Rough surface finish? Try a Vertical Shearing Tool.

E

emtor

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Mild steel is famous for leaving a rough surface finish. Some people use emery cloth to improve the finish, but personally I'm scared of having my hands close to the chuck or a rotating workpiece. -So what to do?
A Vertical Shearing tool is the answer.
I have a couple of swedish HSS blanks laying about so I ground one standard tool and one shearing tool and when trying the shearing tool I was surprised.
The finish on mystery mild steel which usually gives a terrible result came out with almost a mirror finish.
The images from a camera do lie a little. In real life the finish on the right hand side of the round stock is in fact a mirror finish when looking at it with my eyes.
The chips aren't really chips,-they're angle hair as can be seen in the image.
I have a small bench grinder and it took a whole day to grind these tool. The swedish HSS blanks I used are extremely hard and tough, but it was well worth the effort since these tools will last for years.


Surface Finish Mild Steel.jpg
 
I have had excellent luck with Swedish tool blanks and tools. They take their metallurgy seriously
 
Carbide.
Once you master the requirement of carbide, there is no going back. The tangential cutter dulls fast, can't rough in, can't face nor approach a shoulder, and finally if you are making a step pyramid the tangent of the tool contacts the various diameters differently. So you must calibrate at the corresponding dia.

No name carbide inserts and brazed tools. Don't touch them. The have no impact resistance. ISCAR like the one in the photo is fantastic, same of any EU, US, Japan made equivalent.

What about cost? Good carbide is not out of reach for the hobbyist. Look for some brazed carbide from Sandvik , Clarkson or American carbide. invest in an 80grit green bench grinder wheel and a handful of EZE-laps diamond hones to polish the edge. And you are up and running.

20210215_110941.jpg1660497864791.png
 
The results are clear, and I can see the tool in the picture has a curious tight concave cut, and a sharp point leading to the forward face, I don't know what property makes it a "vertical shearing tool". A regular tool also shears the metal, at a point traveling vertically at the time.

Is there some description somewhere, maybe with diagrams about clearance angles, etc. and the theory behind it. I mean sufficient information for one to attempt to grind one? :)
 
Mr. Pete has a couple of videos on shear tools:

 
A vertical shearing tool is my go-to tool for a final pass on mystery metal (or any low carbon stock). The max cut is less than 0.001". The swarf is so fine, it will float away - be careful you don't breath it in. The finish it gives is close to mirror. The down side to these tools is that they need sharpening often.

If you create a tool with a slight convex curve, you can use them to face a piece.
 
I've read alot about shearing bits and I don't doubt the success people have with them, but I've never been able to grind one and use it successfully. Might be that I'm just not understanding the geometry properly. For finishing I use a CCGT insert which I've found to shave a tiny amount of metal off, similar to the pictures above. It can also face and turn to a shoulder, which I find pretty useful for the kind of things I make.
 
Alexander McGilton said: "Once you master the requirement of carbide, there is no going back."

And one of those requirements might be speed and depth of cut.
Carbide cuts not because it's neccessarily sharp but because it's hard. It bulldozes the material away, a blessing for the industry where time is money and lathes are big and weigh more than a normal car.
In the hobby shop where a cheap chinese mini lathe lives it's life, HSS tools can be beneficial.
My lathe is a chinese so called minilathe which is larger and heavier than most minilathes and does well with carbide inserts for the most part but I still get a better finish with a vertical shearing tool if I'm aiming for Abom79 and Joe Pie types of surface finish.
It's a hobby, so lower speeds, feeds and shallower DOC plus sharpening every now and then doesn't bother me much.
One thing that does bother me is a "machined-with-a-lawnmover"-type of finish.
 
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