how can i improve the finish of my bbl threading
- Thread starter rsmithsr
- Start date
BillBrawand
New member
i was told 29.5 last pass go straight half tho go over few times good luck
Engrbill
Member
This shows why 29.5 compound is NOT Effective
https://www.youtube.com/watch?v=PnH_oeOUps4
I also thread like you do. https://www.youtube.com/watch?v=PnH_oeOUps4 straight in.
You just need to practice till you can use more speed.
Please see:
https://www.youtube.com/watch?v=PnH_oeOUps4
I also thread like you do. https://www.youtube.com/watch?v=PnH_oeOUps4 straight in.
You just need to practice till you can use more speed.
29.5 degrees is perfectly effective!
All I get from the video is that the 29.5 degree number is not critical. Certainly it is not, but that is not to say that there is something bad or ineffective about 29.5 degrees.
All I get from the video is that the 29.5 degree number is not critical. Certainly it is not, but that is not to say that there is something bad or ineffective about 29.5 degrees.
J
Joel
Guest
Like most things in machining lots of methods work. Some are more preferred than others but if whatever method you chose works and you are happy with it it's not my place to criticize your method. I was taught in various formal training settings that the 29 or 29 1/2 degrees had several advantages. Primarily less tool pressure and better chip flow. Normally I have the compound angled and the last light finish cuts are straight in using the cross slide. I have limited experience with CNC lathe threading so take this with a grain of salt. In the CNC usage my limited experience the most common pre-canned cycle is by alternating cutting on both sides of the v groove until the finish plunging the finish passes followed by 29/30degree tool path.. I don't remember a pre-canned CNC cycle that straight plunged the complete cycle but as stated I have only used a couple of different conversational CNC lathes for threading.
I tend to take fairly heavy cuts for rough threading and using the compound set at an angle on manual machines aids chip flow. That being said I have used zero degrees and that got the job done.
Some of the carbide tool geometry does not perform well without sufficient SFPM. My preferred insert for threading is the Kennametal NTP style inserts,. It's old school for insert technology but for manual machines I haven't found an insert that I like better.
I tend to take fairly heavy cuts for rough threading and using the compound set at an angle on manual machines aids chip flow. That being said I have used zero degrees and that got the job done.
Some of the carbide tool geometry does not perform well without sufficient SFPM. My preferred insert for threading is the Kennametal NTP style inserts,. It's old school for insert technology but for manual machines I haven't found an insert that I like better.
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Excellent Advice. I too used the Kennametal NTP inserts for years and I get good results with them at as slow as 200 RPM for 16 TPI. There are some new coatings that really improve the performance of these inserts. Unfortunately, for smaller machines like the Grizzly / South Bend Heavy 10, it is difficult to get the holder low enough to get on centerline so I am trying different laydown inserts.
NezRongero
Member
Please allow this rookie to participate. I have a dedicated Jet 1024 for chambering AR15 barrels with compound sort of permanently set for taper boring. Even with this little lathe I thread plunging in with the cross slide. I use laydown inserts for aluminum. They cut 416 SS real well.
Watch "Jet 1024 Threading To A Thread Relief Aided By A Proximity Sensor" on YouTube
https://youtu.be/1D-HoFgNYFg
Watch "Jet 1024 Threading To A Thread Relief Aided By A Proximity Sensor" on YouTube
https://youtu.be/1D-HoFgNYFg
Centerfire
Member
confused a bit
I did not see mention of the type of barrel steel being machined. Is it a 416 SS or a Chrome moly steel?
Does it make any difference regarding the cutter material, rotational speed, or feed?
Centerfire
I did not see mention of the type of barrel steel being machined. Is it a 416 SS or a Chrome moly steel?
Does it make any difference regarding the cutter material, rotational speed, or feed?
Centerfire
most is bbl 416 ss..but i have done cm.
GeneT
Active member
Nez, you have some interesting videos (and not padded with 6 minutes of vapid blather!). I wish you would put a small description on them as I sense a nugget of wisdom in each. Watching the one where you were (apparently) checking the squareness of the front of an AR upper receiver - I'm very curious if you have more data from doing this. I'm looking to confirm my prejudices, of course. I maintain that most uppers are square and that the lapping kits I've seen for sale are a useless gimmick. BUT, I've only had the opportunity to check a few (all square). Have you found any that are seriously out of square with the bolt passage?
Regards,
GsT
NezRongero
Member
Gene,
Thank you for the kind words.
The worst I have seen is about 0.003 and front sort of rounded, that it took about .004 to clean up. Some of the other problems with the ARs are the barrel extensions. I can check everything including thread runout like Jackie described at one point, but when BE is screwed on and indicate it, it will be swinging 0.003.
