Monday, October 17, 2016

Cutting Metal, Test-Fitting Pieces

Time for my (roughly) weekly update on my major project of converting my Grizzly G0704 to CNC control.  This week, I finished all of the metal for the controller box except one piece; the front panel, which I should be able to do tomorrow.  Last week, I showed the back panel with one of the two rectangular cutouts that need to be made.  After that post, I made the other cutout and drilled out the back panel holes for the fan.  It's slow going because this piece is 16" wide, and my Sherline/A2ZCNC system doesn't really travel 16".  I was going to reference everything off the top right corner, but the mill wasn't able to get there.  With this orientation, I could get the last features cut, but to get everything cut I had to use three different orientations: one for the DB-9s, the second for the narrow rectangle, and the last for the fan holes and the bigger rectangle.
This is it, completed, upside down from the position on the panel, but otherwise WYSIWYG.  There's an OOPS on the top rectangular cutout.  That cutout gets the AC input block that was the late addition to the design.  It's bottom, just left of center in this test fit. 
Next up to be made was the mounting bracket to hold the breakout board in position (in that long, narrow cutout on the right, above).   The bracket is just a piece of 1/8" aluminum with a total of six holes drilled in it.  The holes had to be in the right places, but it was the easiest piece I've made in this project.  The bracket, in turn, is screwed to a 2.5 x 1" block of 3/8" aluminum; tapped 6-32 in two places to mount to the bracket and in two places to be fastened to the bottom plate.  This test fit photo shows that hardware on the left, and the AC input block not-exactly pushed into place right of the fan, under the wires.  Nothing here is permanently mounted.  The Breakout Board (BoB) is just sitting on some screws, rather than held on standoffs and fastened in place.  I had to make the 1/4" standoffs, just to keep from having to order them.
As a bonus, no extra charge, I broke off the tap in the last of the four holes, the very last operation of making that little piece of metal, making the hole unusable and threatening the usefulness of the piece.  It includes some heat treated metal, though, so no charge for that!  I don't have any around the house, but the cool way to remove a tap from aluminum is to heat a solution of alum to just about boiling and saturate it, then put the aluminum in the alum solution "for a while".  The steel tap will dissolve away leaving the aluminum.  This has to be done in a ceramic, glass container, or aluminum vessel, otherwise the alum would attack a steel pan just as quickly as a steel tap.  I need to try to find some alum so I can try this. 

I often say that much of my worldview comes from Looney Tunes, so all I know about alum is that when you give it to a character getting ready to eat you, their mouth shrinks up from its astringent action and you can get away.  Or it can be used to shrink an opera singer's head. Who woulda guessed it might save a piece of project I was making?


  1. Don't know how much you need, but styptic pencils are made of alum with some sort of wax binder, although they dissolve readily in water.

  2. I used to think that that the knowledge gained from oopsies would prevent oopsies in the future. Experience seems to prove that the more one learns, the more complicated things one is willing to try, and thus the more complicated the oops.

    Case in point being crown molding.
    Note. If your piece of crown molding has both a square cut and a angled cut, position the angled cut before nailing the crown molding. If you start by nailing the square end, the slight spring you left in the piece of wood will push the angled cut out of position and thus require the use of paintable caulk and some caulk sculpting skills. And yes, the error joint is on the corner I will see most often, the perfect corner joint is above the pantry door and will hardly ever be seen. (and leaving the r out of the word pantry changes the meaning of the above sentence quite a bit)

    Alum. This sounds like a good idea to remove the broken tap. Maybe some sort of plastic tray/container? An aluminum foil lining of a dollar store steel cookie pan?

    1. I have the ability to generate an infinite number of typos. For the finishing cuts on the rectangular cutouts, I used the mode where you enter commands in real time, one at a time, instead of the file. A second file is smarter because Mach3 allows you to visualize the path, and any irregularities stand out.

      In this case, I cut the main cutout with a 1/4" EM with a CNC file I could visualize, and then was going to put a 1/8" EM into the corner manually by issuing one line commands. I was telling the machine to go to some coordinate like "Y-1.50" and typed "Y-1.05". The machine then dutifully chugged off to cut the extra .450. When I hear the cutting sound change, I reach for the kill button but by the time you hear it change, it's already done something visible.

      An aluminum vessel tray would work. I have (what's supposed to be) a Pyrex beaker, and that would be ideal. I need to submerge one end of the 1x2.5x.375 aluminum in solution, which has to be less than half a cup. I don't know how much alum I need; everyone just says use enough water to cover the tap in the part, bring it near boiling and dissolve alum until you can't dissolve any more, then hold it at that temperature. If I bought a pound from eBay, I should probably have plenty for the next time I do this.

  3. Can you just make a dam out of modeling clay around the area , plug the other open end of the drill hole, and fill it with a teaspoon of the solution?
    I have read about this method on Practical Machinist and do not recall the necessity of heating the alum, maybe that is just a step to speed up the process, or to get it to dissolve in water easier?

    1. I could, but it's such a small piece that it's almost no work to take it out and put it some solution.

      I think the answer to the hot water question is both - it'll dissolve more alum and speed things up.

      There are some taps this won't work on. Anything solid carbide or, really, anything other than steel. It's from a decade old Sears set of drills and taps, so my guess is that it's probably not exotic material.

  4. Amazon sells alum in any quantity you want. A 1 lb bag is $8 or $9.