May 28, 2021 -- Punch Cutting (Part 5 of 5)
Time for inspiring background music……
Most things went well with this punch cutting; I’m pleased with the results however it was like a Venn diagram of variables that fortunately ended up in the middle of the chart with a useable result. The major issue was that the punch was inspected after the straight wall engraving; in the holder but out of the machine. It was returned to the machine to do the angle cutting however there is some wear in the holder and the punch proved to be slightly out of alignment after that.
The steel material used for the punch was O6 tool steel, which is unique for its ease of machinability. Called "Graph-Mo" by the original developer, the Timken Company, it is classified as an "Ultra high carbon tool steel" with 1.25 to 1.5% Carbon in the recipe. Compared to other available tool steels, they claim it is easier to work in the annealed state as the excess carbon is situated between grains of steel. It can be hardened like other tool steels, 01 for example. Modern punch engraving craftsmen extol the virtues of old steel (read "Counterpunch" by Fred Smeijers, page 103). From books I have on steel by the Sheffield born author Harry Brearley (inventor of stainless steel), the argument about older steel being the better product was discussed even back as far as 1918. In short, 06 tool steel seems to mimic properties of ‘old steel’, which I believe was steel that was produced prior to the introduction of the Bessemer process.
The first commercial production of Bessemer steel was in Sheffield around 1858, with large quantities of production in starting in the late 1860’s and early 1870’s. I believe it was the impurities in old high-carbon steel that had no where to go and settled in grain boundaries as the steel cooled, which allowed better machining and engraving of punches. Older steel-making processes were limited as to the temperatures they could achieve. I believe the Bessemer process ‘cleaned up’ any steel impurities with higher temperatures and improved processes, which changed its engraving properties for the worse. It would be interesting to see some steel analysis of old punches throughout the ages.
The cutter used for creating straight walls in the punch was a 1/8” diameter carbide “D bit” fashioned on my Deckel cutter grinder, more information to follow in future. In general, carbide does not like ‘interrupted cuts’ where it is prone to chipping, and engraving has lots of interrupted cuts. The carbide used was from a scrap import tool bit; the best carbide I see is domestic grades of ‘micro-grain’ material. Carbide is basically a sintered (heated and compressed) composite material of tungsten carbide and binders, so I’m not sure where grain comes into play. The 1/8” diameter size of the carbide cutter is at the very limit of this engraver, in terms of spindle bearing run-out (creating vibration), cutter diameter and depth of cut. The one variable we can consistently control is depth of cut, which was limited to 0.005” per pass. In future, we could also reduce the cutter diameter with the Deckel cutter grinder, we are also experimenting with carbide cutters equal to the 0.055” diameter of the original Pierpont engraving tools.
May 28, 2021 -- Punch Cutting (Part 5 of 5)
Time for inspiring background music……
Most things went well with this punch cutting; I’m pleased with the results however it was like a Venn diagram of variables that fortunately ended up in the middle of the chart with a useable result. The major issue was that the punch was inspected after the straight wall engraving; in the holder but out of the machine. It was returned to the machine to do the angle cutting however there is some wear in the holder and the punch proved to be slightly out of alignment after that.
The steel material used for the punch was O6 tool steel, which is unique for its ease of machinability. Called "Graph-Mo" by the original developer, the Timken Company, it is classified as an "Ultra high carbon tool steel" with 1.25 to 1.5% Carbon in the recipe. Compared to other available tool steels, they claim it is easier to work in the annealed state as the excess carbon is situated between grains of steel. It can be hardened like other tool steels, 01 for example. Modern punch engraving craftsmen extol the virtues of old steel (read "Counterpunch" by Fred Smeijers, page 103). From books I have on steel by the Sheffield born author Harry Brearley (inventor of stainless steel), the argument about older steel being the better product was discussed even back as far as 1918. In short, 06 tool steel seems to mimic properties of ‘old steel’, which I believe was steel that was produced prior to the introduction of the Bessemer process.
The first commercial production of Bessemer steel was in Sheffield around 1858, with large quantities of production in starting in the late 1860’s and early 1870’s. I believe it was the impurities in old high-carbon steel that had no where to go and settled in grain boundaries as the steel cooled, which allowed better machining and engraving of punches. Older steel-making processes were limited as to the temperatures they could achieve. I believe the Bessemer process ‘cleaned up’ any steel impurities with higher temperatures and improved processes, which changed its engraving properties for the worse. It would be interesting to see some steel analysis of old punches throughout the ages.
The cutter used for creating straight walls in the punch was a 1/8” diameter carbide “D bit” fashioned on my Deckel cutter grinder, more information to follow in future. In general, carbide does not like ‘interrupted cuts’ where it is prone to chipping, and engraving has lots of interrupted cuts. The carbide used was from a scrap import tool bit; the best carbide I see is domestic grades of ‘micro-grain’ material. Carbide is basically a sintered (heated and compressed) composite material of tungsten carbide and binders, so I’m not sure where grain comes into play. The 1/8” diameter size of the carbide cutter is at the very limit of this engraver, in terms of spindle bearing run-out (creating vibration), cutter diameter and depth of cut. The one variable we can consistently control is depth of cut, which was limited to 0.005” per pass. In future, we could also reduce the cutter diameter with the Deckel cutter grinder, we are also experimenting with carbide cutters equal to the 0.055” diameter of the original Pierpont engraving tools.