Just something i am wanting to learn more about. I buy a lot of take off barrels for practice and on most of these barrels the threads are pretty loose. I can take these barrels and screw them onto any of my BAT actions without any issues. Will loose threads cause any alignment issues? Will loose threads cause any accuracy issues? My gunsmith always requests the action be sent with the barrel so he can properly fit the barrel to the action. In some cases i cant take the barrel off the fitted action and put the barrel on another action (BAT) More times than not, it just wont work.
Barrel threads loose or tight?
- Thread starter skeetlee
- Start date
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Dennis Sorensen
Guest
The design of the "V" thread is such that when tightened it will center on itself unless outside influences affect it... with barrels and receivers loose is better than tight for sure...
Jon doesn't make them real tight but they are definitely not loose either. Whats the reason or reasoning behind the alignment shoulder or ring or whatever you call it on a BAT DS? This was also discussed a bit in the warehouse artical. It just made me a bit curious, thats all. Thanks lee
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Donald
Guest
Read Harold Vaughn's book. He deals with barrel theads quite extensively.
Donald
Donald
I haven't read Harold's book but i have read several articles here and there that state the importance of proper fitting barrel threads. On the other hand and after talking with several top shooter and folks i trust they all put a little slop (improper wording I'm sure) in there threads on purpose. I haven't had any issues either way, except for having a barrel or two that i couldn't swap actions with. I haven't seen any differences in performance I'm sure! Lee
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squeakie
Guest
most folks fail to realize that the bigger the diameter of the thread, the lower the thread contact percentage is. A standard SAE 3/4-16 thread is 70%, but when you move up to about 1.125-16 you usually end up with a 60%
gary
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TRA
Guest
Are you sure about that?
OK, I guess I need more info.
Please explain "thread contact percentage" in a way that I can understand.
al
And threads only bear on one side - they are inherently loose! The alternative is galling.
JerrySharrett
Senile Member
Greg Tannel keeps a lathe set up just to salvage where stainless barrels have galled in stainless actions.
Skeet, what do you expect to learn with take off barrels. About all the take off barrels I have ever borescoped look like 90 miles of bad road.
Skeet, what do you expect to learn with take off barrels. About all the take off barrels I have ever borescoped look like 90 miles of bad road.
JerrySharrett
Senile Member
Contact percentage has nothing to do with loose vs tight (Classes of fits). On a SHARP vee thread, the contact percentage is 100%. Back off to 75% and you have a male thread where there is 75% left of the thread depth.
Threaded diameter has nothing to do with thread percentage. For example, 16 TPI the size of the 60 degree triangle is the same whether the threaded diameter is 3/4" or 3". In the 16 TPI example, there are 16 threads per inch, i.e. the base of that triangle is 0.0625" regardless of how large (or small) the threaded item is. Thread percentage, however is based on the relative height, or altitude, of that 60 degree triangle.
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squeakie
Guest
absolutly. Suggest you ask for a thread form hand book from the U.S. Department of Standards (my congressman got mine for me 40 years ago). There's also a lot of very usefull information in the Machinest Handbook, and the Engineer's Handbook. To get seriously tight threads in larger O.D.'s they really need to be ground with the correct helix angle, and then they often will seize. I recommend coating them with Neversieze With Nickel, and cut the torque rating buy about 1/3rd (they actually spec 50%). Also stay far away from Loctite Antisieze. A really good test of actual thread contact is to cut a small section with a female thread, and then clamp it onto a male thread it's mated to. Look at it in a Shadowgraph (it will be tighter clamped than before. You see gaps in there, even when ground. Another problem most people don't realize is that every thread cutting machine has built in lead error. if you cut the male and female on the same machine your better off. Otherwise your maiting two different thread forms (eventhough they are very similar in size and shape)
gary
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squeakie
Guest
I used to run into a lot of these fits when making thread masters (all were ground). If you get them to where you know they're near perfect; they will not thread onto a master gauge. I did find that I got a better master set when I ground them on a Studer universal grinder. That way all the lead error came out the same (eventhough I couldn't adjust the helix angle on the internal thread). I also found that the finer the threads per inch the more problems arose
gary
JerrySharrett
Senile Member
If you want to know the accurate details about screw threads get a copy of Machinerys Handbook, Amazon.com or eBay are good sources.
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TRA
Guest
squeak, Times have changed a little over the last 40 yrs. today tooling for threading is sourced with those those conditions in mind( IE diameter of thread) and wallah ....you source tooling to accommodate the increase in Id, and OD so technology wins again.
You are right about the lead accuracy though, as the advent of CNC equipment has exaggerated this. You'll find those suggesting that threads be lapped were doing it for more uniform contact, thread to thread and not to improving centering the barrel with the action.
You are right about the lead accuracy though, as the advent of CNC equipment has exaggerated this. You'll find those suggesting that threads be lapped were doing it for more uniform contact, thread to thread and not to improving centering the barrel with the action.
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squeakie
Guest
You can also buy it on DVD, and just print out the page you need. Seems like I got it for less than $25
gary
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squeakie
Guest
I was doing it just under four years ago. The application is where you select the equipment. All thread gauges are check with three wires before comming off the machine. On a lathe we often used thread triangles, but they still are not as accurate as wires. I came from a shop that was filled with everything from Monarch lathes to Warner Swasey CNC lathes. Most of the CNC work was run accross Okumas. Not because I liked them, but that was what we were stuck with. If the thread had to be very close and yet turned on a lathe it either went accross a Hardingh or one of the Monarchs. If the material was tough (like 17PH4 stainless) it automaticly went to the Monarchs. We had a couple Excello thread grinders, but it was easier and quicker to grind the threads on a Studer. The old Excellos grind better threads. Most threads that have to be lapped are done because they were not cut right from the start (not always but most of the time)
By the way the only way to get a true uniform thread contact (assuming the threads is cut right and is of good quality) is to stretch the thread into contact. This makes the thread strait, and physicly forces it into proper contact. This is often seen in machine tool building, and is a largely missunderstood concept.
gary