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Embarrassing Question

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  • Embarrassing Question

    I don't know how to do layout work. When I attended classes on machining at a gunsmithing school that was one of the things I tried specifically to learn but the teacher I don't think knew enough to teach it.

    Anyway, is there a good simple book on it. I realize it can be complicated but most of what I am working on just requires the basics.

    Specifically, what I am working on right now is I want to do a drill jig for four holes. This will be used to drill holes in wooden grip panels for reproduction German MG34 Machinegun grips. There are two holes at the top and two at the bottom.

    My "teacher" just had us use calipers and use the tips to scratch marks but I am not going to do that with my good calipers!

    So, what are the 800 different ways to do this?


  • #2
    Get your drill press an x-y table and stop worrying. Work right from the dimensions and never bother scribing lines. A rough pencil layout on the metal to ensure you don't get a tenth of an inch off is all you need.

    They can be had for as little as $80 or so, and are the cat's meow for general close drilling. It won't make your press into a jig borer, but its way better than trying to hit the little cross-mark.

    Mine cost about $70 and has a table 5 1/2 x 12.

    Use a spotter drill before the actual bit.


    • #3
      Yea, that layout fluid is a mess anyway. Spill it and everything is blue or red. Spray it and go on a buzz for a while. I use a Sharpie fine line most of the time. Punch, spot and drill.


      • #4
        Although good layouts can be executed from carpentry tools (as an example), it isn't that costly to acquire nice layout equipment, such as:

        granite plate
        right-angle plate
        vernier height gage
        dykem (or equivalent layout dye)

        The granite plates and right angles are available in many sizes, you may select the ones that accomodate your needs. A twelve-inch height gage is usually adequate for home shop usage. (When I say that these do not have to be costly, obviously I refer to imported devices.)

        X-Y tables are definitely useful, but have limitations. The obvious limitations are travel dimensions but consideration also must be given to the hole sizes that need to be drilled.

        Most drill presses don't have enough spindle travel to accomodate a large range of drill diameters without having to move the table.

        When the table is moved, some means of regaining relative location is required. It can be troublesome -- this is a typical problem with mill/drills.

        In any case, spotting drills can sometimes be eliminated by using screw-machine drills.


        • #5
          I design my layouts on a computer, print it out on a really accurate printer and tape it to the work. Center punch and good to go.
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          • #6
            Well, I've also been using the surface plate less for layouts recently - AutoCAD printout, applied to the workpiece is a good expediency for most work ...


            • #7
              I have drilled PCB's direct through a autocad drawing printed to size 1=1.. FUnny how the integrated circuits just pop right in the holes and everything fits just like in the drawing.
              On my metal projects, I use the sharpie or pencil method mostly, punch the marks, drill with smaller pilot drill then bore to size with correct one.



              • #8
                Printouts are OK, but you should be aware that the government forbids printers and copiers from being perfectly true to size. They are forced to have a size error. This may throw larger dimensions off. In a 14 pin dip IC you wouldn't notice. In the board mounting holes, you might.

                This is to prevent (as much as possible) the copying and printing of our worthless currency (dollarettes).

                People could find it, but machine money acceptors cannot detect that kind of copy as well.


                • #9
                  Try "The Starrett Book for Student Machinists." It talks about all that basic layout stuff.

                  But...I seldom do truly accurate layout. I do layouts close enough so I can tell if I'm really off when drilling/machining, but I rely on the accuracy of my milling machine to put the holes and surfaces where they are supposed to be.
                  Try to make a living, not a killing. -- Utah Phillips
                  Don't believe everything you know. -- Bumper sticker
                  Everybody is ignorant, only on different subjects. -- Will Rogers
                  There are lots of people who mistake their imagination for their memory. - Josh Billings
                  Law of Logical Argument - Anything is possible if you don't know what you are talking about.
                  Don't own anything you have to feed or paint. - Hood River Blackie


                  • #10
                    I use the same technique as "Evan" and then
                    use my mill/drill ( which I fitted with 1"
                    travel dial indicators on "X Y & Z" axis )
                    the paper is a great help to see if I am
                    way off especially if it's a odd ball hole



                    • #11

                      That is an urban legend.

