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  1. #1
    Join Date
    Sep 2012
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    Thumbs up Tangential Lathe Tool.

    Hi Guys,

    Based on a discussion on another forum about Tangential lathe tool holders, I thought that I would do a drawing of one based on a 10 mm square holder and 3 mm diameter tool bits. This holder would be ideal for using those broken 3 mm drills.

    Tangentel tool.png
    I've shown an M3 clamping screw to clamp a 3 mm diameter tool bit. I've also drawn it to set the tool bit cutting edge level with the top of the tool holder in order to be able to hone the tool edge simply by rubbing the whole thing on a sharpening stone. I've also taken the part behind the tool bit back at about 12 degrees, so if wanted you could sharpen the tool bit cutting edge with back rake. The jury is out on whether a flat cutting edge or one with some back rake is best. With a maximum depth of cut of 0.5 mm this tool would suit small lathes and fine work.

    I've yet to make one but will post some pictures as and when.

    Edited to credit Niels Abildgaard ! Its his idea from way back.
    Best Regards:
    Baron J.

  2. #2
    Join Date
    Nov 2017
    Location
    Geelong, Australia
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    Default

    Looks good John. Interested to see how it goes.
    The front of the holder doesn’t have seem to have much wrap around the tool, but I guess it’s only a small tool so only light loads.
    Might it be better to leave out the back rake feature altogether as it could probably be achieved with a bees dick higher stick out on the tool?

    Steve

  3. #3
    Join Date
    Dec 2007
    Location
    Adelaide
    Posts
    574

    Default

    At times I've wanted to try a tangential type tool holder, I believe it is easier to sharpen a tool used in this type of holder, but you know what it is like - when you are not using the lathe you don't need it and when you are using the lathe you just want to get the job done and don't want to stop to make a tool holder.

    From comments I've seen on this and other forums I seems to me that most first time lathe owners/users do not bother with HSS tools but go straight to indexable inserts, believing that being the most modern they are the best.

  4. #4
    Join Date
    Aug 2008
    Location
    Melbourne
    Age
    34
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    1,075

    Default

    Quote Originally Posted by familyguy View Post
    From comments I've seen on this and other forums I seems to me that most first time lathe owners/users do not bother with HSS tools but go straight to indexable inserts, believing that being the most modern they are the best.
    Aside from form tools or needing to make a tool to fit an awkward space, where is carbide not the best?

  5. #5
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    Jun 2007
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    In this mainly hobby based type forum Carbide would/may not be best because users may not be using it correctly.

  6. #6
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    Aug 2019
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    Revesby - Sydney Australia
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    With carbide, I've burnt the edge off, and I've smashed chunks off.

    HSS would be slightly more forgiving on the latter, but a lot worse for the former?

  7. #7
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    Aug 2008
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    Yes, carbide is much more resistant to wear (particularly with all the fancy coatings that are available), but less forgiving to shock and crashing.

    I think the biggest 'misuse' of carbide is that you have to take a decent depth of cut and keep your surface speed up to get the best finish (especially in mild steel) and running a lathe at full speed can definitely feel a bit intimidating.

  8. #8
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
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    Hi Steve, Guys,

    Quote Originally Posted by OxxAndBert View Post
    Looks good John. Interested to see how it goes.
    The front of the holder doesn’t have seem to have much wrap around the tool, but I guess it’s only a small tool so only light loads.
    Might it be better to leave out the back rake feature altogether as it could probably be achieved with a bees dick higher stick out on the tool?

    Steve
    Thanks for your comment !

    If the front edge is machined carefully the jaw grip will be just over half way round the tool bit, about half a mm past the tool bit centre line giving half a mm of stick out of the cutting edge. But I do agree that only 10 mm is not a lot of grip area. But as long as you don't get too aggressive with the cut it should be fine ! But that is something that I will find out when I make the tool.
    Best Regards:
    Baron J.

