Hello,
I'm wondering if anyone else has lapped their locking lugs, and what difference did you notice?
Thank you,
Josh
I'm wondering if anyone else has lapped their locking lugs, and what difference did you notice?
Thank you,
Josh
Gunsmithing Lapping Lugs?
- Thread starter Josh Smith
- Start date
Re: Lapping Lugs?
Lapping ensures a full mating surface. But use caution.....if you lap too much you will alter the head space. Before you do anything, though, look at the locking lugs on tehbolt to see what kind of contact you have.
Lapping ensures a full mating surface. But use caution.....if you lap too much you will alter the head space. Before you do anything, though, look at the locking lugs on tehbolt to see what kind of contact you have.
Re: Lapping Lugs?
Unless your lapping with reclaimed asphalt I seriously doubt your going to alter H/S.
If you do your one patient individual who's destined for greatness in the afterlife.
It's an inspection method to verify surface contact and little more.
Unless your lapping with reclaimed asphalt I seriously doubt your going to alter H/S.
If you do your one patient individual who's destined for greatness in the afterlife.
It's an inspection method to verify surface contact and little more.
Re: Lapping Lugs?
Maybe if you clean your action with clover compound.
To lap something it takes an abrasive. Whether its fine or coarse matters little. That becomes a function of surface finish.
it's likely over time that lugs will burnish a bit but that's about it.
In odd cases they will peen back some and this will alter the H/S. This is most common with actions chambered in boomer type cartridges (think African dangerous game stuff) and/or actions where the lug surface area leaves a bit to be desired and/or soft receivers/bolts.
Through experience we've learned that receivers and bolts cannot be of the same hardness. If they are it'll almost surely chew itself to bits. The "safe" number seems to be around 3-5 points of difference on the Rockwell C scale. (which is just one of many hardness standards uses, Brinnel is another common one used for many SS)
The general practice is to make the bolt a touch softer than the receiver.
Heat treatment does two things for us. It increases the tensile strength of the material (makes it stronger) and it increases the hardness (making it tougher and more lubrice)
It can be too much of a good thing however. Go overboard and the material becomes brittle and prone to fracture.
In the old days actions were case hardened. Think M&M candy. Hard shell with a softer center. The hard shell tolerates the impact and provides a slick surface. The soft center allows the material to give a bit and absorb the shock loading. Works well enough but it can distort/warp parts very easily. It can be a real biche when working with "cased" falling block type actions as the two sides want to either clam up or bellmouth; making the fitting of the block and trigger components a real mother. . . Another downfall is ensuring a uniform "soak" so that the carbon layer (which is what makes the steel harder/tougher) is even throughout the part. Go too far however and you have an egg shell. Again it'll be prone to fracture.
Modern steels allow for complete heat treatment (alters the hardness/tensile strength of the part everywhere) makes for a stronger material.
Some manufacturers (Defiance for instance) has solved the challenge by using heat treated/normalized materials to start with. Rather than start with "soft" material and heat treat later they go right to the hard stuff from the beginning. Steels generally machine very well (especially stainless) when heat treated prior. The "rub" is you must have good tooling and robust equipment. If you plan accordingly its probably the best way to machine an action. Especially when its been normalized as it will be much, much less likely to move around (stress relieve) during machining. One thing in particular about this I like is the receiver ring is less likely to bell mouth. On some actions I've noticed that the thread pitch diameter is looser at the ring and tighter at the bottom near the lug abutments. I'd bet a buck they are heat treated after machining. With prehard stock you would be much less likely to see this.
FWIW this is one advantage with a turning center as it will allow you to turn tapered threads with little drama. Just put an "R+/-" value in your threading canned cycle code and the tool will either plunge/retract in X as it cuts the thread in Z. Simple stuff that gets on with resolving a problem many don't even know exist! The "right" answer of course is to work the receiver threads over but some just want the barrel put on. It can be a little disenchanting though when its a custom action (it happens) that needs the work.
Another way to peel skin from kitty's.
Essentially a stable piece of material is one that won't twist up after being machined. Quite a few materials are full of "indigestion" after heat treatment. If you do it first, then normalize, it's "dead to the world" and will be less likely to move around.
Maybe if you clean your action with clover compound.
To lap something it takes an abrasive. Whether its fine or coarse matters little. That becomes a function of surface finish.
it's likely over time that lugs will burnish a bit but that's about it.
In odd cases they will peen back some and this will alter the H/S. This is most common with actions chambered in boomer type cartridges (think African dangerous game stuff) and/or actions where the lug surface area leaves a bit to be desired and/or soft receivers/bolts.
Through experience we've learned that receivers and bolts cannot be of the same hardness. If they are it'll almost surely chew itself to bits. The "safe" number seems to be around 3-5 points of difference on the Rockwell C scale. (which is just one of many hardness standards uses, Brinnel is another common one used for many SS)
The general practice is to make the bolt a touch softer than the receiver.
Heat treatment does two things for us. It increases the tensile strength of the material (makes it stronger) and it increases the hardness (making it tougher and more lubrice)
It can be too much of a good thing however. Go overboard and the material becomes brittle and prone to fracture.
