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Adventures in Hardware Store CNC

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--- Quote from: unfy on April 15, 2016, 11:50:07 PM ---Brass work.

See, depending on what's done... I'm not entirely sure if it'd be as difficult as you suggest. 
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Where I work, I operate a Hurco CNC mill. The machine will move the table to .0001".  Getting a part to repeat in a holding system is the difficult part. Usually you just let the machine whittle away some extra material not needed in the part. My experience in brass is that it is not very precise. Trying to set up a thin wall "tube" that is not especially precise in a repeatable fixture would be tedious. The machine doesn't care about the part, it just cuts where the computer runs the table and spindle height. All the hand brass tools I have float on the case mouth and just follow regardless of variations (to a usable degree). Even with my .300BLK cases made from .223 a Lee Deluxe case trimmer takes about 2 seconds to load in the press and five or so turns of the handle to knock off .030" of excess length I leave from cutting the .223 neck off the case and maybe some growth from the reform. The trimmer also chamfers inside and outside with floating cutters. Think it was a $25 tool that just drops in the Lee press (breech lock system).


--- Quote from: unfy on April 15, 2016, 11:50:07 PM ---Length milling - that might be more of a concern.  Do you index off the case head such as the bench mount case trimmers ?  Or do you index off of a rod that sticks into the case mouth for length against the primer pocket / webbing area (some hand held tools) ?
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I will offer that the case head is a fixed surface. A rod type cutter I have for .308WIN has a pin on the end of the rod that bottoms on the clamping head surface. A stop for the cutter. For CNC it just means you would set the tool touch off on that pin end and cut to zero (or any offset that gets your needed case length until the pin touches something to stop it.

I will offer that brass is an odd metal to machine. Standard drills and cutters are not of correct geometry for brass. The grand effect is often that a standard tool will bite into brass and just pull its way thru the material...generally a non-desirable result. Usually the bit will pull the part of its fixture if the tool gets too much of a bite. Shallower cutting angles work better for brass or very slow/light cutting.

In CNC the machine just does what you tell it to do. There is no regard for flex, backlash, fixture or part movement or any other movement in the system. The heavier the cut or faster the cut, the harder the material the more flex involved and power required.


But, playing with low cost machines is fun and definitely educational. Cutting soft materials and drilling things like pcb holes doesn't take much more than a Dremel motor mounted in a MDF wood machine.  Plasma/laser is easy since the tool doesn't have any pressure on it. 

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