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@david pierce wrote:
That is true. Also, a reamer should only remove a couple of thousandths of metal. Its purpose is only to size the hole but many people try to use a reamer as the final drill size; bad idea! I like to drill first up to about .015 inches under, then use a boreing bar to get the hole to within a few thousandths undersize, then use the reamer for the final size. For a hole requiring extreme precision such as a valve guide that must prevent oil leakage or an ejector pin on a plastic injection mold, the hole would be reamed slightly undersize (.0001) and then lapped or honed with a SUNNIN HONING MACHINE.
I’ve only used a reamer once so far and that was to create a bushing for my QC tool post bolt to get rid of the wobble from using a smaller bolt than the one it’s set up to accept. I used a standard reaming chart for this, but started out with a center drill, then drilled a pilot hole, then a slightly under-sized drill, and then finally reamed it out to size. The bolt was a tight press fit into the bushing, so everything seemed to work out well. I’ll be sure to keep the above in mind in the future.