Vertical shear bit

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gunboatbay
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Vertical shear bit

Postby gunboatbay » Tue Feb 16, 2010 11:24 am

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.)
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Vertical shear bit.doc
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mechanicalmagic
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Postby mechanicalmagic » Tue Feb 16, 2010 11:53 am

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.
Every day I ask myself, "What's the most fun thing to do today."
9x48 BP clone, 12x36 lathe, TIG, MIG, Gas, 3 in 1 sheetmetal.

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DICKEYBIRD
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Postby DICKEYBIRD » Tue Feb 16, 2010 11:59 am

Milton in Tennessee

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GadgetBuilder
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Postby GadgetBuilder » Tue Feb 16, 2010 12:17 pm

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

caskwith
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Postby caskwith » Tue Feb 16, 2010 12:47 pm

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 :D

10 Wheeler Rob
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Postby 10 Wheeler Rob » Tue Feb 16, 2010 9:24 pm

See something new every day, thinks for the post.

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tornitore45
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Postby tornitore45 » Wed Feb 17, 2010 12:27 pm

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.
Mauro Gaetano
in Austin TX

BryceGTX
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Postby BryceGTX » Thu Feb 18, 2010 11:35 pm

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.
Attachments
0_ShearCuttingBit_100_4562.jpg

BryceGTX
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Postby BryceGTX » Thu Feb 18, 2010 11:41 pm

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.
Attachments
2_SwarfFromCut_100_4559.jpg
Last edited by BryceGTX on Thu Feb 18, 2010 11:46 pm, edited 1 time in total.

BryceGTX
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Postby BryceGTX » Thu Feb 18, 2010 11:43 pm

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.
Attachments
1_PositioningTheCutterInTheMiddle_100_4570.jpg
Last edited by BryceGTX on Thu Feb 18, 2010 11:59 pm, edited 1 time in total.

BryceGTX
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Postby BryceGTX » Thu Feb 18, 2010 11:53 pm

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
Attachments
3_ShearCutterWithRake_100_4567.jpg

Harold_V
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Postby Harold_V » Fri Feb 19, 2010 3:26 am

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


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