# Surface Finish



## bug_hunter (Mar 10, 2022)

Hey All,

Should i be able to achieve a smooth to the touch finish with a 1942 South Bend 9?  I'm using HSS tools.  I started out turning a rusty piece of 2-inch A-36.  All the rust is gone, and getting close to my final desired diameter 1.500.  But no matter what I change (spindle speed, feed speed, depth of cut, tool end, oil), I cannot achieve that smooth finish.  I still feel slight discrepancies when I run my finger across it.  I've attached a photo, but I do not believe you can see much in it.  My best finish comes from a high spindle speed (690), shallow cut (.002), round tool tip (~1/8"), with oil.  

Is it my technique, the lathe, the material, or the phase of the moon?  Let me know if there are any questions i can answer that may help in formulating an answer.

Thanks!


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## Jim F (Mar 10, 2022)

Try a vertical shear bit.


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## bug_hunter (Mar 10, 2022)

Jim F said:


> Try a vertical shear bit.



From the photos I have found, unless I am mistaken, and I may very well be, does the bit cut, or shear from the bottom as opposed to the normal top cutting bit?


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## Jim F (Mar 10, 2022)

It shears from the side, works great for low power machines and hard to finish metals.
As much as I dislike his videos, MrPete has a few on making and using one.


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## woodchucker (Mar 10, 2022)

not enough info:
pics of the tool
was this using a feed, or done by hand?
What was the feed?

First, I notice that when I cut light cuts the finish look eh.. but when I do the right size cut I get a nice finish.... too much and eh...

I don't use a shear tool. I find it dulls pretty quickly in steel. For AL, it's nice .


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## benmychree (Mar 10, 2022)

A36 is not known as a free cutting steel that will finish nicely, it will take filing and abrasives to make a nice smooth finish.


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## woodchucker (Mar 10, 2022)

Jim F said:


> It shears from the side, works great for low power machines and hard to finish metals.
> As much as I dislike his videos, MrPete has a few on making and using one.


why do you dislike his videos? Just curious.


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## Jim F (Mar 10, 2022)

woodchucker said:


> why do you dislike his videos? Just curious.


Too much rambling about stuff that does not pertain to the subject at hand.


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## bug_hunter (Mar 10, 2022)

I had very little expectation, but it works.  Does not make chips, as much it makes little steel feathers.  The finish is a lot smoother, but not like glass.  Maybe one more pass and we'll call it good.

Thanks for the new trick.

I actually did watch one of Mr>Pete's videos on the tool.  I like him.  He may ramble, but at least you can hear him and understand what he is saying.


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## C-Bag (Mar 10, 2022)

Having been partially raised by my grandfather I’m kinda partial to knowledgeable rambly old guys. I don’t always agree with their politics, but I appreciate their knowledge. Mr Pete is a treasure to me.


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## woodchucker (Mar 10, 2022)

bug_hunter said:


> I had very little expectation, but it works.  Does not make chips, as much it makes little steel feathers.  The finish is a lot smoother, but not like glass.  Maybe one more pass and we'll call it good.
> 
> Thanks for the new trick.
> 
> I actually did watch one of Mr>Pete's videos on the tool.  I like him.  He may ramble, but at least you can hear him and understand what he is saying.


what was the trick? I can't tell from that pic...


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## C-Bag (Mar 10, 2022)

This is my version of that. I got this in a bunch of shop ground bits in a garage sale. It’s become my goto. I set it to around straight on for roughing/hogging and then get it close to flat against the work for finish. Had to come up with  jig to do that scoop.


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## bug_hunter (Mar 11, 2022)

woodchucker said:


> what was the trick? I can't tell from that pic...



The trick was to grind the vertical shear bit as suggested.  Probably can't see the bit in the photo as i am a horrible photographer, but you could see the fluffy, feather like ships.


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## bug_hunter (Mar 11, 2022)

C-Bag said:


> This is my version of that. I got this in a bunch of shop ground bits in a garage sale. It’s become my goto. I set it to around straight on for roughing/hogging and then get it close to flat against the work for finish. Had to come up with jig to do that scoop.



C-bag, does your bit shear with the leading edge, or cut from the top?  Is the scoop to provide a breaker or increase the cutting angle?


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## C-Bag (Mar 11, 2022)

When you say leading edge are you talking about the lefthand edge? I get kinda bogged down in trying describe but if the left point is set like a typical tool it cuts great with the scoop being a chip breaker. I typically take .050 DOC and can take up to .080 on steel and .100 on aluminum which is crazy on my Chinese 9x20. Then rotate around to the long edge for the shear tool. It’s all about keeping it sharp and I leave my tool grinder to those relief angles to touch up. Keep thinking I’ll make me a slo speed hone but so far this has worked out great. The tricky part is the scoop because as I reface it the scoop goes away and the whole thing doesn’t work like it did. Especially the chip breaking.


