# Compound Slide Angle



## KevinMaiorka (Aug 1, 2016)

So I have been machining now for 10 1/2 years with a smithy 1220 machine. I have been using the compound for almost all of these years set at a 45° angle when I do general machine work. I have my compound set at this angle due to the fact that if I increase my cut by .010 then the cutter only advances .005 into the workpiece and I only remove .010 from the diameter of the work. Makes it a lot easier for me to do the math in my head and if I only need to remove a thou then only advance it one thou and not have to try for a half thou which is nearly impossible on some compounds. My compound is graduated in .002 divisions so this also makes it a bit more accurate when cutting in my opinion. 

What do y'all set your compound angle at? I see most people usually have there's set parallel with the bed ways. 

Kevin 

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## brino (Aug 1, 2016)

Mine's probably sitting at 29 degrees from the last time I threaded something. 
I tend to only change it when I hafta.
-brino


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## JimDawson (Aug 1, 2016)

brino said:


> Mine's probably sitting at 29 degrees from the last time I threaded something.
> I tend to only change it when I hafta.
> -brino



:+1:


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## Bob Korves (Aug 1, 2016)

KevinMaiorka said:


> So I have been machining now for 10 1/2 years with a smithy 1220 machine. I have been using the compound for almost all of these years set at a 45° angle when I do general machine work. I have my compound set at this angle due to the fact that if I increase my cut by .010 then the cutter only advances .005 into the workpiece and I only remove .010 from the diameter of the work. Makes it a lot easier for me to do the math in my head and if I only need to remove a thou then only advance it one thou and not have to try for a half thou which is nearly impossible on some compounds. My compound is graduated in .002 divisions so this also makes it a bit more accurate when cutting in my opinion.
> 
> What do y'all set your compound angle at? I see most people usually have there's set parallel with the bed ways.
> 
> ...


If you have your compound set at 45 degrees to the cross slide and the bed ways, you advance the tool .707 for every 1.000 that you feed in on the compound.  That means you will cut 1.414 if you have a radius reading compound dial.  If you want to advance .500 for every 1.000 you feed in on the compound, you will need to set the compound at 60 degrees to the cross slide, 30 degrees to the bed ways, which will cut 1.000 on the diameter when using a radius reading dial.  Simple trigonometry learned 50 years ago, still remember the numbers for those angles without a chart or electronic gizmo...


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## T Bredehoft (Aug 1, 2016)

Isn't it wonderful what we can remember. I remember that the diagonal of a one inch square is 1.414, the same figure bob mentioned above,  Somehow, half the diagonal is .707, but I can't remember what its for.  Why can't I remember what I had for breakfast?


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## Charles Spencer (Aug 1, 2016)

brino said:


> Mine's probably sitting at 29 degrees from the last time I threaded something.



Yep.


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## RJSakowski (Aug 1, 2016)

KevinMaiorka said:


> So I have been machining now for 10 1/2 years with a smithy 1220 machine. I have been using the compound for almost all of these years set at a 45° angle when I do general machine work. I have my compound set at this angle due to the fact that if I increase my cut by .010 then the cutter only advances .005 into the workpiece and I only remove .010 from the diameter of the work. Makes it a lot easier for me to do the math in my head and if I only need to remove a thou then only advance it one thou and not have to try for a half thou which is nearly impossible on some compounds. My compound is graduated in .002 divisions so this also makes it a bit more accurate when cutting in my opinion.
> 
> What do y'all set your compound angle at? I see most people usually have there's set parallel with the bed ways.
> 
> ...


I have set my compound to a variety of angles.  29.5º for threading, 0º if I want some extra travel capability on the cross slide.  and I set it at 90º for controlled travel in the z direction.

BTW, setting the compound at 45º advances the feed by .0071" in the x direction for every .010"  If you want to advance .005", the compound angle should be set at 60º.  Setting at 84.3º will advance the feed .001" for every .010" of compound travel.  Note that this angle is measured relative to a plane perpendicular to the spindle.  If your compound dial is set differently, subtract the stated angles from 90º.


