CBN insert boring?

A

alinwa

oft dis'd member
Can someone point me to a CBN boring bar setup suitable for .400 bores? I've never found a source for CBN inserts ground with suitable clearance for small bores..... does such a thing exist?
 
i bought some insert boring bars in amazon
one does 473 based cases barely
you will have to search..i got no data
 
my guess is they flex.
i use a couple and always do multiple cuts at the same depth to get
the desired number
GeneT said:
How are solid carbide bars failing you? (I don't know of any CBN inserts that small, but am trying to understand the problem.)

GsT
Click to expand...
 
GeneT said:
How are solid carbide bars failing you? (I don't know of any CBN inserts that small, but am trying to understand the problem.)

GsT
Click to expand...

Somewhere around RC36-40 carbide just seems to give up the ghost, in certain steels. For example, the drops a fellow sent me are marked RC37-ish, one set is 416 the other is 17-4

I'll have to go down and check but if memory serves the 416 cut and the 17-4 just screeched

This ties in with another post concerning opening sizer dies. I have some carbide insert tooling that cuts Redding dies leaving a glassy-smooth finish. But the case is thin enough that I've cut thru it.

I have many other dies to try cutting and so far nothing carbide has done the trick. I have tried some solid ground carbide as well as affixing a carbide 3/8 endmill sideways

I've always heard of "ceramic" and "boron" as being suitable for stuff harder thn RC40-50 but all the tooling I've seen make it look as though the product is "sintered" or somesuch and needs a lot of bottom support and near vertical support below the cutting edge. ie "overhang" must be minimal to account for low tensile strength.

I've pretty much stopped modifying dies because of this, preferring to just whack out an interim die to use un-hardened while waiting the (year or more??) for a die to be made. It's a pain right now because I've developed 4 different chamberings in the last 6mo as I'm recording youtube vids.....kinda' documenting the "wildcatting" process. I'd like to videotape exactly how I bore out my dies but at this point my success rate is about two dies forward and one die back :)

In other words I've screwed up as many as I've succeeded with. You give me a 300WSM Redding die and I'll modify it perfectly 9/10 of the time but run it in to a 300 RUM depth and things get wikky-wakk

Give me a Forster die, or RCBS and I'll call in every banshee for 6-8 miles

Little 6BR stuff? PPC? I'm OK but not great....depth easy but now diameter becomes a problem
 
well, foo!

alinwa said:
Somewhere around RC36-40 carbide just seems to give up the ghost, in certain steels. For example, the drops a fellow sent me are marked RC37-ish, one set is 416 the other is 17-4

I'll have to go down and check but if memory serves the 416 cut and the 17-4 just screeched

This ties in with another post concerning opening sizer dies. I have some carbide insert tooling that cuts Redding dies leaving a glassy-smooth finish. But the case is thin enough that I've cut thru it.

I have many other dies to try cutting and so far nothing carbide has done the trick. I have tried some solid ground carbide as well as affixing a carbide 3/8 endmill sideways

I've always heard of "ceramic" and "boron" as being suitable for stuff harder thn RC40-50 but all the tooling I've seen make it look as though the product is "sintered" or somesuch and needs a lot of bottom support and near vertical support below the cutting edge. ie "overhang" must be minimal to account for low tensile strength.

I've pretty much stopped modifying dies because of this, preferring to just whack out an interim die to use un-hardened while waiting the (year or more??) for a die to be made. It's a pain right now because I've developed 4 different chamberings in the last 6mo as I'm recording youtube vids.....kinda' documenting the "wildcatting" process. I'd like to videotape exactly how I bore out my dies but at this point my success rate is about two dies forward and one die back :)

In other words I've screwed up as many as I've succeeded with. You give me a 300WSM Redding die and I'll modify it perfectly 9/10 of the time but run it in to a 300 RUM depth and things get wikky-wakk

Give me a Forster die, or RCBS and I'll call in every banshee for 6-8 miles

Little 6BR stuff? PPC? I'm OK but not great....depth easy but now diameter becomes a problem
Click to expand...

Well, I've never tried to do what you're doing, and you may have already tried them, but Sandvik makes some super-rigid solid-carbide boring tools. I have part number CXS-06T098-20-6220R 1025. These have a wedge-shaped back end that is made to mate with a special holder, to ensure 'correct' orientation. I don't have the p/n for the holder, but I've used an ER-16 collet instead and never had an issue getting a good cut. Anyhoo, if you haven't tried them, take a look - they might be worth a shot.

GsT
 
I do have solid boring bars all the way from .090 to .490 both larger and smaller
and use a lot. The insert bar is only used when I need to bore a little deeper and it does a good job of doing it.

Chet


boring bars.jpg
 
Last edited:
Al,
There is a great Youtube channel, Stefan Gotteswinter, and he uses small, often home ground, CBN tools all the time. You may already be aware of his channel, but thought I would throw it out there not as a source of tooling but ideas on how to acquire the pieces/parts and the process needed to make them work.
Not sure if you have the grinding part of the equation in your shop, but could be helpful if you end up using them frequently.
Good luck with your search,
Mike
 
savet06 said:
Al,
There is a great Youtube channel, Stefan Gotteswinter, and he uses small, often home ground, CBN tools all the time. You may already be aware of his channel, but thought I would throw it out there not as a source of tooling but ideas on how to acquire the pieces/parts and the process needed to make them work.
Not sure if you have the grinding part of the equation in your shop, but could be helpful if you end up using them frequently.
Good luck with your search,
Mike
Click to expand...

I checked it out, thank you
 
Boring Hard 17-4

Hi Al,

When I was in the business of carving that hard 17-4 and 416, I used coated carbide and ran fast. I would drill as close to bore size as possible, then take cuts of equal amount with plenty of coolant. Light cuts, or slow cutting speed are death to some carbide inserts. The coolant may or may not make a big difference depending on the coating.
I do use CBN inserts, but for very hard stuff like taking a little off the bottom of a size die or other heat-treated tool steel parts. Over RC 50.
 
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I got a nice one quarter inch pilot hole drilled through the 416 no problem, and I can machine it with my carbide tooling. The 17-4 is an entirely different animal. I wrecked a couple of good drill bits and when I put a carbide end Mill up against it it just squealed, I don't have any long carbide bits and it looks like I'm kind of at an impasse with the 17-4. Both of them are marked at 38 hardness
 
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