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## projectnut (Mar 11, 2022)

It looks to me like the cutting edge of the tool comes to a sharp point.  It also has signs of discoloring from heat.  It's hard to know if the discoloration was done when the tool was ground, or it's heat buildup when turning. Personally, I would radius the edge a bit more, and use some cutting oil.  Rule of thumb is the radius of the cutting edge should be a minimum of 1.5 times the distance the tool moves with each revolution of the spindle.  An example might be the spindle turning at 700 rpm with a feed rate of 2.00" per minute.  In this case the tool would move appx. .003" per revolution.  The cutting-edge radius should be a minimum of .0045".  A .010" radius would give a better finish but would leave a more radiused shoulder at the end of the cut.


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## mikey (Mar 11, 2022)

bug_hunter, can you show us your original tool and the angle you used to do the original work? I ask because Benmychree is right; A36 doesn't usually finish well. However, it can finish acceptably with the right tip geometry and if you use the right part of the tool to do the finish cutting. If you show us a close up of the tool from the top, side and front then we can maybe give you some help. A HSS tool depends on its tip geometry to work well and you need to use the right lead angle so the desired cutting area comes into contact with the work.


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## bug_hunter (Mar 12, 2022)

mikey said:


> bug_hunter, can you show us your original tool and the angle you used to do the original work?




OK, first off, the shear bit did a pretty good job, but it would be nice to be able to achieve a smooth finish with a single tool.

Top:




Side:




Front:




The bit was presented to the work at about a 5 degree angle to avoid rubbing. and to try to achieve a leading shoulder.

Let me know what else is needed for an assessment.

Thanks!


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## mikey (Mar 12, 2022)

Okay, I think the tool is a big part of your problem but that's a good thing because we can fix it. 

The overall shape of the tool is fine. The shape is typical for a roughing tool.

You have side rake and that's good. You have no back rake and that's not good. 

The biggest problem is that you have no side or end relief so your tool is rubbing and not cutting. 

The nose radius is too big so it is contributing to the deflection.

At a 5 degree lead angle, you are cutting with the nose radius and you cannot get a good finish that way. The best finish is produced by a shearing edge. On a turning tool, this edge is typically the end cutting edge.

Okay, so what to do. I suggest you re-grind your tool. Go here and read up on how to get the angles right and what those angles should look like. Show us the tool after you regrind it and we can tell you how to angle the tool so that it cuts with the area it should cut with. Then we'll see how your lathe works with A36.


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## bug_hunter (Mar 12, 2022)

mikey said:


> Show us the tool after you regrind it and we can tell you how to angle the tool so that it cuts with the area it should cut with. Then we'll see how your lathe works with A36.








Looks to me that I still have too much nose radius, and need to drop the top a bit more.  I stopped because the top edge started getting red while grinding.


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## mikey (Mar 12, 2022)

Okay, now you have adequate relief on both the side and end - very good!

I suggest you pay attention to flattening to top of the tool. You need to choose how much back rake you want and draw a line on your tool rest; 10-15 degrees works good. Push the tool straight into the wheel while holding the bit at the angle of the line until the top is flat. You see how the tip of the tool droops down to the end when viewed from the side? It isn't supposed to droop like that.

Please fix the top of the tool and don't grind anything else. Then let's take a look again when you're done.


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## bug_hunter (Mar 13, 2022)

mikey said:


> Please fix the top of the tool and don't grind anything else. Then let's take a look again when you're done.



How does this look?  I only adjusted the top.  No appreciable change on angle, only depth.  I probably should have just
	

		
			
		

		
	





	

		
			
		

		
	
 started over instead of regrinding the original bit.  Not sure if it saved me anything or not.  Lots of grinding.


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## mikey (Mar 13, 2022)

No, that looks a lot better. You now have good relief angles on the side and end, good side and back rake. If you haven't done it yet, hone each flat with a stone and then put a really tiny nose radius on it. I normally just put a 1/64" flat across the nose where the side and end flats meet. Keep that flat even top to bottom, then blend or round each side of the flat into the side and end. Make it round and then go back to the top of the tool and give it one or two light honing strokes to clean it all up.

Now you can use the tool.

For most turning, try using the tool with the shank of the tool perpendicular to the work. It should allow you to rough and do finer cutting with the tool in this position. However, if you need a really fine finish then you can turn the tool tip counterclockwise and do a very light shearing cut with the area just behind the nose radius. You are using the end cutting edge just back of the nose. That edge is capable of both fine and heavy cuts but it will surprise you at how nicely it finishes. Give it a try.


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## SLK001 (Mar 13, 2022)

You'll also get a better finish with a finely honed surface on your tools.  Use a diamond plate, or an India oil stone to finish them.

