1

I would like to know if it is possible to reduce a drill bit diameter (the body and not the shank). From times to times I need to work with dimensions that are not integer number or half number.... example: where I live I can only find drill bits 6mm or 6.5mm or 7mm..... however, in some cases I really need to have a dimension of 6.25mm.

Is this even possible to do, if yes how?

2
  • 3
    I imagine this would need a lathe, special cutting tools and probably a process to recreate the hardening of the drill's cutting edge? But if you have those tools wouldn't it be far better to make a bit from steel rod stock? Jun 25, 2014 at 9:36
  • 5
    Use the 6mm bit, and wiggle it a bit to widen the hole to 6.25mm. If you're dealing with such precision, you should probably be using specialty tools. For reference: 6.5 mm = 0.255906 in., 6.25 mm = 0.246063 in. A difference of 0.009843 in. or ~5/512 in. (0.009765625).
    – Tester101
    Jun 25, 2014 at 11:10

3 Answers 3

7

I would suggest that you look a little farther. Drill bits are available in many more sizes than you mentioned. One big supplier on-line, McMaster Carr shows available metric sizes for heat resistant cobalt steel jobbers drill bits in all of the following metric sizes:

enter image description here

If you can find access to a supplier that has drills on the numbered gauge scale or the lettered scale they cross reference to metric sizes as shown here:

enter image description here

1

In theory, yes, you would need to remove the hardening by heating to the proper temp and slowly cooling, turn it on a lathe, mic in your specs, re-harden... Best bet would be buying more drill bits. Like recommended above, McMaster Carr is an excellent source for more tools than you thought existed. Maybe you need SAE/inch pattern? 6mm=.236in 6.25mm=.246in 6.35mm=.25in 6.5mm=.256in 3/16in=4.763mm 7/32in=5.555mm 1/4in=6.35mm 9/32in=7.142mm

2
  • I'm not sure how this answer adds any additional information?
    – bib
    Jun 25, 2014 at 23:39
  • so I can not sharpen a bit without annealing it first..Nonsence! Reduce the lands by grinding, keep it cool or use a wet stone machine. If access to a lath use a tool grinder attachment for a precision grind.
    – gary
    Aug 27, 2018 at 20:32
0

You can buy metric and imperial drill bits.

If your local hardware don't sell both you can buy them online. (ebay) or other site.

Also if you try to machine a drill bit down it won't be as strong.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.