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Eye Master
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Discussion Starter · #1 ·
So we were shooting the bull on another thread about gritty triggers, and I had a thought:

You can stone your triggers and hammers for smoothness, but getting two mating surfaces to be smooth on each other is best done by exactly getting those surfaces to ride against each other, in the exact orientation that they will see in operation, and let the surfaces polish each other.

This is why a well worn WWII rifle will have a butter smooth trigger, while a new trigger feels gritty.

So can we hurry this up? If we put lapping compound on the sear surfaces of a trigger/hammer, would they polish themselves faster/nicer. I'm wondering if I could put together a kit with 4 or 5 different grits of lapping paste, starting with maybe 400, then 600, 1,000, 1,800, and 2,400, you could put in a drop, cycle the trigger 50 times, clean it out, go to the next finer lap, repeat, etc. You could take a new trigger that feels a little gritty, and with an hour of effort, and not even needing to disassemble the trigger group, end up with something butter smooth.

Anyone up to try it? Send me an email and I'll send you a kit.

I don't take any responsibility for outcome, though the good news is that unless you are starting with a setup where someone has shortened the hooks, you are very unlikely to ruin anything. We are talking here about taking off enough to polish a surface, not enough to change dimensions.

Thoughts?
 

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I'm in

pg
USA2
 

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If you feel roughness in the 2nd stage pull, that probably means there is a lot of 2nd stage 'creep'. Reducing the amount of 2nd stage creep would give better trigger action than 'smoothing the creep'.

Jay Kosta
Endwell NY USA
 

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You can stone your triggers and hammers for smoothness, but getting two mating surfaces to be smooth on each other is best done by exactly getting those surfaces to ride against each other, in the exact orientation that they will see in operation, and let the surfaces polish each other.
Thoughts?
If your lapping enough to make any discernible difference, how could you possibly retain a sharp edge? Just spend $5 and buy a stone.
 

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What if the lapping compound and the removed metal, migrates into something in the trigger group that you would rather not have the removed material in?

You would need to flush the trigger group several times during the process to prevent the above.
 

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Eye Master
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Discussion Starter · #7 ·
Based on my examination with measuring microscopes, match triggers typically wear to about a 0.001" or 0.0015" radius tip. I recommend a trigger be set up with 0.005" of sear overlap at the second stage.

Lapping compound has grit that is way smaller than that. 800 grit uses abrasive that is 0.0004" in diameter, so 1/4 of the size of the tip radius in a match trigger.

Net, I do not think the material removed by lapping is even in the same ballpark as the amount of material you need to remove to affect performance.

As to where the stuff goes - you are correct. You want to clean this stuff out, lest it remains and wears out over time. Luckily, we are talking about applying really tiny amounts, but still, after each session, you need to take q-tips and solvent and clean out all the grit from the last operation before applying smaller grit. So I don't think this solution will make this task much easier, but I think it will give a better solution if done right. Nice thing about the M1/M14 trigger design is that I think you can clean out the grit without disassembling the trigger, so it won't be horrible. With an AR, you need to pull the components.
 

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Eye Master
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Discussion Starter · #10 ·
Thanks to everyone who replied. Here's an update:

I'm putting this experiment on hold until/unless I figure out a better way to do it. It's not as easy as just putting lapping paste in between the parts.

We spent 2 days in the shop trying this on usgi AR triggers.

Yes, the lapping got rid of grittiness, but it also made the sears feel 'sticky'. Keeping in mind that the top edge of an AR trigger is a sharp edge, and the sear design of an AR has that edge highly loaded, the pressure between the tip of the trigger and the hammer sear is enormous. I don't know if the pressure is crushing the grit, or if it is embedding the grit into the steel (that's what it almost feels like).

To me the telling experiment was that I have some ultra soft rubber wheels for my Dremel that have 600 grit mixed in with the rubber. If I just barely touched the surfaces that I had lapped, wow! they went from a satin look to a mirror polish, and boy were those triggers smooth. When I then put 3000 grit lapping compound, which is ultra fine, in between them, the mirror shine went away, and they felt sticky again.

In thinking about it, to get a mirror shine on something, you use jewler's rouge on a felt bob. The felt conforms to the surface, so it keeps the pressure way low.

Anyhow, we'll continue to play with it, and if I have any breakthroughs, I'll post them, but on the surface it looks like my idea of just putting lapping paste on the sear surfaces was not my best.
 

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Thanks to everyone who replied. Here's an update:

I'm putting this experiment on hold until/unless I figure out a better way to do it. It's not as easy as just putting lapping paste in between the parts.

We spent 2 days in the shop trying this on usgi AR triggers.

Yes, the lapping got rid of grittiness, but it also made the sears feel 'sticky'. Keeping in mind that the top edge of an AR trigger is a sharp edge, and the sear design of an AR has that edge highly loaded, the pressure between the tip of the trigger and the hammer sear is enormous. I don't know if the pressure is crushing the grit, or if it is embedding the grit into the steel (that's what it almost feels like).

To me the telling experiment was that I have some ultra soft rubber wheels for my Dremel that have 600 grit mixed in with the rubber. If I just barely touched the surfaces that I had lapped, wow! they went from a satin look to a mirror polish, and boy were those triggers smooth. When I then put 3000 grit lapping compound, which is ultra fine, in between them, the mirror shine went away, and they felt sticky again.

In thinking about it, to get a mirror shine on something, you use jewler's rouge on a felt bob. The felt conforms to the surface, so it keeps the pressure way low.

Anyhow, we'll continue to play with it, and if I have any breakthroughs, I'll post them, but on the surface it looks like my idea of just putting lapping paste on the sear surfaces was not my best.
Lapping is embedding the abrasive in something "soft" (sacrificial). With what you are doing, neither piece is sacrificial though you may be embedding the abrasive in both pieces. You want something soft enough to absorb some of the abrasive, leaving enough "tooth" above the surface to cut, yet strong enough to move the "teeth" across the steel. That material may be as simple as a piece of paper "charged" with the grit you want. Wetted if dry paper is too stiff. "Wetted" may be with water ,oil, etc such that while flexible, the paper still retains some tensile strength.

Totally quick and dirty is wetted and folded (Abrasive facing out on both sides) wet/dry auto body paper which I have found up to 2000 grit and have seen 3000 grit used to polish fiber optic ends.
 
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