The Home Machinist!

I recently read an article on the internet citing the advantages of a "vertical shear bit" for turning round material on the lathe; smooth finish, non-critical height adjustment, ease of grinding, etc. Can anyone comment, that has used such a bit?? I made a drawing based on the author's description (atch.)

If the "Top" view is really the side view, then this is a fairly standard tool grind. Otherwise, I don't get it.

Dave J.

My guess is that it is my article you read so I'm not an unbiased observer, of course.

You failed to mention the vertical shear tool's major limitation: it is purely a finishing tool because depth of cut is limited to about 3 thou. On most materials it leaves a very smooth finish and works best with fine auto-feed, as you might expect. It's the only lathe tool I've used that will remove a fraction of a thou reliably while leaving a smooth surface.

As MechanicalMagic noted, the tool shape is unusual - I've had a few letters from visitors who can't believe what the pictures show

It's pretty quick and easy to grind so why not try it yourself? I suspect you'll be pleasantly surprised.

John

I have a lot to thanks you for this tool bit. Its great for working on brass and alu etc but the major benfit for me has been for my pipe making. It allows me to put a fine finish on briar and bog oak which usually tend to tear out a bit with conventional tools. If i want a smooth finish that will require minimal sanding then after shaping i take 3 or 4 light passes with this tool and it comes up beautifuly.

THankyou

See something new every day, thinks for the post.

Rob

Looks exacltly like my regular LH turning bit for brass (zero rake).
Turned upside down is a RH shear bit for HRS.

Got to try it.

GunBoatBay and GagetBuilder... Thanks for bringing this to my attention. This bit really does a fantastic job. I ground one of these bits and proceeded to test it on 1.5 inch hot rolled 4140.

As stated, this bit could easily skin off a 0.001 DOC or 0.002 in diameter. It does this at slow speeds and feeds as predicted.

Here is the bit I used.

Previously I could get a high shine finish on 4140 using TCMT 21.50 at high speeds, and depth of cuts that needed to be at least 0.005. A single DOC of a few thou could be done afterwards. Subsequent small DOC produced varied results with 4140. So the finishing passes had to be right.


This bit consistently cuts easily with HSS as many times as you wish at 0.001 DOC. It produces a extremely consistent finish with no circular lines in 4140. Quite impressive. Here is pict of the part with swarf.

The swarf comes off in stright strings. Not curls.

A point about the usage of this bit that may not be clear to everyone is that the cutting edge is on the side, not top of the bit. So the top of the bit will not be on centerline. Rather the middle bit will be on centerline as shown in this picture.

The vertical shearing comes from the side of the bit.

This bit was unable to cut at under 0.001. I tried 0.0005 DOC, but it did not cut consistently in the 4140. It would cut 0.001 DOC passes all day long.

So I added some rake to the cutting edge to see if I could get a smaller DOC. Unfortuneately, there was no benefit at all. The finish was worse and the cutting was less consistent. So do not add rake as I have done in this picture.

The solution presented here with this vertical shear bit is quite slick. If you have not tried it, you will not be disappointed when you do.

Thanks guys..
Bryce

Those that have machined mild steel with an end mill, using the periphery, not the end, will agree that the finish is not bad as compared to the cuts generated by the end. I would attribute the improved surface finish to the same principle that is applied with the tool in question. End mills have a shearing action as well, and yield quite nice finishes, especially when climb milling.

I must say, in all my years in the shop, I've never given such a tool a go. It sure would have come in handy for some of the tight tolerance jobs I've done in the past, where finish was critical. It's likely the solution to machining mild steel, for sure. It loves to tear by conventional machining methods.

Harold

That is a good point.. the side of the end mill would cut quite the same as this bit. The side frame of my engine in this pic is cut out using an end mill. Very nice finish on edges of CR 1018.
Bryce

When I was running my shop, I built a lot of tooling for Litton Guidance and Control. It wasn't uncommon for them to specify mild steel for the basic framework, or base, depending on the nature of the tool. The vast majority of my experience with mild steel, in particular C1018, was on lathes. I was pleasantly surprised at the exceptional finishes I got when milling the stuff. That appears to be the norm.

Harold

There is a thread about the shear cutting tool on HSM and at first I was doubtful of the claims. The cutter is really just a left hand turning tool turned upside down so I ground one and tried it. It did turn a better finish than my standard right hand turning tool but the real advantage to me is a constant diameter with a serviceable finish.

A lot of the time when you start taking .001-.002" cuts to get to finish size the finish looks terrible so most the time I turn over size and file to size. It takes some time to do that and it's something you have to learn to do.

To me it will be useful for long shafts that have to be constant diameter the full length. If the finish is not suitable I can leave .001" and file or emery cloth to the desired surface finish.

It's not really a tool I would use a lot but I do intend to use it.

GadgetBuilder, I have some questions. Since you have probably already experimented with the angle of the shear (that would be the angle of the side clearance on the tool right side up) what have you found to be the best or, is there a best angle? I had about a 15 deg shear angle on my tool.

I ran the tool at 300 rpm, .003" feed and .002" DOC on CR and the finish was nice but still had marks. As I returned the carriage I didn't retract the tool and it drug on the surface so I made another pass and retracted the tool before moving the carriage back. That told me I was feeding to fast and maybe the rpms were to low also. You mentioned a grind that would have a curved relief like a big radius chip breaker would peel the metal off better and I will try that.

What have you found about the rpm/feed aspect?

Where is your article so that I may read it?

I prefer using a file and or emery cloth to attain a smooth fine finish to size but on long runs that is time consuming and problematic. With the correct use of the shear tool long runs at a constant diameter would be easy and then I could polish it with emery cloth if needed.