precisionworks
Flashaholic
Starrett makes a collet adapter (Part 28314) to hold a 3/8" edge finder in a milling collet. Nice tool if you use that diameter edge finder, but it doesn't work for a 1/2" edge finder.
Building an adapter shouldn't be too hard (yea, right :devil: ). 1144 Stressproof would have been the first choice had any been on the shelf, but 4140HT was chosen because it was there.
1144 has nice machinability (83%) and good strength (110 ksi), while 4140HT has lower machinability (50%) and higher strength (140 ksi).
[FONT="]“[/FONT]Machinability” is not an exact term. It means “the ease with which a given material may be worked with a cutting tool.” The cutting process is impacted by variables like cutting speed, dimensions of the cut, tool form, tool material, the cutting fluid, rigidity of tool holding device, and the level of tool/part impact relative to constant or intermittent contact. However, the machinability rating provides a starting point for understanding the severity of a metalworking operation.
Machinability ratings are “relative” ratings. They compare the ease of machining an alloy to a standard. That standard is 160 Brinel hardness B1112 cold drawn steel machined at 180 surface feet per minute. B1112 was assigned a score of 1.00. The machinability of all other alloys is compared to the standard score of 1.00. The American Iron and Steel Institute (AISI) tested many alloys and compared the normal cutting speed, tool life and surface finish to that obtained when machining B1112. Materials with scores above 1.00 are easier to machine than B1112. Likewise, materials with scores of less than 1.00 are more difficult to machine.
Will Q showed photos of threads cut in 12L14 (free machining leaded steel) ... it has a MR of 193%, and can be turned at 350 sfpm :)
1144 is certainly strong enough for this part, and can be run at 150 sfpm. 4140HT is stronger, but cutting speeds are lower, about 90 sfpm1144 Stressproof would have been the first choice had any been on the shelf, but 4140HT was chosen because it. At the tool & die shop, most parts are 4140HT, so I'm familiar with turning, boring, drilling & tapping speeds.
First op is to cut a piece 3" long. Just visible in the photo below is the candy stripe appearance of the material, resulting from the stress relieving process. 1144 also has the candy stripe, but 1144 is very dark when received, while 4140HT is so shiny that it looks polished.
Installed a 1" collet in the 5C chuck:
Indicated the bar stock, which showed +/- .0002", showing that the 5C chuck was well centered:
Drilled a starter hole using a 15/32" twist drill (.468"). Drilling speed was 30 sfpm (250 rpm) using a peck drill cycle - advance the drill .100", retract out of the hole, clean the drill flutes, squirt TapMagic into the hole, advance .100", etc.
Inserted the 1/4" boring bar in the 5C collet block on the tool post, and used an adjustable parallel to make sure the flat on the top of the bar was parallel with the top of the collet block. This has to be done to set the insert at the correct relief angle:
Set the height of the insert tip to .010" above center (something I always do) to make sure there is no rubbing below the tip of the insert:
Changed the speed to 500 rpm (65 sfpm) and took the first boring pass at .010" DOC, which calculated to take the .468" drilled hole out to .488" diameter:
Used shallower DOC as well as spring passes to sneak up on the final hole diameter. If more than one of these had to be made, a reamer would be purchased, which would have saved probably 30 minutes at the end of the boring cycle. The shiny & reflective bore is typical of 4140HT, possibly something to do with the chromium content in the metal.
My Starrett edge finder mics .49965-.49970", so I initially stopped boring at .50010". The tool just slipped into the bore but the fit was way too tight. A couple more spring passes were taken, not moving the boring bar from its last setting, which opened up the hole to .50025". Not too hot, not too cold, just right :thumbsup:
The clearance is so small that a "piston fit" resulted. The edge finder has to be slowly pushed into the bore, to allow air to escape. And it has to be slowly removed from the bore, to allow air to enter. It is about as tight a fit as can be used on a tool that has to be inserted and removed.
