I have to cut down a half dozen hardened gears on the lathe, these are about 10" diam., and I'm taking off a 0.5" off the OD. I'm guessing they are probably about 40-45 rockwell and are likely 8120 steel. I wind up going through a couple of inserts per gear. Would CBN inserts do the trick, or will they limit me to only taking off 5 thou per pass? The part of the gear being cut is not an interupted cut, ie. gear teeth.
oldjag wrote in news:1177825704.686706.191070 @n76g2000hsh.googlegroups.com:
You should be able to take a lot more that 5 thou per pass with CBN, as long as it's not interrupted. How much horsepower do you have?
Can you grind them? Or heat them while turning to anneal the OD?
Gunner
"I don't want to abolish government. I simply want to reduce it to the size where I can drag it into the bathroom and drown it in the bathtub.
-- Grover Norquist
No, they cannot be annealed and at least with my grinding equipment, it would take way to long to grind. I can cut them on the lathe in about 1/2 hour, but it kills regular carbide inserts.
If there's too much problem with your present procedure try to do it another way by using waterjet cutting.
I would suggest you use a different grade of carbide. CBN would work but it's expensive. How rigid is your lathe? If it is not rigid you are out of luck doing that intermittant cut with carbide or cbn tooling. One trick is to set the lathe for the diameter you want to cut and tighten up the gibbs as much as you can and make the cut or lock the cross slide and compound in some other manner. Be sure to loosen them after the cut. The other way to do it is with a tool post grinder.
John
I agree with John that you should try another grade of carbide. If you want to try this on the cheap and don't mind making a holder, email me your mailing address and I'll send you a couple inserts that I've found to work well turning hardened steel. Rather than a radiused edge, they have small (a couple thou) chamfer. The inserts are square or rectangular and have a countersunk hole. A holder for light use could be as simple as piece of cold rolled with a tapped hole and a step to prevent the insert turning.
I believe the inserts were intended for a large Waukesha/Walter face mill and are probably a proprietary grade similar to C-6. I've got over a thousand, so I'm not likely to miss a few in my lifetime.
Ned Simmons
It's not an intermittant cut, it's continuous. The lathe is a 10 Hp
19" x 54" Leblond HD toolmaker and while made in 1965, seems pretty sturdy and tight. I have a tool post grinder, but I think this is way two much metal to remove with the TP grinder. If CBN inserts will do the job, I'll try one out if I can get them in small quantity, and they don't require a expensive dedicated tool holder.
Thanks for the offer on the inserts, but I think it would be easier for me to order an chamfered insert to fit one of my existing toolholders. I see where the chamfer would help make the edge stronger.
How big are these gears? They should only be case or induction hardened. If you take a turn and a face cut to get under the hardened surface, the rest should be fairly soft. With that Leblond you should be able to get under the hard surface with one cut.
If its not a continuous cut, a ceramic insert should do the job. They are a lot cheaper than cbn and come in several sizes and shapes. That lathe should have no problem cutting the gear. Watch the grade of cbn if you go that way. I am most familiar with BN300 since we cut hard castings but for your application it would require a different grade. A tipped insert would work fine but dont it get hot or the braze will melt and the tip will fall off.
I would suggest that you might call Kennametal support for some advice on inserts too,
John
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