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Small Boring Operation on Lathe

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  • #16
    Originally posted by loose nut View Post

    This works great, make very ridged boring bars and doesn't cost anything. Grind off all the teeth but one, make sure you grind them well back and there you have it. Easy to sharpen one tooth too.

    If you can't sharpen dull end mills this will also work for making old 2,3,4 tooth end mills into new single tooth end mills or fly cutters.
    Just by visualizing it, I don't think you need to grind off the other teeth. If you have teeth at 12, 3, 6 and 9 o'clock with the 9 at center height and closest to the front of the lathe, then I don't think that the trailing tooth at 6 will be touching, and the leading tooth at 12 will only be making a very shallow cut, if any. The 3 o'clock tooth will not be touching the far side unless the diameter of the hole is equal to the size of the end mill. Hmmm... I think that I may have to test this.
    At the end of the project, there is a profound difference between spare parts and left over parts.

    Location: SF East Bay.

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    • #17
      I've used a couple of sizes of two flute end mills as short reach boring bars for quite a while now. These are end mills that I chipped or otherwise wore out and needed "proper" sharpening. I don't have that ability in shop yet so I re-purposed them to act as boring bars. So far they have worked fantastically.

      A regular 1/4" size end mill with a 3/8 shank makes a great short boring bar which should work for what you're doing. For a longer reach one of the double ended end mills with a 1/4" shank size would be ideal.

      As mentioned you can either make a split holder out of some 1/2" square key stock or similar or you can use the AXA holder that has a little groove along the lower shelf of the tool cutout.

      Over time it would be good to add to your boring bar collection by expanding on both the larger and smaller sizes than what you have.
      Chilliwack BC, Canada

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      • #18
        Originally posted by danlb View Post

        Just by visualizing it, I don't think you need to grind off the other teeth. If you have teeth at 12, 3, 6 and 9 o'clock with the 9 at center height and closest to the front of the lathe, then I don't think that the trailing tooth at 6 will be touching, and the leading tooth at 12 will only be making a very shallow cut, if any. The 3 o'clock tooth will not be touching the far side unless the diameter of the hole is equal to the size of the end mill. Hmmm... I think that I may have to test this.
        Loose nut was possibly talking about taps.

        Sharp endmills work as-is as a boring bar but are prone to chatter. Turning the toolpost couple of degree helps so that entire flute is not trying to cut if things start to chatter.
        Location: Helsinki, Finland, Europe

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        • #19
          OR, you could get an adjustable reamer for that size and ream the hole in steps to your spec. Another possibility is to keep the hole diameter you have now and decrease the diameter of the shaft to fit the hole.

          How are you measuring your hole diameter now? If you used a 0.302" drill, you probably don't have a 0.302" hole.

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          • #20
            Originally posted by MattiJ View Post

            Loose nut was possibly talking about taps.

            Sharp endmills work as-is as a boring bar but are prone to chatter. Turning the toolpost couple of degree helps so that entire flute is not trying to cut if things start to chatter.
            That's what I've done with the end mills I'm using. I just angle it so that when I look down from above it's just clear that it's not parallel. So 2 or 3 degrees or so.

            It started out as a "WTH" test about a year and a half ago with a 3/8" size and worked so well that I'm using a 5/8" and a 3/16 as well. So far it's all positive.
            Chilliwack BC, Canada

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            • #21
              I've had that problem from time to time. One solution was to mount a piece of bar in the toolpost, then drill into it using a drill bit mounted in the chuck. This makes the hole on center. Then you drill and tap a hole into the side for a set screw. Then make a D bit out of a drill bit, either HSS or carbide, and secure it into the hole. You can play with the stick-out to suit, and you never need to shim the holder. One I use a lot is made with a 1/4 inch hole, and I use a carbide shank which had broken so I ground a D bit into the end of it.

              Alternatively you can use an end mill, which will give you two or four cutting edges, or if the hole is to be blind, then you're limited to one cutting edge. The rest have to be ground away for clearance at the bottom of the blind hole.

              My main holder is drilled on both ends, 1/4 inch at one end, and 3/16 at the other. I had at one time picked up several long shank 3/16 bits from Boeing Surplus, so I made some cutters from that. In the 1/4 inch hole I sometimes use an old tap which has been broken, so I grind a suitable cutting edge on it for boring. I think this is where I learned that all HSS are not equal. The Boeing bits were quite good, what I'm calling real HSS, and some taps are good also. Some are ****e, like much of the Chinese HSS drill bits.

              Oh, and the shanks of the taps are not always 1/4 inch- I've never seen them larger, but often they are smaller than .250.
              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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              • #22
                Make one, the tang of a file works, red heat, bend the tip, air cool file or grind to shape harden and temper fairly easy to make really, I have gone beast mode on a 3/8 square toolbit and ground one out, slow but workable, I found loads of ways I could make a tool to bore a hole to the wrong size, it’s a talent “ the knack”
                mark

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