Probably a stupid question, But

R

Reynard

Guest
I am wondering if some one can tell me the answer to this.

I have watched numerous videos on re barreling. I am finding it hard to get my head around this. When the barrel is set up and trued in the lathe to lets say between 0.0000 and 0.0002. The tennon is cut and the threads are then cut. How come on every video I watch, when the Smith is test fitting the action to the barrel. He will get it threaded on to the barrel easy for the first 3/4 of its length to then have it bind up on him.
I would have thought that if the Barrel is dialled in true and the threading tool is cutting towards the chuck, which I would have thought would have more rigidity than where the thread started.
My novice way of thinking is that the action should screw on the same for its entire length.
There will be an obvious answer. I would appreciate someone sharing that answer with me.

Cheers
 
Great question.

I've actually hands-on done what you're describing and that's exactly how it goes.

Dunno why, cumulative friction I guess.

al
 
Boyd Allen said:
Are you assuming that the action threads are not tapered?
Click to expand...

Mr Allen
One of the videos that I watched, The action was trued before the barrel was threaded to fit the action. The action was trued in the Lathe using an action truing jig and a mandrel with two 0.0001 indicators. part of the truing process was single point cleaning up the threads.

Now I am a novice as stated earlier. I would take a guess, that in order to cut a tapered thread, something would have to be off set. Could you confirm to me that action threads should be tapered or they should be inline straight. As you are correct I was assuming that the action threads are not tapered.

Now. If the threads have to be cut deeper to allow the action to thread all the way onto the barrel. Then surely when all is tightened up, my way of thinking, is that the threads that the barrel were able to screw on easily in the first test fit are now more loose after taking another cutting pass.

Does this mean that the threads that were tight after the first trial fit are the threads that are now taking the biggest part of the holding of the barrel in the action.

Mr Alinwa. Next time your doing a barrel fitting. You should take a reading of the diameter of the threads that the action can easily screw onto the action and then a reading from the threads that the action can not screw on to. I wonder what the difference would be. Could we be talking 0,00005", or more.
If it is cumulative friction, like you suggest. One would think that the same friction would be there when cutting a test bar to check for tailstock alignment. This is really how I came to be mulling over this conundrum. The threading example was an easier way to highlight what I was trying to say.

Thanks for replying to my ?, a lot of people looking at the thread. Not a definitive answer yet.
 
The resistance should NOT change over the entire length of the threads. If it does, then you're making your threads too tight!
 
Last edited:
goodgrouper said:
The resistance should NOT change over the entire length of the threads. If it does, then you're making your threads too tight!
Click to expand...

Mr goodgrouper. Your reply does not make sense to me. My question related to the last 1/4 of the length of the tenon threads. If the resistance was the same for the full length of the thread. I would have thought you would not be able to gat a start screwing on the action, therefore another cut would have to be made to the threads. What I take from what you are saying, is that once the thread starts, you are saying it will screw all the way home. Am I reading into this wrong.

Sorry if I ain't picking things up too quick. Probably has to be explained in layman's terms for me to understand it.

I appreciate you taking the time to reply.

Cheers
 
goodgrouper said:
The resistance should NOT change over the entire length of the threads. If it does, then you're making your threads too tight!
Click to expand...

Sorry Reynard but Grooper is correct. Friction. As more threads engage the accumulated friction load increases.

A well known gunsmith in the US, Greg Tannel, keeps a lathe set up whose purpose is to remove stuck tenons where the fitter insisted on too tight threads. This occurrence is more common where stainless barrels are being fitted to stainless actions.

Which videos are you watching anyway? Some of the youtube videos I've seen give bad advise!!
 
Please do no apologise Mr Sharrett. I am here to learn. I was only airing my thoughts on the matter and am not qualified to say that Mr goodshooter was wrong.
I still feel that reading his reply and then your reply saying he is correct. To me you are both saying different things. He is saying that friction should not change and you are saying it increases as the load increases. Your explanation is one that I can understand. I thank you for that.