It has been mentions that a shear tool will give you a good finish on many hard to machine metals.  Here is my shear tool:







The front is recessed in the middle to make honing the edge quicker - same with the side relief.  There is about a 5º relief (not critical) on the very front.  The cutting edge itself is vertical (no relief).  To use it, take no more than 0.001" off the radius per pass - I aim for 0.0005" per pass.  I find that if I just touch the work, that is just about right.  Set the tool so that the middle of the tool is on the centerline.  I usually use oil, but I have run it without also.  I believe that the oil helps preserve the edge from excessive wear.  This tool is subject to more wear than usual tools, so keep an eye on the edge.  If it looks ragged, then take it over to your stones and spruce it up. 

The swarf that comes off the tool should be almost gossamer like and will actually float in the air.  Take care not to breath in the swarf.

This grind of the tool is for a right to left feed only.  Mirror the grind for a left to right feed.


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## bug_hunter (Mar 13, 2022)

I tried a .005, .010, and .015 DOC.  .001 gives me the smoothest surface, and thee still appears to be stripes on the steel.  For roughing, I guess I can try a .020 DOC, but i would hate to ruin a good thing.   Also, I am getting a lot of long tight curly chips.  Some of which a wrapping around the tool and tool post.  Suggestions to alleviate this?



mikey said:


> if you need a really fine finish then you can turn the tool tip counterclockwise and do a very light shearing cut with the area just behind the nose radius



Please clarify.  Would I rotate the tool from a perpendicular shank position to a position almost 75 degrees counter-clockwise?

Thanks to Mikey for all the help and patience.


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## bug_hunter (Mar 13, 2022)

SLK001 said:


> It has been mentions that a shear tool will give you a good finish on many hard to machine metals. Here is my shear tool:



SLK, take a look at post #9.  I tried successfully with the shear tool.  Next I'll give the recess on the shear tool a try.


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## mikey (Mar 13, 2022)

bug_hunter said:


> Please clarify.  Would I rotate the tool from a perpendicular shank position to a position almost 75 degrees counter-clockwise?


Yes, turn the tool CCW and cut with the end edge, just behind the nose radius. Take very light cuts, increase speed a little and slow down feed a little and it should produce a nice finish.


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## mikey (Mar 13, 2022)

bug_hunter said:


> Also, I am getting a lot of long tight curly chips.  Some of which a wrapping around the tool and tool post.  Suggestions to alleviate this?


Increasing the feed rate is the best answer. However, when playing around like this I would just accept the stringing while you learn what depth of cut, feed and speed works best for you.


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## Jim F (Mar 13, 2022)

mikey said:


> Increasing the feed rate is the best answer. However, when playing around like this I would just accept the stringing while you learn what depth of cut, feed and speed works best for you.


C's and 6's are only going to apply to inserts, correct ?
I do not see how it is possible to grind a true chip breaker in a small (3/8) size HSS tool.


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## SLK001 (Mar 13, 2022)

bug_hunter said:


> Also, I am getting a lot of long tight curly chips.  Some of which a wrapping around the tool and tool post.  Suggestions to alleviate this?



Here's where a chip-breaker helps (see comment below).  I also use a 12" piece of ~3/4 x 1/4" oak to stick into the curls coming right off the tool to break them up.  These can be dangerous to have flopping around, so break them up as soon as you can.  The stick will get hot and occasionally catch fire, but just dunk it into oil to keep the inferno to a minimum!



Jim F said:


> C's and 6's are only going to apply to inserts, correct ?
> I do not see how it is possible to grind a true chip breaker in a small (3/8) size HSS tool.



It is, but is difficult.  I use a Dremel tool with a small abrasive disk to cut the groove just behind the edge.


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## mikey (Mar 14, 2022)

Jim F said:


> C's and 6's are only going to apply to inserts, correct ?
> I do not see how it is possible to grind a true chip breaker in a small (3/8) size HSS tool.


You actually can grind a chip breaker into a HSS tool but it just isn't worth the time and hassle to do it, at least not in my opinion. Even with inserts, light cuts produce strings in mild steels. If you want chips from these materials, take big bites and increase your feed rate. Under these conditions, even aluminum will chip.


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## Hoghollor (Mar 14, 2022)

bug_hunter said:


> Hey All,
> 
> Should i be able to achieve a smooth to the touch finish with a 1942 South Bend 9?  I'm using HSS tools.  I started out turning a rusty piece of 2-inch A-36.  All the rust is gone, and getting close to my final desired diameter 1.500.  But no matter what I change (spindle speed, feed speed, depth of cut, tool end, oil), I cannot achieve that smooth finish.  I still feel slight discrepancies when I run my finger across it.  I've attached a photo, but I do not believe you can see much in it.  My best finish comes from a high spindle speed (690), shallow cut (.002), round tool tip (~1/8"), with oil.
> 
> ...


What material are you cutting? Are you using home made cutting tools? If you’re cutting steel you probably need to slow rotation down I’m thinking to around 185 or so


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