Shear grinding Lathe tools

Discussion in 'Gunsmithing' started by J E Custom, Aug 12, 2018.

  1. J E Custom

    J E Custom Well-Known Member

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    How many Gunsmiths on this site use the shear grind for finish cuts. I would like to learn more
    of your experiences with this type of cutting tools.

    Any information you could share would be appreciated.

    Thanks

    J E CUSTOM
     
  2. J E Custom

    J E Custom Well-Known Member

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    No one ?

    In an earlier post on contouring, the finish came into play and we talked about the use of abrasives to finish the barrels. As stated, i don't like to use abrasives on my lathe to get a finished look on a barrel.

    I saw this Video a while back, and tried grinding a tool this way and got ok results but not any better than the High speed tools I ground for this operation.



    It realy works on softer metals so I was hopping that someone could share some tricks to grinding the shear tools. This is not a production process so it is not used in a production shop as far as I know.

    In most of the high end machine shops, abrasives are forbidden because of the multi million CNC Machines and its effects of them.

    I will keep on slugging along and try to perfect this type of lathe tool in search for a better finish without abrasives. Any suggestions are welcome.


    J E CUSTOM
     
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  3. Trickymissfit

    Trickymissfit Well-Known Member

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    I'm thinking your referring to actually cutting the metal of the main body, rather than simply pushing it off like carbide. Of course you can actually push the metal off with high speed as well. My very first tools were simply Gorham AA and low end Rex, and I was taught the simplest grinding method. When using them, we rarely got past 300 rpm on a 3" diameter. Did ok on most steels, and brass. Ampco was an issue. Pretreat steels actually cut well. Then I got into some 330 stainless steel. I could get about twenty inches of cut and the cutting edge was gone. At lunch I called the Old Man and ask what was going wrong? He said tool pressure was causing heat, and then work hardening the part. Had me grind up a new tool that just had a slot ontop with a knife edge and maybe ten degrees clearance. Used a Rex 95 tool, and he said if it didn't hold up to get a Vasco Supreme blank. What I soon discovered was that excessive tool pressure leads to excessive inaccuracy. Fast forward to cutting threads on some really nasty stuff. That would be Air Die and some Graphmo. The stuff literally laughed at me and my generic thread cutting process! Put one of the junk pieces in my pocket and made a stop on the way home. I was laughed at! He goes back to a room and brings out this green plastic tackle box. Opens it and hands me three or four tool bits, and said to try these. On a piece of paper he wrote the cutting speeds in surface speed (new to me), and hands me a Machinist Handbook plus another little book of formulas. Then he writes down a formula for mixing a cutting fluid. Bacon grease, Sulphur, and a couple now outlawed goodies. I read the little book and a couple chapters over the weekend, and I'm ready. On the job I changed everything, and the threads came out a satin silver color. On the shadow graph they were a work of art. No fuzz or distortion like carbide. Then I find out it was all a joke as they always planned on grinding the threads after heat treat! So now Howard wants to know how I cut the threads, as they didn't know how.

    What I learned was that tool pressure becomes your enemy real fast. Heat build up eats tools, but there are ways to get past that. You want the heat in the chip string, and not in the part. Tool pressure in small parts becomes a major issue, and leads to inaccuracy. Yet sometimes pressure is just part of the process (cutting a radius with one pass)
    gary
     
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  4. climb-101

    climb-101 Well-Known Member

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    if you search abom79 on youtube he did a video on shearing tools for the lathe.

    this guy is also very good on a lathe and explains stuff well.
     
  5. Trickymissfit

    Trickymissfit Well-Known Member

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    "shearing" is actually the incorrect name for that tool. It's normally called a parting tool, or in some circles just cut off tool. Surface speed is critical, and this is why so many have minor wrecks during the process. yet it's also why it works better in the CNC lathe. Add to this the fact that 75% are sharpened wrong.
    The carbide tipped ones work well as long as you get zero surface vibration. I once again prefer high speed.
    gary
     
  6. Timnterra

    Timnterra Well-Known Member

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    I’ve never tried a shearing tool. But I will the next time I profile a barrel, it looks like a great idea. I usually put in a new insert when i make the finish cut profiling a barrel, it leaves an okay finish. I have a barrel spinner and finish on the belt grinder that way I don’t get any abrasive on the lathe.
     
  7. J E Custom

    J E Custom Well-Known Member

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    I do a lot of barrel contouring and have never been able to get the finish cut using Carbide that I have with high speed tools. They wont take as big of a cut as Carbide but the finished cut is much better.

    I have tried the shear tools and they also do a nice job, but they wont take more than .005 to .007 thousandths cut. When I make the final cut on a barrel with high speed tools I normally take less than .010 thousandths (Carbide doesn't like light cuts).

