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Shell Mill Insert Questions

Cannonmn

Stainless
Joined
Jun 25, 2016
A few photos. In 1 and 2, I haven’t run this yet, I’m getting it ready by replacing missing inserts. I don’t have any gold-colored inserts but I do have the same size/shape with a silver-colored finish. Is there any performance difference or can’t we tell because the box with info on it got lost?

In photo 3, there’s a different shell mill on which the inserts are canted at a much steeper angle to the face than on the mill in pic 1/2. I’m replacing or indexing the damaged inserts. What does the steeper angle say about the purpose of this mill as opposed to the other one?
 

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I'm pretty sure those are both negative rake face mills, but it's harder to tell on the second cutter due to the angle of the photo. It may be possible that they are negative in one direction and positive in another also. The angle formed by the leading top edge of the insert is what determines that. Look at the line formed when you draw a line from the outside edge of the insert to the centerline of the cutter. If the inside edge of the insert is above that line the cutter is negative. If the inside edge is below that line the cutter is positive. If the inside edge is on that line the cutter is neutral. The insert having side relief does not make a negative cutter into a positive one. An insert with a large chip breaker or high positive geometry on top can change the geometry in a negative cutter to positive geometry.

But that's not the case with those flat top/parallel inserts at least in the angle that I can see. It would appear that the photos are showing inserts that are generally used in a positive facemill with a relief angle (SPG) in a negative facemill, which means it still has negative geometry. See attached photo. Normally that cutter would probably be used with SNG inserts, which would be parallel top and bottom with square edges that have no relief. The relief is created by the cant of the insert. Using SPG inserts in that cutter will cause accelerated edge wear with tougher materials due to the increased clearance, but will be be okay for aluminum or brass, etc. If the pockets are positive in the other direction (viewed from the side) then you would still need to use the SPG inserts to make sure there's clearance in that direction. Would need to see a side photo to determine that.

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As far as the A/B insert comparison, you shouldn't use inserts from different boxes in a facemill unless you measure them and make sure they're the exact same size. You won't be able to tell whether they are similar inserts without at least a grade marking if you no longer have the boxes. The "cant" angle you're taking about is actually called the "lead" angle. That angle helps thin the chip for a given feed and gives a little less banging as the insert enters and exits the cut, also adds a little end clearance angle since it's creating more of a point contact with the corner of the insert, which can help cut down on chatter if you don't have great rigidity. Any way you look at it I would not even attempt using those in something like a Bridgeport (since the previous poster did mention it) unless it was a finish cut. As I recall though you've got a 50 taper mill, those would be fine in there.
 
Thanks, these tools are on nmtb40 arbors used on our only 40 taper machine, the Enshu Accumill, about 3 tons, 5 hp as I recall, it is a prehistoric 1982 CNC mill. We have an adapter and can run them on the heavier 50 taper mills if that works better, but we’ve got other facing heads so we don’t have to run them if there’s an issue, or it’d be easy to tag them “for aluminum only” if they’d work better that way. Dunno why the photo turned sideways, it was right side up when I added it.
 

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From that new angle it looks like they may be pos/neg. so you'd need to stick with the SPG inserts in that cutter at least. You should be fine in steel as long as you have the proper geometry inserts in the cutter (and the right grade of carbide, of course). Many of these older cutters will have an engraved part number that sometimes list the insert (SP or SN in the part number). 40 taper should handle those okay, but not for heavy cutting (1/4"+ DOC, .010"+ FPT) as well as 50 taper, for obvious reasons.

Whether you can get anywhere near that will depend on your setup rigidity too, and you reallly don't have the HP with only a 5HP drive motor. At lighter cuts you'll probably be fine.
 
Those are not 40 taper tools. If you are using them like facemills and taking .020" cuts or something then fair enough, but that's not what they are designed for and means you are just burning up the corners of big inserts for no reason. Your money will be much better spent on a more suitable modern tool. If you are taking deeper cuts with those in your 40 taper mill, stop.

