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    I should add that I like a stub cutter and/or one with a large diameter shank going back into the tool holder so there can be little or no twist and chatter from a reduced diameter shank such as a common reamer might have.
    Buck

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    Quote Originally Posted by RayG View Post
    Hi Nick,

    The Paul Horn mini's look good to me. Paul Horn super mini en mini draaien - YouTube

    I like the way they filmed that with the cut away side... interrupted cut? seems like they are very robust

    I think that AIS 4137 is 34CrMo4, 42CrMo4 is AIS 4140, which machines nicely, so you should get a good finish.

    Are you going to harden them yourself?

    Ray
    That is a NEAT video, and for complex internal features I have seen people cut a part in half AFTER machining then cast the features in woods metal. Makes me wonder how much time could be saved by starting with a half part to begin with ?? Many features could be direct measured pretty easily, then checked on a reflecting compactor or microscope. A "full round" part will machine a but differently, and chip buildup in the hole might be a issue, or maybe not because from appearances they did not use coolant on the half parts.

    Thinking with modern video editing software it might be easy to just remove some frames from a section of video to accomplish the same thing as would be done with a strobe in the "old days" ??

    Bill

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    I just need to make a few of them. 4 or so. If I get more out of the stock, I'll make more of them.
    Surface doesn't have to be super-duper, but nice and sellable.
    There is a rod going into that cone (rod is conical too). All that is for the pushrod of a clutch.

    A friend (whom I make parts for) asked me, wether I could harden and grind rods 245 mm long 6 mm diameter. I can't. I suggested him to look for ejector pins. He ordered some. And for some odd reason (he didn't want to ask me for that) thought that he can turn the taper in the lathe. So he came back to me to grind the cones on the rods. He sent one rod to his customer and got a complaint that they don't fit. The reasons was, that somone messed around with the matching tappet. Now, I have to make these tappets too.
    Doesn't make me rich, but I have to return a lot to him. So I like to do that and take the chance to learn a bit more about making boring tools.

    Re-checked the material. The data sheet says 42CrMo4 is AISI 437, 437H or ASTM A331, A505, A519, A646. Out of my head, I would have said it is 4140.
    Whatever. That stuff is a bit tuff, but really nice to turn.

    I'll show pictures and follow Markus' tips.

    Thanks so far!

    Nick

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    That is a very nice grinder.
    Buck

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    To both Nick and Marcus, I'd be very interested in seeing photos of your setup to do the grinds on you cutter grinders. I've now done a number of different sharpening configurations and have that clear in my mind, but no scratch built tools like this. It would therefore be great to see the process here.

    Marcus your description wasn't gibberish at all, but I'm a "visual" guy, and a picture really is worth two thousand words to me. Unfortunately I don't understand exactly what it is that Nick is doing, as I was going to suggest a reamer ground as George described it, or grinding a conventional reamer down to size, however it's obvious that this is not the issue so I'll re-read the challenge and look forward to seeing how its solved.

    Edit: ok got it now, the talk of D bits had me mentally picturing a parallel bore, as I've personally only ever used them for that. The 3 mm initial bore prevents a small boring tool boring the taper. Interesting problem Nick. Is it a through bore? If so can you reverse the part and use a mini boring tool back the other way?

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    Quote Originally Posted by Nick Mueller View Post
    <>

    Re-checked the material. The data sheet says 42CrMo4 is AISI 437, 437H or ASTM A331, A505, A519, A646. Out of my head, I would have said it is 4140.
    Whatever. That stuff is a bit tuff, but really nice to turn.
    <>
    Nick
    This is 4140 and if you find it nice to turn it must be pre-hardened and not annealed. Annealed it is gummy stuff on which it is very hard to get a nice finish. Pre-hard is sweet especially if you run it really fast on the finish cut with a fine glowing chip coming off.

    http://www.ovako.com/Global/Download...%2042CrMo4.pdf

    Denis

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    The 4140 is QT, yes.

    I made a (lousy) sketch to make things clearer.
    The small diameter is 3.4 mm and the big diameter is 7 mm (it is a blind hole, not drawn to any standards). Cone is 9 long, cylindrical part 3 long. I can cheat a bit at the small end (drill a bit deeper). The 7 mm also are not critical. I just have to be "precise" with the location of the cone (0.1 mm off won't hurt).

    loch.jpg


    Nick

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    I see Marcus's tapered reamer as a kind of simplified countersink mill.

    The geometry of these mills is much more complexe than one would think at first glance.
    There's a positive rake on each flute but the back of the flutes is also relieved both radially and axially.

    The lack of axial relief is probably what leads Marcus to feed his tool with pecks of 0,02mm.
    May be this is what what made your previous experiments less than satisfying ?

