Speed and threading chart?

[Wreck™Wreck]

Sounds like the compound is set at the wrong angle. It should be rotated 29.5* counter clockwise from perpendicular to the spindle axis. Or clockwise 60.5* from parallel with the spindle axis.

Tom

Bloody Hell, there is a good deal of bull floating around on the web about this subject.

One may make excellent threads from the cross slide, contrary to what hundreds of Youtube "how to" videos will tell you.
No, this will not cause abrupt tool failure.
No, this will not render a thread unusable.
No it will not cause your machine to explode in a hail of shrapnel.

It will however **** off traditionalists in search of 1935 era copies of Machinery's Handbook.
Choose wisely

 

[brino]

Bloody Hell, there is a good deal of bull floating around on the web about this subject.

Perhaps, but let's try to clear up some confusion in this thread.

@higgite is totally correct that setting the compound to the wrong angle and then using the compound to feed the threading tool can give "off angle" threads. That is a very likely explanation for Andy's threading problem when using the compound.

One may make excellent threads from the cross slide

That is also absolutely correct!
In fact, this method only requires the tool bit to be ground to the proper angle and then set square to the work with a fish-tail gauge.
Since you then use the cross slide to advance the tool the angle of the compound has no consequence.
This is a very likely explanation for Andy's success when using the cross-slide.

What I have seen is that on my small, sloppy lathe I get better results when threading with the compound since I am only cutting on one side face of the threading tool, it seems to put less force on everything, reducing chatter and giving a better finish.

Here are a couple links to similar discussions to give some pictures:
http://www.hobby-machinist.com/threads/what-am-i-doing-wrong.54207/#post-449384
http://www.hobby-machinist.com/threads/threading-help.49488/

-brino

 

[Wreck™Wreck]

Perhaps, but let's try to clear up some confusion in this thread.

@higgite is totally correct that setting the compound to the wrong angle and then using the compound to feed the threading tool can give "off angle" threads. That is a very likely explanation for Andy's threading problem when using the compound.

-brino

Single point threading is a form tool operation, the included angle is fixed by the tool shape.
If the tool is square to the work moving either the cross or compound slides can not alter the angles of the tool form, this can only be accomplished by changing the angle of the tool itself which would require another axis of motion.

In other words the tool angle remains constant regardless of the approach angle, advancing the tool from the compound set at an angle alters the position in the X and Z axes not the tool angle itself.

 

[brino]

Sure the tool angle is constant.
But in the case with the compound set to the wrong angle that constant angle is also wrong.

I am NOT talking about a rotated tool. The tool gets fed in on a bad diagonal.

One edge of the cut thread is indeed controlled by how the tool bit angle meets the work.
However the other edge is controlled by a possibly bad angled compound.

Sorry, my CAD skills are not up to supplying a drawing.....and I don't even have visio on this computer.....

-brino

 

[higgite]

Bloody Hell, there is a good deal of bull floating around on the web about this subject.
.
Choose wisely

Yes, there is. But, discounting a widely accepted method of doing something in favor of another widely accepted method of doing the same thing doesn't do much to clear it up for beginners who might be interested in learning the proper way to apply both methods. Both of the forum threads that Brino posted links to above have illustrations of the proper angle vs the wrong angle for threading with the compound, for those who would like to compare both methods before they choose wisely.

Tom

 

[Wreck™Wreck]

Sure the tool angle is constant.
But in the case with the compound set to the wrong angle that constant angle is also wrong.

I am NOT talking about a rotated tool. The tool gets fed in on a bad diagonal.

One edge of the cut thread is indeed controlled by how the tool bit angle meets the work.
However the other edge is controlled by a possibly bad angled compound.

Sorry, my CAD skills are not up to supplying a drawing.....and I don't even have visio on this computer.....

-brino

The thread included angle CAN NOT be altered by the Approach Angle, it is fixed by the tool shape. A 60 Degree included angle tool shape will always produce a 60 Deg. included form on the part, the angle of approach does not change this relationship in any way.

I think that this makes the idea far more clear, a threading form tool produces a fixed included angle defined by it's shape, it will make a V at that angle regardless of the approach. One may advance the tool at any angle, this will not alter the form on a manual machine. The theoretical sharp point of the tool may move yet the form remains.

 

[Dan_S]

The thread included angle CAN NOT be altered by the Approach Angle, it is fixed by the tool shape. A 60 Degree included angle tool shape will always produce a 60 Deg. included form on the part, the angle of approach does not change this relationship in any way.

I'm sorry but this is wrong.

It is only a form tool when the angle of the compound is less than 30 degrees to perpendicular. When the angle is greater than 30 degrees, it will only be a form tool on the left cutting edge, because the right side of the tool has clearance.

The image below shows what would happen with the compound set to 45 degrees and 8 passes taken to get to depth. As you can see you are left with steps. As the number of steps goes to infinite, you get the black line. That would yield a thread angle of 75 degrees. This is why all the machinists I know take the last few light passes using the cross-slide, regardless of what angle they set the compound to. This turns the the toolbit back into a form tool.

https://drive.google.com/file/d/1uEs240xor_thckPBB5CpzwJbPBjjjkdk/view?usp=sharing

 

[Wreck™Wreck]

Indeed, doing so will leave steps on one side but the angle remains unchanged.
Did not recommend doing so merely pointing out that the tool angle is constant.
Like so.
For practical purposes this will not work well for reasons that are obvious.

This has been one of the most entertaining threads that I have seen here, keep it going.

 

[higgite]

This has been one of the most entertaining threads that I have seen here, keep it going.

What's the point in keeping it going? Looks to me like we have reached an impasse. Hopefully, the OP understands the various explanations well enough to choose wisely.

Tom

 

[Aqua-Andy]

Wow, thanks for all the info. My compound angle was not correct. I blindly set the compound to 29.5* and tried to cut threads. Well on our lathe the compound scale is set to 0* being parallel with the shaft. So today I played around some and set the compound to 60.5* and cut a perfect looking thread. This machine has been there for over twenty years and I'm the first to use it to cut threads. I was even told that the lathe is too worn out and inaccurate to cut threads. I found all the change gears to do the full range of threads the machine is capable of, they were packed away in a box and still had the cosmoline on them. every time I use this machine It seems like I learn something new.