Can someone explain jig incompatibility to me?

[Whiterabbit]

Hi guys,

the 80% jigs seem to come with a disclaimer. Works with this 80, not that 80, make sure your 80 is the kind this jig works with...Our jigs work with billets, ours work with forged, dont use our jig with forged lowers, not compatible, etc etc etc...

What's the deal? milspec is milspec, right? Well, wrong, obviously.

Where do the jigs hang up on? why is there no "universal" jig (for aluminum lowers). Are lower makers arbitrarily beefing up the outside of their lowers, making the jigs not fit?

[umd]

Billets are not "milspec", they all have different external shapes and protrusions so they aren't compatible. This jig I have is supposed to be somewhat universal; so far I have used it on 3 different lowers.

[Whiterabbit]

so why cant I just dril holes or mill grooves where there are protrusions and make any jig "universal"? can the protrusions interfere with the datum points on other lowers?

Also, what jig do you have?

[ke6guj]

What's the deal? milspec is milspec, right? Well, wrong, obviously.

billet lowers aren't milspec

Where do the jigs hang up on? why is there no "universal" jig (for aluminum lowers). Are lower makers arbitrarily beefing up the outside of their lowers, making the jigs not fit?

yup, many of the different billlet manufacturers do their own custom external dimensions to make them stand out from everyone else. as such, the matching cut-outs from one jig might not line up with that extra material on another brand lower.

but you can often re-machine the jig to clearance those issues on your mill.

[ke6guj]

so why cant I just dril holes or mill grooves where there are protrusions and make any jig "universal"?

you often can.

can the protrusions interfere with the datum points on other lowers?

yup, mill too much clearance for one lower and it might not work properly with a forged lower anymore because it isn't properly supported.

if you are going to mill out a ton of different lowers, you might end up with 2-3 different sets of jigs in the end. big deal, a couple hundred bucks extra in tooling. if you are going to only be dealing with one or two brands, just buy the proper jig from the manufacturer.

[Whiterabbit]

that would be easy enough, assuming it doesnt make the jig not work with other lowers.

I was looking at the Ares Armor kit, they say the jig works with billet only, not forged.

[umd]

Also, what jig do you have?

http://www.elementalarms.com/products/blue-jig

The Original Blue Jig is back and now better than ever. Redesigned to be used with many of the popular forged and billet 80% AR-15's on the market.

[Mellon]

Universal jig? Maybe this?

http://www.desertwarriorproducts.com/ar-15-80-percent-lower-adjustable-universal-jig-kit

No experience with it. Happened to run across it today when I was checking out DWP.

[BroncoBob]

Universal jigs do not always fit.