Shear grinding Lathe tools

J E Custom · Aug 16, 2018

Trickymissfit said:
You might consider scrubbing the cut area with a brown Scotchbrite pad and then a new green Scotchbrite pad. After that you might try something like a well worn green pad. I've seen them polish with glossy news print and a mixture of light spindle oil and Comet scrubbing powder for a single digit micro.
gary

I have done this a few times but didn't like the polished finish on barrels (It looks to much like chrome for me).

I just like a good machined finish as long as it is very smooth and true.

I know/think that most all barrel makers use the sanding method like shortgrass described, but that leaves to much room for error by the operator and the original reason for machining the final finish. I have set barrels up that looked great at first while checking for run out and found flat spots and concentricity issues that the eye could not detect.

These imperfections may not cause issues, but true, concentric and straight can only help. I realize that I am anal about some of this stuff, but i am retired and have the time and patience to try and improve where I can. (Never to old to learn).

Always looking for a better mouse trap.

J E CUSTOM

Gord0 · Aug 17, 2018

J E Custom said:
I do a lot of barrel contouring and have never been able to get the finish cut using Carbide that I have with high speed tools. They wont take as big of a cut as Carbide but the finished cut is much better.

I have tried the shear tools and they also do a nice job, but they wont take more than .005 to .007 thousandths cut. When I make the final cut on a barrel with high speed tools I normally take less than .010 thousandths (Carbide doesn't like light cuts).

I'm not sure that a shear grind tool is the answer to a better finish, but i will keep experimenting with then until i feel they are better or not the answer.

Thanks Gary and Timnterra for your comments.
Keep them coming !

J E CUSTOM

Not a gunsmith, just a machinist that has been turning handles for a little over 20yrs. I program cnc, but still use manual equipment every week. I can tell you that a lot of the info you hear about carbide, and a lot of things said in this thread are only partially true. Cheap carbide, the wrong grade, wrong profile. All those things can cause carbide to need to smear material off instead of actually cutting it. Get the right tooling and itlit do wonders. Widia has application engineers that will work with you, sandvik does too. Those are probably two of the better lathe tooling suppliers. Call or email them and they'll help you out.

I can tell you from watching that video on shear cutting that it will put an enormous amount of stress into the very top layer of steel on the barrel. I cut very thin walled parts out of aluminum every day. As in down to .02" wall thickness. Some 8"x10" .08" floor thickness parts that have flatness call outs of .002". You need to have sharp tooling (which you can get with carbide) and your surface speed needs to be correct. Too fast and material smears, too slow and it tears. Both leaving residual stress in the surface.

J E Custom · Aug 17, 2018

Gord0 said:
Not a gunsmith, just a machinist that has been turning handles for a little over 20yrs. I program cnc, but still use manual equipment every week. I can tell you that a lot of the info you hear about carbide, and a lot of things said in this thread are only partially true. Cheap carbide, the wrong grade, wrong profile. All those things can cause carbide to need to smear material off instead of actually cutting it. Get the right tooling and itlit do wonders. Widia has application engineers that will work with you, sandvik does too. Those are probably two of the better lathe tooling suppliers. Call or email them and they'll help you out.

I can tell you from watching that video on shear cutting that it will put an enormous amount of stress into the very top layer of steel on the barrel. I cut very thin walled parts out of aluminum every day. As in down to .02" wall thickness. Some 8"x10" .08" floor thickness parts that have flatness call outs of .002". You need to have sharp tooling (which you can get with carbide) and your surface speed needs to be correct. Too fast and material smears, too slow and it tears. Both leaving residual stress in the surface.

Thanks.
Your advice is well taken.

J E CUSTOM

livetohunt · Aug 17, 2018

For me personally when I'm trying to get a good finish on stainless, a standard tool room large will have the rpms to turn at the speed I would want, but when turning chromoly, the toolroom lathe at work peaks at 1800 rpm and I will struggle to get a decent finish on chromoly. The other manual has the rpms I would want, but too short.

I really only use carbide bits when turning steel and I like to rough with a .03 rad insert. Ideally, your pass would be .06" off the diameter. At this point your maximizing the tool life of the insert because that is how they are Designed. So if I am turning something that I will want a very good finish and minimal deflection, I step down to a much smaller radius insert, such as a .008 or .004. As mentioned above, a larger tool radius puts more stress into the part. So a smaller tool radius for a finish cut works better. Leave yourself the correct amount of material to take as a Finish pass based on your finish tools radius.

Just my 2 cents.

