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Thread: HSS Boring bar geometry
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19th Jan 2021, 12:55 AM #1Senior Member
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HSS Boring bar geometry
HI all I'd like to grind a boring bar out of a single HSS piece but I can't find any good images of the required geometry. Does anyone have a good link? I will be boring aluminium so positive rake I guess.
There are plenty of course of right and left hand turning tools.
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19th Jan 2021, 01:17 AM #2
Hi J3d, Guys,
The big problem with making an all HSS boring bar is the amount of material that you are going to loose, unless it only a very small one. I've made small boring bars out of HSS rod intended to be used in small diameter holes 10 mm in diameter. Anything smaller and I make a "D" bit, though having said that I've made "D" bits 22 mm in diameter.
My preference would be to use a piece of round bar that will go into the bore that you want and make a cutting tip from a broken drill or cutter and fasten it using a grub screw in the bar end. You can then grind any profile that you want to make your cutter.
The hardest part would be drilling the cross hole after you have drilled and threaded the bar end for a grub screw. You have to go careful when doing the cross hole to prevent the drill grabbing and breaking as it cuts into the threaded hole.
HTH.Best Regards:
Baron J.
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19th Jan 2021, 08:12 AM #3Most Valued Member
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In that case it doesn't have to be HSS. I made a boring tool from O1 steel. You can turn down the shank, leaving a larger radius piece on the cutting end. Grind away most of the waste at the tip to get the desired shape, heat treat and temper to straw colour. Finish grinding and honing in the hardened state.
In terms of the geometry, I didn't get too scientific. The front clearance angle needs to be more severe as the diameter of the hole decreases. You can rotate in the tool in the holder slightly to change the effective back rake.Chris
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19th Jan 2021, 08:32 AM #4Most Valued Member
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Here's a commercial solid carbide boring tool to give you an idea of geometry.
Chris
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19th Jan 2021, 09:42 AM #5
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19th Jan 2021, 09:51 AM #6Most Valued Member
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We don't know what diameter hole the OP wants to bore. It may be too small for a boring bar with and inserted cutting tool. I assume that's why he wants to grind it from a single piece of HSS.
Chris
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19th Jan 2021, 10:15 AM #7Golden Member
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A boring bar cutting edge is in essence a LH cutting tool so I always use the same geometry as I would for a LH cutting tool.
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19th Jan 2021, 04:30 PM #8Gear expert in training
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19th Jan 2021, 05:51 PM #9Most Valued Member
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19th Jan 2021, 11:09 PM #10
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19th Jan 2021, 11:12 PM #11
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20th Jan 2021, 12:47 PM #12Senior Member
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20th Jan 2021, 05:45 PM #13Gear expert in training
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I know it's nice to be able to make tools yourself, but I firmly believe that the age of using HSS for general machining has long gone. If you were boring small holes that need expensive fancy holders and inserts then it makes sense, but a cheap insert boring bar set will outperform HSS pretty much every time and you can get down to about 10.5mm bore with an 8mm bar.
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20th Jan 2021, 09:05 PM #14
A 30 mm diameter hole ! That's enormous. I have a very old 1/2" square forged boring bar that would do that easily. It will just fit into a 20 mm hole.
15-09-2018-001.jpg 15-09-2018-006.JPG
A 30 mm hole in 1" inch thick EN1 flat bar. This picture is from when I made my Norman tool posts.
I can't find the picture with the boring bar at the moment.Best Regards:
Baron J.
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21st Jan 2021, 03:30 PM #15
Bars
The big enemy of boring bars is flexing. If you are making your own bars don't use something like mild steel unless it's a large bar of solid proportions. Try to use tool geometries that lessen the stresses on the cutting edge , this is easier said than done.
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