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Need mini boring bar recommendations

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  • Need mini boring bar recommendations

    I am trying to find a reasonably priced boring bar for use on a Chinese mini lathe. I need something that can fit in a <0.25" hole and go about 3/4" deep. This isn't something I'll use much so looking for middle of the road quality. In other words, maybe something like Shars quality and price?
    Thanks, Scot

  • #2
    Make up a holder for a two flute 1/4" end mill. They actually do quite well for home shop boring use. You can't load them up like a solid bar because of the reduced strength due to the flutes. But we're not in that much of a rush.... usually

    If you get the usual Weldon shank style with the 3/8 body the 1/4" cutter might or might not get you a full 3/4" into the bore. But if you can find a double ended 1/4" end mill that has 1/4" shank in the middle (pretty typical for double ended cutters) you can reach in further and do so more cleanly.

    Now the trick is that you will need to cock the end mill SLIGHTLY tip to you so the side flutes don't rub. But it only takes a hair of an angle to do that. And if you're working to a blind ended hole you may also want to grind away the opposite tooth that will try to dig in when it reaches the bottom of the hole.

    I've used a couple of small size old end mills in this manner for something like a dozen or more jobs over the last 6 years and I still have both of them intact. One is 1/4" and the other is 3/16. I limit the 3/16" to something like a .007 to .01 cut and feed slowly to where it just makes clean chips instead of dust. But it's handling that like a champ. The 1/4" cutter has no issue at all with up around a .015 to .02 cut in steel using hand feeding to get the same sort of light chips being formed. And they are cheap and easily replaced.
    Chilliwack BC, Canada


    • #3
      What do you want to do with it? Could you use a reamer instead?

      Solid carbide boring bars in that size range are the bees-knees, IMO. They are much more rigid than steel bars but they are also pricier. If they are out of the budget, I'd just get some blank HSS and grind your own. It wouldn't take that long at a bench grinder to make one up.

      Example solid carbide boring bar:


      • #4
        I've got a couple homemade solid carbide (and HSS) bars for boring under 0.25".

        Nothing cheaper than taking a broken or dull EM or reamer shank and making a boring bar from it.


        • #5
          Single Iscar and Sandvik mini carbide bars come up on ebay for about £15 each in the UK, I was lucky a couple of years ago, when I picked up 10 Iscar Picco's and the holder for about £30.


          • #6
            Originally posted by Dan Dubeau View Post
            Nothing cheaper than taking a broken or dull EM or reamer shank and making a boring bar from it.
            +1. I've got an insert set that goes pretty small, but not that small. I'd grab a broke solid carbide endmill (or new for about $10) and go to work. If you are set on a boring bar proper, maritool as a solid carbide 0.200" min bore, up to 1.3" depth for $24.


            • #7
              Micro 100/s are nice.




              • #8
                Shars quality and price? Go with McMaster-Carr. They're 1/6 the price and solid carbide. Plus, you'll get it in 1-3 days. The choice is a no-brainer.


                • #9
                  Thanks for all the replies! That one from McMaster is perfect...priced right for my budget and should work great. The DIY route is good, but I’m always short on free time so ready made is easier for me. Good ideas for when I can’t wait and need it now though.


                  • #10
                    Add Horn solid carbide boring bars to list. Made holder for them and love those.
                    Location: Helsinki, Finland, Europe


                    • #11
                      I would recommend the mini Borite sets, they're not cheap but work well and go down to 1/16 which can be very handy. Made in US
                      in Toronto Ontario - where are you?


                      • #12
                        As far as home made goes, I really like my converted 1/4 inch diameter broken carbide end mill. As suggested, give it a slight angle and the cutting edge will bite. The deeper you go, the larger the hole should be to start with, or you machine away material in steps to create the clearance. I usually start with a 5/16 hole, but I can start in a 1/4 inch hole.

                        I've also had good luck using an unbroken carbide burr. If you turn it just so in the holder you will have one tooth in the right position to cut. For through-holes there's no need to grind it for clearance. But because the shank is ground to create so many teeth, the effective diameter is less than 1/4 inch and it will be prone to breaking off.
                        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                        • #13
                          The use of the carbide burr if it has a rounded end is a great idea. At least for depths of cut that are within the size of each tooth or if you're willing to see the one tooth and the next up sharing.

                          But a flat nosed burr would have no end clearance. So that's fine if you're pulling the cutter outwards. But it would cause an issue if pushing straight ahead. No? I'm curious about this.

                          Of course depending on the maker of the burr if there is cutting edges on the front face then there goes that concern.

                          taking this to the next level I'm now also thinking that a four flute end mill would have more core material and should be stiffer than a 2 flute. I'll try that.

                          I'll grant "us" that the purpose designed small size bars suggested in this thread are the proper and better way to go. But for home use that only comes up occasionally I think there's much to be said for just re-purposing an end mill to get the job done without needing another bit of tooling that only sees occasional use.

                          Solid carbide would be better. But again for occasional use there's nothing at all wrong with using an HSS end mill that is already in our possession. Bird in the hand and all that ya know...
                          Chilliwack BC, Canada


                          • #14
                            If you want cheap grab a 5/16 square hss blank and start grinding.

                            If you have bucks to spend these are really good.
                            Bokum Tools makes boring bars to fit as small as 1/16 inch entry hole. They have over 2000 sizes.. I think they will have what you need. Hss or micrograin carbide..


                            • #15
                              If I were going to grind my own I think I'd rather start with a 1/4" round HSS blank and then make up a small square to round split holder to use it in the tool post. Even grinding a 1/4" square HSS blank down to suit would be a LOT of time at the grinder.
                              Chilliwack BC, Canada