[How do I?] Using/Maintaining Brazed Carbide Boring Bars

[MyLilMule]

I have a couple questions in regards to those sets of boring bars with brazed on carbide. I bought a set from Shars with 3/4" shanks to fit into a boring head on the Bridgeport.

1) What should the relief angle be when I seat it into the boring head? I was thinking 5-10 degrees, but curious if that's correct.
2) I suspect that not all of the carbide is sharpened to the point it should be, and without a carbide tool grinder, what's the next best way to sharpen, or at least hone the carbide to ensure I am getting the best performance I can from them?

 

[dbb-the-bruce]

I bought a cheaper set - actually the bars with carbide brazed on came with the budget boring head. Didn't have a very good experience trying to use the kit on my mill. I just need to spend more time with it but haven't needed to use it since.

At a later point I read a post on this forum that said that the cheaper sets generally need to be sharpened before the will work well. On examining mine, it was clear that there was a lot of variation in the relief angles.

I ended up needing to use a few on my lathe without the head. At that point I had acquired my D-Bit grinder with diamond wheels and as able to accurately touch up the carbide bits. And as the post / comment suggested, it made a world of a difference in the results. So for me - a more rigid setup (on the lathe not using the boring head) and correctly sharpening the bits made a huge difference.

As to honing without some sort of wheel / sharpening setup, I do use a set of hand held diamond hones for touching up. However, the carbide is quite hard and the surface being honed it quite narrow - it is very easy to just end up rolling and basically ruining the edge.

I have used a diamond cut off wheel in a handheld rotary tool - it's a little easier to control because it will cut the carbide faster. Still fussy though. If I really had to do it by hand, I'd probably work out a way to hold the bit and hone it against a large flat diamond plate on a flat surface.

Regarding the relief angle - I'm sure someone will chime in with a specific number, but from my personal experience it is usually not that critical as long as you have the clearance you need. I think I reground my bits to ~7 deg from the flat / top.

With a boring bar, you can adjust the rake (top) by rotating the bar a little bit. This of course is limited by the relief / clearance and the size of the hole.

 

[C-Bag]

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[MyLilMule]

It was worth it to me to buy a used Baldor clone type carbide grinder.

I've been looking here and there, and it seems these are still pretty expensive (to me, anyway). The ones I have found with the twin diamond cups with the slanted rests are easily $300-$500 or even more. This one here is $500 on FB - even though it is nowhere near me, the point is, they are a lot more expensive that I would have thought. I'm guessing these are sealed motors?

 

[C-Bag]

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[f350ca]

Recently bought 3/8th and 3/4 shank sets from Busy Bee (usually lower quality than your Harbour Freight ). Was surprised, they were properly ground and honed. Cut right out of the box.

Greg

 

[Karl_T]

You need to grind the relief to a bit smaller radius than the hole you are boring. relief right at cut edge of maybe 5 degrees crude drawing edn view.

top view - should cut right at the front edge with a tiny, 1/64 or so, radius. Then 5 degree relief going back.

Its going to cut best right at lathe center with cutter level - 0 rake angle.

Just like HSS, most of the work is in the correct tool grind.

 

[C-Bag]

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[C-Bag]

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[C-Bag]

won't be "bothering" you anymore.