Optimum compound angle

[Chriscb]

Afternoon all,

I'm 4 weeks into new ownership of a 7x14 seig lathe. Steep learning curve, but also quite a few transferable skills from turning wood.

My background is not engineering ( it's medical physics) so there are chasms of empty space in my learning and understanding of stuff that many seasoned metal lathe users take for granted.

My questionsimply put, is there an optimum angle for the compound on the 7x14 lathe? I would appreciate explanations to support the answers please (to better understand the logic). I'm fairly certain I know, but confirmation is always useful. Currently it's set to 10 degrees.

A second question is the optimum position of the tool post. Currently I have it positioned just left of centre on the saddle - would it be better dead centre?

Thanks for your time.

regards,
Chriscb

 

[magpens]

@Chriscb
I don't really understand the full import of your questions.
I have been using a Sieg 7x14 for over 10 yrs for pen-making.

As far as I can tell, the tool post has only one position ... centered on the threaded hold-down stud.
It can, of course, be twisted on the stud. . I often do that simply to present a different part of the cutting edge to the workpiece.
But maybe you are thinking of moving the tool post left or right with the feed screw handle on the right end of the compound slide ??
I don't worry too much about that .... just keep the tool post approximately centered above cross-feed handwheel.

As for the angle of the compound, I normally keep that at 0 degrees based on the degree markings provided for the compound.
The only time I depart from that practice is if I want to make a tapered nib for a pen or want to create a conical shape for some reason.

I am wondering if we are using common terminology ? . Good diagrams are hard to find, but this one's not bad ....

 

[darrin1200]

I think you may be over simplifying the cross slide. Positioning of the cross-slide and the toolpost holder will be very dependent on the task you are doing. (ie face cutting, side cutting, parting or threading). The angle to which the tool is presented to the work, will be dependent on the cutter you are using as well as the task.
It's not a simple setup and go. I am by no means an expert, but if you were to list what cutter you have, what material you are cutting and what type of cut you are taking, someone could give you optimum settings to get you started for that task.

Here is a review video of that lathe, which gives some detail discussion of the cross-slide and tool post

Good luck with your new machine. The more you learn the more fun it will be.

 

[Dehn0045]

IMHO it is more a matter of convenience than performance. With small lathes some people remove the compound when not needed to increase rigidity.

 

[Oliver X]

I've never given it a whole lot of thought and I've been a professional machinist for a couple decades. I used to do a lot of manual lathe work and have a couple very small lathes at home. Typically, you want to reduce leverage on the tool, maintain clearance and have the compound handles and protuberances out of the way. Every axis that isn't being used should be locked down. If there is some optimum angle I haven't the foggiest what it is.

 

[Chriscb]

@Chriscb
I don't really understand the full import of your questions.
I have been using a Sieg 7x14 for over 10 yrs for pen-making.

As far as I can tell, the tool post has only one position ... centered on the threaded hold-down stud.
It can, of course, be twisted on the stud. . I often do that simply to present a different part of the cutting edge to the workpiece.
But maybe you are thinking of moving the tool post left or right with the feed screw handle on the right end of the compound slide ??
I don't worry too much about that .... just keep the tool post approximately centered above cross-feed handwheel.

As for the angle of the compound, I normally keep that at 0 degrees based on the degree markings provided for the compound.
The only time I depart from that practice is if I want to make a tapered nib for a pen or want to create a conical shape for some reason.

I am wondering if we are using common terminology ? . Good diagrams are hard to find, but this one's not bad ....

View attachment 316163

Evening,

Ahh.. I guess I should have defined terms. No matter - the diagram you found is excellent in doing just that. The confirmation I was looking for was the position of the tool post over the cross feed hand wheel, which you very succinctly gave.

Thanks.
Chriscb

 

[Chriscb]

I think you may be over simplifying the cross slide. Positioning of the cross-slide and the tool post holder will be very dependent on the task you are doing. (ie face cutting, side cutting, parting or threading). The angle to which the tool is presented to the work, will be dependent on the cutter you are using as well as the task.
It's not a simple setup and go. I am by no means an expert, but if you were to list what cutter you have, what material you are cutting and what type of cut you are taking, someone could give you optimum settings to get you started for that task.

Here is a review video of that lathe, which gives some detail discussion of the cross-slide and tool post

Good luck with your new machine. The more you learn the more fun it will be.

Evening Oliver,

Video is excellent, thank you. I have actually seen this video before I'd bought the lathe, and at the time didn't attach any great significance to it. Watching it again has made much more sense. As you say, learning is fun!