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## KevinMaiorka (Aug 1, 2016)

Bob Korves said:


> If you have your compound set at 45 degrees to the cross slide and the bed ways, you advance the tool .707 for every 1.000 that you feed in on the compound.  That means you will cut 1.414 if you have a radius reading compound dial.  If you want to advance .500 for every 1.000 you feed in on the compound, you will need to set the compound at 60 degrees to the cross slide, 30 degrees to the bed ways, which will cut 1.000 on the diameter when using a radius reading dial.  Simple trigonometry learned 50 years ago, still remember the numbers for those angles without a chart or electronic gizmo...


Bob, I do not have a radius compensating compound. My wife (high school math teacher) and I are now trying to figure out your assessment on this and understand your math. We are not having luck doing so far. Please explain further as my wife will not be able to sleep until she understands this. 

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## KevinMaiorka (Aug 1, 2016)

RJSakowski said:


> I have set my compound to a variety of angles.  29.5º for threading, 0º if I want some extra travel capability on the cross slide.  and I set it at 90º for controlled travel in the z direction.
> 
> BTW, setting the compound at 45º advances the feed by .0071" in the x direction for every .010"  If you want to advance .005", the compound angle should be set at 60º.  Setting at 84.3º will advance the feed .001" for every .010" of compound travel.  Note that this angle is measured relative to a plane perpendicular to the spindle.  If your compound dial is set differently, subtract the stated angles from 90º.


Please explain further as my wife and I are going crazy now trying to understand this. She is a math teacher with many years under her belt. 

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## Bob Korves (Aug 1, 2016)

T Bredehoft said:


> Isn't it wonderful what we can remember. I remember that the diagonal of a one inch square is 1.414, the same figure bob mentioned above,  Somehow, half the diagonal is .707, but I can't remember what its for.  Why can't I remember what I had for breakfast?


If the hypotenuse is 1.000 then the other two shorter sides of a 45 degree right triangle are .707.  If the short sides are 1.000 then the hypotenuse is 1.414.


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## KevinMaiorka (Aug 1, 2016)

Okay so here is the wife's drawing and we need clarification on this please. I have been doing this for many years and have never had an issue with it not equaling what I have needed it to. 

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## KevinMaiorka (Aug 1, 2016)

Well hell she just educated me and now I understand. Y'all are right and I guess that is why I have always had a bit of trouble with taking off a small cut. 

Goofy special triangles. 

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## Bob Korves (Aug 1, 2016)

OK, Kevin, I cancelled the post I started...

Pythagorean theory.  My dad taught me this when I was a young boy.  I apologize in advance that it is not politically correct, but it is useful in situations like this:

There were three indian squaws.  One laid on a deer hide, and gave birth to a son.  The second laid on a elk hide, and also gave birth to a son.  The third laid on a hippopotamus hide, and gave birth to twin sons.  This proves the age old theorem that the squaw of the hippopotamus is equal to the sons of the squaws of the other two hides.

Show that to your wife and see what it does for her...   8^)


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## KevinMaiorka (Aug 1, 2016)

Way too funny Bob! Not too big on being politically correct myself so it's all good. By the way I had the definition of "political correctness" explained to me as such.......it is the thought that it is totally plausible to pick up a turd by the clean end. 

Showed to wife and she laughed. She had never heard of it before but did like it though. Of course she can never use that one in class though. She did remark that "it would have been funnier had the hides all been squared" 

Thank you for educating me and helping me learn something new. This is exactly the reason I joined this group and look forward to learning more. I have mostly taught myself what I do know and I know some of that is not the way it is supposed to be done though. 

Kevin 

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## Bob Korves (Aug 1, 2016)

KevinMaiorka said:


> Well hell she just educated me and now I understand. Y'all are right and I guess that is why I have always had a bit of trouble with taking off a small cut.
> 
> Goofy special triangles.
> 
> Sent from my LGLS991 using Tapatalk


Small cuts are always a pain.  I try to avoid them whenever possible...