  9. #9
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
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    Default

    Hi Elan,

    Quote Originally Posted by elanjacobs View Post
    Aside from form tools or needing to make a tool to fit an awkward space, where is carbide not the best?
    Like all things the use the right tool for the job ! Carbide has a place as does HSS ! If you look at the development of carbide cutting tools, it was developed with industrial practice in mind, certainly not small low powered machines that have neither the speed or the power to take advantage of the material.

    Though as time has progressed these carbide insert tools have become much better ! I openly admit that I use carbide insert tool bits for threading ! They have a much much better form than anything I could grind up !
    Best Regards:
    Baron J.

  10. #10
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
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    Default Tangential Build Log. First steps !

    Hi Guys,

    Since I posted a detailed drawing of this lathe tool, I though that I might as well go ahead and make one. So here we go !

    I thought that I still had some 10 mm square key steel kicking about, but I've not been able to lay my hands on it, so because I've got a number of 1/2" diameter printer shafts I decided to cut a piece off 65 mm long and fly cut flats on it to get my 10 mm thickness. No pictures of that job, but I'm quite sure that you will be able to find some suitable material.

    08-06-2020-003.jpg

    This is the piece of bar that I've fly cut flats onto. Here I've marked it out and spotted it ready for drilling. Note that I cut a 65 mm long piece. This is to allow for the diameter of the tool bit which in my case is a 3 mm diameter broken drill.

    08-06-2020-001.jpg 08-06-2020-002.jpg

    These pictures show how I achieved the correct angle of 58 degrees for drilling the 3 mm diameter hole for the tool bit to go into. In order to get a reference parallel to the lathe bed I used a piece of 25 mm round bar. I had already set the correct centre height for the hole from a line scribed across the end of the work piece. So I now needed to set the angle of the work piece.

    The Norman tool holder on the lathe will hold a 13 mm thick tool so the 1/2" thick piece of bar fits easily. Since I machined a flat on both sides of the bar it fits snugley against the back of the slot and because the back of the Norman tool holder is parallel with the slot I'm able to use it to set the correct drilling angle.

    08-06-2020-004.jpg 08-06-2020-005.jpg 08-06-2020-006.jpg

    At this point I now have to set the cross slide so that the drill will be in the correct position to drill the hole. I used an MT2 arboured 1/4" drill chuck with a centre drill in it to position the work piece.

    Now at this point it would be very difficult to use a normal drill, so I used a 3 mm diameter slot drill to start the hole and drill about half way through the work piece. This hole will act as a guide for the 3 mm drill to follow.

    08-06-2020-007.jpg

    Once I had finished with the slot drill I changed to a normal 3 mm drill bit and finished the hole.

    After which I removed the workpiece and checked that the hole was not only the right size but square to the flats on the workpiece one both sides.

    Next part coming up !
    Best Regards:
    Baron J.

  11. #11
    Join Date
    Sep 2012
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    Thumbs up Tangential Build Log. Continued !

    Hi Guys,

    Having got the workpiece drilled at the correct angle, it time to check it.

    08-06-2020-008.jpg 08-06-2020-009.jpg 08-06-2020-010.JPG

    These pictures show the tool bit inserted into the tool holder. You can see the 58 degree angle here.

    The next step is to machine the tool holder so that the tool bit is half a mm proud of the holder face

    08-06-2020-011.jpg 08-06-2020-013.jpg 08-06-2020-012.JPG

    In these three pictures I'm showing the method that I used to set the work piece in the milling vise at the correct angle to fly cut the end down to the required level. I used a pair of parallels to set the work piece at the correct angle by inserting the tool bit and resting it on the parallels and then holding the work piece against the edge of the vise side rail so that the flat aligned the work piece so that the through hole was at 90 degrees to the body.


    08-06-2020-014.jpg

    I removed the parallels and tool bit before fly cutting. When I reached the edge of the through hole I zeroed the depth gauge and set a 0.6 mm cut. This depth leaves me with the required half a mm plus 0.1 mm clearance. The tool holder has enough wrap to hold the tool bit firmly.


    08-06-2020-015.JPG

    Seen here after deburring the tool bit fits in there nicely.

