Insert recommendations for turning down Lowthar Walther barrels

Hello

I was wondering if anyone had any specific recommendations for an insert that will give the best possible finish on Lowthar Walthers proprietary chrome moly. I'm currently using a generic TPG style and the results are okay but not great. They work well under some load but fail miserably at fine cuts.

Since I am not a gunsmith, I will translate "Lowthar Walthers proprietary chrome moly" as 4140PH.

I would use an 80 degree insert with a 2 nose radius. WNMG or CNMG are good general purpose turning inserts. You want a steel cutting grade like a Sandvik 4225 or Seco TP2000.

However, you mentioned TPG, so I'm going to guess that none of that stuff I just said make sense, or is in your budget (not trying to be a prick).

TPG insets are the lowest common denominator of carbide. I would put them just above brazed carbide tools. They have no chip breaker, are terribly brittle, and no rigidity.

As with all inserts, you need to have a minimum depth of cut equal to the nose radius. That would usually be .030 on a side minimum. If you take "light cuts" like you imply, the result is usually diminished tool life or poor surface finish, or both.

The next thing to check is the surface footage. Carbide needs speed to get a good finish. Depending on your machine, that may not even be possible at small diameters like a gun barrel. Even in 4140 material, you should be up around 400 SFM.

If you really need to take "light cuts", use either a very sharp honed insert like you would use for aluminum, or a very sharply ground HSS tool.

I always turn barrels with hand ground high speed and lots of water. After turning I make about four cross cuts on the barrel spinner with a 100 weight belt on the belt sander and four cross cuts and two 90 degree cuts with a 320 belt and they are polished. Total polishing time is about 3 or 4 minutes. The belt sander and barrel spinner will knock .015 to .020 inch off the OD of the barrel so fast it will make your head spin and one way or the other the barrel has to get polished anyway so the lathe finish has never been one of my bigger concerns. My only real concern is having no chatter when turning.

ewlsey said:

Since I am not a gunsmith, I will translate "Lowthar Walthers proprietary chrome moly" as 4140PH.

I would use an 80 degree insert with a 2 nose radius. WNMG or CNMG are good general purpose turning inserts. You want a steel cutting grade like a Sandvik 4225 or Seco TP2000.

However, you mentioned TPG, so I'm going to guess that none of that stuff I just said make sense, or is in your budget (not trying to be a prick).

TPG insets are the lowest common denominator of carbide. I would put them just above brazed carbide tools. They have no chip breaker, are terribly brittle, and no rigidity.

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Not trying to be a prick but there is one reason why I never ask questions on this site and this is it. I asked a question here some years ago and the resulting answers made me decide it was more effective to translate my questions into german and then translate the answers into english....something to think about fellas

I live in the great white north so cost of tooling is not a factor as I guarantee shipping will always be more. Because the closest tool store is at least a 1000 miles away you buy what you can get and TPG happens to be it. I'm sure there is a reason why it's commonly available even in the middle of nowhere. Could it be possible that it is because it actually does a decent job at a wide variety of small tasks.

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These TPG321 inserts are $16 each. Hardly the cheapest thing out there. In fact I can buy 4 WNMG inserts for the same cost. And yes I do know what that is as I am a gunsmith and machining is a part of the trade....16 months of nothing but machining time in fact. And my untrained eye may be deluding me but I'm sure I see chip breakers.

Further, a .030 cut? C'mon, I'm a gunsmith not a train axle maker. Some of my parts are smaller than the cut your suggesting. I'm sure that the reason there is a "gunsmith" section here is because gunsmithing requires a very specialized form of machining. Mostly manual, without the use of CAD/CAM and heaven forbid probably no CNC either. And chances are none of us need a backhoe to haul the chip.

So if there is any gunsmiths out there that can say "hey man, I've used insert XXX and it works pretty good" I would love to here from you.

Speerchucker
Thanks for the reply. Yes I'm using similar techniques and they work pretty well. They only difference being is I use soluble instead of water and I find it gives a slightly better finish and lubes the follow to boot. And I use a dynafile rather than a belt...but same difference right.
I guess I will go back to HSS. I had some really good results using the method by Leo St Clair....but admittedly popping in an insert appeals to the lazy side.

RifledAir said:

Not trying to be a prick but

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Well maybe you were not trying to be but you succeeded in spades...

You asked a question and you got a good logical response but it wasnt the one you wanted so you have your feelings hurt? The photo of the insert you have shown is not a TPG insert so make sure you know what insert you have. You will not get a good finish with the TPG insert unless you take a heavier cut just as ewlsey mentioned, on steels if you take too light of a cut you just get a gravel road like surface as the tool just tears bits out rather than shearing the metal.

