QCTP holders and Boring bars

[Splat]

Guys, I have a few carbide shank boring bars. I'd rather not secure them in a qctp holder via set screws right down on the bars. I have two qctp holders of a different type that I can use to hold my bars. The first is the type with a "V" in the bottom. Now I would still use a slit bushing to hold the carbide bar in this type: View media item 96558
The second type of holder is this one. The hole diameter is 1-3/16". It would be one heck of a slit bushing for my smallest 5/32" bar to fit it into this holder. Would a slit bushing even work in this scenario?
View media item 97108
I figure I could use the "V" type holder for the smaller bars in slit bushings and the larger bars in the other holder with slit bushings. Thoughts or recommendations appreciated.

 

[BGHansen]

I think you'd be hard pressed to have an OD 1 3/8" bushing be "crushable" with an ID hole of 5/32". I'm thinking you'd be better off making a solid 1 3/8" bushing with a set screw or two clamping directly on the boring bar. Maybe grind a flat on the bar for the set screw if that makes sense.

Bruce

 

[mikey]

The second type of holder is this one. The hole diameter is 1-3/16". It would be one heck of a slit bushing for my smallest 5/32" bar to fit it into this holder. Would a slit bushing even work in this scenario?

Sure, a split bushing will work in the second type holder. Just make a partial slit opposite the through slit and it will allow the bushing to compress right down. I make the partial slit so that about 1/8" is left on that side of the sleeve.

All my boring bar sleeves have two slits like this and they compress and hold solidly, no problems.

 

[Wreck™Wreck]

Why not hold a carbide bar with set screws in the V provided?

You would be hard pressed to find screws that will leave a mark on a carbide tool shank, screw them down and have at it. If drilling from the tool post with carbide drills you may push the drill through the holder if held on the round with screws so grind a flat on the shank or back it up with a steel round that the screws can get into.

 

[darkzero]

Why not hold a carbide bar with set screws in the V provided?

You would be hard pressed to find screws that will leave a mark on a carbide tool shank, screw them down and have at it. If drilling from the tool post with carbide drills you may push the drill through the holder if held on the round with screws so grind a flat on the shank or back it up with a steel round that the screws can get into.

I agree. Most of my boring bars are carbide, every single one of them is held by set screws. My smaller bars are held in a QCTP holder with V-grooves. My 2 larger bars are held a QCTP holder with a large hole & sleeves similar to the one posted but it's not a multifix type. But the holders I have still use set screws to secure the bars rather than pinching/clamping via the slit on tge holder. Never had a problem or a concern about the shanks chipping, not even my tiny Micro 100 carbide bars. Then again I am using flat point set screws.

I prefer to use set screws cause they index the bar if I need to extend or shorten the length. Although those clamp type holders for larger boring bars have been around for a while, I don't to use that type so I don't have to mess with realigning the boring bar when adjusting length. I suppose they're good for adjusting for more or less rake if you need. Since my large boring bars still use set screws, the sleeves I made have a wide slot rather than a slit to clear the set screws.

 

[Splat]

Sounds good. I was just checking out ER32 collet chucks which might help me out instead of making sleeves for each bar I have.

 

[mikey]

Have a look at the attached article by Dr. Uwe Heinrich of Micro 100. It might provide some food for thought about how you hold your bars.

 

[darkzero]

That sounds expensive! For the large boring bar holder, you don't have to make a split sleeve to use your smaller bars. As long as the bars are small enough & there's enough room, just make a bushing & use set screws to secure the boring bar in the bushing. Then the boring bar holder just has to clamp on the bushing & you don't need to worry about making a second slit on a thick sleeve. But either way will work perfectly fine and both are easy & cheap to make.

 

[Splat]

Thanks guys. I'm going to try the bushing route then, which was my original intention but I started overthinking about it. Oh, Mikey, thanks for the PDF. I'm going to read it right now.

 

[4GSR]

I have a QCTP holder fitted with a ER-32 collet chuck just for carbide bars. I've seem guys not clean out the BB holder so when they drive in the 2" carbide boring bar and tighten the crap out of the setscrews. And when they start a cut, the BB touches the workpiece and goes "ping", another $2000 BB down the drain! Same shop, they managed to break in half a 3" carbide bar. It was found in the dumpster buried in shavings. Nobody fessed up to that one!