I've heard from a friend that he's planning using a drill press like a milling machine to finish some 80% completed AR-15 rifle recievers.
I thought it was an interesting proposition, but I'm not a metal guru. We spent a while looking around town for a flat bit that would work for this rather than a normal drill bit... what do you guys think? Is it possible? if so, what type of bit and where would we get it? Also, does anyone make a jig that could hold the piece while we 'machine' it?
Jason, trying to mill with a drill press will be a total failure and probably mess up receivers and cutting tools. You don't describe the nature of the milling cuts your friend hopes to do, but virtually all milling cuts apply significant side loads on the cutter and spindle. As stated above, drill press spindles are simply not rigid enough to make such cuts without deflection and chatter. Additionally, drill press chucks, by their very nature and operating mechanism will release their grip on a milling cutter subjected to cyclic side loading that reverses each revolution, no matter how tight you tighten them.
Depending upon the type of cuts he wants to make, you might consider a table-top mill-drill with an X-Y table. The spindle will be a little stiffer than on a drill press and the collet-type cutter holder can sustain milling side loads and hold on with precision.
Oh, yeah. For starters, go to the websites for Enco, Rutland Tool, Airgas, KBC Tools. Browse their catalogs. See if there is a store nearby that you can visit and get advice from. (Not all counter poeple are knowledgable about machining, but some are. Give it a try.)
Check out a starting machining course in your local community college.
Visit your local independent used book stores. While used books on machining are relatively rare (compared to the flood of books on woodworking), I have found some really useful books on machine shop practice.
Ask your friend if he's ready to buy a new drill press 'cause he's about to need one.
Drill presses are NOT designed for the side loading that milling requires - drill press stresses are strictly vertical and NOT horizontal.
FWIW, I have a drill press that, after part replacement, cost me about $200 - the drill press was a freebie - after it was used in just this way. (It might have been cheaper to have simply bought a brand new one.)
This reminds me of the guy who was going to solder together an electronics project. His first project was to be a music synthesizer. I told him to start with a battery, switch, and light bulb.
I got a mill 5 years ago. Two guys who operated mills for many years for a living came over and watched me try to square up a block. When they did it, there was .001" of run out. When I did it, there was .010" of run out. I am glad I did not start out on an AR15 lower.
The spindle will be a whole lot stiffer than on a drill press. The much-maligned mill drill is a milling machine in every respect. They aren't as versitile as knee mills but for the price you get a real mill. They also make great drill presses with adjustable tables for precise hole location.
There's a lot more to milling than just having the equipment. A receiver for a rifle is the last place to start learning, even if you have a good machine.
I hate to put it this way, but, there may be a reason why the receivers are only 80 percent done. They may be rejects already.
Other posters have commented about side loads, etc., but there is also a potential problem with the end mill (the "flat" drill bit) pulling itself out of the chuck. This can be an insidious process, not noticed until the end of the cut, for instance. I once did some light milling with my drill press, cutting a couple of 1/8" wide, 1/8" deep grooves about 2" long. I got away with it, but probably due to the small diameter (1/8") end mill that I used.
X-Y table problems. I assume that your drill press has an X-Y table or you wouldn't even be asking this question. But, it you have one of the inexpensive tables from, for instance Harbor Freight, they have a lot play in their slides. If this isn't accounted for properly, you will find your cutter (end mill) digging in to the workpiece deeper than you want. It takes experience to deal with this problem.
Take comfort in the fact that you can legally bugger any guy you want up the ass, even though you can't cut certain shapes of metal. Makes perfect sense to me.
I called my local suburban police when I was thinking of building a black rifle. I asked if machining a lower was legal. He asked if I was planing on shooting it in the city, I said "no", he said: "Then, why would we care?" But, here in Ohio, we can't marry our but-buddies...yet.
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