On a skinny barrel if you want to take lighter cuts then the HSS is a great option or as mentioned you can try the sharp aluminum type inserts. I usually go with CCMT style myself but you do need to spin the part pretty fast to get a nice finish and long skinny barrels dont like to spin fast without whipping a bit.

Dont go fussing with people who take the time to write you a detailed and appropriate response just because you didnt get the answer you wanted. We dont take our time to sit down and type this stuff out because we dont want you to succeed.

Charles

Sorry, but this is a machinist forum with a gun sub-section, not the other way around. A lathe is a lathe, no matter what you are turning. My advice is sound, and will get you the desired results. Manual or CNC, CAM or no, large or small parts, the fundamentals are the same. If you don't know how to calculate SFM or minimum depth of cut, you will never get to where you want to be without dumb luck.

You had better recalibrate your untrained eye if you think that picture shows a TPG insert. Here is a hint, T stands for "triangular". TPG is not a good insert style, it is popular because it is dirt cheap and a lot of shops don't know any better, or run ancient tools that were designed at the dawn of carbide when the TPG shape was all you could get.


"Further, a .030 cut? C'mon, I'm a gunsmith not a train axle maker. Some of my parts are smaller than the cut your suggesting. I'm sure that the reason there is a "gunsmith" section here is because gunsmithing requires a very specialized form of machining. Mostly manual, without the use of CAD/CAM and heaven forbid probably no CNC either. And chances are none of us need a backhoe to haul the chip."

If you can't take a .030 cut, get a different tool. There are 1 nose radius inserts, then the cut could be as low as .015. Carbide is made to increase the metal removal rate by allowing higher speeds. If you don't need or want that, then it is wrong choice for you.

When I say water I mean water soluble oil (Kut-Sol, cutwell etc) I tried that green leprechaun pee that Kennemetal used to sell but outside of it cleaning the machine I didn't like it.

I have used carbide and still do in some cases but on long barrels I find I can't balance the tool pressure and I get to much chatter. With the carbide inserts I turn the barrels at around 300 to 400 RPM but I have to take pretty heavy cuts to keep it from chattering, up to .040 inch. You might try starting with carbide and then switching back to high speed when your muzzle gets to .650 inch. I often use re-ground inserts and put a bunch more rake in them and drive them at almost 90 degrees to the barrel with some success or use hand ground cemented carbide. You need a fair amount of rake and pretty high feeds.

I know a guy that polishes with an air file but he gets ripples because of the narrow belt and has to finish by hand. Plus it takes him 3/4 of an hour to an hour and a half to polish a barrel. It works but it would drive me nuts. LOL

ADD NOTE: The problem with turning barrels seams to be the damned hole in the middle which reduces the stiffness and mass of the work piece. Eliminating the hole would eliminate most of the trouble. But to date I have had trouble selling that to my whiny customers. I think the real answer is to make an air follow rest. Princess Auto has some small air cylinders for about $50 a piece and one should be able to just take an old steady rest and replace the fingers with the cylinders and bolt it to the carrige ahead of the tool post 1/2 inch. Maybe when things slow down in the spring I will make one just for shits and giggles. Other people use them with good success but I just don't turn a lot of barrels anymore so its hard to get motivated.

http://www.princessauto.com/pal/pro...ke-Aluminum-Pneumatic-Double-Acting-Cylinders

speerchucker30x3 said:

I have used carbide and still do in some cases but on long barrels I find I can't balance the tool pressure and I get to much chatter. With the carbide inserts I turn the barrels at around 300 to 400 RPM but I have to take pretty heavy cuts to keep it from chattering, up to .040 inch. You might try starting with carbide and then switching back to high speed when your muzzle gets to .650 inch. I often use re-ground inserts and put a bunch more rake in them and drive them at almost 90 degrees to the barrel with some success or use hand ground cemented carbide. You need a fair amount of rake and pretty high feeds.

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This is likely part of the problem. A good coated carbide insert will run best around 400-500 SFM. 400 RPM is about 1/3 as fast as the insert wants to be run (assuming a 1" diameter).

Carbide can run below it's intended speed, but the result is usually premature tool failure.

Speerchucker
Yes it would be a lot easier if we could convince them it would be better without the hole
The latest fads around here are slow rust bluing and custom made big bore airguns. Folks are spending $4k+ on these air cannons....who knew. But that compounds the problem as the barrels are even lighter than normal. 16mm in the blank

I see in the everede catalog an insert made from MC32 carbide ISO class K30 with a max DOC of .007" and a rate of 150. Its recommended for O2(which I use a lot for reamers) and CrMoly alloys. Does anyone have an idea if that might work?

