Drills

[Billh50]

BillyG I also learned that trick when I first started in machining some 40 odd years ago. I had to tap a hole in a part that was getting carburized and heat treated and didn't have an oversize tap. The old toolmaker next to me said "throw a rag over the hole first". I thought he was nuts til I tried it. Worked like a charm. Never forgot that trick.

 

[Bill Gruby]

Off track a bit but useful here. There was a story years ago about a company the made wire so thin you needed a microscope to see it. They sent a sample to another company in Switzerland. Upon returning the sample the Swiss company added a note to the package. It read, "Look at it again." The Swiss company had drilled it full of holes at equal intervals. Moral -- As Tony said, because you have never seen one or disbelieve does not mean it does not exist.

"Billy G"

 

[Wreck™Wreck]

You can also wrap twine around a tap to make it cut oversize.

I have been told by old timers, (older than myself that is) that dulling one flute of a chucking reamer will change the size of the hole produced. I have never tried this approach and probably never will, I already dislike reamers generally.
This is a personal preference and should not be considered as fact in any way.

 

[Bill Gruby]

This will work. Because of the unequal pressure on the dulled flute the remaining flutes will push away from the wall of the hole making the hole slightly smaller. Another old timers trick.

"Billy G"

 

[Wreck™Wreck]

For a basic tap drill size reference you can use this. If memory serves this chart lists the drills for 75% thread engagement.
http://www.brokenbolt.com/images/starrett-inch-metric-tap-drill.pdf
.

This is exactly what I dislike about hobby machinist sites,(as much as I like them and try my best to help) you just provided a link to Brokernbolt.com, this will teach you nothing, ever. You also provided a link to Starrett, most likely you will never buy a new tool from them or Mitutoyo.
However I enjoy the people here and will carry on dispensing information, good bad or otherwise (-:

 

[Bill Gruby]

With all due respect did you click on the link or just read it. It takes you directly to a PDF chart from Starrett, nowhere else. It is only one link, not two.

"Billy G"

 

[Billh50]

I always try to give some tips from things I have learned through the years as a toolmaker. Some of the tips may sound strange but they do work and probably have for a hundred or more years. Most of the tips I have learned I learned from the old toolmakers where I worked. They could teach you stuff you won't find in any books. But they will only teach you if you are willing to learn. Laugh at them and call them names and they will watch you make mistake after mistake without ever helping you. But listen to them and show them you want to learn and they will keep you from making a lot of mistakes.

 

[Dan_S]

This is exactly what I dislike about hobby machinist sites,(as much as I like them and try my best to help) you just provided a link to Brokernbolt.com, this will teach you nothing, ever.

What part of the bolded and italicized word "basic" did you not understand. The other reason I gave it was because it could be downloaded without a login. You can get the exact same PDF from Starrett, but you need to make a login to get it.

You also provided a link to Starrett, most likely you will never buy a new tool from them or Mitutoyo.

Oh really, Will a picture do, or do you need part numbers as well?

 

[Tony Wells]

Settle down, guys.

 

[Wreck™Wreck]

This will work. Because of the unequal pressure on the dulled flute the remaining flutes will push away from the wall of the hole making the hole slightly smaller. Another old timers trick.

"Billy G"

I find it difficult at times to hold a tolerance with a reamer when 100 or more holes are required, I suspect that this may be a personal problem (-: