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Discussion Starter · #1 ·
Modulus jig review.

This is not intended to be a tutorial, Modulus already has some excellent videos on their website that walk you right through each step. This is just an overview of my experience using their product. Keep in mind that I'm not a machinist by trade but I've made some chips in my time.

Continued from this thread. http://www.gunco.net/forums/202-gun...modulus-arms-only-need-common-hand-tools.html
 

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80% blank I will be using for this review along with another one that I recently finished using my mini mill. Instructions downloaded from Modulus' website. Bosch PR20EVSK router. (model recommended by Modulus)


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The Modulus jig indexes off of the receiver extension (buffer) tube mount and the front pivot pin bosses. The cnc gunsmithing jig locates off of the same pivot pin boss in the front and the take down pin hole in the rear.
This is a big deal on all but the latest version of 80% blanks. Previously you had to break down your set up halfway through in order to remove the alignment pin from the take down hole in order to machine out the rear shelf. This is not an issue with the Modulus jig.

I didn't waste time documenting the jig assembly simply because Modulus has an excellent video on their site that covers that step.

Pics 1 & 2 show the jig with the drill guide and side plates installed. pic 3 is template only. The swarf will be a flyin' tomorrow

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Discussion Starter · #7 ·
One of the really nice features that is included with the jig is this handy drill/mill depth gauge. It is marked in 1/4" increments, which is the maximum depth Modulus recommends per cut. I found I got much better results when going only about 1/3 of that. (roughly .083) Taking a 1/4 cut made the endmill try to walk out of the collet.

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Jig set up to mill trigger slot

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Trigger slot finished

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The end mill can pull down if you take a pretty deep depth of cut. The mathematics behind the actual removal of material show that it acts like a screw and can try to pull out, especially if you are roughneck with the router. You should clean the end mill and collet when you install it and it should be fine if you crank it down good and tight. Like he mentioned there is no plunge milling with the end mill. You always enter into a full depth hole.

I am glad its going well for you. Its a pretty easy deal once you read the instructions.

We have a deal on the site right now for 199 for the Jig and a lower. Its a great deal for anyone interested.
 

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OK time to finish it off.

Jig set up to drill axis pin holes.

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Just as a side note. When I got into doing these AR lowers I picked up this 5/32" drill-reamer combo. It delivers dead nuts holes. (IIRC I got it from MSC @$40)

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Here it is in all it's glory.

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