Murf thanks for the link. HSS inserts may be a perfect fit

Insert in the picture is a CNMG-432 the most common insert on the planet.

With your current holder you might want to try a CNMP. The "P" means that the form molded in the top is dished more (more positive cutting action). I also means it is easier to chip as the cross section doing the cutting is thinner.
Better yet would be a CNGP. The "G" means a ground OD on the insert. The ground sides rub less as the cut material slides past the insert which helps reduce friction and chatter.

I have no idea where the myth started that you need to cut the depth of the radius.
If this is so, how deep do you need to be to use a 3/4 inch round?
Larger radius/ small depths load the tool in/out pushing on your part making it harder to hold size, mostly this is a problem when using the wrong edge prep or using a molded insert when you should be using a ground one.
Smaller radius tools load the part lengthwise. Now you can push like heck and the part won't flex.
Bad thing is they "thread" the the part leaving a rough finish.

Outside of some very special milling operations I don't know of any part on a automobile where the finish cut is anywhere close to the nose radius. In turning ops where you need a smooth finsh at high feeds we will often use a .094 rad .003/.005 deep.

Take a look at the edge of your tool under a microscope. Many generic steel cutting inserts will have the edge intentionally rounded .002. This is called a hone in the insert world. We do this by thowing the insert in a vibratory deburring machine for 6 hours or hit it with an abrasive filiment brush.
Almost all "M" insert will be honed. We do this to also help smooth the "flashing" on the tools edge which comes from the molding process.
Ground finishing inserts and most aluminum cutting insert will have a razor sharp edge.
This type tool works much better on long skinny parts.

My poor little SB 13 1/2 will only spin 1100 RPM tops and we make .160 to .060 pins from 4140 on it on a regular basis (plugs to repair torn out screw holes in toolholders).
While I have 50 or so of them I have not used a HSS bit in it in over 15 years.
If you run carbide at low speeds you need a sharp tool and lots of positive top rake.

Big advantage to HSS is it is easy to grind your own.
Grinding a high rake carbide tool by hand and keeping the chips under .0001 takes very fine grit special order wheels and a whole bunch of practice. This is best done on very specialized grinders that few here would have access to.

By far the biggest mistake I see people make in using carbide is the edge prep and there are a ton of variations here. On production machines we will spend over a hundred hours of testing optimizing this.
If you do not look at the cutting edge under a 30X stereo-scope you won't know what you are using.
It's very hard to take .0005 with a tool that has a .002/.003 rounded edge.

People will chip a honed tool because of the tool pressure and get afraid of going to a higher rake. Very high positive tops and up-sharp cutting edges are your friend at low speeds. I'D be into CPGT and TPGT inserts here in a holder with 5-7 degrees top rake built in. This is not your common e-bay holder.

Yes I know, this whole deal is confusing to say the least which is why most like to stick with HSS where they can find a custom grind that they can do in their own shop that works.
You are making barrels, the last thing you want to do is spend 4-8 years becoming an expert in carbide tooling.
Me, I make carbide, but to be point blank honest, you don't use enough carbide to get somebody like me to come help you out.
This sucks and makes me feel really bad, I wish I could offer more to the small shops, but I have to make a living wage somehow.

Most likely this long post leaves you more confused with no answers, I wish I was standing in front of your machine.
Bob

As mentioned, I find the triangular tools are very prone to chipping and premature wear at the speeds required to turn barrels. Some types of carbide can't be used with water either as they shock and chip. I use the tool stye on the left at 90 degree to the barrel but have had the most success with the style on the right. I generally will finish with high speed steel. I switch to high speed when the muzzle gets to .650 inch. The one on the left requires pretty heavy cuts and high feeds. The one on the right will not make as heavy a cut but makes a better finish.




As to BB guns. I had a Theoben 25 cal for about 3 months but I had to fill the reservoir with a scuba tank. It shot well enough and thwackettaed the snot out of gophers at 60 yards but it was expensive to shoot, and in general, a nuisance so I sold it to one of my crazy friends. I preferred the recoilless 22 caliber Feinwerkau that I used to own as long as ranges didn't exceed 50 yards. The 177 BB guns are about as useless as spitting at any distance. 223 is much cheaper and effective in the long haul and if your really cheap a 22RF.

Take a look at the edge of your tool under a microscope. Many generic steel cutting inserts will have the edge intentionally rounded .002. This is called a hone in the insert world. We do this by thowing the insert in a vibratory deburring machine for 6 hours or hit it with an abrasive filiment brush.
Almost all "M" insert will be honed. We do this to also help smooth the "flashing" on the tools edge which comes from the molding process.
Ground finishing inserts and most aluminum cutting insert will have a razor sharp edge.
This type tool works much better on long skinny parts.

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Brilliant! Yes mine has this. I can see it plain as day under my 20x loupe. That makes perfect sense with regards to the cut, skip, cut action.

Ground finishing inserts and most aluminum cutting insert will have a razor sharp edge.
This type tool works much better on long skinny parts.

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Awesome!

If you run carbide at low speeds you need a sharp tool and lots of positive top rake.

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Got it

I'D be into CPGT and TPGT inserts here in a holder with 5-7 degrees top rake built in.

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I will find it. Hopefully in a small holder.

You are making barrels, the last thing you want to do is spend 4-8 years becoming an expert in carbide tooling.
Me, I make carbide, but to be point blank honest, you don't use enough carbide to get somebody like me to come help you out.

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Absolutely correct. I make barrels and rely on people to give me solid understandable advice on everything else. Thank you so much. PS..There is no way any company would send anyone where I live...unless you were a rep for dog sled runners

but it was expensive to shoot, and in general, a nuisance so I sold it to one of my crazy friends.

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Very true but they say there is nothing stranger than people.

Currently I'm working on a new 223 cal coming out of the Netherlands. Performance is between 22RF and 22Mag. They are competing at distances of 300m...on air

I'm going to track down the suggested positive rake toolholder and some ground inserts and I will report back on it.

RifledAir said:

Very true but they say there is nothing stranger than people.

Currently I'm working on a new 223 cal coming out of the Netherlands. Performance is between 22RF and 22Mag. They are competing at distances of 300m...on air

I'm going to track down the suggested positive rake toolholder and some ground inserts and I will report back on it.

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I knew that smokeless powder was just a passing fancy. Being of Danish decent, I always wondered why my grand parents had little good to say pertaining to the Dutch. If Dutch technology keeps increasing at this rate they will be up to rocks and poky sticks in less than a decade.

⎝ᄽ‿ ᄿ⎠ he he he

CarbideBob said:

I have no idea where the myth started that you need to cut the depth of the radius.
If this is so, how deep do you need to be to use a 3/4 inch round?
Larger radius/ small depths load the tool in/out pushing on your part making it harder to hold size, mostly this is a problem when using the wrong edge prep or using a molded insert when you should be using a ground one.

Outside of some very special milling operations I don't know of any part on a automobile where the finish cut is anywhere close to the nose radius. In turning ops where you need a smooth finsh at high feeds we will often use a .094 rad .003/.005 deep.

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Plenty of automotive work going on this area. We run .031 minimum depth of cut on all finish passes. Turning with CNMP 432 inserts, milling with APKT style inserts.

The only time we run less DOC on the finish is if we run PCD inserts. They don't seem to care as much. This is all cast aluminum or iron.

Listen to Murf. Arthur Warner HSS inserted tooling is great. LW CM cuts great with HSS. Their LW50 SS is very similar to 14-4 and is a challenge. You need a lot of speed and feed. Never has any trouble with their CM.

Butch Lambert said:

Listen to Murf. Arthur Warner HSS inserted tooling is great. LW CM cuts great with HSS. Their LW50 SS is very similar to 14-4 and is a challenge. You need a lot of speed and feed. Never has any trouble with their CM.

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I fitted and chambered Blackstar barrel,then later turned it to a lighter profile, they used Lothar Walther blanks I think ? I just used a steady and did it in sections with a sharp HSS tool and LOTS of feed. It was for me, myself, and I so I had no need to hurry, but that is indeed a tough alloy to machine.

Butch Lambert said:

Listen to Murf. Arthur Warner HSS inserted tooling is great. LW CM cuts great with HSS. Their LW50 SS is very similar to 14-4 and is a challenge. You need a lot of speed and feed. Never has any trouble with their CM.

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If you ever talk to them Butch ask them if they have ever designed any HSS tooling specifically for turning barrels. I always end up grinding my own for the lack of finding anything that works well. If I did more I would get some split line bearings and make an attachment for my belt sander to do it. I have a sneaking suspicion that a lot of the barrel makers grind their barrels. At least they finish grind the last bit anyway. Barrel makers are mighty quiet about what they do. Partly because they think they have something special and partly because they don't want to scare people. LOL

I have a sneaking suspicion that a lot of the barrel makers grind their barrels.

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Yup I can say for sure that the match barrels our olympians are using over in London are ground.

I sent an email to Arthur R Warner to ask a couple questions about their bits and recommendations for barrels. And to see if I could convince them to ship the bits in a padded enevelope rather than the usual big empty box stuffed with peanuts