    08-06-2020-017.JPG 08-06-2020-016.JPG

    The next part will deal with drilling the remaining holes.

    More to come.
    Best Regards:
    Baron J.

  12. #12
    Join Date
    Mar 2011
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    Southern Flinders Ranges
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    Default

    Maybe its because I currently have nighshift brain, but I'm having a hard time figuring out how this actually works. I use a shear tool for finishing mild steel and ally but that's just a square tool with around a 30deg angle cutting edge that runs top to bottom of the tool and something around 10deg relief where required. Like this https://grabcad.com/library/hss-vert...ear-tool-bit-1
    Based on other images I looked at on the internet this looks near enough the same just built into a tool holder using a broken drill for a cutting bit.
    If someone could explain what I'm missing I'd appreciate it.

  13. #13
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    Nov 2017
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    Essentially the angle of the tool stock in the holder forms the front and side clearance, so the only feature you need to grind on the tool is the top face to get the back and side rake.
    It’s not a shear tool - just “normal” geometry.

    Steve

  14. #14
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    Sep 2012
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    Default Tangential Build Log. Part three !

    Hi Guys,

    Thank you for the thanks and likes !

    I been finishing the tool this morning and have taken lots of pictures of the work done and the flow of it.

    09-06-2020-002.JPG

    First job was to drill the holes in the tool holder. I started with the one that ought to have been M3, but picked up the 3 mm drill without realising it, so I re-drilled it 3.2 mm tapping size for M4. There is plenty of metal that the size difference doesn't matter.


    09-06-2020-003.JPG 09-06-2020-001.JPG

    While I had the work piece set up in the drill, I put a counter bore in. It just makes it a flat surface when you come to thread the hole and support the screw head.

    Then I turned the work piece over and drilled the 7 mm hole. In hindsight 6,5 mm would have been better. This hole is designed to allow the metal to flex and bend trapping the tool bit when the screw is tightened up.

    09-06-2020-005.jpg 09-06-2020-004.JPG

    Next step is tapping the M4 thread for the clamping screw. Actually I cheated here and started the tap by putting it into the drill chuck whilst it was still set up for drilling, I then finished tapping the hole by hand.

    09-06-2020-006.jpg

    Next step slitting the work piece so that the clamping screw could pull the two half's together to clamp the tool bit. This is the slitting saw blade that I used. Manufactured by a company called Findllay, in Birmingham, UK.

    The blade is 28 thou thick (about 0.71 mm) and is 2.375" inches in diameter. You can see from the date code that it was made in march 1969.

    09-06-2020-009.jpg 09-06-2020-008.JPG 09-06-2020-007.jpg

    I put the blade onto an MT3 arbour in the mill. The above pictures show the set up that I used. I ran the blade at 300 rpm and 75 mm a minute feed, using diesel fuel as the cutting oil.

    09-06-2020-010.JPG 09-06-2020-011.JPG

    I'm not a fan of milling using the lathe, but in this case it was easier to set up the work to machine the angles on the work piece sides. Note the use of the mirror so that I could see where I got to with the milling.


    09-06-2020-013.JPG 09-06-2020-014.jpg 09-06-2020-015.jpg 09-06-2020-012.JPG

    The pictures above show the completed tool along with the piece of broken drill. That last picture shows the broken drill bit having been ground down square with the top of the tool holder. All I did there was to use a piece of square HSS as a spacer and hold it against the guide on the grinder to get the top flat. You can still see part of the flutes of the broken drill bit.

    09-06-2020-016.JPG 09-06-2020-017.jpg

    These last two pictures are of the very quick test that I did using a piece of 30 mm black bar and a 40 thou cut under power at 620 rpm and 6 thou feed. That finish looks worse in the picture than it actually is. I did expect the tool bit to get pushed down under cutting load, but it didn't. So I'm quite happy with that.

    OK that's it Guys. Job finished ! Now let me see the ones that you make !

    Thanks for looking.
    Best Regards:
    Baron J.

  15. #15
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    • Nice slitting blade !
    • Good idea to use a mirror

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