Cheers
 
Reynard said:
. To me you are both saying different things. He is saying that friction should not change and you are saying it increases as the load increases. Your explanation is one that I can understand. I thank you for that.

Cheers
Click to expand...

Raynard, don't get accumulated friction, as I said, confused with physical interference.

Physical interference, in some of the newer import lathes of poor quality, sometimes is caused by the pitch of the lathes lead screw does not match the true pitch of a custom action that was threaded on a high-precision CNC lathe.
 
Last edited:
Reynard,
I am a novice as well. My first lathe was a $3,000 lathe and I was experiencing the same issue and just thought it was the way it was supposed to be and maybe it is. I have since upgraded my lathe and that issue went away. When I get the thread pitch correct the action screws on all the way with no tightness. I have since removed all the barrels I chambered on the first lathe and re-chambered on the new lathe. Like I said I am a novice and just telling my experience I had.
 
Same answer, different way of saying it.....

In this case, what you are seeing is the fact that the threads are not yet cut to the right size. They are close enough to get the action started on, but as you engage more threads, the lack of tolerances start to stack up against you.

Think of it as trying to run in water. The deeper you get the harder it is to run. Once you get deep enough, you ain't running anymore. If the water was the same depth ( say ankle deep ) the entire length of the run, the resistance would stay constant and you could make it to the end.

-------------Jeff
 
Jeff Walker said:
Same answer, different way of saying it.....

In this case, what you are seeing is the fact that the threads are not yet cut to the right size. They are close enough to get the action started on, but as you engage more threads, the lack of tolerances start to stack up against you.

Think of it as trying to run in water. The deeper you get the harder it is to run. Once you get deep enough, you ain't running anymore. If the water was the same depth ( say ankle deep ) the entire length of the run, the resistance would stay constant and you could make it to the end.

-------------Jeff
Click to expand...

Jeff is absolutely correct. To prove this, the next time you are threading a tenon check your action fit when you get close. Usually the first few threads will fit perfectly then start to tighten up. Take another .001 cut and the action will fit a few threads further up the tenon. On each additional .001 pass, the action goes further on the tennon until it finally fits up to the shoulder. Until the threads are cut to the proper depth, there is interference at the sides of the 60 degree slanted wall of the thread. If you tightened the barrel on the last few threads,(with great force), it would be called an interference fit. This type of thread is used in some applications where you don't want the piece to come unscrewed thru vibration.
 
Another angle

Bob Pastor said:
Jeff is absolutely correct. To prove this, the next time you are threading a tenon check your action fit when you get close. Usually the first few threads will fit perfectly then start to tighten up. Take another .001 cut and the action will fit a few threads further up the tenon. On each additional .001 pass, the action goes further on the tennon until it finally fits up to the shoulder. Until the threads are cut to the proper depth, there is interference at the sides of the 60 degree slanted wall of the thread. If you tightened the barrel on the last few threads,(with great force), it would be called an interference fit. This type of thread is used in some applications where you don't want the piece to come unscrewed thru vibration.
Click to expand...

If your lathe and set up is rigid then threads should be the same from start to finish. This is why machining students are tought in school to take multiple passes without changing the compound settings the closer one gets to the final pass.

Bob's Snake oil helps keep the the tool bit cutting the same throughout the pass.
Nat Lambeth
 
Jeff Walker said:
Same answer, different way of saying it.....

In this case, what you are seeing is the fact that the threads are not yet cut to the right size. They are close enough to get the action started on, but as you engage more threads, the lack of tolerances start to stack up against you.

Think of it as trying to run in water. The deeper you get the harder it is to run. Once you get deep enough, you ain't running anymore. If the water was the same depth ( say ankle deep ) the entire length of the run, the resistance would stay constant and you could make it to the end.

-------------Jeff
Click to expand...

Thanks Jeff. That is the kinda explanation my inexperienced head understands. Thank you for your input. Thank you to all that took the time to help me understand this.

