Small Diameter Boring Bar

[Tin Falcon]

First of all you have been given lots of otion and I will attempt to not repeat to much.

I'm trying to bore a hole 3/8" Diameter to a depth of ~1". The problem I'm running into is all the boring bars I've been able to find online for that diameter have a maximum bore depth of 3/4".

There is a very good reason for this . The rule of THREE that is a steel boring bar should not stick out more than three times its diameter. This goes for work sticking out of a chuck and lathe tools as well. And less is better. And do not feel bad if you do not know this it seems to be some dark hidden secret barely talked about much less published.
As bogs pointed out the answer to the above limit is solid carbide. carbide is stiffer so the length limit is 7 times the diameter.
So search MSC, enco, travers etc for solid carbide mini boring bars.

I've tried grinding my own boring bars out of 1/4" HSS bar but grinding the bar is taking an obscenely long time, partly due the hardness of HSS as well as the fact that the blank heats up fairly quickly when removing such large amounts of material.

first of all a quality cobalt bit may be in order here. second use a good wheel . The gray import wheels are ok for General purpose grinding and a quick touch up but white wheels are a lot better for HSS . If you really want something that will run cool get a norton blue wheel. A bit pricey at $30 for one wheel. but they were developed to grind tools fast and cool. Also use a grit coarse enough to remove some material. Then a finer grit to finish and i do the last bit by hand on fine oil stone.

Tin

 

[goldstar31]

As most will have guessed, I make most of my tools whenever possible. I tend to forget what other people are buying- and whether things are correct for the purpose intended.
Consequently, I am wondering whether our poster is getting the right information in buying stock Boring bars and whether they are correct tools for brass.

Brass is ideally turned with 'negative rake' as I am reminded that when I finish this little tool holder for my Kennet tool and cutter grinder.

I leave it there.

Norman

 

[tornitore45]

Brass is slippery. I never tried Negative rake but most likely will result in not "biting" right.
Positive rake is not recommended because of self feeding, I always got good results with zero rake and can reuse the same tool for small cut on steel.

 

[goldstar31]

It came to me following old experience with a hand held graver. Having said that, I tend to diamond hone tools rather than use something straight from the grinder. Maybe it is a 'My' thing but it seems to be common on a lot of carbide inserts. I have to pass on them- sorry!

Norman

 

[MachineTom]

I use solid carbide for a job like that. Micro100 is brand, get a size of .31 with a 1.2 length. Ebay is a good source. The can be sharpened with diamond wheel. Cuts stainless Ti AL and other stuff fine.

 

[benster]

I ended up using a boring bar that claims the minimum starting hole is 3/8" but I drilled a hole to 11/32" and was able to get the boring bar in and bore to 3/8".