In the old days actions were case hardened. Think M&M candy. Hard shell with a softer center. The hard shell tolerates the impact and provides a slick surface. The soft center allows the material to give a bit and absorb the shock loading. Works well enough but it can distort/warp parts very easily. It can be a real biche when working with "cased" falling block type actions as the two sides want to either clam up or bellmouth; making the fitting of the block and trigger components a real mother. . . Another downfall is ensuring a uniform "soak" so that the carbon layer (which is what makes the steel harder/tougher) is even throughout the part. Go too far however and you have an egg shell. Again it'll be prone to fracture.
Modern steels allow for complete heat treatment (alters the hardness/tensile strength of the part everywhere) makes for a stronger material.
Some manufacturers (Defiance for instance) has solved the challenge by using heat treated/normalized materials to start with. Rather than start with "soft" material and heat treat later they go right to the hard stuff from the beginning. Steels generally machine very well (especially stainless) when heat treated prior. The "rub" is you must have good tooling and robust equipment. If you plan accordingly its probably the best way to machine an action. Especially when its been normalized as it will be much, much less likely to move around (stress relieve) during machining. One thing in particular about this I like is the receiver ring is less likely to bell mouth. On some actions I've noticed that the thread pitch diameter is looser at the ring and tighter at the bottom near the lug abutments. I'd bet a buck they are heat treated after machining. With prehard stock you would be much less likely to see this.
FWIW this is one advantage with a turning center as it will allow you to turn tapered threads with little drama. Just put an "R+/-" value in your threading canned cycle code and the tool will either plunge/retract in X as it cuts the thread in Z. Simple stuff that gets on with resolving a problem many don't even know exist! The "right" answer of course is to work the receiver threads over but some just want the barrel put on. It can be a little disenchanting though when its a custom action (it happens) that needs the work.
Another way to peel skin from kitty's.
Essentially a stable piece of material is one that won't twist up after being machined. Quite a few materials are full of "indigestion" after heat treatment. If you do it first, then normalize, it's "dead to the world" and will be less likely to move around.
Re: Lapping Lugs?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: C. Dixon</div><div class="ubbcode-body">Unless your lapping with reclaimed asphalt I seriously doubt your going to alter H/S.
If you do your one patient individual who's destined for greatness in the afterlife.
It's an inspection method to verify surface contact and little more.
</div></div>
Well stated. One can get faster results by using a more aggressive valve lapping compound avail at the auto parts store, but be aware that this stuff will gunk raceways and lug areas so even after cleaning, some grittyness will still be evident.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: C. Dixon</div><div class="ubbcode-body">Unless your lapping with reclaimed asphalt I seriously doubt your going to alter H/S.
If you do your one patient individual who's destined for greatness in the afterlife.
It's an inspection method to verify surface contact and little more.
</div></div>
Well stated. One can get faster results by using a more aggressive valve lapping compound avail at the auto parts store, but be aware that this stuff will gunk raceways and lug areas so even after cleaning, some grittyness will still be evident.
Re: Lapping Lugs?
what is optimum contact with the lugs? my gunsmith lapped my bolt when blueprinting it and told me there is now approx 94% contact on my action.
what is optimum contact with the lugs? my gunsmith lapped my bolt when blueprinting it and told me there is now approx 94% contact on my action.
Re: Lapping Lugs?
Thats optimum
Thats optimum
Re: Lapping Lugs?
Hi Dixon
Thanks for the explanation I had some reservations about lapping lugs and head space as I had to touch up mine on a new action. To me it seemed like I had a high spot which caused some galling even with appropriate lube (My belief), once I stoned them the lugs had greater surface contact and this appears to have corrected the problem.
Trevor
Hi Dixon
Thanks for the explanation I had some reservations about lapping lugs and head space as I had to touch up mine on a new action. To me it seemed like I had a high spot which caused some galling even with appropriate lube (My belief), once I stoned them the lugs had greater surface contact and this appears to have corrected the problem.
Trevor
Re: Lapping Lugs?
I have lapped the lugs on my custom Arisaka. Under the watchful eye of my local smith and friend. He was very clear in letting me know that you can go to far lapping lugs. He said that some lugs are harden on the surface or just barely into the lug. He told me that he has had more then one bolt that has been ruined by people trying to lap it and gone to far into the "Soft metal"
I have lapped the lugs on my custom Arisaka. Under the watchful eye of my local smith and friend. He was very clear in letting me know that you can go to far lapping lugs. He said that some lugs are harden on the surface or just barely into the lug. He told me that he has had more then one bolt that has been ruined by people trying to lap it and gone to far into the "Soft metal"
Re: Lapping Lugs?
have a need to lap the lugs.......which must be done with the barrel off the action
if you see the action making brass, then a lap job may be in order.....otherwise all that mechanical masturbation may be for naught.
have a need to lap the lugs.......which must be done with the barrel off the action
if you see the action making brass, then a lap job may be in order.....otherwise all that mechanical masturbation may be for naught.
