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Small diameter brazed boring bar

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  • no704
    replied
    +1 use an end mill.

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  • BCRider
    replied
    Originally posted by quadrod View Post
    I had never heard of a flat bottoming drill bit, time for me to sacrifice a drill bit to the grinder for this project.
    One option is to just use a suitable size two flute end mill. But if it's an oddball a flat bottom drill isn't too tough to make up. This one came from my drill index full of "specials".

    It's tough to get a truly flat bottom due to needing SOME relief. And with the curve of the flute this introduces a very slight curve in the cutting lip due to the relief angle. You can see that slight waviness in the side on view below as the line crests slightly at the tips and the center.

    Due to the shallow chisel point angle the drill will no longer self feed either. So it auto-stops when you flatten the bottom of the same size starter. hole.

    Hope this helps with your grinding visualization.

    Click image for larger version

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  • Mcgyver
    replied
    I would silver solder. You can do this delicately and keep the highest temps away from the cutting edge. Fixture it somehow some how, ideally so the fixture isn't a heat sink. Use lots of flux and place a small length (like a1/4 inch) piece of 1/16 SS at the joint. start heating - propane/air is easiest. concentrate heat on the bar, give the HSS a shot of heat as the bar comes up to temp and you can get the the SS to wick in. The edge of the tool will be no where near read hot. Very often I'll dab around the area with some wet paper towel right after to take some heat out before it travels to the edge.

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  • small.planes
    replied
    Originally posted by mikey553 View Post
    How long is your bore? Brazing HSS will damage it if cutting edge gets to a red color, at least I think this way.
    Not really true.
    HSS is designed to be hard at hot temperatures.
    For instance this article has the time temper graphs and shows a drop of 2 points for an increase in holding time of 3 hours at 600c.
    If you are taking that long to braze your HSS then I think you should probably take up knitting

    Dave
    Attached Files

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  • quadrod
    replied
    I had never heard of a flat bottoming drill bit, time for me to sacrifice a drill bit to the grinder for this project.

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  • Bob Engelhardt
    replied
    Originally posted by mikey553 View Post

    According to a Machinery's Handbook 26 the tempering temperature for high speed steel is 900-1200 deg. F.
    And this is what I've got from Google on silver solder:
    Solidus 1145ºF (618°C) Liquidus 1205°F (652°C) Brazing Range 1205°F- 1400°F (650°C -760°C) Electrical Conductivity 8.32 (%IACS) Density 4.93 (t.o./cu.in.). BRAZING PROPERTIES: A cadmium free alloy with a narrow melting range Safety Silv 56 is the lowest melting temperature high silver brazing filler metal.

    So I would think that brazing a short piece of HSS would most likely overheat it , which results in a lost hardness.
    Originally posted by Richard P Wilson View Post

    Well, I've done it and no, it doesn't seem to harm it.
    Yeah, me too. Not that I tested the HSS for hardness, but it cut like it should have.

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  • Richard P Wilson
    replied
    Originally posted by mikey553 View Post

    According to a Machinery's Handbook 26 the tempering temperature for high speed steel is 900-1200 deg. F.
    And this is what I've got from Google on silver solder:
    Solidus 1145ºF (618°C) Liquidus 1205°F (652°C) Brazing Range 1205°F- 1400°F (650°C -760°C) Electrical Conductivity 8.32 (%IACS) Density 4.93 (t.o./cu.in.). BRAZING PROPERTIES: A cadmium free alloy with a narrow melting range Safety Silv 56 is the lowest melting temperature high silver brazing filler metal.

    So I would think that brazing a short piece of HSS would most likely overheat it , which results in a lost hardness.
    Well, I've done it and no, it doesn't seem to harm it.

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  • Fasturn
    replied
    Originally posted by Bented View Post
    Boring depth beyond 8X the bar diameter will become problematic at best.
    In your case beyond 4".
    Chucking reamer on a thru hole. If square bottom , blind - use bottom drill to finish. You can bore the hole under size with a short bar, then ream.

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  • boslab
    replied
    Anyth, funny I’m now officially bloody useless, I swear I heard the drill in the shop, I reckon the spiders are building something.
    mark

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  • Dan Dubeau
    replied
    Originally posted by quadrod View Post
    Thank you all for the replies, I'll let you know how it works out. Don't hold your breath though I'm a little slow to complete projects.
    You're in good company here . Some of us never finish anyth

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  • mikey553
    replied
    Originally posted by Richard P Wilson View Post

    I've silver soldered HSS tips onto tools. The heating does not affect it, and no, you will not have to quench it after heating.
    According to a Machinery's Handbook 26 the tempering temperature for high speed steel is 900-1200 deg. F.
    And this is what I've got from Google on silver solder:
    Solidus 1145ºF (618°C) Liquidus 1205°F (652°C) Brazing Range 1205°F- 1400°F (650°C -760°C) Electrical Conductivity 8.32 (%IACS) Density 4.93 (t.o./cu.in.). BRAZING PROPERTIES: A cadmium free alloy with a narrow melting range Safety Silv 56 is the lowest melting temperature high silver brazing filler metal.

    So I would think that brazing a short piece of HSS would most likely overheat it , which results in a lost hardness.

    Leave a comment:


  • quadrod
    replied
    Thank you all for the replies, I'll let you know how it works out. Don't hold your breath though I'm a little slow to complete projects.

    Leave a comment:


  • Richard P Wilson
    replied
    Originally posted by quadrod View Post
    I need to bore a small diameter hole in machinable stainless steel, .452" . I have acquired a 5/16 carbide bar 4" long and want to braze or silver solder some HSS to the bar to grind to my cutting angles. Will the brazing affect the HSS adversely? Will I have to quench the tool after brazing? Thanks, Rod Williams
    I've silver soldered HSS tips onto tools. The heating does not affect it, and no, you will not have to quench it after heating.

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  • BCRider
    replied
    Originally posted by quadrod View Post
    I have thought about that, but if I braze on a 1/2' long peace of HSS I gain some usable length to the bar.
    In that case you should be looking at a 7/16 diameter carbide bar, not 5/16.

    The only reasonable use for a 5/16 shank bar with a long extended cutting length is to worry the hole big enough to accept a 3/8" bar with cutter. And then to nibble at the bore until you can fit a 1/2" round bar. The 1/2" being either the final size or if you get tired of listening to the high pitch of boring bar chatter to switch to a 3/4" bar which should be able to finish the job.

    I know that the other guys are saying max of 8x the diameter. But especially when working with steel bars I found that more like 6x was still a PITA of major proportions. I prefer more like 4x extension numbers... and maybe 5x in a pinch. Mind you I work with steel. I understand that carbide, being stiffer, is better. So perhaps with lighter cuts 8x is doable. But I bet it's a nervous sort of doable.

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  • Bented
    replied
    Originally posted by quadrod View Post
    The bore depth will be approximately 3.750. And I do expect it to be a PITA. Rather then brazing I just ordered a 6" long carbide rod.
    At that small diameter a chucking reamer would be a better choice especially if multiple parts are required.

    .4515 to .4525 for less then $50.00 each.
    https://www.mcmaster.com/chucking-re...nk-reamers-10/
    Last edited by Bented; 12-29-2021, 09:48 PM.

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