The thread of the font of the dividing head

[Michael G]

In Ewan's thread on his dividing head (https://www.woodworkforums.com/f65/al...g-head-172639/) he was admiring the font that the graduations were stamped in. I rather boldly stated they could be duplicated on an engraver but then after logging off wondered whether I was right.
Today I had a go at doing it -
I suggested in the thread that good photos were required. I didn't have any so used a couple from Ewan's show and tell, fortunately all the digits were at least there.
P1010873 (Medium).JPG
I then traced them from the photos onto a piece of plastic and blew it up to a large size. As you can see, due to distortion from point of view and perspective within photos, none of the numerals were really the same size. (This is where the good photos would have been handy).
P1010876 (Medium).JPG
Using the tracings to get the proportion I made up a CAD drawing of each numeral. A couple of the proportions were changed slightly to get a more balanced font, but nothing major. I had calculated that 2.5mm was the smallest size that was likely to be required so as my maximum reduction was 7:1, the guide numerals needed to be 17.5mm high. As the minimum reduction is 2:1 (there is a 1:1 device available but is rarely available second hand), the CAD plot was printed out at 35mm high.
P1010867 (Medium).JPG
The gravograph font carriers take a font just under 1 1/4" high. Standard commercial fonts are in 1.6mm thick brass. For this exercise plastic is fine, so I made up some strip the right width and with the 30 degree edges so they would lock into the carrier properly (a pain when using a thin thermo plastic on a table saw). This photo shows the strip mounted in the engraving vice part way through the exercise. I found that for straight lines it was so much easier to run the pointer down a rule as a straight edge. The curves still had to be done free hand. I also found dragging a steel scriber around the path after engraving seemed to iron the plastic out a little too.
P1010869 (Medium).JPG
I made up 2 sets of numbers because there is always one occasion that requires the same digit twice. Using them to engrave on a scrap piece of plastic, the result was not bad. These characters are 4mm high in real life. Line thickness is controlled using the angle of the engraver tip as well as the DOC. In the lower string the first characters were done at 1/2 maximum DOC, the next with 1/4 and the last 2 with 1/8. I confess that I did not remember to allow for the graver thickness when spacing the numerals horizontally however, all I need to do is put a spacer between when setting the font next time.
P1010872 (Medium).JPG
Any of the jitters I had when free handing the curves has been shrunk so while not as smooth as I'd like them, at life size (4mm) it is barely noticeable. Looking at the output I think that the bodies of the 6's and 9's could be smaller but other than that it can be done. Next mod is a 1:1 arm so that I can copy characters directly to further chase that uniformity of letter.

Michael

[Anorak Bob]

Nice Michael.

What was the plastic you used for the fonts? Have you or are you going to bevel the font edges and are you going to cut the strip of numerals into individual numerals? And while I'm at it with the questions, what angle cutter(s) are you using and is it carbide or HSS? Oh and one more , how are you sharpening your cutters.

( An explanation Dear Readers as to why the barrage of questions. Michael and I both have Gravographs. Michael's is a later model.)

BT

[Michael G]

What was the plastic you used for the fonts?

Some 1.5mm thick Styrene sheet - bought I think from a model shop

Have you or are you going to bevel the font edges and are you going to cut the strip of numerals into individual numerals?

I beveled the edges (top and bottom) of the blanks (30 degrees) while the material was in a strip. I used the table saw for that but had to clean up with a file. I think if I were going to do a lot of this I would be making up a jig for the mill. Styrene has a nice "score and snap" action so a deep cut with a Stanley knife was all that was needed. The final picture was post snap.

What angle cutter(s) are you using and is it carbide or HSS?

Cutters look to be HHS (magnet test) and most are 50 degree included angle, although I do have 2x 75 degree included angle, including one that was used to cut the letters

How are you sharpening your cutters.

At the moment I'm not as the engraver came with new-ish 6 cutters. When I do I can see a sharpening jig being invented, with a round bit for the cone (and perhaps a cam to get the relief) and then something to touch up the flat and do the tip - may only need to be a diamond hone.

Michael