    I'd be curious to hear more from Buck about the mod of a tap into a tapered reamer as this would seem pretty difficult to me.
    With any serious taper, there will be significant variation of the rake angle because as you get in the gullet toward the center of the tool, the rake angle decreases.
    At some point, you don't even have no rake angle nor gullet anymore because you are in the "web" ?
    I've already tried myself at converting "regular" cylindrical endmills into tapered ones and found it really difficult (if possible at all) without having to regrind the inside of the gullet too due to this problem.
    I did it on some occasion, but only when the taper to cut was not too steep.

    Very interesting question anyway.

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    The tap source is simply a tool blank that can be bought for a low price or even found in scrap that can be near a tool requirement size, in various materials (carbide, HSS, ect) with having a stub shank and having straight, right or left hand spiral flute design. With threads easily ground away taps can become good tool blanks. For nick’s tool the M 8.75 tap would have minor diameter of 7.08. A M9 tap minor dia 7.466. M10 minor dia 7.96. Any one could be a blank source.
    I mentioned 3 flute because there is more space to roll or grind a bit of OD clearance and 3F might cut into a taper better than a two flute and have more chip space than a tap having more flutes. Picking up the flute and tapering it down to 3MM (or so) should not be a problem for any TC grinder with a work head and index, and/or a riding finger or gashed for a spiral. It could be even ground down to the point and with one flute to center would cut the entire form. For Nick’s material I don’t think a full form tool would work. (Although with a very rigid machine a pecking process and a flood of oil it might.)
    Again there is nothing relevant about it being a tap it is simply a near size blank.
    *And this is not a proven tool just another something to try if the D drill does not work.

    One could even make the D drill from a tap blank.
    Buck
    Last edited by michiganbuck; 01-21-2014 at 11:24 AM. Reason: added "than a tap having more flutes"

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    Hi Nick,

    Thats my way of dealing with conical holes, a tapered single flute cutter:
    img_1959.jpg

    I grind the taper, then split it right on center and grind the relief on the tapered surface - angle of the relief is something around 10°.

    Works very well with low rpm/feed and produces a good finish, the part machined was toolsteel (1.2379 - I think its D2 for the american readers):
    img_1921.jpg

    Stefan

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    Default More on tapered cutters.

    Hi All:
    I think the key thing that has come to light is that the cutter whether it's single lip or multi flute is that it must have relief if it's tapered, which answers Nick's original question about D bit geometry and why his first efforts with unrelieved cutters were not successful.

    Many think that all reamers have a land that is unrelieved, and while this is true for cylindrical reamers, it is most definitely not true for tapered ones.
    The corollary to that, is that a tapered reamer cuts very differently from pretty much any other tool that is plunged, which brings us to two other thoughts.

    First, the delicate peck increment and gentle feedrate: since the cutter is cutting over it's whole length with each flute, it is much more highly stressed than any tool that cuts only over a small area like a cylindrical reamer or a twist drill or a cylindrical D bit.
    This very high loading of the cutter forces a conservative chip load, both in feedrate and in peck increment.
    If you violate it, you risk snapping the cutter.

    Second, the number of cutting edges matters, and a lot depends on the rigidity of the machine the cutter's going to be used on.
    A single lip cutter will tend to make the machine spindle or the machine tool saddle wobble around if it's not really rigid, and this is a result of the high side load that comes from the very broad contact edge of the cutter.
    2 flutes or even 3 flutes make this problem go away, and I've found 3 to cut the smoothest but 2 to be easier to measure, so I most often make 2 if I need the geometry to be accurate.

    I pointed out the importance of the amount of relief in a previous post; it's instructive to look at the relief on a countersink.
    If you are sceptical, take a standard countersink and increase the relief, then try to use it freehand in a pistol drill; it'll be almost uncontrollable.
    If you take a properly ground countersink and run it exactly the same way, it'll cut much more cleanly, and it's because the relief has been reduced to the point that the cutter cannot take a very big chipload; the reduced relief prevents it from taking a big bite by bottoming out on the surface of the hole when you push it hard.
    That's really it in a nutshell.
    Cheers

    Marcus
    Implant Mechanix – Design & Innovation - home
    Vancouver Wire EDM -- Wire EDM Machining

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    Many think that all reamers have a land that is unrelieved, and while this is true for cylindrical reamers, it is most definitely not true for tapered ones.
    That is, to some extent right. Even endmills do have (sometimes) a very narrow land (0.1 mm).

    My experience with single lip cutters (like Stefan showed) were not so convincing. They simply tend to wobble. Mo matter what method you chose:
    1.) Primitive with no reliev (does work in brass and aluminium)
    2.) Relief, but just one flat that doesn't relief the full 180°. Small chips collect in the relief facet and marr the surface.
    3.) Relief over full 180° like for a single lip cutter. There's no way of guiding the reamer.

    So, here is what I made:
    p1233560.jpg
    It ended live as a 12 mm endmill and will reincarnate as a reamer ...
    Ground the OD and the cone in the cylindrical grinder.

    p1233561.jpg
    Gashing the flutes (following the cone) 0.6 mm deep.

    p1233562.jpg
    After gashing in the T&C grinder ...

    p1233564.jpg
    other view.

