feedrate to 100 IPM). Cutting 1/2-20 threads at 1900 RPM is a joy to behold!
--
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| Scott Logan - ssl "at" lathe.com |
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I leave the top of threading bits dead flat when I surface-grind them precisely. They won't take quite as big a chip as the hand-ground ones with top rake but they certainly do work, even HSS on stainless.
jw
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As Harold said, the top should be perfectly flat. AFAIK, the term "side rake" does not apply to threading (form) tools. Lately I have been learning to cut miniature threads. This is done with a standard carbide threading tool except the flat on top is not 1/8th pitch as per normal. Machinery's Handbook says the flat on the tip which forms the root of external threads should be about .321 x pitch rather than .125 x pitch. I've been practicing single-pointing 00-90 threads in drill rod; ultimate goal being to make some very small taps and dies. Standard threading tools are reground and sharpened with a 1200 grit diamond wheel; Glendo's Accu-finish Series One. It took me a while to tumble to the idea of very small advances of the tool. In drill rod, anything larger than aprox. .0003" per pass will break the tool's point. In brass, I can get away with .0005" advance per pass. Without Glendo's diamond sharpening rig, I would have gone broke buying new tools every time the point gave way during the learning cycle.
Bob Swinney
wrote:

I leave the top of threading bits dead flat when I surface-grind them precisely. They won't take quite as big a chip as the hand-ground ones with top rake but they certainly do work, even HSS on stainless.
jw
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wrote:

know
up?
problem,
catalog
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Wayne, I'd be very interested to know more about the details involved in the proess you described here.
If you happen to use this setup again for something similar, please take some pictures to share with the rest of us.
The lathe modification of adding gears is interesting too.
If you have web pages showing any of the setups, please post the URLs.
--
WB
.........
metalworking projects
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