Engraving a degree scale

First, let me say that no scale as coarse as one degree will give you any degree (ulp... sorry!) of accuracy in cutting tapers. The scale marks are only a starting point for tweaking your tapers. A precise taper would be obtained by measuring amount of taper per foot - inch,whatever - in thousanths, and even tenths. You start with a first cut on a scale mark, measure the actual taper over a given length, then make vernier adjustments to get to the precise taper you want.

So, although it's nice and very pretty to have the taper gauge accurately marked, since it's not the ultimate source of your accuracy, it's not all _that_ important.

Now, if you wanted to go as far as adding a precision vernier gauge to the bar, it could be close enough for most work... but it wouldn't be if only marked in degrees.

So... that said, if the gauge is long enough and substends a small enough arc, it's a simple compromise to just space marks out linearly on a line chordal to the arc the bar will describe, and it'll be accurate enough for most work's starting point.

That, you can do with simple trig.

LLoyd

So you are saying my best bet is to simply mark the lines by hand and scribe them with engraving tools?

Gary

IF they're as coarse as one-degree marks, sure. Lay them out carefully, yes, but not much need to get them to minute-of-degree accuracy.

I wouldn't lay them out by hand. You'll know in advance how many thousanths apart they need to be (by the trig).

Clamp up the plate in a mill, and use a pointed scriber as the tool to mark out and scribe in one pass, using the x-feed for distance between marks, and the y for the length of each mark. Don't mess yourself up with cumulative errors... print out a table of the math for ALL the marks to four significant digits, and set the x-feed to EACH mark's nearest half-thousanth location, rather than advancing a fixed distance from the last mark for each new mark. And, of course, only move one direction in X... if you pass a point, move WAY back and then again to the mark to avoid backlash problems.

LLoyd

You *can* make them nice. But for precision, the best is a sine bar.

Nick

I've used plotters in the past, but any Postscript capable printer can get you 300 dpi accuracy, and some are better. It's possible to program (in the Postscript language) such a printer to do your scale, and you can photo-etch metal to that pattern.

For best performance, use a copy camera to make a film negative of your positive printer-output master, at suitable reduction. Graphic arts shops can undoubtedly do this for you. Etching materials for copper are easily available in the printed-circuit-board technology. I've done it in stainless with the same chemistry (but cleaning is tricky).

So, you can (1) become a graphic-arts shop, or (2) hire one. My application was some customized meter faces, and it turned out well.

half-thousanth

Do you have a rotary table? Just use it. With it you can add your marks at any degree you want to. You could even make a vernier. I'd use a 1/32 ball end mill if you don't have a tool grinder to make an engraving tool.

Something I bumped into while looking into building a quorn.

Not sure if this is applicable but wth.

Wes

I've made a couple degree scales, last week with a rotary table and and a slitting saw on the horizontal mill - worked nice. Before I had the mill and rotary table, I fastened a tape measure around a 10" 4 jaw chuck, used a calculator for the measurments, and crank the cariage back and forth with a lathe tool to cut the marks.

Wayne Sippola Moose Jaw

Photo etching is probably the most accurate way to go about it. IC's are done that way to 60 nm. At most electronics supply companys you can get some spray on photo etch and photo resist aerosol spray. I don't remember all the details but you make a mask on a clear film of what you want to etch. you spray the piece with a positive or negative photoactive spray and let it dry. You then put the clear film over the sprayed surface and expose it to a bright uv lamp. Then you wash off the non activated material and this washes off the material under the lines that were on the clear film. You then apply some etching chemical and this will etch the lines in the metal.

Second choice used by knife makers and others that want a fine etched logo of design.

Elctroetching.. Make a stencil of your lines and with a transformer, a pad with chemicals on it, you etch through the stencil. I would recommend the second method.

John

I'd guess his taper jig's arm will be much longer than the workable radius of any rotary table he could use, even with a huge overhang. It could be made to work, with an outboard work support, etc... but it sounds like a cludge.

LLoyd

I can't help this. I did a Google search for quorn and found this near the top.

Yes, it is the latter. There is a yahoo group on it if interested.

Wes

I suspect Lloyd is right. I have an 8" rotary table but the arc created by the taper attachment will be closer to a 15" radius. The Lathe idea has merit but again, my lathe has a 12" swing.

I'm inclined to try the etching idea.

Gary

That's not a problem. You're engraving, not cutting a huge pocket. Bolt a heavy plate to your rotary table, and clamp the arm to the plate. Take light cuts, and you'll be fine.

Gary - don't bother with a scale. When the taper is installed on the lathe and set to a zero taper, find a spot at a known distance from the pivot point (presumed) with a convenient measurement via a caliper between the taper and a fixed point 90 degrees to the taper. Record that measure for later use & buy a "scientific" calculater with trig. functions. That's roughly $10 at Walgrens. The sine of the desired angle times the distance from the pivot is the needed offset. Add or subtract that to the first measurement and it's set. There is an error with this if the measurement is at a fixed distance from the pivot instead of at a constant radius. Paper & pencil can be handy here. However the error can be calculated & added/subtracted to the first.

Hul

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