Home made tool ?

[Joe Meirhaeghe]

I'm wanting to make a chisle that has both ends ground. One end as a round nose scrape & the other end as a square end scraper. I have a piece of M2 HSS 3/8 X 3/8 X 7" long. I plan to made a ferrull out of 3/4 " black steel pipe with 1/4" set screw to hold chisle in the handle.
My question what size drill bit should I use to drill the hole to tap for the 1/4" set screw??? I plan to use a fine thread set screw because the pipe isn't that thick & it wiil take more threads with fine threads.
Thanks Joe.

[Andrew Goossen]

Joe-
It looks like that would take a #3 bit. You can go to Google and type in tap thread charts and about the second or third hit has good reference charts to refer to for all metals and plastics. Most hole sizes are 75% of the thread depth. Fine threads are not very deep so the hole needs to be fairly precise.

Andrew

[neil mackay]

Joe,

http://www.prescottengineering.co.nz/Tap%20drill%20sizes.pdf

http://www.rwc.yertiz.com/tapchart.pdf


some thing like this is what your looking for

[Reed Gray]

There is a traditional tool used by the Oregon Coast Myrtle wood turners that is called the "Big Ugly Tool". It is a piece of 3/4 inch square stock with a piece of 7/8 wide by 2 inch long by 3/32 thick Tantung steel silver soldered to each end. One end is more square, the other more rounded. The Tantung can last through a half day of production work without needing sharpening. A leather glove is worn on the hand that holds the end that isn't cutting. They turn at about 4,000 rpm. I have a 'civilized version of the tool that some one made for me, and love it. In the hands of a master, you can cut amazingly detailed finials. You have to see it to believe it.
robo hippy

[Randy Privett]

There is a simple formula that is used to figure the tap drill size. For a 1/4-20 set screw, you would take the diameter of the size of screw that you have, in this case it would be .250. Subtract the 1" divided by the number of threads per inch; 20. Looks like this. .250-1 divided by 20. The answer is .200. The closest to that is a number 7 drill at .201. You can use this for any drill tap.

For metrics, such as 3.5-.6. Subtract the .6 from the 3.5, leaving 2.9. Multiply 2.9 times .03937, and this will give you the decimal equivilent of .114, which would be a #32 (.116) or #33 (.113) drill.


Randy