Small diameter brazed boring bar

[boslab]

Anyth, funny I’m now officially bloody useless, I swear I heard the drill in the shop, I reckon the spiders are building something.
mark

[Fasturn]

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

Chucking reamer on a thru hole. If square bottom , blind - use bottom drill to finish. You can bore the hole under size with a short bar, then ream.

[Richard P Wilson]

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.

Well, I've done it and no, it doesn't seem to harm it.

[Bob Engelhardt]

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.

Well, I've done it and no, it doesn't seem to harm it.

Yeah, me too. Not that I tested the HSS for hardness, but it cut like it should have.

[quadrod]

I had never heard of a flat bottoming drill bit, time for me to sacrifice a drill bit to the grinder for this project.

[small.planes]

How long is your bore? Brazing HSS will damage it if cutting edge gets to a red color, at least I think this way.

Not really true.
HSS is designed to be hard at hot temperatures.
For instance this article has the time temper graphs and shows a drop of 2 points for an increase in holding time of 3 hours at 600c.
If you are taking that long to braze your HSS then I think you should probably take up knitting

Dave

[Mcgyver]

I would silver solder. You can do this delicately and keep the highest temps away from the cutting edge. Fixture it somehow some how, ideally so the fixture isn't a heat sink. Use lots of flux and place a small length (like a1/4 inch) piece of 1/16 SS at the joint. start heating - propane/air is easiest. concentrate heat on the bar, give the HSS a shot of heat as the bar comes up to temp and you can get the the SS to wick in. The edge of the tool will be no where near read hot. Very often I'll dab around the area with some wet paper towel right after to take some heat out before it travels to the edge.

[BCRider]

I had never heard of a flat bottoming drill bit, time for me to sacrifice a drill bit to the grinder for this project.

One option is to just use a suitable size two flute end mill. But if it's an oddball a flat bottom drill isn't too tough to make up. This one came from my drill index full of "specials".

It's tough to get a truly flat bottom due to needing SOME relief. And with the curve of the flute this introduces a very slight curve in the cutting lip due to the relief angle. You can see that slight waviness in the side on view below as the line crests slightly at the tips and the center.

Due to the shallow chisel point angle the drill will no longer self feed either. So it auto-stops when you flatten the bottom of the same size starter. hole.

Hope this helps with your grinding visualization.

[no704]

+1 use an end mill.