I'd ditch that first cutter altogether. It's an ancient shoulder mill, and definitely not a 40 taper tool. It doesn't look like those are the correct inserts for it, and even if you get ones that fit properly it's going to be a really nasty hard cutting bastard of a thing knocking the crap out of your spindle geartrain. Better consigned to the skip.

The second one is an actual facemill. The inserts appear to fit correctly and the lead angle will make it cut much more freely. It's still a 50 taper tool, and designed to cut the full depth of the insert. Use it for slabbing down bigger blocks in your 50 taper machine, as it will still work fairly ok for that.
 
Those are not 40 taper tools. If you are using them like facemills and taking .020" cuts or something then fair enough, but that's not what they are designed for and means you are just burning up the corners of big inserts for no reason. Your money will be much better spent on a more suitable modern tool. If you are taking deeper cuts with those in your 40 taper mill, stop.

I'd ditch that first cutter altogether. It's an ancient shoulder mill, and definitely not a 40 taper tool. It doesn't look like those are the correct inserts for it, and even if you get ones that fit properly it's going to be a really nasty hard cutting bastard of a thing knocking the crap out of your spindle geartrain. Better consigned to the skip.

The second one is an actual facemill. The inserts appear to fit correctly and the lead angle will make it cut much more freely. It's still a 50 taper tool, and designed to cut the full depth of the insert. Use it for slabbing down bigger blocks in your 50 taper machine, as it will still work fairly ok for that.

I would mostly agree with this, with the caveat that I would change "Those are not 40 taper tools" to "Those are not efficient 40 taper tools." They will work for intermediate level cutting but will definitely not be as efficient as a good modern cutter with more free-cutting geometry. And yeah they will probably bang like holy hell in a small spindle with any real depth of cut.

These cutters were designed for use at a time when the machines using them had mega horsepower, heavy spindles with lots of mass, inertia and rigidity. I used to commonly use one that was ~10" diameter on a 6"+ diameter spindle milling machine (probably 40-50HP at least) many years ago when I couldn't get my hands on the 12" diameter 45° double positive facemill because someone else was using it (MUCH more pleasant to use and faster to boot). More modern machines are generally not cut out for these regardless of taper. While they will work on lesser machines, they are not going to be able to be pushed very hard.
 
Look like cutters made for cast iron, so only marginally good for steel and likely to have/leave a greater burr.
Still, they may prove Ok with loop watching the wear land ..and with perhaps .040 wear land pull and turn to a new corner... before they begin to break.
Flood coolant or run dry.

Cutting forces very high with whacking off chips.
 
Other one: Futuremill ZNP30M 0406 372 RH
 

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How 'bout it Bob? Neg/Pos?
Do I look like the Shell answer man?

Yes, both are Neg/Pos bodies.
The ZNPOM takes a SPC-63A6 or a SPG-63x. pick your radius a #3 recommend.
This is a true 90 wall cutter.
The ZNP30M takes a SCH-6309 which is a negative rake insert with positive rake flatted corners. Good luck finding any of those.
I think it will work with SPGs in the pockets although heel on the bottom may be a concern as the flat on the standard insert is at 15 degrees.
Bob
 
Actually I might have some of those. Last place I worked was gonna throw a bunch of old inserts out and said take 'em if you want 'em. I'll have a look-see. I remember seeing them.
 
Sounds good, take your time, no rush here, over the years I’ve accumulated about 20 mounted shell mills, all 50 taper but these two and a few R8’s. A couple are 12”, scary looking.
 
QT digger: [I'll bet you doo have a labcoat with your name on it.]

We used to run a pretty much neutral rake (no rake just flat) homemade carbide mill cutter in a bridge port whacking about .010 - .020 x 1/4" tool steel chips making TCT cutters.

It sounded like a machine gun whacking off red hot bullets.

What is he smell? Darn, my shirt is on fire again.
 








 
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