Parting tool question
- Thread starter Caleb85
- Start date
shortgrass
Silver $$ Contributor
Out here in the 'world', where we make precision parts for a living, when you have tooling troubles you make one change/adjustment at a time and try it, so next time you have trouble it's not such a problem. That was rule number 1, learned over 42yrs ago. Make 3 or 4 adjustments/changes all at once and you don't know which change/adjustment was the one that did the trick.
Kings X
Gold $$ Contributor
Turn the tool over and run lathe in reverse. Now part is trying to jump on top of cutter. Upside down put the force opposite.
Old turret lathes have the cutoff tool on the holder on the backside. That way you don't have to stop and reverse the direction - losing time. And in a production shop - time is money.
Old turret lathes have the cutoff tool on the holder on the backside. That way you don't have to stop and reverse the direction - losing time. And in a production shop - time is money.
Square to work, sharp, 50rpm with a steady feed with vipers venom works for me. I run a live center in the end and a steady rest as close to the cut as possible. Also get a little oil on my hand and rest it out in the middle of the barrel as it seems to dampen vibration
shortgrass
Silver $$ Contributor
It's been awhile since I had a Broughton barrel blank, but as i remember, there was a sticker on each and every one that said; "do not shorten this barrel with a parting tool,, use a saw". That's probably not an exact quote, but it's close. The thought being, a cut-off tool not set-up properly might harm the barrel blank. You might have a wreck (like discribed in previous posts) or whatever. Just stick to the basic machining principals, make sure the tool is centered, work as close to the chuck/collet as feasible, make sure the tool is sharp , use proper feeds and speeds IF YOU HAVE A FLOOD COOLANT SYSTEM TO CARRY THE HEAT AWAY. I don't remember ever grinding a chip breaker into a "P" style cut-off blade. When 'parting off' we always use an angle across the cutting edge. That way there is no 'ring' left behind on the part (in the case of a part that has a hole all the way through it) or there's no 'tit' left on a solid part.
Roeder
Silver $$ Contributor
The reason that Broughton and others recommend against parting a barrel, especially at the muzzle end, is the possibility that the stress and heat from the parting cut might cause the bore to change dimension. It might either "bell or choke" slightly depending on whether the rifling is buttoned, hammer forged, or cut. I know that some successful builders use a parting tool to cut all their barrels without any known issues. I use a slow, fine toothed band saw myself.
Another important thing is the rigidity issue. Most of the popular Asian lathes in use by many gunsmiths these days are no where near as rigid as older US made machines. Even the ones that look beefy and have a large 2" or more inside diameter can be flimsy and a poor platform for parting tools. The thicker the tool, the more stress and the greater the likelihood of chatter or worse.
shortgrass
Silver $$ Contributor
I figured Broughton recommended saw cutting because there are so many inexperienced guys 'doing their own barrel work'. Manage to get the tool set above center and you're exerting a lot of 'push' instead of cut. Set the tool below center and spindle rotation wants to pull the tool under the barrel. Or, they're working too far away from the chuck/collet. Any of these conditions isn't good. I'm sure there are some who try to turn too fast without flood coolant to carry away the heat, but I'd be surprsed if those that turn slow aren't putting at least a few drops of oil on while cutting. HS tooling won't take much heat before it fails, so I'd not think you could generate enough heat to make a barrel bore open up without the tool failing first. There's no big mystery to parting off with a HS cut-off blade, you just have to stick to basic machine practice. Carbide can be a lot more forgiving, 'cause it'll take a lot more heat before it fails, but you still have to ahear to basic machine practice. I usually cut-off what barrel I don't want, with the metal cutting band saw (w/flood coolant), but I have cut-off with a HS cut-off blade. Depends on the circumstances present at the time.
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Johnny_V
Silver $$ Contributor
I agree, parting tool must be supported as rigidly as possible. Too much tool extension = chatter.
If you have a worn out old junk lathe or a light weight one that is a little loose you will have all kinds of problems that you will not be able to cure.
Put the same tool that will not work on a junker on a rigid machine and it will cut like butter.
The old rocker type tool holders are particularly troublesome. Put your parting tool in an Aloris quick change holder on a real machine and you will not believe the difference.
Put the same tool that will not work on a junker on a rigid machine and it will cut like butter.
The old rocker type tool holders are particularly troublesome. Put your parting tool in an Aloris quick change holder on a real machine and you will not believe the difference.
butchlambert
Site $$ Sponsor
A Heavy 10 shore ain't heavy. I always cut my barrels with a bandsaw and then indicate and machine. Lots of good info here. Don't hang your part out any further than necessary. In this case, according to the photo if could be cut right at the jaws. I have a lot less trouble if my cutting tool is hanging out only enough to do your depth of cut. I have had a lot less trouble parting if I use the power feed. Yea, I flood cool it also.
shortgrass
Silver $$ Contributor
I've cut-off tens of thousands of parts on turrent lathes, hundres of thousands of parts on multiple spinde automatics, never have supported with a live center. Seems like that would 'trap' the cut-off blade as the part was cut off. Another 'wreck' just waiting to happen.......
hogpatrol
Silver $$ Contributor
As others have stated, parting tool set just enough to get to center, move the workpiece as close to the chuck as possible, run at the proper speed and use coolant/lubricant. I part off using very high speed with cutting oil. Having said that, if your machine has slop in it ANYWHERE (cross slide leadscrew, headstock bearings, toolholder, compound, etc.), you're probably spinning your wheels and live center for parting? Absolutely not. If this is a barrel, don't beat your head against the wall parting off excess material, use the saw. On another note, go to a cutting tool website and see what recommended speeds are listed for all types of materials. A very common mistake in metalworking is running too slow.
Some good videos on parting. For the newbies, watch parts 1,2, and 3. In video #2 check out the speeds he is running on steel.
Some good videos on parting. For the newbies, watch parts 1,2, and 3. In video #2 check out the speeds he is running on steel.
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Has been my method on rifle barrels for 7 years, no train wrecks yet, and still using the same parting tool..
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