Live threading question

Dz cues,
He is right. If you look up thread milling in the Machinery's Handbook (The Machinist's Bible). It explains it well. Your video clip of the thread grinding shows the correct way. Just because we cut threads on a much smaller scale does not change the theory. A single pont cutter revolving at 30000 rpm is no different than a solid disc as per the large grinding stone. When you thread mill at right angles to your piece you are not accounting for lead of thread. It is just not practical to tilt the axis of your cutter as to your lead. As such we accept the slightly less than perfect thread form. If you think about standard single pont threading where your tool is stationary you always grind a relief on the leading edge of your cutter to account for the lead. You cant do that with live tooling. Having said all that you would have to inspect with a microscope to actualy see the less than perfect form because it is on such a small scale. If you wanted to do it theoreticaly correct than you would have to tilt your cutter on an angle equal to the lead. So with our router set up you would keep the tool parallel to the bore but tilt your cutter front to back. So in other words if you are looking over top of the lathe the cutter or bar is parallel to your bore but lookig at your lathe from the front your router would be tilted at an angle equal to the lead. So having said that your bar would have to be small enough to give you adequate clearance.
 
dzcues said:
Hi Neil,

I don't mean to be contentious & I'm always happy to learn something new...but I must admit that you pose some things I never heard of.

I've seen a lot of thread milling on all sorts of CNC machines, vertical & horizontal & I NEVER saw anyone adjust the tool angle. On most machines you cannot adjust it. Your tool MUST be aligned with both the spindle & the axis of its movement, otherwise, the thread form is no longer square to the axis of the thread.

As for staggered tooth thread mills, I've only seen that apply to "tap" style thread mills...not the single form (multi-tooth) thread mills. See attached pic. They do reduce the cutting pressure but only because you have half as many teeth engaged at any given time. These, too, are always used in-line with the thread axis.

I'm hoping the distortion in the thread form you describe is more theoretical than real as I've never heard about this in the past. I've also inspected many oddball threads that were generated with both styles of T-Mills and never noticed any concavity on an optical comparator.

Please enlighten me if I'm mistaken or misunderstanding you.
Click to expand...

The reason you do not see that style of tool for sale is because, a bit like uneven fluted reamers, were only made by toolmakers for particular jobs that required chatter free round holes,that could not be honed,bored or jig ground.
For the thread milling, I made lots of those cutters 20 + years ago, they were made because the threads were proprietary thread forms and had to be accurate. We would thread mill the threads of the inner and the outer parts. The concave is very small in the .014mm to .02mm . Sometimes we would make threadforms that bolged, ie Convex on the face to allow for shrinkage and then form a straight face after moulding.
The bigger the diameter,the lesser the helix angle, and the smaller the cutter,the less this effect has. Of course, the tool has to be big enough to maintain it's rigidity through the cut. The uneven left and right cut thread cutting tools is not a new idea.The man who showed me, was a Toolmaker from England who finished his apprenticeship in 1943.There were alot of tricks needed back in the day to make some things.
Most things that are made, do not require this level of precision or accuracy.
You are correct about the multi form thread tools, they have to be in axial alignment and are very effective in producing a thread in a small amount of time.
 
Canadian cue said:
Dz cues,
A single pont cutter revolving at 30000 rpm is no different than a solid disc as per the large grinding stone. When you thread mill at right angles to your piece you are not accounting for lead of thread. It is just not practical to tilt the axis of your cutter as to your lead. As such we accept the slightly less than perfect thread form. If you think about standard single pont threading where your tool is stationary you always grind a relief on the leading edge of your cutter to account for the lead. You cant do that with live tooling.
Click to expand...

Ahhh. Now that I can understand. Despite the relief that is ground on the thread mill, it effectively becomes a solid disc at speed. I couldn't see past the fact that the cutter DOES have clearance. The high speed makes it a whole 'nuther animal. Thanks for making it easier to see.

And, you're right, Neil, about the difficulty of noticing an error of .0007" in the thread form. I never saw it but then again, it wouldn't be as noticeable on external threads due to the extra clearance on an OD that is not available on internal threads.

Thanks guys, I learned something new today.

One more question: if you tip the tool to match the lead angle, you are also changing the thread form from 60°, as seen from the thread axis. Was this something you had to account for when making your custom tooling?

And a note to other inquiring minds: do not let this dissuade you from trying live tooling. The problems discussed here, though real, are so slight as to be unnoticeable. Give it a try.
 
dzcues said:
Both the shank & cutter head are 1/4" diameter. I hope you noted that the front part of the bore was enlarged to register the locating barrel on the joint pin. The attached sketch shows how everything fits in the hole.

These cutters have clearance built into them beneath the cutting edge & therefore do not need to be "tipped". If you can fit the tool into a hole, you can safely cut any reasonable thread without running into clearance problems.

There seems to be a misconception that was seized upon by this forum about the need to tip a router to match the helical angle of the thread. I forget who the perpetrator was but I recall the oohs & aahs when he said this & thinking "oh-oh". Since he touched upon a concept that was new to the forum, everyone accepted it as gospel. In this situation, he was completely wrong.

