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- Jun 12, 2014
- Messages
- 4,828
I make many of these type of parts out of 01 drill rod which can be further hardened if needed. You could bore the center with a 0.250 drill, or if you need to be slightly over, I often use a 0.251" reamer for final sizing. For the 0.268 hole you can purchase a 6.8 mm drill for less than $10, this will give you a 0.2677 hole which most likely will come out to 0.268" when all is said and done. If you need to be very precise or a square transition, you could mill a cutter/reamer out of 01 steel (or some type of tool steel) that would be hardened to get the precise final dimension, otherwise use some form of hone/grinding compound used with a round pin for a final fit. On the external thread, I use adjustable round dies for final thread sizing, I can adjust the cut depth for a very precise (almost zero tolerance fit). You may want to do some form of surface hardening if this gets a lot of repetitive wear.
http://www.ebay.com/itm/Hertel-2677-6-8MM-SE-Drill-NEW-in-Package-QTY-1-Overstock-/182186024779
http://www.ebay.com/itm/New-Garr-Tool-End-Mill-6-8-MM-Micrograin-/172707840136
http://www.ebay.com/itm/Hertel-2677-6-8MM-SE-Drill-NEW-in-Package-QTY-1-Overstock-/182186024779
http://www.ebay.com/itm/New-Garr-Tool-End-Mill-6-8-MM-Micrograin-/172707840136
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