GREAT Gunsmith Lather FS

[NezRongero]

Part 1 has what you need to know about grinding cutting bits. If you are using a quick change toolholder you'll grind the angles differently than using Armstrong toolholders. The effective angles will be the same. I'm sure you can figure it out
http://www.campkahler.com/files/How_to_Run_a_Lathe_SB_1of2.pdf
http://www.campkahler.com/files/How_to_Run_a_Lathe_SB_2of2.pdf

Thank you for the information.

 

[TRA]

Justin,

Thank you.


I will have to figure out better set; DOC, speed and feed. Inserts are the only cutters I have, I have a grinder, but have no clue how to grind cutting bits.


nez

Simply put, metal removal and surface finish requires force, as it's really rubbing off the chip, not cutting it. If not enough force is applied, ie, via speed, feed and depth, you end up scratching off the metal which leaves a rough surface and gouges in the part. It's not unusual to use a .020-.050 finish pass on high quality steel to get a fine finish and hold tolerance.If you find yourself needing to remove another .002, you missed the finish depth. That's the point where the files and sand paper come out of the drawer. A .002 cut is doable but you will need extreme rpm to get away with it. You try to avoid ending up .002 short at all costs.

Of course that's hardly practical machining barrels, but the cutting tool does not know the difference.

Tool grinding is a skill all it's own. There is a work around though and that is HS inserts that are available that allow one to have precision quality cutting tools without the 20 year learning curve. Tools that are better suited to the operations a gunsmith employes. BTW, most inserts designed specifically for stainless are actually HS and not Carbide. FWIW most exotic metals are not machinable with carbide.

 

[NezRongero]

Simply put, metal removal and surface finish requires force, as it's really rubbing off the chip, not cutting it. If not enough force is applied, ie, via speed, feed and depth, you end up scratching off the metal which leaves a rough surface and gouges in the part. It's not unusual to use a .020-.050 finish pass on high quality steel to get a fine finish and hold tolerance.If you find yourself needing to remove another .002, you missed the finish depth. That's the point where the files and sand paper come out of the drawer. A .002 cut is doable but you will need extreme rpm to get away with it. You try to avoid ending up .002 short at all costs.

Of course that's hardly practical machining barrels, but the cutting tool does not know the difference.

Tool grinding is a skill all it's own. There is a work around though and that is HS inserts that are available that allow one to have precision quality cutting tools without the 20 year learning curve. Tools that are better suited to the operations a gunsmith employes. BTW, most inserts designed specifically for stainless are actually HS and not Carbide. FWIW most exotic metals are not machinable with carbide.

TRA,

Appreciate the input. When I got the machines a friend from Memphis, who is a machinist by trade, insisted that I learn how to grind cutters. In my anxiousness to learn how to run the machines I went with indexable cutters. I bought mostly from Arthur Warner, and later bought all kinds of stuff from eBay trying out different ones. I even bought a couple of tangential tools. It was not the cheapest route, but it got me up the learning curve on how to run the machines.

Someday I just have to stand in front of that grinder and force myself to learn how to grind 'em bits.

It has been a journey.

 

[TRA]

TRA,

Appreciate the input. When I got the machines a friend from Memphis, who is a machinist by trade, insisted that I learn how to grind cutters. In my anxiousness to learn how to run the machines I went with indexable cutters. I bought mostly from Arthur Warner, and later bought all kinds of stuff from eBay trying out different ones. I even bought a couple of tangential tools. It was not the cheapest route, but it got me up the learning curve on how to run the machines.

Someday I just have to stand in front of that grinder and force myself to learn how to grind 'em bits.

It has been a journey.

I'm lazy, I buy my tooling. I even insist that my workers do not sharpen smaller drills like >1/2". Life's short and labor rates have driven tool sharpening costs into orbit. Tool sharpening on the shop floor is a dead horse. I do have special tooling made when necessary but even that is avoided is possible. We machine a cerrain part about every six months that a pallet covered with them is about 90,000.00. 4-6 pcs. We remove .0007 and have to keep them flat and parallel. The last thing we want to happen is to find a cutter was not ground properly. We cannot go OOOOOPS and keep cutting them till they are all the same. Like leveling a table.

Don't ever forget that grinding grit and your eyeballs are not compatible. Don't ask me how I know.

 

[JerrySharrett]

Nez,

I got the same looking finish on a part the other day. I too was using an insert tool and was taking light passes of a couple thou' or so. When I took deeper cuts, the surface finish improved. I think it had to do with burying the radius of the insert into the work. I rarely use an insert tool, though, so maybe somebody with more experience can opine on that.

