How to make a 5/16" bore with this boring bar?

[eotrfish]

I recently purchased this boring bar from KBC. Note that the minimum bore is specified as 5/16"

I've asked KBC to explain how I would create a 8mm (0.315") bore with this bar but no response so far.

 

[Former Member]

If you purchased in store they should exchange it or give a refund. They should have an issue with it. If it was ordered and sent it might take a little longer.

 

[John Conroy]

I would just grind the profile of the right side to reduce the width to less than .300

 

[LenVW]

I think you caught KBC with an incorrect size ‘spec’.
It is impossible to bore 0.3125“ with a tool that is 0.3275”.

Am I missing something ?

 

[phaxtris]

Magic, that's how

 

[eotrfish]

Am I missing something ?

No - you're not missing anything. I had the same thought.

Heard back from KBC. They checked stock and all of the bars spec'd as 5/16" min. bore are oversize. Now they are checking their stock back east.

It's not a big deal since I found a miniature Chinesium 6mm boring bar in my stash - mission accomplished. It just pisses me off that the QC dept let this slip by.

I would just grind the profile of the right side to reduce the width to less than .300

I did grind the backside of one that I already had but it wasn't long enough to clear an upset on the part.

 

[Chipper5783]

Like John says, grind to get what you need. With that style BB you can expect to grind it. KBC was kind enough to give you a little extra material, and didn’t charge you for it.

 

[PeterT]

Hopefully yours are an improvement of the import brazed boring cutters I had. It was many moons ago but the geometry was so messed up you could not even rotate the shank relative to boring head axis to get the proper cutting tool angle. I kept them just for occasional use in lathe tool post but even that was a clumsy setup without a flat reference on the shank. One of the YouTubers had a whole episode on 'remediating' them. But that's a dated generalization, maybe they are better now.

Borite has a line of cobalt cutters in nominal shank ODs which are pretty decent & I think you can get them individually from KBC.

 

[PeterT]

Borite if KBC was willing to do partial exchange, but I didn't check min diameter

 

[PeterT]

Somewhat related to small bores FWIW. I bought some of these carbide cutters form Ali along with a matching (6mm shank) tool holder. They cut really nice. So far used the straight boring & internal groove, the internal thread will be next. Good value compared to USA counterparts. I've only used these in lathe thus far but I don't see why an adapter couldn't be made for boring head socket.

 

[eotrfish]

I don't see why an adapter couldn't be made for boring head socket

The oversize KBC bar was actually a blessing in disguise. It still was not long enough to clear the upset on the part so I had to go search in "other stuff" drawers. I found a 12mm x 6mm tool holder and boring bar that worked perfectly. I used the 12mm x 6mm tool holder directly in my boring head. Since the holder has two opposing flats it is plenty secure for boring 6061. I didn't bother shimming it to 1/2" dia.

I have the tool holders in 4, 5, and 6mm with a selection of boring, grooving and trepanning tools. The internal grooving tool is sweet for 1mm cross section o-rings. I would highly recommend these Ali tools and holders for small precision work.