As to the tasks I've been completing on the lathe, they vary from making a tommy bar from an old Forster bit, to rounding off acrylic blanks and making a prototype fountain pen from wood with acrylic inserts. I've used both HSS and indexable tools to do the cutting. I've found that both style of tools have their uses - uncoated carbide tips make short work of acrylics and leave a very good finish.

Thanks for your input.

Regards,
Chriscb

 

[Chriscb]

IMHO it is more a matter of convenience than performance. With small lathes some people remove the compound when not needed to increase rigidity.

Evening,

That's an interesting thought which needs some investigation.

Thanks.
Regards,
Chriscb

 

[Chriscb]

I've never given it a whole lot of thought and I've been a professional machinist for a couple decades. I used to do a lot of manual lathe work and have a couple very small lathes at home. Typically, you want to reduce leverage on the tool, maintain clearance and have the compound handles and protuberances out of the way. Every axis that isn't being used should be locked down. If there is some optimum angle I haven't the foggiest what it is.

Evening OIiver,
This is exactly what I was after - succinct and shooting from the hip. Makes lots of sense, and on reflection I've been doing just that so thanks for the confirmation.

Regards,
Chriscb.

 

[bmachin]

The only thing that I would add is with regards to the tool post: The one thing you DON'T want generally speaking, is to have the tool post unsupported; ie having the compound cranked out to where it is not centered on the cross slide. Otherwise you are looking at introducing vibration and chatter.

Larger lathes generally have a slot in the compound for positioning the tool post side to side. In addition some machinists, particularly those who are trying to get the absolute best finish and precision that they can out of their somewhat undersize/underweight lathes will remove the compound altogether when it's not needed (which is usually) and bolt their tool post to a substantial block that has been fixed to the cross slide to replace the compound. (See Stefan Gotteswinter)

All that said, sometimes the compound just gets in the way, so move it to where it isn't.

Bill

 

[magpens]

One thing that has never been clear to me is . . . . why the term "compound" is used for that part of the metal lathe ?

Our common usage of the term in everyday life implies a union of 2 or more parts/substances . . . . think of a "chemical compound".

So what aspect of the features or uses of this part of a lathe justifies calling it "the compound" ?

 

[rherrell]

It slides in and out and it also rotates so it has a compound movement.

 

[leehljp]

One thing that has never been clear to me is . . . . why the term "compound" is used for that part of the metal lathe ?

Our common usage of the term in everyday life implies a union of 2 or more parts/substances . . . . think of a "chemical compound".

So what aspect of the features or uses of this part of a lathe justifies calling it "the compound" ?

Mal, I never thought of that - as it relates to a lathe. Yep, on a round turning rod/blank there is only one effective angle - IF the rod is turning. I can see "compound" if doing an end cuts. Unless "compound" is used to describe the tool and not the effect. A compound tool angle from a users perspective will only have a single directional cut on a turning lathe, where as a compound cut on a board by a saw will have a multi dimensional cut in relation to the surface.

 

[Oliver X]

One thing that has never been clear to me is . . . . why the term "compound" is used for that part of the metal lathe ?

Our common usage of the term in everyday life implies a union of 2 or more parts/substances . . . . think of a "chemical compound".

So what aspect of the features or uses of this part of a lathe justifies calling it "the compound" ?

It is a union of two parts. It's a secondary axis carried on the cross slide and distinct from it. Also angles in more than one axis are referred to as compound in the machining trades. Not sure about elsewhere.

 

[Curly]

Compound it I set the wrong angle!!!

 

[magpens]

Compound it I set the wrong angle!!!

Do you mean "conFound it" ??????? . . . . . . . . OOOPS !! . . . There goes my cantspell-checker !.!.!.!

 

[Curly]

Do you mean "conFound it" ??????? . . . . . . . . OOOPS !! . . . There goes my cantspell-checker !.!.!.!

It was a joke Mal. Must be your can't tell if it is a joke checker.
Shouldn't "cantspell-checker" be can'tspell-checker?

One of the important uses of the compound is with single point threading. It is set to something like 29 1/2º and with each thread cutting pass it is advanced to deepen the thread. The 1/2º from 30º is to keep the back edge of the cutter (right side of the V being cut) from dragging on the thread making it rough, the left side and a bit of the tip doing the cutting. At least as I understand the theory of it. Someone like Rick Herrell might be able to explain it better than I.

I put the tool post and set the compound slide to where ever it is best positioned for the cut at hand or is out of the way. I have a bigger lathe so thus far don't have much in the way of rigidity issues. You watch, next time it will shake rattle and roll.

 

[magpens]

@Curly

Yes ..... I know it was a joke ..... but .....