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## Bob Korves (Aug 1, 2016)

KevinMaiorka said:


> Way too funny Bob! Not too big on being politically correct myself so it's all good. By the way I had the definition of "political correctness" explained to me as such.......it is the thought that it is totally plausible to pick up a turd by the clean end.
> 
> Showed to wife and she laughed. She had never heard of it before but did like it though. Of course she can never use that one in class though. She did remark that "it would have been funnier had the hides all been squared"
> 
> ...


Too funny about the turd!  And yes, she is right about the square hides.  We have just improved my dad's story...


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## Tony Wells (Aug 2, 2016)

My compounds stay at 45° 90% of the time. I thread straight in, but I like having the ability to cut 45° chamfers and break edges with cutting tools rather than files. Works OD and ID. There are some parts that require a 20° bevel angle for leading a seal into a bore, or transition angles between two different OD sizes,  but I don't do too many of those any more. And that angle may or may not be 20°....could be anything, so no point in setting it to anything specific except the 45° for me.

BTW, I don't believe I have ever seen a compound dial graduated in radii, so bear that in mind when using it at an angle to give finer control over DoC. I'm not saying they don't exist, but I've been around a lot of lathes and never seen one built that way. Maybe some of the smaller, newer imports, but it would be new to me.


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## MozamPete (Aug 2, 2016)

My default is 23.2 degrees from the axis of the work.  It's an old  lathe with imperial dials, but I tend to work and measure in metric.
At that angle 10 thou on the compound dial (0.01" or 0.254mm) moves the tool 0.1 mm perpendicular the work (i.e an extra 0.1 mm off the radius). Makes measuring in metric and then just dialing what extra to take off easier (plus a bit finer control).


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## Tony Wells (Aug 2, 2016)

That's an excellent application of the trig functions using your compound. Great thinking.


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## T Bredehoft (Aug 2, 2016)

Yeah, its the sine function, the sine of 30º is .5, or 1/2.


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## RJSakowski (Aug 2, 2016)

KevinMaiorka said:


> Please explain further as my wife and I are going crazy now trying to understand this. She is a math teacher with many years under her belt.
> 
> Sent from my LGLS991 using Tapatalk


Kevin, the paths of the cross slide and compound describe a right triangle with the com[pound path being the hypotenuse.  From trigonometry, the cosine of the include angle is the side adjacent/hypotenuse.  For every .001" that the compound is advance, the tool is advanced .001 times the cosine of the included angle.  Because congruent triangles maintain the same ratio between the lengths of the sides, the ratio holds regardless of distance traveled.  Here is a drawing of some of the more popular compound angle settings.


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## Bamban (Aug 2, 2016)

RJ,

That is a nice and simple illustration of the compound slide angle.


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## KevinMaiorka (Aug 3, 2016)

Okay so yesterday evening after work I went to the lathe to see for myself and put a dial indicator on the ways and turned the quick change tool post so that the dial was contacting a flat area on it. Left the compound at the 45° angle  and sure enough it was off! Man y'all are smart! I believed y'all and my wife as well but I just couldn't get it through my thick skull that it was the way it was. Moved it to 30° on the compound and sure enough it is exactly half of the movement on the compound that I thought I was getting at the 45° before. 

Still blows my mind that it works the way it does but I learned something and I will be forever grateful for yalls help with this. I had always thought my lathe was just off or something and that was all I could do about it. Thank you again and thanks for adding me to the group and I look forward to learning more. 

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## KevinMaiorka (Aug 4, 2016)

Okay so one more question. Why is it that we have to set the compound angle at 29.5° setting for cutting threads? On my smithy I have cut threads once and it was a pain but I did it. It does not have a thread dial so it was quite an adventure. 

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## MozamPete (Aug 4, 2016)

It keeps the tool cutting on the leading edge as you advance the compound for each pass.  
If you just feed in with the cross slide the point of the tool move forward and both side of the point cut. If you feed in with the compound at  29.5deg (just under half of the 60deg thread angle) the right hand side of the tool follows the thread side and all the cutting is done on the left hand side of the tool.


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## KevinMaiorka (Aug 4, 2016)

Thank you for explaining it to me. I always wondered why it was done that way and didn't quite understand it. 

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## Strangerthings169b1 (Mar 27, 2017)

And this is why I joined this site. Way over my head but that just means I have to learn more.


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