Do all these matter, hard to quantify, I have not done any systematic testing to validate any. I put them in the it-cant-hurt category. I am not in the business, I am retired, time I have. Supporting 18 kids in the State Team keeps me busy.
If you can believe this guy, this is so far the only write up I've seen on incremental improvements on the platform verified on a machine rest.
Maximizing The AR-15: A former military armorer reveals his secrets for cutting AR-15 group sizes in half. - Free Online Library
https://www.thefreelibrary.com/Maxi...y+armorer+reveals+his+secrets...-a05207138981
These were taken last night, the kid wants to see how straight his barrel is. Thread was cut with uncoated carbide laydown for Aluminum at 34 RPM on the variable speed 1440, untouched, just cleaned up thread with brush, and air blown. The BE is pretty straight. Got it from WOA.
Watch "12 Aug 2020 Testing Thread Runout" on YouTube
https://youtu.be/CEFUO028lVI
Watch "12 Aug 2020 Testing BE Runout" on YouTube
https://youtu.be/CM434kOxx0s
On squaring the AR10 face I have been using a split ring (borrowed from Mike Bryant) and TS spider screwed on to a Royal live center.
Thank you for the kind words.
The worst I have seen is about 0.003 and front sort of rounded, that it took about .004 to clean up. Some of the other problems with the ARs are the barrel extensions. I can check everything including thread runout like Jackie described at one point, but when BE is screwed on and indicate it, it will be swinging 0.003.
Do all these matter, hard to quantify, I have not done any systematic testing to validate any. I put them in the it-cant-hurt category. I am not in the business, I am retired, time I have. Supporting 18 kids in the State Team keeps me busy.
If you can believe this guy, this is so far the only write up I've seen on incremental improvements on the platform verified on a machine rest.
Maximizing The AR-15: A former military armorer reveals his secrets for cutting AR-15 group sizes in half. - Free Online Library
https://www.thefreelibrary.com/Maxi...y+armorer+reveals+his+secrets...-a05207138981
These were taken last night, the kid wants to see how straight his barrel is. Thread was cut with uncoated carbide laydown for Aluminum at 34 RPM on the variable speed 1440, untouched, just cleaned up thread with brush, and air blown. The BE is pretty straight. Got it from WOA.
Watch "12 Aug 2020 Testing Thread Runout" on YouTube
https://youtu.be/CEFUO028lVI
Watch "12 Aug 2020 Testing BE Runout" on YouTube
https://youtu.be/CM434kOxx0s
On squaring the AR10 face I have been using a split ring (borrowed from Mike Bryant) and TS spider screwed on to a Royal live center.
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GeneT
Active member
Dave Tooley
Active member
I did a lot of work for one manufacture that used a BE for a large caliber bolt gun. Being the curious type I immediately started checking the BE's. Curious = CYA some of the time. All it took was one and I went through 123 to get 30 I would use. Those 30 barrels showed a marked improvement in accuracy over previous barrels. I checked concentricity as well as run out on the inboard and outboard side of the shoulder. They changed suppliers and the story had a happy ending for the next 400 or so barrels.
Some of the same people involved in that project moved on to other companies and now I get good extensions for their piston gun.
Some of the same people involved in that project moved on to other companies and now I get good extensions for their piston gun.
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Butch Lambert
Active member
Gene, I just received my Wife's upper that Nez built for her. Work is over the top!
killswitch505
New member
What kind of repeatability are you getting from your prox? I went with a 5 micron limit switch I’m getting about .0005 at 150 rpm
https://youtu.be/Ncc72aKgzVY
NezRongero
Member
I don't have a DRO on that 1024, just a dial indicator. It gets to 0.001 or whatever you can accept as the repeatability of the dial indicator. I set the indicator to zero where I want to stop for a given RPM, needle stops on zero. What that is in actual precision, never bothered to verify and don't have the means to do so. So, I just accept what the dial indicator is telling me. For threading to a relief, it is more than adequate.
I do not use the prox to turn to shoulder.
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killswitch505
New member
Shoot man that’s why I built mine takes the pucker factor out of threading to a shoulder I went from threading at 70 rpm to 300 ive kind of settled at 150rpm and I never have to disengage the half nuts
NezRongero
Member
I do thread to shoulder when I have to, but thread relief when not needed depending on the barrel extension or flash hider/brake/suppressor adapter. Some have reliefs, some don't. The only bolt gun I ever work on is my brother's glued VFS. That I thread close to the shoulder so when I set back the barrel the extended thread looks decent. It does not make a difference if the thread is interrupted, it just looks pleasing when there is not a big gap between the old and the new thread.
Here is what I use when working on my brother's barrel. See how close the center tip is to the right side edge. I spec'ed it for Thinbit to make for me. The item is not a catalog item, but modified from existing design.
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