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Parting is Not Sweet Sorrow

INTJ

When I first started chambering barrels about four years ago I has SEVERAL rifle builders tell me to NOT use a parting tool to cut a barrel to length. They said parting put stress in the barrel and that it was much better to use a bandsaw.

So I bought a bandsaw. Then later I had the shop buy a bandsaw for work. The bandsaw works great and is usually how I cut off barrels. However, there are times when it's much more convenient to part off in the lathe. Not to mention grooving.

For grooving, I had bought a HSS parting tool, but it was .125" wide which was wider than I needed. However, it seemed to work okay.

I recently had a master machinist tell me that the idea that parting introduced stress was incorrect. He used a different term. So I started digging a bit and found that it was just using a parting tool
INCORRECTLY that was the issue.

I also now had a need to use a thin carbide parting tool. I found a youtube video where a guy showed how to use one correctly. So I did it how he said and it works great.

The keys for me are:

1. Make sure the parting tool is square to the chuck

2. Make sure the height is set correctly. If anything, fudge a tad bit high, but never low

3. Turn the RPM down. 95 seems to work great. 70 works as well

4. Feed rate is whatever it takes to get a nice chip rolling off the tool

5. Use cutting cluid

It now goes quick and easy with good looking parts and grooves. My mistakes in the past were using way too high of an rpm and not having the tool height as precise as I should have.

Hope this helps someone.
 
Last edited:
Exactly!

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I'll keep my horizontal saw, as I cut many other materials than just barrels. I feel that parting on the lathe may induce stress , it you are not working as close to the work holding device as possible. I don't know what size tool post you have, but I'm using HSS P3N (.093") cut-off blades for some grooving, or a Nikcole insert that's .070" wide, but limited as to what depth can be cut. I have a 2nd holder set-up with a HSS P3 (1/8") cut-off.
 
My m.o. somewhat dependent on diameter and material, for parting with a carbide insert tool is max rpm to achieve proper surface speed at initial diameter, tool on center and square, run cross slide in as fast as it will go, don't need no stinkin coolant. I wish I would have taken videos of some of the parting jobs I had over the years. I watched others struggle with parting, mostly by running too slow and improper tool setting. Having said that, the CNC machines increase rpm to maintain a constant surface speed when parting. The common theme not understood by newbies is surface speed. This goes for all machine tools and machining operations.
Happy New Year!

Demo:
.
 
hogpatrol said:
My m.o. somewhat dependent on diameter and material, for parting with a carbide insert tool is max rpm to achieve proper surface speed at initial diameter, tool on center and square, run cross slide in as fast as it will go, don't need no stinkin coolant. I wish I would have taken videos of some of the parting jobs I had over the years. I watched others struggle with parting, mostly by running too slow and improper tool setting. Having said that, the CNC machines increase rpm to maintain a constant surface speed when parting. The common theme not understood by newbies is surface speed. This goes for all machine tools and machining operations.
Happy New Year!

Demo:
.
Click to expand...
S.F.M. surface feet per minute. A wise subject to research for those who don't know. Maybe, "you don't know, what you don't know".
 
INTJ said:
When I first started chambering barrels about four years ago I has SEVERAL rifle builders tell me to NOT use a parting tool to cut a barrel to length. They said parting put stress in the barrel and that it was much better to use a bandsaw.

So I bought a bandsaw. Then later I had the shop buy a bandsaw for work. The bandsaw works great and is usually how I cut off barrels. However, there are times when it's much more convenient to part off in the lathe. Not to mention grooving.

For grooving, I had bought a HSS parting tool, but it was .125" wide which was wider than I needed. However, it seemed to work okay.

I recently had a master machinist tell me that the idea that parting introduced stress was incorrect. He used a different term. So I started digging a bit and found that it was just using a parting tool
INCORRECTLY that was the issue.

I also now had a need to use a thin carbide parting tool. I found a youtube video where a guy showed how to use one correctly. So I did it how he said and it works great.