No ..... cantspell-checker ..... "cant" as in "angle" !! . . . . . Get it ? ? ? ? ? ?

CANT Scrabble® Word Finder

10 Playable Words can be made from Cant: an, at, na, ta, act, ant, can, cat, tan, cant

scrabble.merriam.com

Merriam-Webster Scrabble Dictionary . . . .

cant . . . . verb . . . . to tilt or slant

But . . . . .
Your description of single-point threading is no joke . . . . . and I wish I could understand it . . . . . but have never done single-point.

 

[Curly]

Since this is in part sort of a wood turning/working forum lets use the sawmill term cant. https://www.woodweb.com/knowledge_base/Understanding_the_Sawmilling_Term_Cant.html

 

[Dehn0045]

Given the direction of this thread I'm thinking we should go with the earliest uses of cant: "ostentatious conventionality in speech" or "the jargon of criminals and vagabonds"

On a more serious note, I've heard the description of threading and 30 degrees only cutting on the left side of the tool from many different sources. @Curly, I know that isn't necessarily what you are saying, at least not with the level of certainty that I've heard elsewhere. But recently I saw a video about this that was pretty eye opening. While the 30 degrees minimizes the amount of work done by the right side of the tool, it doesn't eliminate it (unless you do an infinite number of passes). This demonstration by Joe Pieczynski illustrates this pretty well and really helped me visualize what is going on.

 

[rherrell]

Using the compound to advance the tool for thread cutting is old technology, it was necessary for chip control when using hss cutting tools. With todays modern carbide inserts it's no longer necessary to use the compound. I feed straight in using the cross slide and my threads turn out fine. Another advantage to this method is you have a direct reading on your thread depth. If you use your compound set at 29 degrees then for each .001" you advance the compound it's not .001" but some fraction of that.

HAVING SAID ALL THAT...I still use the compound at 29 degrees when cutting larger threads, 8tpi and under, because at this point the threading insert becomes more of a form tool and using the compound set at 29 degrees will reduce chatter.

The threads we use for pens are so small that I wouldn't worry about using the compound UNLESS you have a small, lightweight lathe like a 7x10, then I would use the compound.

 

[Curly]

Thank you gentlemen. Happy to learn something and to be corrected.

 

[rherrell]

Thank you gentlemen. Happy to learn something and to be corrected.

Don't get me wrong Curly, using the compound is not "wrong", just unnecessary for the type of threads used for making pens.

CNC machines still use the compound infeed angle of 29 degrees so there is obviously some benefit to it but for making small threads on plastic it really isn't necessary.

 

[rherrell]

Sorry if I hijacked your thread, here's my answer to your original question...

It doesn't matter what angle the compound is at if you're not using it, I keep mine at 30 degrees because it's out of the way there. The important thing is to have the top(sliding part) flush with the end of the bottom part, this will give you the best compromise of rigidity and reach.

This pic shows the position at the end of the compound, notice how I keep it flush on the end.

This shows the angle, right between the saddle lock on the right and all the other handles on the apron...

Just find a comfortable spot and keep it there until you need it for something.

 

[Chriscb]

Sorry if I hijacked your thread, here's my answer to your original question...

It doesn't matter what angle the compound is at if you're not using it, I keep mine at 30 degrees because it's out of the way there. The important thing is to have the top(sliding part) flush with the end of the bottom part, this will give you the best compromise of rigidity and reach.

This pic shows the position at the end of the compound, notice how I keep it flush on the end.

View attachment 316401

This shows the angle, right between the saddle lock on the right and all the other handles on the apron...

View attachment 316402

Just find a comfortable spot and keep it there until you need it for something.

Evening a Rick,
Hey no worries. It's worth the highjack for the advice. As I said at the beginning, I've no doubt that this sort of basic information was passed on almost as an aside from one grizzly machinist to the young un on the shop floor.
So thanks.
Chriscb

 

[Chriscb]

And, on reading that back, no way are you the grizzly machinist... just the guy with a long beard

 

[Penultimate]

IIRC, if you set the compound at 30 degrees then the tool advances 1/2 the compound reading perpendicularly into the workpiece.

 

[farmer]

Now picture the lathe turned off with 24 evenly locking positions on the chuck, called a indexer
Use a indexer and a live cutter on the tool post .
Using the compound slide
Now you can make diagonal cut inlayed decretive rings or trim rings.
A lathe is one of the only machines in the world that can reproduce it's self.

These are not a compound cut but hopefully help you understand what I am saying .
The indexer is on the left side and is the row of holes drilled into the drive pully.

 

[farmer]

double post