As soon as I read Jeffs post, I immediately thought of the post regarding threading the old Sako. How some people are cutting the threads with a UN thread pitch, when I think it should be a mm thread pitch, with the UN pitch being close enough, but over a longer threading length there would be issues with the threads binding. Nice when the penny drops and you understand something.

In reply to Mr Sharret's question. Yes I watched videos on youtube as well as Gordy Gritters and Richard Franklins. If its about rifles I tend to watch it. That is when I have spare usage on my satellite Broadband. I live way up in the hills of the Scottish Borders. I pay £72 per month for 25 gige usage, shared with two computers. That £72 equated to roughly $110. A lot of money. It is the only option that is available to us. We are too far away from the exchange to get Broadband by telephone line. Worth every penny when you consider I can come onto a Forum and ask a silly question to you guys that are well schooled in this kinda thing, and get an answer pretty quick.

Cheers
 
Rustystud said:
Bob's Snake oil helps keep the tool bit cutting the same throughout the pass.
Nat Lambeth
Click to expand...

I have spoke with Mr pastor via email. very generous man. Just too far away for me to be able to buy his Snake oil. Maybe he could share the ingredient recipe with me and I could make my own here in Scotland. I would roll my left trouser leg up and put my hand on my heart and hell, I will even tell him the Goats name, If he were to do that. For personnel use only. Molly Dee is also not available here in the UK.

I thank you too Nat as I have also spoke with you via email. Thank you for the F-Class stock pictures that you emailed me.

My experience in this country that I live is that men with knowledge and experience in a given subject. are not willing to give information to someone like my self with a thirst for knowledge. they would rather take their secrets to their graves with them. It is very refreshing to come on Forums like this and have people that are at the top of the ladder in this given subject, take the time to actually share their knowledge with us novices. I have respect for each and every one of you.

Bt the way. Can I just point out that my name is not Ray and I sure ain't no Nerd. I like my Fox shooting as well as my Deer hunting. The male Red Fox is called Reynard. I think it is French. I have used this name for a long time on many Forums. I once pissed an American off on a gaming forum and he typed in to the chat box. ------Ray you are a Nerd for sure------, Made me laugh for a bit. I also, I am embarrassed to say, also had a Manlichter rifle and for one day I used a screen name Manlichter1. If you can not work out why I changed the name pretty darn quick, please do not ask.

Cheers
 
Since you cant get Snake oil or Moly Dee over there, can you get Tap-Magic or Dark Sulpher pipe cutting oil? I mix The dark oil with 10% Tap-Magic. If you want what the old toolmakers used, try Lard Oil. You can make it by melting lard and filtering thru a coffee filter, bacon grease works too, but the salt in it can cause rust issues.
 
MilGunsmith said:
Since you cant get Snake oil or Moly Dee over there, can you get Tap-Magic or Dark Sulpher pipe cutting oil? I mix The dark oil with 10% Tap-Magic. If you want what the old toolmakers used, try Lard Oil. You can make it by melting lard and filtering thru a coffee filter, bacon grease works too, but the salt in it can cause rust issues.
Click to expand...

Thank you Mr MilGunsmith. I appreciate the info that you have given. I just googled the Tap magic. MidwayUk sells it. Tap Magic Cutting Fluid with EP-Extra 4 oz. I am not sure what you guys can buy this for in the states but they want £9 for the tin which equates to roughly $13.50. Midway UK sells the mandrel that you use to square the action up in an action truing jig for more numerical value in £'S than $'s. I will check out the Dark sulphur oil to see if I can get that here. I use a Rocol product for threading, it is a thickish dark Oil. It is quite expensive as well.
Who said Scotsmen are tight. It said if a Scotsman dropped a Silver Dollar it would hit him on the back of the neck.

Interesting you mention Lard. As I actually made my own Mutton Lard last year. Was very easy to do and I used some of this Lard to make up a Leather rub that I used to rub on to Kangaroo leather before Braiding it. Worked a treat. I have also made my own Bacon, Dry Cured. Was delicious.
I Butcher my own Deer and make my own Sausages. Life is good.

Cheers
 
You must log in or register to reply here.
Back
Top