The keys for me are:

1. Make sure the parting tool is square to the chuck

2. Make sure the height is set correctly. If anything, fudge a tad bit high, but never low

3. Turn the RPM down. 95 seems to work great. 70 works as well

4. Feed rate is whatever it takes to get a nice chip rolling off the tool

5. Use cutting cluid

It now goes quick and easy with good looking parts and grooves. My mistakes in the past were using way too high of an rpm and not having the tool height as precise as I should have.

Hope this helps someone.
Click to expand...
Been a machinest for over 50 yrs. Set up on a cut off tool is everything. Bad set up is a disaster.
 
Dusty Stevens said:
If it chatters or moans at all youll need to reindicate. A portaband doesnt carry this risk
Click to expand...

Neither does a full bandsaw, and you have to take the barrel out of the lathe anyway. Further, you can't do a proper dial-in until the barrel is very near its finished length.

Still, parting isn't the big boogeyman many make it out to be. Square tool to chuck, set the height to center or a tiny by high, use cutting fluid, and find a feed rate that gives you good chips at the rpm you pick. Slower rpm is easier.
 
You should be able to part in 416R or 4140CM @ 80-90SFM. 1 1/4" diameter 'shank' @ 80SFM calculates to 244rpm. My old Republic Steel "Machining Data for Cold Finished Bars" say you should be able to feed a HSS 1/8" wide cut-off @ .0015" - .002" per revolution, depending of course on the rigidity of the set-up. Carbide tooling can increase SFM x 2 or 3 on the lathes most use for their barrel work. Turn too slow and the tool rubs some, leaving a poor surface finish and poor tool life,,, turn too fast and tool burns and dulls prematurely (overheats). On 'production' machines I can increase SFM with carbide x 5 or 6.
 
I cut my barrels to rough length in a vertical Work-A-Matic saw (virtually identical to a Roll-In). I have no problem parting in a lathe but I don’t need to part barrels if I pre-cut to length before they go in the lathe.
 
These are awesome and super fast. The heat goes out in the chip. Part is still cool to the touch. Just take care of the blades as they add up and don't take hot rodding well. Just a smooth, even but firm pressure works best for me. You can buy blades for specific materials, like ss.
You can buy the name brands at a higher price but this one works well and won't break the bank. It's on sale now. Google up some videos on them. Awesome say in a fab shop, as long as the user takes care of it.
Guessing here but cuts a 1.250 bbl in maybe 15 seconds or so. Give or take. Very square cuts. I use it to cut the breech end off of bbls to give the customer and where I'll crown it. I can cut it about the thickness of a dime and the part still doesn't get more than just warm. Dull or beat up blade won't do as well, though.

 
^^^I have a Dewalt carbide blade chop saw. Never thought of dragging it out for a barrel though. It gets used cutting tubing and angle iron for steel fab projects. The steel stays relatively cool but the chips come off hot and blue. I can totally see it working fine for barrels. I've got a Bobro cold saw that needs spindle bearings. One day I'll get time to get it running.
 
gunsandgunsmithing said:
These are awesome and super fast. The heat goes out in the chip. Part is still cool to the touch. Just take care of the blades as they add up and don't take hot rodding well. Just a smooth, even but firm pressure works best for me. You can buy blades for specific materials, like ss.
You can buy the name brands at a higher price but this one works well and won't break the bank. It's on sale now. Google up some videos on them. Awesome say in a fab shop, as long as the user takes care of it.
Guessing here but cuts a 1.250 bbl in maybe 15 seconds or so. Give or take. Very square cuts. I use it to cut the breech end off of bbls to give the customer and where I'll crown it. I can cut it about the thickness of a dime and the part still doesn't get more than just warm. Dull or beat up blade won't do as well, though.

Click to expand...
is that the same as an abrasive cutoff saw except for the blade? or are their differences like the rpm ect?
 
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