Basic Layout Question

[Doug Gray]

Basic layout question. As you can see below I have used my centre finder to scribe a line (1 o'clock to 7 o'clock) thru the centre of the part. Now I want a line thru the centre 90 degrees to the first line. What tools/techniques to use?
Sorry for the poor photo.

 

[francist]

Place the disc in a v-block on surface plate, adjust scribed line to vertical using machinist square on surface plate, scribe horizontal line using surface gauge on plate. Centre can be established by measuring diameter of part using micrometer or calipers, then height gauge down 1/2 of that dimension from the top of the disc as it rests in the v-block.

 

[Winegrower]

I would probably draw another line just like you already did, but use a small machinist square to make sure the new line is perpendicular to the first line.

 

[AmericanMachinist]

With a compass set to the length of the chord between one of your two points and the point where the perpendicular line intersects, you could scribe overlapping arcs (one from each of the two existing points). If they don't meet at the edge of the part, adjust until they just about do. Rotate your center finder until tbe new line will cross the midpoint of thr arcs at the circumference.

Or, as said above put a square on the existing line.

 

[AmericanMachinist]

Place the disc in a v-block on surface plate, adjust scribed line to vertical using machinist square on surface plate, scribe horizontal line using surface gauge on plate. Centre can be established by measuring diameter of part using micrometer or calipers, then height gauge down 1/2 of that dimension from the top of the disc as it rests in the v-block.

Appears to be a thin washer. Whats the best way to hold it in a V-block,?

 

[SLK001]

Since the inch lines on your rule line up on both sides, adjust the rule so that the 3" lines line up with your scribed line, then lock it down, then double check that the 3" line is still in line with your scribed line. If they are lined up, then scribe away. Depending on the accuracy required, you may have to adjust the rule a couple of times to get them lined up as you want.

 

[francist]

Appears to be a thin washer. Whats the best way to hold it in a V-block,?

I don’t know about best way, but I might try backing it with a short stub of material to try to get it stay vertical. Failing that I might lay the thin disc flat on a plate and work the v-block standing on its end and see if I could get at it that way. I didn’t see that it was a washer to begin with, for some reason I was thinking it more depth to it.

 

[mickri]

Use your center finder with a line on the ruler lined up with the scribed line. Then scribe a line. Should be perpendicular to the first line. As a cross check put the center finder on the other side and scribe a line. The lines should be on top of each other. Keep trying until they are. This is what I have done in the past.

 

[woodchucker]

I agree about using the compass and striking arcs on both sides of the line and drawing through. I would probably use the compass to draw a point slightly in from the edge on both sides for my compass point.


Size of the object complicates things, the smaller you go, the harder it is.

 

[Mini Cooper S]

One way to do it is to use a 1-2-3 block or a 6" square against the scale with the centering head. Carefully line it up along the first line, then scribe your 2nd line.
Laying out a part is done for speed or reference not super precision. If the job requires high precision, set up the mill or Jig Bore or grinder. Something that I learned a looong time age while working in a Tool and Die shop, is that they are selling time and expertise. The faster that you can make something to the required level of precision, the better. (2 place decimals are there for a reason) As long as you are laying out the part, there is a certain level of inaccuracy that goes with the process. Don't get me wrong, with very careful layout, considerable accuracy can be achieved!
The compass method by American Machinist is another good method.
Richard