I'm more of a mill guy so I'm far from an expert on turning. I will say I'm always jealous how good lathe finishes look vs. a milled finish!

Gord0 · Aug 18, 2018

Ive never turned a stainless barrel, but I would try a .03" rad max for roughing it in, and then switch over to an aluminum grade and profile inserted finisher with a sharp edge and a .007" rad. Run it around 1000rpm with a .002-.003 feed.
I'm sure your method works well, you turn out some great work. Mine is just a suggestion, and may look like crap if attempted.
Not sure if these part numbers are correct, but the pictures are what I would try. I would also use an uncoated tool, as the coating dulls the cutting edge.
Edit: up the feed to .004-.006 with light cuts if some smearing occurs. Coolant/cutting fluid in a constant flow highly recommended to keep the fine chips from wrapping back around and making smear marks. For the same reason I would go with the 30° diamond insert. It keeps chips from wedging and smearing the area you already cut.

J E Custom · Aug 18, 2018

Thanks GordO.

That is some more good information, and I like the looks of that Insert.
I use mostly Sandivk carbide tools, but I will have try Some of those.

Spindle RPM is the real Problem with shop lathes when using a carbide insert. Mine only goes to 1800 and anything past 5 or 600 rpm scares the crap out of me, plus I don,t have a good oil flush system because of the requirements to cover up the machine. So I do things at a slower pace to save my tooling. When chambering, I use anywhere from 45 RPM to 175 RPM depending on what the reamer likes. (Most do their best at 45 to 70 RPM and don,t require any polishing)

With the different steels used in barrels everything has to be adjusted for best results depending on the barrel material. most stainless barrels are ether 416 R or 17-4 PH and they have different requirements.

CNC machining is an entirely different process and what works best for it doesn't for the shop lathe most of the times.

All the tips posted so far are appreciated and I will try to use them if possible. Again , thanks to everyone for their post.

J E CUSTOM

Gord0 · Aug 18, 2018

J E Custom said:
Thanks GordO.

That is some more good information, and I like the looks of that Insert.
I use mostly Sandivk carbide tools, but I will have try Some of those.

Spindle RPM is the real Problem with shop lathes when using a carbide insert. Mine only goes to 1800 and anything past 5 or 600 rpm scares the crap out of me, plus I don,t have a good oil flush system because of the requirements to cover up the machine. So I do things at a slower pace to save my tooling. When chambering, I use anywhere from 45 RPM to 175 RPM depending on what the reamer likes. (Most do their best at 45 to 70 RPM and don,t require any polishing)

With the different steels used in barrels everything has to be adjusted for best results depending on the barrel material. most stainless barrels are ether 416 R or 17-4 PH and they have different requirements.

CNC machining is an entirely different process and what works best for it doesn't for the shop lathe most of the times.

All the tips posted so far are appreciated and I will try to use them if possible. Again , thanks to everyone for their post.

J E CUSTOM

Sandvik makes those same profile inserts too, they're just going to charge you about $25 an insert. With a sharp insert like that you don't need the rpm like a more blunt edge carbide, especially in stainless. More rpm will just cause it to chip.

http://www.pts-tools.com/cgi/CGP2SR...PAHDID=000000193902988&PARDID=875632048060946
Something like this for cutting fluid works well (I use something like it in a manual lathe when finishing) No covering everything up, just a submersible pump and a valve with a nozzle. Drains into the bed and back to the container. When the water evaporates from it, it leaves a thin layer of oil on everything protecting it from rust. Then you can make an adapter to go on the end of the barrel while reaming to flush chips from the reamer.

J E Custom · Aug 19, 2018

Again , Thanks to all for all the post.
It did help and I now feel that the shear grind is realy no better than the high speed steel tools for finishing a barrel. I modified my normal procedure and the Last contour I did was the best. it surpasses the sanded finish by a large margin.

The shear grind tools did a nice job but was to slow. (On the 416r I could only take .002 thousandths cuts to get the outcome i was looking for) and some barrels require up to .200 thousandth removal and it would be to slow. On softer alloys, it works great and .006 or .007 thousandths cuts still work good.

I use carbide inserts to rough cut and .030 to .040 cuts are possible and then switch to the high speed tools for final finish. I did increase the spindle speed as much as I could stand and the results were better.

Now I have a way to re-contour barrels true and don,t have to sand and take a chance of messing it or my Lathe up. I promise to post some pictures as soon as i can.

Everyone has been very helpful.

J E CUSTOM

Shear grinding Lathe tools

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