The bored cylinder will go to the mill and get drilled & tapped for a setscrew. Then back to the lathe for the final step cuts. More to follow.
Building an adapter shouldn't be too hard (yea, right :devil: ). 1144 Stressproof would have been the first choice had any been on the shelf, but 4140HT was chosen because it was there.
1144 has nice machinability (83%) and good strength (110 ksi), while 4140HT has lower machinability (50%) and higher strength (140 ksi).
[FONT="]“[/FONT]Machinability” is not an exact term. It means “the ease with which a given material may be worked with a cutting tool.” The cutting process is impacted by variables like cutting speed, dimensions of the cut, tool form, tool material, the cutting fluid, rigidity of tool holding device, and the level of tool/part impact relative to constant or intermittent contact. However, the machinability rating provides a starting point for understanding the severity of a metalworking operation.
Machinability ratings are “relative” ratings. They compare the ease of machining an alloy to a standard. That standard is 160 Brinel hardness B1112 cold drawn steel machined at 180 surface feet per minute. B1112 was assigned a score of 1.00. The machinability of all other alloys is compared to the standard score of 1.00. The American Iron and Steel Institute (AISI) tested many alloys and compared the normal cutting speed, tool life and surface finish to that obtained when machining B1112. Materials with scores above 1.00 are easier to machine than B1112. Likewise, materials with scores of less than 1.00 are more difficult to machine.
Will Q showed photos of threads cut in 12L14 (free machining leaded steel) ... it has a MR of 193%, and can be turned at 350 sfpm :)
1144 is certainly strong enough for this part, and can be run at 150 sfpm. 4140HT is stronger, but cutting speeds are lower, about 90 sfpm1144 Stressproof would have been the first choice had any been on the shelf, but 4140HT was chosen because it. At the tool & die shop, most parts are 4140HT, so I'm familiar with turning, boring, drilling & tapping speeds.
First op is to cut a piece 3" long. Just visible in the photo below is the candy stripe appearance of the material, resulting from the stress relieving process. 1144 also has the candy stripe, but 1144 is very dark when received, while 4140HT is so shiny that it looks polished.
Installed a 1" collet in the 5C chuck:
Indicated the bar stock, which showed +/- .0002", showing that the 5C chuck was well centered:
Drilled a starter hole using a 15/32" twist drill (.468"). Drilling speed was 30 sfpm (250 rpm) using a peck drill cycle - advance the drill .100", retract out of the hole, clean the drill flutes, squirt TapMagic into the hole, advance .100", etc.
Inserted the 1/4" boring bar in the 5C collet block on the tool post, and used an adjustable parallel to make sure the flat on the top of the bar was parallel with the top of the collet block. This has to be done to set the insert at the correct relief angle:
Set the height of the insert tip to .010" above center (something I always do) to make sure there is no rubbing below the tip of the insert:
Changed the speed to 500 rpm (65 sfpm) and took the first boring pass at .010" DOC, which calculated to take the .468" drilled hole out to .488" diameter:
Used shallower DOC as well as spring passes to sneak up on the final hole diameter. If more than one of these had to be made, a reamer would be purchased, which would have saved probably 30 minutes at the end of the boring cycle. The shiny & reflective bore is typical of 4140HT, possibly something to do with the chromium content in the metal.
My Starrett edge finder mics .49965-.49970", so I initially stopped boring at .50010". The tool just slipped into the bore but the fit was way too tight. A couple more spring passes were taken, not moving the boring bar from its last setting, which opened up the hole to .50025". Not too hot, not too cold, just right :thumbsup:
The clearance is so small that a "piston fit" resulted. The edge finder has to be slowly pushed into the bore, to allow air to escape. And it has to be slowly removed from the bore, to allow air to enter. It is about as tight a fit as can be used on a tool that has to be inserted and removed.
The bored cylinder will go to the mill and get drilled & tapped for a setscrew. Then back to the lathe for the final step cuts. More to follow.
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