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Small diameter brazed boring bar

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  • Small diameter brazed boring bar

    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

  • #2

    If you have a carbide bar how about use it as both cutter and bar? There's lots of low cost diamond tooling out there to fit something you already have I'm sure. And while a lot of it is really coarse you could use it to rough the shape and then use a fine grit diamond knife hone to refine the cutting edges.

    Click image for larger version  Name:	self cutting round bar.jpg Views:	0 Size:	76.4 KB ID:	1977553
    Last edited by BCRider; 12-29-2021, 07:23 PM.
    Chilliwack BC, Canada

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    • #3
      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.

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      • #4
        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.
        How long are you going to want the bar sticking out?
        I think at 5/16” diameter even being carbide you are going to be pushing it if you take full use of the 4” piece even taking tool holding into consideration.

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        • #5
          I plan on very light cuts,

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          • #6
            How long is your bore? Brazing HSS will damage it if cutting edge gets to a red color, at least I think this way. No, you cannot quench it and expect good results.

            Did you think about brazing your carbide bar to a steel shank of a bigger diameter. Doing so you may be able to bore 3.5" deep.

            2-nd option. You can get a cheap imported boring bar set. The smallest bar is 3/8" in diameter and 6" long. It accepts 3/16" round cutters, you can make one out of a broken end mill.

            3-rd option. If the bore is very deep, can you make a simplified gun drill of a proper diameter and use it as a reamer to get to a final size. I have not used one on my own, but seen it done by others. You can get very good results this way.

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            • #7
              Boring depth beyond 8X the bar diameter will become problematic at best.
              In your case beyond 4".

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              • #8
                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.

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                • #9
                  I often silver solder used carbide inserts to the end of solid carbide bars and grind them into boring bars. That said that’s a long way to stick a tool out. I would give it a lot of positive top back rake to make it cut easier.

                  Jimsehr
                  Last edited by jimsehr; 12-29-2021, 09:48 PM.

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                  • #10
                    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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                    • #11
                      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.
                      Chilliwack BC, Canada

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                      • #12
                        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.
                        'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

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                        • #13
                          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.

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                          • #14
                            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.

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                            • #15
                              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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