Small Hole Boring Bar

B

bosephus

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i need a small hole boring bar , i have been looking at a few 5/16 size bars that use inserts .
and knowing next to nothing about carbide inserts i am a bit stumped on the what is the best style insert to use

shars sells one that uses a ccmt 21.51 or ccmt 21.52 insert .
and i have found some solid carbide bars that use a tbgt520.5l
and some that use a dcmt 21.51


i'd be more partial to spending the extra cash on the solid carbide , but i could use the input on the inserts .
my main use will be in 01 tool steel
 
Hi BO can you give a bit more information on the type of material you are wanting to bore and how deep?

Most of the sizes of that diameter that I bore, I use HSS tools that I have ground my self.

David
 
I like the insert type boring bars. I have one of the small shars bars that takes that insert mentioned above. It works really well and stays fairly rigid for what it is. I'd stay away from the solid carbide bars because of the price and if it snaps you're out a lot of money. Carbide will snap without warning. If you chip an insert it ain't a major catastrophe. I've also ground small boring bars out of hss but it's really time consuming, because there's a lot of material to remove along the shaft just to produce a small boring bar. Sometimes you gotta grind one out because that's the only way to get the job done when a small bore is called for.

Marcel
 
I have a little (1/4") Circle Machine Co, FCBI-250-4-5R (solid carbide). It takes TDAB-505 inserts. The insert is arranged for radius cutting (don't be facing the bottom of a hole with it). I don't doubt xalky's comment that it would be easy to break (and result in great sadness). However, it is absolutely awsome to use. If you have to, you can hang the bar crazy far out (obviously light cuts).

The solid carbide bars are very nice. After playing with this little one, I promptly went and bought a 1/2" solid carbide bar (not a Circle one, just a cheapie) - it is also very nice to use. I did take the time to make up a good sized tool holder, with a reamed hole to grip the boring bar.

I needed to open up the ID of some ball bearings (I don't recall the bearing number, but it had an extended inner race that I was just able to get a grip on) - I'm not sure how hard it was, but pretty darn hard. The little Circle bar did the trick. In fairness, a larger steel bar would have worked fine as there was plenty of room and the bearing wasn't very thick.

If you can find some carbide bars in your price range, I'd encourage you to go for it.
 
I used a piece of 5/8 drill rod, turned 3/4 length to .500, with a 1/8 shoulder. drilled and reamed it to 3/16, and made a hack saw cut length wise. I put a 2 flute 3/16 end mill in it and put the whole thing in an adjustable boring bar holder for my lathe. I bored a number of holes to .250 with it, only .200 deep, but after all, that's what I wanted to do.
 
ideally i would like a tool to fit in .375 bore and i can live with anything that fits in under .390 and for a high quality tool found at a reasonable price it needs to fit in .425 .

and i need to be able to very my depth from nothing to 2 inches at minimum , its sole use will be as a finish tool ( radius cutting) . thanks chipper . and is going to see a lot of use in 01 tool steel .


i have a budget of around $100 or less in mind . and i have found quite a few nice solid carbide bars in my price range but choosing the right style insert has me baffled .
 
Here's a picture of my little 3/8" carbide boring bar with a 1/2" steel boring bar behind it for a size comparison.

boring_1.jpg

The 3/8" boring bar uses CCMT 21.51 inserts while the larger boring bar uses the larger CCMT 32.51, which are the same style inserts I use for all my lathe turning tools. For inserts for both sizes, I use AR Warner HSS, normal carbide and shiny/sharp carbide (for AL) and change as needed. I like this shape of insert because you can turn and face without moving the toolpost which I hate doing.

The carbide boring bars are expensive, but they are really, really nice especially in a small size where the extra rigidity really helps. I do a lot of fine work and many times even a 1/2" boring bar is too big, so I end-up using the little one most of the time. I also have a very small Micro 100 non-insert carbide boring bar that I breakout on very special occasions.
 
I learned something new today. I'd never seen a solid carbide boring bar that takes an insert. I always thought the carbide ones were non insert type. So I take back what I said, about carbide snapping, I was referring to the small non insert types that I've seen and used. That little carbide insert boring bar must be nice and rigid.
 
Stefan Gotteswinter just posted an excellent video on making a set of boring bars: https://www.youtube.com/watch?v=O9d_I0A4kzg

It's true he's using HSS rather than carbide, but for small holes-- as the OP spec'd in his question-- HSS (with colbalt), could well be an easier solution, a lot cheaper with the satisfaction of making your own.

One thing I really enjoyed about the video is the way he shows how to grind the bits.

Gotteswinter_boring_bars.png
 
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