how can i improve the finish of my bbl threading

R

rsmithsr

Well-known member
i do not do much lathe work. i am on my SECOND bbl this YEAR.
i thread, reverse, upside down going away from the head stock.
TIn coated carbide threading tool in a very solid tool holder.
currently i an slow...45 rpm, .003 cut with oil...the multi-pass guy.
but my threads look like krap compared to "real" gunsmiths.
they produce smooth shiney threads.....mine pretty rough.
if i go up in speed( like carbide shoot be) i get concerned abiut halfnut engagement
talk to me...
my threads work..just do not look good
 
I thread with a vertical TIN Coated insert at about 250 rpm using Rigid Dark Cutting oil. Insert tools like surface feet per minute to cut at optimum.

You have to practice. Machine work is like anything else, the more you do, (correctly) the better you will get.
 
DARK it is, i'll have to just practice.
jackie schmidt said:
I thread with a vertical TIN Coated insert at about 250 rpm using Rigid Dark Cutting oil. Insert tools like surface feet per minute to cut at optimum.

You have to practice. Machine work is like anything else, the more you do, (correctly) the better you will get.
Click to expand...
 
For good quality threads on barrel steel you need a tool with POSITIVE top rake and set on vertical center. not above or below center.

Also with the tool retracted slightly, manually run the tool to where you want it to stop in relation to the barrel shoulder, then make a good mark on the left bedway and carriage wing. with the tool retracted, practice watching that convergence mark, not the tool itself.

Always thread toward the shoulder and use a good grade of cutting oil. with a tool with positive top rake (TPG for example),that way the cutting oil is at the cut.


.
 
Is your compound set to 29.5*? You can thread by plunging the cross-slide, but the angle is easier on less rigid setups. Of course choke up on your tools as much as practical. Either speed up the lathe, or switch to HSS. If you're using a standard quick-change toolpost, Aloris makes a pre-ground threading tool that's simplicity itself to sharpen. Finally, you can polish your threads with a Cratex stick - it won't remove chatter marks, but it'll make a decent thread smoother.

GsT
 
GeneT said:
Is your compound set to 29.5*? You can thread by plunging the cross-slide, but the angle is easier on less rigid setups. Of course choke up on your tools as much as practical. Either speed up the lathe, or switch to HSS. If you're using a standard quick-change toolpost, Aloris makes a pre-ground threading tool that's simplicity itself to sharpen. Finally, you can polish your threads with a Cratex stick - it won't remove chatter marks, but it'll make a decent thread smoother.

GsT
Click to expand...

Strange, but in all of my years as a Machinist, I never use a compound at 29.5 degrees. I thread straight in.
 
i am using a solid tool holder, 0 degree and cutting away.
sorry just no tool crash on a good part.
yes i clean them up, they thread on smooth...but i know they can be better
 
rsmithsr said:
i am using a solid tool holder, 0 degree and cutting away.
sorry just no tool crash on a good part.
yes i clean them up, they thread on smooth...but i know they can be better
Click to expand...

I thread kinda same way you do.. With my inserts RPMs helped. Can't hurt anything going away from the shoulder. At least 250 or more. Good luck.
 
i was taught in lathe school to use 29. jackie was taught by his dad as i recall, not in a class.
i use 0 with my current setup.
anyone have a fact based comment on toward or away from the shoulder ? or was that based on 29*

Louis.J said:
I have often wondered why not Jackie I too was taught to use the compound and thanks for sharing that.
Click to expand...
 
rsmithsr said:
i was taught in lathe school to use 29. Jackie was taught by his dad as i recall, not in a class.
I use 0 with my current setup.
Anyone have a fact based comment on toward or away from the shoulder ? Or was that based on 29*
Click to expand...
i w3as taught 29.5 after last pass go straight in 1 tho
 
JerrySharrett said:
For good quality threads on barrel steel you need a tool with POSITIVE top rake and set on vertical center. not above or below center.

Also with the tool retracted slightly, manually run the tool to where you want it to stop in relation to the barrel shoulder, then make a good mark on the left bedway and carriage wing. with the tool retracted, practice watching that convergence mark, not the tool itself.

Always thread toward the shoulder and use a good grade of cutting oil. with a tool with positive top rake (TPG for example),that way the cutting oil is at the cut.


.
Click to expand...

Jerry,

Is that for HSS as well? I ask because I have the Warner HSS threading set-up and they recommend their positive rake threading insert for aluminum, and the neutral rake insert for steel.

Justin
 
Raise the RPM´s to 5-800 and your finish should improve greatly. I´m normally running around 600rpm treading away from the shoulder with a full profile carbide insert. I´m taking about 50% of the depth of cut suggested by the mfg, taking about a dozen cuts to finish the thread. Make sure you have the tool on center. I´m feeding straight in to be able to use the DRO with a locked cross slide.

I chamber at most 10 barrels per year and have way to little lathe time to feel secure theading towards the shoulder with enough SFM to get a decent finish!

Regards,
Peter Ericson
 
jackie schmidt said:
Strange, but in all of my years as a Machinist, I never use a compound at 29.5 degrees. I thread straight in.
Click to expand...

I've heard several pros say that (and at least one that threads at 29.5*). It may be that it only helps on lighter machines and/or less rigid setups. Worth a shot, imo, if you're having problems.

GsT
 
my class was for small southbend lathes.
GeneT said:
I've heard several pros say that (and at least one that threads at 29.5*). It may be that it only helps on lighter machines and/or less rigid setups. Worth a shot, imo, if you're having problems.

GsT
Click to expand...
 
Carbide Blues

rsmithsr said:
i do not do much lathe work. i am on my SECOND bbl this YEAR.
i thread, reverse, upside down going away from the head stock.
TIn coated carbide threading tool in a very solid tool holder.
currently i an slow...45 rpm, .003 cut with oil...the multi-pass guy.
but my threads look like krap compared to "real" gunsmiths.
they produce smooth shiney threads.....mine pretty rough.
if i go up in speed( like carbide shoot be) i get concerned abiut halfnut engagement
talk to me...
my threads work..just do not look good
Click to expand...


Id suggest HS cutters. Carbide inserts when new are fine but they arent worth much at slow speeds compared to HS. HS is much more forgiving especially at slower speeds. You have to look at carbide under magnification to see the micro edge chipping. Be dead on center when cutting threads with the proper back angled relief. The numbers are in the machinist handbook or online.
 
i do have hss, maybe i should just try that since i am so slow.

i remember why...too big..cannot get close to shoulder.........
the carbide tool and holder let me get close

WallyDog said:
Id suggest HS cutters. Carbide inserts when new are fine but they arent worth much at slow speeds compared to HS. HS is much more forgiving especially at slower speeds. You have to look at carbide under magnification to see the micro edge chipping. Be dead on center when cutting threads with the proper back angled relief. The numbers are in the machinist handbook or online.
Click to expand...
 
rsmithsr said:
i do have hss, maybe i should just try that since i am so slow.

i remember why...too big..cannot get close to shoulder.........
the carbide tool and holder let me get close
Click to expand...


One of the biggest benefits of HSS is that you can readily modify it at home. Either grind that cutter that's too big, or just buy a blank and grind the cutter you need - it's not really that difficult and it's a great skill to have.

GsT
 
GeneT said:
One of the biggest benefits of HSS is that you can readily modify it at home. Either grind that cutter that's too big, or just buy a blank and grind the cutter you need - it's not really that difficult and it's a great skill to have.

GsT
Click to expand...

Like Gene says HSS/Grind. How close do you want to get to the shoulder?


hss shoulder.jpg
 
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