    TBC

    Nick

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    p1233565.jpg
    Sweeping the cone in the T&C grinder.

    p1233566.jpg
    Grinding relief facets (I was lazy and didn't sweep, just made several facets).

    p1233567.jpg
    Done

    p1233568.jpg
    and done. My hands didn't get much cleaner.

    Made one poppet and gave it to him (he was in a hurry with that). Will make a few more in the next days.

    Makes a nice finish with cutting oil and makes real chips with thin oil. RPM were 200 (7 mm OD).
    Relief is 7° and I decided for 0° rake. Was a bit anxious because of the material and didn't want to risk breakouts in the edges. So it takes a bit of pushing in to make it cut. OTOH, it makes fine dust when dwelling.

    Thanks Marcus, that went well!

    Nick
    Last edited by Nick Mueller; 01-23-2014 at 03:36 PM. Reason: Marcus, not Markus (the German spelling)

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    Thanks for putting up the pictures Nick, much appreciated.

    Stefan, how do you grind the relief? I've only ever ground relief as facets, often multi-facets, but yours looks quite different. The only way I could think of to grind it like that was with a eccentric holder, but I can't see myself being able to easily do that if presented with a similar problem.

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    Stefan, how do you grind the relief? I've only ever ground relief as facets, often multi-facets, but yours looks quite different.
    Don't know what heads Stefan has.
    But the usual procedure (if a Deckel S0 is what you have) is:
    Grind cone etc. Split. Rotate work by the angle of relief (7°) and grind the facet right to the edge (I use a sharpie to better see what is left to be ground). Then, rotate work by 180°.
    So the relief starts with a flat and then continues with a cone with a smaller diameter than the cutter.
    You don't need an off-center work head for that work.

    If you do have an eccentric work head, the whole relief is a cone (or cylinder) and doesn't start with a flat. Also, you don't need to tilt your head or rotate work for the relief to start.

    My T&C grinder can tilt the grinding head, so things get a bit simpler.
    As I use to say "My T&C grinder has more axes than I have brain cells".


    Nick

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    Hi Nick, I'd use a Clarkson for this, not as versatile as yours, though it probably does indeed still have more axes than I have brain cells

    Yes I didn't see the flat on Stefan's however, that's why I wondered how he ground it. It looks like the cone goes right to the cutter lip.

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    It looks like the cone goes right to the cutter lip.
    Can't see it clearly too.

    Nick

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    Quote Originally Posted by Pete F View Post
    Hi Nick, I'd use a Clarkson for this, not as versatile as yours, though it probably does indeed still have more axes than I have brain cells

    Yes I didn't see the flat on Stefan's however, that's why I wondered how he ground it. It looks like the cone goes right to the cutter lip.
    On a Cincinnati work head with not having a axial cam movement I have ground the clearance angle just to make sharp (or circle land if that is the wish) with an in feed of perhaps .003/.005 (again if that is the wish for cut depth) and then roll around (short of hitting next tooth) to make the rest of the grind cylindrical. Often using the wheel OD or a smaller diameter wheel OD For a very small or high number of teeth cutter to avoid hitting next tooth..

    With the RO work head (or RO type) one can generate almost anything.

    Nick I noticed that vertical T slot arm.. That is really nice.

    * Thanks for the follow up Nick.. A job well done.

    Buck

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    Hi Marcus,

    Quote Originally Posted by implmex View Post
    Here's a link to an example on my website:

    Implant Mechanix ? Design & Innovation » Precision Grinding

    Go down toward the bottom of the page and you'll see a series of photos about a mini plasma nozzle that was made using such a cutter.
    I need to make some good-quality tapered holes, and would like to see your cutters. Are they still on your web site? A pointer would be very helpful.

    Cheers,
    Bruce

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    Good morning Bruce:
    I will be happy to help in any way I can.
    What were you hoping to see?

    I know, from following your postings on PM casually, that you are well equipped and highly skilled too.
    You should have no difficulty at all; just let me know what you want to make and where you want to begin.

    To answer your question more directly; yes the little reamer is still on my website.
    Here is a link to the proper page:
    tool grinding |.

    The hardest part of this job was to gash the blank.
    I have a custom fixture I made decades ago for just this purpose...we use still mostly Imperial cutters here in Canada, so it's for 1/8 inch diameter blanks and I use broken carbide endmills a lot for cutter material.
    (This cutter happened to be HSS for strength, so a 1/8" drill blank was used.)

    So for me to gash a 1/8" blank is easy.
    I can show pictures of that if you wish.
    Once the blank is gashed, putting the cutting edges on if you have a Deckel SO or equivalent is also easy.
    It's a little more involved if all you have is a surface grinder, but not horribly so.

    Once the cutters get bigger, the job gets correspondingly easier and more forgiving, so you don't need the super contraption anymore and you can just gash your blank with a grinding vise and a little rectangular reamed block with a setscrew to hold the blank on the surface grinder at the proper angle.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining


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