The ONLY time you need to tip your cutter is when the cutter has NO CLEARANCE. The best example I can think of is a Thread Grinding Machine, in which threads are machined using a large diameter grinding wheel. Since the wheel is one solid piece, it must be tipped to the exact helical angle deterimined by the diameter & pitch of the threads being ground.

To finally get around to answering your question, Chris, no, there are no problems with angled threads or clearance. You will kick yourself for not trying these sooner.
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I don't have any sound on my computer so I missed the double step, but should have known it after seeing the type of pin you were using. The multi flute thread mill would not allow you to install pins with full threads on them. But for intalling pins with the shoulder in the middle I think I like your set up better than the single flute bits. I have those bits or similar ones and have used them for making a few things, but my pins are threaded all the way. I have used the multi flute bits to make brass pins on my Deluxe lathe. I even made a stainless pin with shoulder in the middle, but it did the bit in, so brass is as much pin making as those bits can do.
 
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cueman said:
I don't have any sound on my computer so I missed the double step, but should have known it after seeing the type of pin you were using. The multi flute thread mill would not allow you to install pins with full threads on them. But for intalling pins with the shoulder in the middle I think I like your set up better than the single flute bits. I have those bits or similar ones and have used them for making a few things, but my pins are threaded all the way. I have used the multi flute bits to make brass pins on my Deluxe lathe. I even made a stainless pin with shoulder in the middle, but it did the bit in, so brass is as much pin making as those bits can do.
Click to expand...

Did you see how long the shank was sticking out of the router? The neck can be extended by grinding part of the shank down. This is done for the tool that cuts the threads in the shaft, and the same tool could cut the threads for an all thread pin.

Kelly
 
Kelly_Guy said:
Due to risk of vibration?

Kelly
Click to expand...

Yeah...but it might work. That's why all the "probably's". My shaft cutter is relieved a total of 1 9/16" back & it works fine. If you take 2 or 3 cuts & it should be OK. The problem with carbide is it works fine until it fails catastrophically.

I guess I'm gun-shy after showing my a$$ earlier in this post.

Go for it. The results will be worth it if it holds up. Worst case scenario - you lose one cutter.
 
dzcues said:
Yeah...but it might work. That's why all the "probably's". My shaft cutter is relieved a total of 1 9/16" back & it works fine. If you take 2 or 3 cuts & it should be OK. The problem with carbide is it works fine until it fails catastrophically.

I guess I'm gun-shy after showing my a$$ earlier in this post.

Go for it. The results will be worth it if it holds up. Worst case scenario - you lose one cutter...
Click to expand...

...and an eye. Since I am using the same pin you are, Chris, I will let you try it. :p

Kelly
 
Bob,

If you notice with the thread mills like you use, they always have a listed range of applicable threads that mill can cut. The reason for this is the same thing you guys are talking about here. I know I actually use them beyond the recommended range, but even then the differences in the thread formed are so small they have no bearing on what I do.

Great new site, and videos! As always.

Royce Bunnell
www.obcues.com
 
one flute or four

dzcues said:
Ahhh. Now that I can understand. Despite the relief that is ground on the thread mill, it effectively becomes a solid disc at speed. I couldn't see past the fact that the cutter DOES have clearance. The high speed makes it a whole 'nuther animal. Thanks for making it easier to see.

And, you're right, Neil, about the difficulty of noticing an error of .0007" in the thread form. I never saw it but then again, it wouldn't be as noticeable on external threads due to the extra clearance on an OD that is not available on internal threads.

Thanks guys, I learned something new today.

One more question: if you tip the tool to match the lead angle, you are also changing the thread form from 60°, as seen from the thread axis. Was this something you had to account for when making your custom tooling?

And a note to other inquiring minds: do not let this dissuade you from trying live tooling. The problems discussed here, though real, are so slight as to be unnoticeable. Give it a try.
Click to expand...

I showed your video to my friend ( well known high end cuemaker) he says it's really a nice video and really a nice product youre' making. Likes the threads a lot .... I guess there's always a faster gun??lol (or better way)
 
One more question: if you tip the tool to match the lead angle, you are also changing the thread form from 60°, as seen from the thread axis. Was this something you had to account for when making your custom tooling?

And a note to other inquiring minds: do not let this dissuade you from trying live tooling. The problems discussed here, though real, are so slight as to be unnoticeable. Give it a try.[/QUOTE]


The tools do not need compensation when inclined to the correct helix angle.
There are lots of advantages to live tooling.
Now just to figure out making a cutter for the radial pins.
 
Carom shafts

Just to make sure so I don't cock up here :
Would these work to make the stock carom wood threads or are these a special breed for the carom industry?
I have no Carom shaft to measure at but would be kind of nice to have a tool which would work for this work as well - not just in the construction it self.

Boy I have been looking for these - thanks Joey :thumbup2:

K
 
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