Justin

Cutting tools, mill or lathe, with zero or negative rake cutting edges (or radiused or k-land) will not leave a good finish taking skim cuts. Just like hi-positive rake edges are not suitable for heavy cuts.

Facts of life!

.

 

[alinwa]

A .002 cut is doable but you will need extreme rpm to get away with it. You try to avoid ending up .002 short at all costs.

Of course that's hardly practical machining barrels, but the cutting tool does not know the difference.
.

Did I miss something? You're talking strictly carbide here??? I don't "avoid .002 cuts at all cost" with anything but carbide....... You must be saying that removing a couple thou WITH CARBIDE is a problem?

IMO carbide melts off the metal often leaving a toughened skin on the surface while HSS does actually shear it like a knife or a plow.

I sneak in with cuts down to 1/2 or 1/5 that using HSS cutters quite often. And I often work with parts that preclude use of the sort of tool pressure required to get the carbide cutters into "melt mode" for a shiney finish....but can easily achieve "600 grit finish" with HSS (I have no equipment for measuring surface finish, I just wipe sandpaper across to see does it remove tooling marks)

I agree with Jerry Sharrett's post (sorry Jerry) and even grind high rake tools to "push" or "pull" the part from the tool...

 

[JerrySharrett]

Did I miss something? You're talking strictly carbide here??? I don't "avoid .002 cuts at all cost" with anything but carbide....... You must be saying that removing a couple thou WITH CARBIDE is a problem?

IMO carbide melts off the metal often leaving a toughened skin on the surface while HSS does actually shear it like a knife or a plow.

I sneak in with cuts down to 1/2 or 1/5 that using HSS cutters quite often. And

I agree with Jerry Sharrett's post (sorry Jerry) and even grind high rake tools to "push" or "pull" the part from the tool...

There are several alloys (grades) of "carbide" metal cutting tools. The coarse catagorical families are catalogued as C1 through C7. Within those groups of material offered Carbide inserts are made up of several compounds. Titanium carbide, tungsten carbide, taladium carbide, etc. when you get into the upper grades, C5 thru C7, much can be done to finesse these tools microstructure. Sandvik is probably the leader in making cutting inserts that will literally "shave" micronic amounts of material off (also dependent on the machinability of the material).

In the early '50's GE/Carboloy was the first to offer a "Carbide" (cemented) to a tool steel shank. That first offering was about like their grade 870. The industry has come a long way since. Space age alloys provided much of that demand.



.

 

[alinwa]

There are several alloys (grades) of "carbide" metal cutting tools. The coarse catagorical families are catalogued as C1 through C7. Within those groups of material offered Carbide inserts are made up of several compounds. Titanium carbide, tungsten carbide, taladium carbide, etc. when you get into the upper grades, C5 thru C7, much can be done to finesse these tools microstructure. Sandvik is probably the leader in making cutting inserts that will literally "shave" micronic amounts of material off (also dependent on the machinability of the material).

In the early '50's GE/Carboloy was the first to offer a "Carbide" (cemented) to a tool steel shank. That first offering was about like their grade 870. The industry has come a long way since. Space age alloys provided much of that demand.



.

Thank You

The only sharp carbide tooling I have is called out for AL which I feel it does actually shear. It cuts cool.

 

[Mike Bryant]

This thread was cut with a Carmex partial profile tin coated threading tool. Speed was 250 rpm.

 

[Butch Lambert]

Beautiful Mike.

 

[TRA]

Thank You

The only sharp carbide tooling I have is called out for AL which I feel it does actually shear. It cuts cool.

You will probably find those AL inserts are also for stainless and are H13 or similar and not carbide. BTW, Carbide threading tooling and milling inserts are just as sharp as AL inserts, may be sharper.

The depth of cut with today's tooling technology is more about the size of the insert than whether it's positive or negative. Negative tooling takes tons of iron, tool pressure and lots of horsepower to make deep cuts. Negative tooling is also cheap, durable and has usually twice the cutting edges, thus it's popularity. Negative-roughing, positive-finishing. Having said that I've got a ~200.oo insert in my hand and it's only got 2 cutting edges, negative rake and will not tolerate deep cuts.

I hope for those reading all these bits of wit, that everything being said is not universal and is subject to application. Machining 12" dia 4000 series heat treated steel and plain cold rolled is not in the same universe. Neither is 416 comparable to real stainless in everyday use. Whether you are doing one part at a time or 1000, it's all relative to your application.