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Author Topic: Easy Jig method change to improve the finished lower  (Read 14839 times)

Jefe

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Easy Jig method change to improve the finished lower
« on: October 19, 2014, 01:13:40 PM »

Here are two possible changes you may want to make when using the Easy Jig. The first may make the finish on your trigger slot cleaner (less ragged) and the second can be of benefit for those not comfortable with the "hover and plunge" method of finishing the final router passes.

The first change deals strictly with the finish of the trigger slot but it also feeds into the second change. Often the trigger slot will have a somewhat ragged cut. I believe this is because the end mill is relatively long and the cutting surface is very far from the base of rotation (the router). This causes the end mill to vibrate which results in chatter marks when cutting the trigger slot. While this is really a minor matter, since the slot is never really seen and has no affect on function, some may prefer a cleaner cut if possible. We can accomplish this by creating a base of support for the end mill. We do this by cutting a full-length trigger slot from the top of the fire control group pocket to the bottom. Normally this is one of the last operations we do when using the Easy Jig but there is no reason we can't make it the first thing.

Begin by attaching the (REAR) jig template with the round trigger hole to the jig just as you would normally. That means the trigger hole is closer to the receiver extension (buffer tube) hole. Using the 19/64" bit drill completely through the fire control group pocket and through the bottom of the receiver. Be careful you do not drill into any integral trigger guard the receiver may have. The first two pictures below are from the original procedure which is why the fire control group pocket is already drilled. The jig setup is the same though.



Then remove the template and install the (MAIN) jig template and spacer in order to mill out the trigger slot.



Note that I have also started the 3/8" holes which I will use as a starter when pre-drilling with a 1/4" drill bit.



Just like when milling the fire control group pocket it is a good idea to add some tape to the inner perimeter of the template to make it easier to see in low light. This is not necessary if you have the shorter cutting length end mill but for the full-length end mill this is a good idea. I used a brass guide this time and that keeps the end mill from touching the jig template. I like this change but I also want to point out that when you are milling the fire control group pocket you will eventually have to take the guide off because it interferes with the maximum cutting depth. This isn't an issue because the end mill cutters will have cleared the template by that time.



Now start the end mill over the hole you just drilled and mill the entire depth of the fire control group pocket in incremental steps until the trigger slot is complete. You will not be able to use the depth gauge for this milling because the gauge is on the underside of the template. Just start by bottoming out the end mill on the top of the receiver and then make incremental cuts from there. You'll want to make the cuts in about 1/8" cutting increments. The full length slot you have milled will limit the amount of movement the end mill can move past the template which will give less chatter and a smoother edge.



After that is complete you can return to the normal Easy Jig procedure of drilling and milling out the fire control group pocket and rear takedown pin pocket. I decided to try another modification and that is to pre-drill the 3/8" fire control group pocket holes with a 1/4" drill bit. The theory here is that by removing this material it will make the final drilling with the 3/8" drill bit easier. Since I have a relatively small drill press this sounded like a good idea, especially in 7075 aluminum. Here's what that looked like.



I have to say it didn't really help. The drill press still jammed up when drilling. I don't know if my drill press is getting worn and losing power or if the motor was just hot. Even though I was able to make it work I am seriously considering getting a full size drill press. What did help was to drill down as far as I could with the 3/8" bit and then use the router to mill the pocket until that depth was reached. Then I switched back and again drilled as far as I could with the 3/8" bit. And so on until I neared the bottom of the receiver and then proceeded to the final modification tried today.

As you approach the bottom of the drilled holes, which have a coned bottom due to the drill shape, do not hover the router above the holes and then slowly lower the router down. Instead start the router bit over the trigger slot which has already been milled. This negates the need to hover and lower the router into the coned bottom. Just start the bit over the trigger slot, which has no "bottom", and then work your way out from there.

This second change was proposed by forum member number6mbw and I think it is a good idea, especially for inexperienced router users. His method only differed in that regard and he did not start the process by milling out a full-length hole. Instead he followed the normal steps until he neared the bottom of the drilled holes. Then he moved the position of the REAR trigger template, drilled out the 19/64" trigger hole and then switched to the MAIN template and spacer to mill out the trigger slot. After that slot was complete he switched back to the REAR template and spacer to finish milling out the fire control group pocket starting the end mill over the trigger slot.

The second change can work with or without the first change but if you do the first you can do the second with no additional steps or jig changes needed.
« Last Edit: January 21, 2016, 09:55:49 AM by Jefe »
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number6mbw

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Re: Easy Jig method change to improve the finished lower
« Reply #1 on: October 21, 2014, 08:40:05 PM »

Have you had a chance to use this method? Curious as my trigger slot is just a little burred.
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nickstone

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Re: Easy Jig method change to improve the finished lower
« Reply #2 on: October 22, 2014, 12:56:05 PM »

This is the recommended method by Modulus Arms using their jig.  Their jig and instructions state this is the way to do it to produce a cleaner trigger hole.
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number6mbw

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Re: Easy Jig method change to improve the finished lower
« Reply #3 on: October 22, 2014, 11:32:51 PM »

Have you tried adjusting the belts on the press for more torque? I'm using a small harbor freight drill press, and while I haven't done a 7075, it easily drills the 6061.
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Jefe

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Re: Easy Jig method change to improve the finished lower
« Reply #4 on: October 23, 2014, 07:58:40 AM »

Have you tried adjusting the belts on the press for more torque? I'm using a small harbor freight drill press, and while I haven't done a 7075, it easily drills the 6061.

Yes, all of the way down to 620 rpm. 7075 is much tougher to get through than 6061. The first lower I did was a 6061 80% Arms and I didn't even have to change the drill press belts down. 7075 will really show you the limitations of your equipment.
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DEW_0341

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Re: Easy Jig method change to improve the finished lower
« Reply #5 on: May 28, 2015, 11:39:43 PM »

Just to be sure I understand this you start with the prescribed depth of cut for your final 2-3 passes with the router( where you would plunnge cut to start) and just start with those depths of cut in the trigger hold and move into the material from there?
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Jefe

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Re: Easy Jig method change to improve the finished lower
« Reply #6 on: May 29, 2015, 11:29:21 AM »

Just to be sure I understand this you start with the prescribed depth of cut for your final 2-3 passes with the router( where you would plunnge cut to start) and just start with those depths of cut in the trigger hold and move into the material from there?

That's correct. The same amount of cutting depth but start above the previously machined trigger slot.
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DEW_0341

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Re: Easy Jig method change to improve the finished lower
« Reply #7 on: May 29, 2015, 12:01:35 PM »

Ok awesome, I start my first lower today! Using 80%arms easy jig and ares armor 7075 forged raw lower
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