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Posted: 6/1/2010 3:13:39 PM EDT
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First time poster here. Thanks to all who make this forum what it is. The most impressive collection of information on a subject that I have seen anywhere on the net. Stop me if you've heard this before.
I dont own an AR-15 but I have jumped right into the middle of machining an 80% lower for myself. Some may think that is foolish, but I did not come here to announce myself a fool. Though my posts may support that theory at times. I am using a drill press for this project and have seen the ray vin tutorial and the cncmachining tutorial. I have the cnc jigs. The trouble is that my drill press doesnt have a good vertical depth gage and I have not been able to accurately mill the bottom of the fire control pocket or the shelf. The fire control pocket is about 1/16" too deep and the shelf is also about 1/16" too deep. On the shelf, I stopped machining when I realized my error and milled the remainder of the shelf bottom to spec so I have one 3/8" wide spot in it that is deeper than most of the shelf. Here are my questions... 1. Is the additional depth in the FCP a fatal flaw? What about the shelf? 2. Should I leave the shelf alone as it is or finish milling it to the deeper depth such that the bottom is uniform? 3. Can anyone recommend a good place to get a good aftermarket depth gage for the drill press that wont cost an arm and a leg? I have looked at enco but cant seem to find one which is discouraging since they seem to have everything else. Thanks in advance for the help. Bubba |
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Well, let's see how many different opinions you get. Here's one.
The excessive cutting in the trigger area will weaken it, but I think you'll be able to make it work. If you still have the forging seam flash on the exterior trigger area, I would leave that for the remaining strength it will provide. I wouldn't remove more metal just to make the error less obvious. The error in the shelf area won't hurt a semi. It may for an auto rifle, but I'd defer to somebody that knows autos for the definitive word there. I'd go ahead and beautify the shelf since there is still plenty of metal in that area. You may have to get creative for vertical travel measurement. You can often find a way to use a dial indicator and mag base to follow a homemade arm attached to the quill somehow. Another way is to use a stop or collar to set the depth before you cut. This is pretty common with a drill, but I'm really not sure about doing it with an end mill. If you would post photos of your drill press or a link to a photo elsewhere, people will probably see ways to help you rig something up. Welcome to another learning experience. |
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The shelf depth being .060 of so too deep will affect nothing but maybe a DIAS. The pocket being milled .060 or so will affect nothing but maybe structual integrity to the degree of not even worth thinking about it. Milling flat to your deepest depth is really a waste of time since you will not see it.
I go over the spec to 1.260 in the fire control pocket. Can't help you on the Drill press question but I have a little progress guide you might find usefull. http://www.ar15.com/forums/topic.html?b=3&f=4&t=498268 |
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Thanks for the help. It's encouraging that it seems the extra depth wont be a problem.
I still cant find an aftermarket depth gage for the drill press. I am having a hard time believing that they arent out there. I used a stop collar on the 3/8" milling bit, but the collar wasnt the roght size. Perhaps if I get a correctly sized collar, I will have better results. If anyone else has any ideas on the depth gage issue, please keep them coming. Thanks. |
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Properly sized stop collar, initially set shallow. Drill 1st hole, measure, adjust stop collar a small amount. Repeat until you get the depth you want and then lock the collar down hard for the rest.
For the low spot, there's always Devcon Liquid Aluminum - pricey, but effective |
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Thanks all for the input.
I wanted to update on my solution for my drill pres depth gage. I bought a $20 set of 6" calipers with digital read out from harbor freight. The $10 set was plastic so I opted for the steel set. In hindsight, I may have been better off with the plastic. The plan was to mount the calipers to the drill press and use it as a depth scale. Not sure if I mentioned it previously, but my drill press has a dial type depth indicator. Looking back, I should have kept shopping for a drill press with a rod depth indicator and stop system. Anyway, I figured out that if I mounted a piece of angle to the round drill press quill just above the chuck and shimmed it out, I could establish a plane along he front of the machine and then attach each side of the caliper to the frame and the quill and have a digital depth gage. Seemed simple enough. First I had to cut the tail off the calipers o it would fit under the belt housing. Probaly should have bought 4" calipers instead. But after cutting, the calipers still had enough travel to exceed that of the drill which was good. I drilled and tapped a hole in the drill press qull and mounted the angle. I then attempted to drill the steel of the calipers. The steel was too hard for me to drill. I then mixed up some JB weld and fastened the calipers to the drill press. I couldnt get a clamp to work very well so I used a magnet to hold the calipers in place while the epoxy cured. The magnet worked very well. I havent drilled with it yet, but it seems like I am set. I will brobably still need to use a stop collar but at least with the digital calipers, I can see if the depth adjustment gets loose and then I can tighten it up. |
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I used my calipers with the drill bit in my press and then used a black marker to draw a line on the bit and drilled to that depth, I'm sure it's not perfect but close enough for an AR.
You could also put tape on the drill bit to mark it again it's not that critical. |
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