    I'm not sure that a shear grind tool is the answer to a better finish, but i will keep experimenting with then until i feel they are better or not the answer.

    Thanks Gary and Timnterra for your comments.
    Keep them coming !

    J E CUSTOM
     
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  8. Timnterra

    Timnterra Well-Known Member

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    What profile do you grind on your HSS finishing tools? I’m not very proficient with the tool grinder that’s why I use carbide inserts for most things. I’ve experimented with several different brands of insets and found that the Mitsubishi (can’t remember the part number) ones made specifically for stainless tend to be sharper and produce a better surface finish than others I’ve tried.
     
  9. J E Custom

    J E Custom Well-Known Member

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    Some people grind by looks and hold the tool in there hand without the tool rest on the grinder. I found this method to be inconsistent in cut quality from one tool to the next. So I take the time to set the grinder rest to the degree desired. when I grind high speed steel tools, I normally grind more than one at a time.

    You can grind right hand and left hand tools at the same time just by changing sides on the rest. First I start with the end of the tool (Called the face) and set the rest on 5 to 7 degrees depending on the material to be machined. you can grind the compound angle on the face using the same setting of 5 to 7 degrees.

    The next angle I grind is the side rake (The left or right side of the tool depending on left or right cutting looking down from the top of the tool, This angle is normally about 3 degrees.

    The last angle is from 2 to 4 degrees on the top rake and greatly effects the way it cuts different materials. When I don't want long curls coming of the tool, I grind a chip breaker (Most carbide tools have this feature on top of the insert).

    And last but not least, I find that Honing with a good stone will improve the quality of the cut and the life of the tool. Just be careful
    not to change any of the angles at the cutting edge. I hone my threading tools also if I am using High speed steel.

    If you set the grinder at the proper angles for each rake angle you will see the consistency. and with some practice will be able to free hand most tool grinding and sharpen on the fly. but i still like to set the grinder rest to the optimum angle for the first time for the job. (This also gives me a guide to resharpen a worn tool in a pinch)

    Just the way I grind my lathe tools.

    J E CUSTOM
     
    Last edited: Aug 14, 2018
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  10. oldfortyfiveauto

    oldfortyfiveauto Well-Known Member

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    tublacain is a buddy's bother. He's a retired high school machine shop teacher and despite that he's very sharp.
     
  11. Trickymissfit

    Trickymissfit Well-Known Member

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    surface finish is usually better with a radius on the tip. .025" R. is plenty, but the radius also causes stress in the metal that will bite you later. Carbide like to be "plowed" at a petty good surface speed, and this is where high speed shines.

    An old man once told me that if the finish is bright and shiny after the cut; you'll be fighting it from then on. It took me a couple years to figure out what he was talking about, but boy was he right!

    I've had pretty good luck with diamond inserts, and ceramic to a certain extent. The real issue is that a hand lathe and inserts are not made for each other.
    gary
     
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  12. shortgrass

    shortgrass Well-Known Member

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    I don't think you're going to duplicate the finish that you find on the outside of custom barrel blanks by just turning, no matter what tool you use. Why? Because after DSCF1321.JPG the blank is turn by the barrel maker it is mounted on a barrel spinner and sanded using a 2" wide belt sander away from any of the machine tools. They start at 60-80 grit and finish up with the grit belt (usually 240-320) that suits their fancy. It is another step after rough turning, done away from the machine tools.
     
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  13. J E Custom

    J E Custom Well-Known Member

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    As soon as I can figure out how to post pictures from my phone I will show some of the examples of some of the reasons for re-contouring.

    Some of the things I have found are from the factory sanding. Many have flat spots because the operator did not use the sander correctly. others have a straight bore but a out of concentric OD to the bore from a poor contouring. (Normally from to much tool pressure. not to
    long ago, I re-contoured a custom barrel simply to make it lighter for my friend it had a factory sanded finish and when I finished contouring, the new cut area was a better finish than the factory sanded finish. I start contouring with a carbide tool to reduce the size and change to a high speed tool for the last few cuts. I layout the starting points and the shank location I need to best fit the stock and work from there. In the picture you can see the improvement over the sanded part of the barrel. Hope fully I can get my friend to help me post some of the pictures of past projects.

    I think I have figured out the parameters for a better cut finish, but was just wanting to see if the shear tool would do even better.

    J E CUSTOM
     
    Last edited: Aug 15, 2018
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  14. Trickymissfit

    Trickymissfit Well-Known Member

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    You might consider scrubbing the cut area with a brown Scotchbrite pad and then a new green Scotchbrite pad. After that you might try something like a well worn green pad. I've seen them polish with glossy news print and a mixture of light spindle oil and Comet scrubbing powder for a single digit micro.
    gary
     
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