aaarrggghh -- need help with Aloris #8 threading tool

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

So what's the problem? Chatter, squeal, heat?

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

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

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

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

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."

Bill Clinton 1993-08-12

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

If it is what I think it is, it has no side relief.

It *can* be rotated to match the pitch angle of the threads.

Positive side rake and positive top rake should help.

Wes

rake" does not apply to

threads. This is done with a

external threads should be

single-pointing 00-90 threads in

Standard threading tools are

Accu-finish Series One. It took me

drill rod, anything larger

get away with .0005"

gone broke buying new tools

Robert,

I spent a few days trying to get decent threads for making 0-80 and 00-90 taps in O1 drill rod. I found I needed to use a steady rest consisting of a piece of bronze rod in the tailstock chuck that had been drilled with a drill held in the headstock collet. An endmill was then used to mill about a 120 deg section of the rod away through which the threading tool can reach the rod to be threaded. With this, you can do the full depth in about 3 passes. It prevents the rod being threaded from bending away or up.

I was using a heavily modified 7x10 with two additional change wheels held in on bars that bolt to the change wheel banjo.

On my lathe, I found I could only get a consistant cut if the tool was set a couple thou high and then finger pressure was used to preload the tool back to the proper height. With the tool set on center, there was enough flex in the system to push the tool too low to cut properly, and if it was set higher, it wouldn't cut. With the tool pushed down (couple of pounds pressure) it would consistently cut a nice curl. I was just hand grinding the HSS tool, and the finish was not as nice as I would have liked, but I did end up threading about 60 stainless 1/16" rods to 0-80, made several taps, and another 20 studs in 00-90.

Then I found a set of 00-90 and 0-80 taps on ebay for something like $12. Much nicer than my homemade taps. And the bought taps were used to make better dies than I could make with my homemade taps. I think the same seller has another set ( may have recently sold ). Maybe he regularly lists these. It got me thinking that I would like to set up a rig to grind the threads vice cut them. Not sure if I would use the lathe, my homemade tool and cutter grinder or a purpose built machine.

Wayne Sippola

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.

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

Welcome!

I figured that would be the case.

Harold

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

on form.

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

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......)

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

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

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

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