                      I worked for Xerox for 23 years. The reason that copiers would make the copies slightly oversize has nothing to do with money. It is so that an image of the shadow of the edge of the original would fall off the edge of the copy. This avoids leaving a black line on the edge(s). On some machines they opted to make exact size for size copies and blank the edge out for about 1/8 to 1/4 inch instead. Many of the machines including the 9200, 9400, 1075, 1090, 6500, and many others would copy to exact size. That includes the color copiers.

                      Most printers today are extemely close to correct size and the biggest source of error is humidity change changing the size of the paper. If you need a really stable printout use film instead of paper. Even it is affected by humidity but not as much. My Epson 1200 will print to about .010" over 10 inches. That is .999 accuracy, good enough for most jobs. Also handy is that it prints up to 13"x19".

                      FYI, the government DID insist on one thing. All color copiers print an invisible serial number on all color copies. It is composed of a series of single pixel dots of yellow toner distributed over the entire print. It cannot be seen by eye even with magnification but it floureces under short wave ultaviolet. The manufacturers don't talk about this and when I worked for Xerox I had to sign a NDA saying I wouldn't either. All color copier serial numbers are recorded together with info on who purchased it. This no longer matters much as inkjets don't do this.

                      [This message has been edited by Evan (edited 09-18-2003).]
                      Free software for calculating bolt circles and similar: Click Here


                      • #12
                        I bought a 30 dollar cheap pair of 12" calipers(made in china)..I use this pair just for scribing lines in metal...I don't want to use my nice calipers for scribing..It will still take a lot of scribing to wear out the tips...Thats the best advice I can give...To properly layout work, you need a height gage, maybe even a granite surface plate, a good compass..etc..all of this adds up in cost..just buy a cheap pair of calipers and some dykem, and scribe away...



                        • #13
                          Urban legend?

                          Maybe, maybe not....My source was actually a US treasury employee.......independently confirmed by an engineer who works for a company making coin and bill acceptors. Neither would go any further with the explanation....

                          I did notice that the copy error was different in the x and y dimensions, none in X , a small amount in Y.

                          That accorded perfectly with the information I had gotten.........

                          In any case the size is not perfect in general, whatever the reason.


                          • #14

                            The treasury employee probably believed what he told you was true. The reason the error is different in X vs Y is that in scanning copiers the optics determine the error in one direction (slight) and the optics PLUS the drive accuracy of the transports and optics drive (for scanning optics) determine the error in the other dimension (greater). With the introduction of xenon flash lamp optical systems, first used in the Xerox 9200 in the late 70's, these errors disappeared. In particular, the Xerox 1075 had less than .01% size error in x and y.

                            Even some of the scanning optics machines had a provision for "size-for-size" copying, as it is known. The Xerox 1038 copier when set to 100% default mode would copy at 102% to avoid the above mentioned edge line problem. But, if you selected 99% and then back to 100% it would produce a true 100% copy.

                            I assure you that there never was any truth to the story that the gov mandated that exact size copying not be possible. It has been available for over twenty years.

                            I also worked on coin and bill acceptors as some of the machines were coin/bill operated. The bill acceptors of the day used a number of density readings with photocells at strategic points on the bill. If the density reading didn't match the correct profile then it was rejected. Having an oversize copy would certainly cause it to fail but that is not necessary. It is nearly impossible to make a copy, B/W or color, that has the correct density at all points. Color copy toners especially have far different densities than printing inks. The Xerographic process has very poor dynamic range and tends to make dark areas much darker and light areas much lighter. There is no way it will match a printed item. In this case, size really doesn't matter

                            [This message has been edited by Evan (edited 09-18-2003).]
                            Free software for calculating bolt circles and similar: Click Here


                            • #15
                              There is one interesting story that is true.

                              Quite a few Xerox reps worked for the CIA during the 60s and 70s. They repaired photocopiers in the embassies of the east bloc countries. The photocopiers were fitted with a microfilm camera that snapped a picture of every document copied. It was made to look like a standard component of the machine and needed frequent "preventive maintanence". It would hold enough film to take several 1000 pics before changing. That was usually plenty and the service reps made sure the machines were not too reliable so frequent service was required.

                              [This message has been edited by Evan (edited 09-18-2003).]
                              Free software for calculating bolt circles and similar: Click Here