Locating features

[homebrewed]

I've found that most of the dimensions on my lathe and milling machine happen to be nice multiples of 1mm. So if I'm making/modifying something and the measurement taken from my machine is, say, 17.95mm I will round it up to 18 with a high degree of confidence it really is 18mm.

Also. Unless absolutely necessary don't drill holes according to their close fit specification. Go with standard fit or (if you really are uncertain about the exact distance) a little more generous than that. I'm not talking about holes that are meant to be tapped, of course.

Transfer screws are a nice thing to have, too. While a set can be expensive you can make your own. I have made a few using socket-head allen screws. Using your lathe drill a hole on the socket end that's a bit smaller than the socket, then insert a sharpened piece of music wire in the hole once you've installed the allen screw. Bring your piece-to-be-drilled up to the one you want to match and tap to mark the desired location of the hole(s). Pull the sharpened bit out with needle-nose pliers and then you can back the allen screw out of the hole, ready for the next time you need it.

These also can be handy for this sort of thing, if you're working with through-holes.

 

[RJSakowski]

I've found that most of the dimensions on my lathe and milling machine happen to be nice multiples of 1mm. So if I'm making/modifying something and the measurement taken from my machine is, say, 17.95mm I will round it up to 18 with a high degree of confidence it really is 18mm.

Also. Unless absolutely necessary don't drill holes according to their close fit specification. Go with standard fit or (if you really are uncertain about the exact distance) a little more generous than that. I'm not talking about holes that are meant to be tapped, of course.

Transfer screws are a nice thing to have, too. While a set can be expensive you can make your own. I have made a few using socket-head allen screws. Using your lathe drill a hole on the socket end that's a bit smaller than the socket, then insert a sharpened piece of music wire in the hole once you've installed the allen screw. Bring your piece-to-be-drilled up to the one you want to match and tap to mark the desired location of the hole(s). Pull the sharpened bit out with needle-nose pliers and then you can back the allen screw out of the hole, ready for the next time you need it.

These also can be handy for this sort of thing, if you're working with through-holes.

I also will assume that dimensions are nice round numbers. However, that is less likely to be true going forward as a CNC mill or lathe doesn't care what the dimensions are. On another note, when I was making a backing plate for a chuck, I found that the three mounting holes were not spaced evenly at 120º apart. This is fairly common on Chinese products. So it is wise to always check.

 

[Shotgun]

So there's no specific method.

As close as I can tell, the ability to use the available methods to accomplish a particular goal is what separates a guy with a machine tool from a machinist. The "specific method" only applies to a "specific end goal", constrained by "specific tools".

 

[Chewy]

In reading through the posts, are you asking how to get the numerical number for the location? Say X1.253 Y2.556? If so go through the Jo Pi videos on angle locations. He has about a dozen on locating features or milling to a radius intersection. It is all simple right triangle calculations. You can use an online calculator or charts in the machinist book. As stated. an 18mm dimension probably won't measure 18mm. Measure a 10mm bolt and it is 9.something mm. Draw a picture of what you want to make.Then using the gauge pins, mic's etc, put down the dimensions that you get. Draw some intersecting lines and you see what information you need. In the case of locating a handle on a circle, that is right triangles, chords and maybe tangent lines. All are very easy to find if you go slow. In the case of dovetails using two pins, there are lots of videos out there showing how to measure or use adjustable parallels. Milling to a specific location on an angle is a right triangle.

Anytime I make something complicated or really weird, I review his videos and then make an order of operations. Hasn't let me down yet.