| Gallery, Projects and General > How do I?? |
| D Bits revisited |
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| Chuck in E. TN:
I need to make a 'D bit' to ream a bearing for a connecting rod. I purchased 1/4" O1 drill rod for this purpose. This is my first "D bit", as well as my first reamed hole. I cut a 3" piece, chucked it in the lathe and faced the ends. Next, I placed the blank in my mill vise on a paralell and attempted to mill to 1/2 the diameter. I touched the mill cutter to the top, zeroed the Z axis DRO, and lowered the Z axis to .125, locked it, and milled the blank for approximately 1/2". The bearing is 1/4" thick brass. When I removed the blank from the mill vise it measures .118 on the "D" part. Is this going to work? How critical is this thickness to the accuracy of the reamed hole? Do I need to try again? Chuck |
| Country Bubba:
Chuck, IF your rod was actually .2500" dia to begin with, and if you now have .118" left, this means the diameter is now .2496" . IF your starting rod diameter is less than .2500", then it will be even smaller. Everything depends on your tolerances. This just might work and if it is to small, you can always make one a bit bigger, but sure can't go the other way. HTH |
| Chuck in E. TN:
--- Quote from: Country Bubba on January 06, 2013, 02:24:39 PM ---Chuck, IF your rod was actually .2500" dia to begin with, and if you now have .118" left, this means the diameter is now .2496" . --- End quote --- I'm not sure what you mean. Looking at the end of the bit that was milled, it looks like a D, and measures .118 from the flat to the fattest part of the D shape. The drill rod measures .2495 as it came from the store. |
| Country Bubba:
Chuck, Hopefully this "sketch" of the end view of the rod will help: If you start with a rod that is .2495" dia and remove a .125section so the remaining thickness of the D is .118", the diameter of the flat on the D will be .2491" as opposed to what I previously posted as I "assumed" a diameter of .2500" as the starting diameter. |
| andyf:
Chuck, are you trying to say that you wanted to mill down to a diameter of the drill rod (in other words, down to the half-way line) but your result seems to show you went a bit too far so that, looking at the end, you've got a bit less than a semicircle left in your D? I seem to recall that the D should be a bit more or a bit less than a semicircle, but can't for the life of me remember which. Maybe it would be easiest to harden and temper what you've got, and try it in a bit of scrap brass. Then reverse it and try the shank end (or the remainder of the drill rod you cut the required length from) to see if a 0.2495" diameter rod fits without undue looseness. Andy |
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