Help, please: Undercuting problems

[Doc Mark]

Undercutting problems

I have been experimenting with different tools for undercutting gold inlay lines. So far I have not been very successful. I'm trying to inlay some very fine curved lines, about 3/10ths of a millimeter in width. This is close to the GRS QC-36 flat in width. It's the smallest flat they make. I can't find a tool shape that can negotiate the curves and cut an undercut without scaring the opposite edge of the line. I've tried a tiny flat with a very narrow chisel edge, an almost needle shape with a 45 degree bevel on the tip and even a very narrow onglett. All of them break very quickly. I've made them from small carbide drill stock but don't have any HSS stock small enough to try. I'm also having difficulty making the gold stay in the very tips of long very slender taper shapes. When I make the main cuts with a 90 degree graver and taper the final point, there just isn't enough room to make even a few teeth, much less an undercut of the channel. I've seen some of the tiny lines that others have inlayed with gold, so what am I doing wrong?

I appreciate any help I can get!

 

[KCSteve]

Since they're lines I'd try the alternate method I learned in a GRS class (from Lee Griffiths I think, who was passing it along):
Cut your line with a flat so you have nice, upright walls. Then use the same flat to 'tooth' the bottom. Cut down into the bottom with the flat to kick up a tooth (make sure it isn't higher than the surface. Cut the next tooth about twice as far down the line as you think you should. When you get to the other end of the line, turn around and cut a set of teeth pointing the opposite direction, centered in between the original teeth.

Between the straight up and down side walls and the teeth along the bottom the inlay is not going to come out.

 

[fegarex]

I feel your pain Doc..
About the only thing I found that works for fine tapered lines is a screwdiver shaped chisel similar to a screwdriver. You actually punch in the undercuts like you would with a cold chisel. It can be done with air assisted graver but is done straight down. It will move the metal up around the edge and have to be stoned/sanded down. You have to resharpen the chisel a lot as it wil break a lot too. If the metal isn't super hard I would suggest using HSS steel. No simple solution but this works.

 

[Martin Strolz]

Mark,
The lines you engrave do not need to have vertical walls. But they must be the correct shape and width. Flats gravers wont work, I use a simple onglette.
For the punches I use HSS square graver stock which I grind to very fine tips. Breaking mainly and very likely occurs when the angle of the tool is changed as long as it intense contact after a blow of the hammer. The chips of broken tools must be brought out of the line in any case! Otherwise the next tool will break at the same point. Of course: For undercutting use a small hammer:hammer: instead of a handpiece! In order to prevent exessive tool breaking, you can make and use a tool without a really sharp edge first. After preparing the line with that tool rework the undercut with a VERY sharp edgeed tool. My undercutting tools are so sharp that they actually would stick in the metal after a blow of the hammer. It is the fine outer edge in the undercut that will hold the gold.
Grind the surface of you work even in order to have full control of the shape of your lines during undercut work. Clean it with pressurized air from you compressor.
As to tools shape please see the attached drawing. You basically need 4 tools, small and wide straight, small and wide curved. For the curved tool just grind one side by rolling it during grinding. You can adjust the radius easily that way. Use the curved side for the outer side of a line, a straight one for the inner side of a curved line. The tools must be used quite steep, especially the straight side..
Martin

 

[SamW]

I do much as Martin with a very similar chisel. I do however use a very narrow "flat" made from a no. 1 knife graver flattened to the width I want. Mostly my lines are about .012 which is your .3 mm. As Rex says, the wall is raised a bit and needs to be stoned or sanded down smooth and the straight wall of the cavity helps keep the width of the line smooth. I always had trouble with that when using a V shaped tool as inconsistent punching for the undercuts meant inconsistent line width making it jagged.

There are occasions I do not want to have to stone or sand down the steel, only trim the gold, and on those occasions I have found using a scribe to "scratch in" the under cut works well. In fact, I use a scribe quite a bit, especially in hard to reach places and tight curves. Practice this first as a slip is hard to remove.

 

[Doc Mark]

Man, these are GREAT IDEAS!
Steve, I do use the small flat in the manner you mentioned. But, it's when the line tapers down to a fine point that I run into trouble. I've never really learned how to be comfortable with hammer and chisel, but I may have to learn! Martin, thank you for the very clear drawings of your tools. I too had been using a chisel end but never thought to radius one of them, wonderful idea. Sam, I really like the scribe idea. I think I know right where I'm going to try that idea first.

Keep these suggestions coming in folks, I think this thread will become a wonderful addition to the "Tips Archive".

 

[mitch]

Hi Mark-

could you post a pic or two of what you're trying to inlay, with maybe a ruler in the shot for scale? 0.3mm is not all that narrow. way back when i thought every engraving job was a flippin' contest or something i routinely inlaid gold lines about a fourth that wide- maybe .003" or <.08mm. you shouldn't be having that much difficulty with .012"-.015" lines. really tight curves cause more headaches with inlaying than mere line width. are you handling straight lines ok?

 

[jerrywh]

I use all the methods described by the other guys depending on the situation. I have put in wires half the size you mentioned. .005 in width. The method described as Lee Griffith’s works very well in a tight spot. Also the tool does not break as often as the regular undercutting tools seem to for me . The best inlay video I ever saw was by Sam Welch. You can get it on the FEGA web sight.