I need to engrave a degree scale on my evolving gizmo. One degree increments will be fine. I can indicate the part on my RT, translate the 1.25" or so to the scale location, and use the RT to locate the angles.
I am not clear on what to use to actually cut the lines. A quick search reveals scribes, awls, pin vises, etc., but most of them look like they are designed to be hand-held. I have scribe that I use for layout work, but it would need to be "modified" (read destroyed) to fit on the spindle of my mill-drill.
Any suggestions for the cutter and how to mount it in the spindle?
How about a "pin chuck" - Enco model number 891-5498? The material is Al, so is steel good enough to engrave it, or do you still want carbide or even diamond?
If you don't need much life from it and are not going deep enough to need flutes, grind a point on a broken drill and clamp it in the drill chuck, or a broken end mill and use the end mill holder. You can true up the point by grinding as it rotates.
Get a Mcmaster # 1604T13 Diamond Drag bit. This is a 1/8" diameter shank about an inch and a quarter long, with an embedded diamond in the tip. Very commonly used for single line drag engraving (no rotary action necessary). It is best used though with a spring loaded holder, of which I know some have just bored a 1/8 hole in a piece of 3/8 or larger drill rod and incorporated a stiff spring above the bit.
Or use a regular end mill 45 degrees down the side of the dial so it makes a 90 degree vee cut. If you have a sharp dovetail cutter you can almost duplicate the engraver bit's lines. A lathe threading bit in a flycutter should work but the end will taper out excessively unless you cut all the way across the dial. You might want to leave the OD large and take a cleanup cut afterwards to remove the burrs. If you polish it use a rigid backup block or a long strip of fine sandpaper, not finger pressure.
The biggest problem I have with dials is losing count of which lines should be longer while trying to remember the different ending points.
That'd work. Or you could grind a nice cutting point on a piece of tool steel and insert it in the tool holder or chuck or whatever.
Get a Mcmaster # 1604T13 Diamond Drag bit. This is a 1/8" diameter shank about an inch and a quarter long, with an embedded diamond in the tip. Very commonly used for single line drag engraving (no rotary action necessary). It is best used though with a spring loaded holder, of which I know some have just bored a 1/8 hole in a piece of 3/8 or larger drill rod and incorporated a stiff spring above the bit.
first cut them *all* to the length of the shortest lines. Then reset the index head arms for the spacing of the next longest lines, and work your way around making those longer. Then do the next longer (which is probably all you need -- units, fives and tens). Then use some very small number metal stamps to mark the longest lines with values. (Nicer would be if you have a CNC mill with a CNC index head -- you could both automate the cutting of the lines, and engrave the number markings as well.
The issue I had with cutting lines twice was that the cutter didn't retrace its previous cut exactly, probably because it wasn't moving much metal the second time, so the lines were wider with a burr in the bottom.
CNC? My indexer is from a Brown & Sharpe Tool Grinder and looks like it was made before 1900.
The last project that I did similar to this, I used a dividing head on my Bridgeport with an engraving cutter to do the degree lines accurately and then moved to a CNC'd mini mill with a temporary stepper mounted as a 4th axis to engrave the actual numbers where the relatively low resolution of the 4th axis wasn't an issue. This was engraving on anodized AL.
Hmm ... make the longer lines slightly deeper on purpose, so they are wider and stand out a bit more.
Or -- start out with the thing set up for the longest, mark them with one color of paint pen, then the next shorter, (skipping the ones already marked) and mark them with another color of pen, then finally cut the shortest, skipping the marked lines, cut the next longer (going for the one color) only, and then the longest (going for the first color).
Then wash off the paint with an appropriate solvent.
The simple final answer was to write down the ending points and look at the dial to see which one to use next, instead of trying to remember everything. I only mentioned this because it was an unexpected problem.
No CNC mills around here. In case it makes any difference, the mechanism uses rings that fit into holes bored in plates; they allow the "payload" to be manually rotated around its axis. The lines will be radial on the surface of the plate, with one line on the corresponding ring.
I have an 8" RT which I will center under the spindle and then bump the parts. It will be interesting setting the zero angle on the ring, as it does not have many references. There is a notch that will probably suffice. I had to re-mount the other ring[*] with some accuracy, and was able to use an off-axis hole to zero the RT. I did so by translating the mill table to where the hole would be at zero angle, and then brought the hole under the spindle according to the drill bit that made the hole - not perfect, but with you guys sworn to secrecy, it will be good enough. Consistent spacing is important to us; a small shift in angle is not important (even unavoidable considering the entire setup). Clearly the correct thing to do would be to do the subsequent milling before removing the part from the table; easy enough to do if I ever have to make another copy of the ring.
[*] the scale could go on that ring, though the one I have in mind is the logical choice.
The bottom line is that an 8" RT will be in the horizontal position, and the lines will be scribed on a plate clamped flat on it. The RT's dial will do the indexing.
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