Hard shaping with CBN inserts?

Hi,

I want to learn hardening tool steels, so I wanted to make some projects that would involve hardening and tempering tool steel. The problem is that I don't have a surface grinder and I don't want to waste tool steel just for the sake of hardening it. That made me think - I have a metal shaper, which I think can make a pretty flat surface. I know it won't come very close to a ground surface, but there are certain projects that don't require accuracy close to a micron, like parallels for roughing, tool holders for qctp or a non-precision v-block.

So I was thinking - if hard turning is a thing, maybe hard shaping could also make sense (for a hoobist that is). I was thinking about making an insert holder for a shaper and buying a CBN insert (and yeah, I know they're expensive, but I was also planning to try hard turning, so it seems like an interesting thing to try). Has anyone here heard about it or tried it themselves?

Depends on how TOUGH the cbn is. Shaper by nature delivers a HAMMER BLOW to cutting edge every stroke on entering the cut

HARDENED work piece of course makes this worse

If you do try it I hope you will keep us updated. I would be interested to hear about your results. I know there are some pretty tough grades of cbn now, but I haven't tried any hard turning or milling yet.

My name is Brian and I'm a toolaholic.

Given the inherently intermittent nature of the cut I would think you would be better off with one of the tougher carbide grades? No need to graduate to CBN just because you're machining hardened steel, carbide will do the job and is a lot cheaper to try!

Carbide requires a minimum surface footage to function correctly. I am no expert with CBN, but does CBN also require that, and will your shaper give you that surface footage? What kind of surface footage would you be cutting at with your shaper?

Gobo said:

Carbide requires a minimum surface footage to function correctly. I am no expert with CBN, but does CBN also require that, and will your shaper give you that surface footage? What kind of surface footage would you be cutting at with your shaper?

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It has been my experience that the minimum SFM is not very important. At least with dowel pins, Kurt vise jaws, and case hardened shafts.

drogus said:

Hi,

I want to learn hardening tool steels, so I wanted to make some projects that would involve hardening and tempering tool steel. The problem is that I don't have a surface grinder and I don't want to waste tool steel just for the sake of hardening it. That made me think - I have a metal shaper, which I think can make a pretty flat surface. I know it won't come very close to a ground surface, but there are certain projects that don't require accuracy close to a micron, like parallels for roughing, tool holders for qctp or a non-precision v-block.

So I was thinking - if hard turning is a thing, maybe hard shaping could also make sense (for a hoobist that is). I was thinking about making an insert holder for a shaper and buying a CBN insert (and yeah, I know they're expensive, but I was also planning to try hard turning, so it seems like an interesting thing to try). Has anyone here heard about it or tried it themselves?

Click to expand...

.
my experience with hardened steels is only take .001 or .002" depth of cut. if you take more with carbide it just breaks the corners off the tool

johnoder said:

Depends on how TOUGH the cbn is. Shaper by nature delivers a HAMMER BLOW to cutting edge every stroke on entering the cut

HARDENED work piece of course makes this worse

Click to expand...

That would be my worry as well, but I was hoping that light finishing cuts could make it work.

aarongough said:

Given the inherently intermittent nature of the cut I would think you would be better off with one of the tougher carbide grades? No need to graduate to CBN just because you're machining hardened steel, carbide will do the job and is a lot cheaper to try!

Click to expand...

I'm rather new to machining, but I thought that carbide is not very good for interrupted cuts, because of it's brittleness. That said, I might try to buy some quality inserts and see how it goes (at the moment I own only Chinese inserts, which work OK for my needs, but I doubt they would withstand any bigger forces, they're rather easy to chip if I'm not careful).

DMF_TomB said:

.
my experience with hardened steels is only take .001 or .002" depth of cut. if you take more with carbide it just breaks the corners off the tool

Click to expand...

Thanks! I was also thinking about locking all the things that can be locked before taking the cuts (ie. lock vertical table movement and lock the gib on the head) to make it as rigid as it can be.

Another thing to consider is that planers and shapers are designed to use gravity and top rake to pull the cutter into the piece. That is, the leadscrew of the tool-slide is rather holding the tool-holder from falling into the piece, than pushing it into the cut.
By tightening the gib, using negative top rake, etc., you could probably force it into the cut. But I don't think the results will be very flat and pretty.

Paolo

I've done some hard turning with interrupted cuts. We make a part with an internal taper with a keyway and have violated just about every rule of using CBN and succeeded. The small dia is 3/4' so we use a small boring bar with a TPG insert, the SFM is too low and the DOC is only .001/.003 which is less than the edge break on the CBN insert. We have found Sumitomo BN200 to be pretty forgiving, a harder grade might not be. The hardness of the part is only 52-54, which probably helps, but that's against the rules too. We've used the same insert for years on small batches of parts, maybe 50 at a time. We do have to be careful to get a straight taper in the ID,so tool deflection doesn't make it wavy. We started in a manual lathe with the compound rest, now it's easier done in a turning center. Turning the uninterrupted OD is cake. I think you'll do fine with a shaper.

Ceramic inserts are an intermediate step between carbide and CBN, perhaps that's an option. Unfortunately I have no experience with ceramic, I jumped directly to CBN.

If the shaper has a powered lift on the clapper box, it might work. If it drags the tool over the work on the back stroke, it might not work:- Two days ago I was facing a hard part with a CBN insert in the lathe. Went a little bit past centre, so the work was 'lifting' the tool. No more CBN insert . It just peeled half the CBN off the carbide it was bonded to.

The cure for not having a powered lift is to have enough travel to clamp a piece of leather to the back of the tool. On the back stroke the leather keeps the tool from dragging on the work.

My name is Brian and I'm a toolaholic.