Tool Stubby Drill Bits

[mickeyf]

At risk of blasphemy....

The "ideal" drill bit sizes listed in all the engineering books are merely "ideal", not magic. There is generally a standard fractional size that is within a couple of thou', or some tiny percentage of error larger. For example, compare a #7 to a 13/64". For 99.9% of what I do, which is neither Swiss watches nor space shuttles, that's fine. Also, intuitively at least, if you are able make your threaded hole a few threads deeper that extra engagement will make up for the fact that your hole was 0.002" larger in diameter. 72% engagement rather than 75% is no problem unless it that's enough to make your flying machine fall out of the air. Yes, as you get into smaller and smaller sizes things get fussier, but for say, 3/16" (5mm ish) and upwards there is generally wiggle room.

I do have number and letter drills, and use them, but sometimes it's easier to just grab one that's "close enough". Regular imperial size drills can be had for pennies at yard sale and places like the Habitat For Humanity Restore, and resharpened - possibly cut down to a length you are happy with. And if you are sharpening them anyway, you can make the point whatever angle you need.

 

[140mower]

At risk of blasphemy....

The "ideal" drill bit sizes listed in all the engineering books are merely "ideal", not magic. There is generally a standard fractional size that is within a couple of thou', or some tiny percentage of error larger. For example, compare a #7 to a 13/64". For 99.9% of what I do, which is neither Swiss watches nor space shuttles, that's fine. Also, intuitively at least, if you are able make your threaded hole a few threads deeper that extra engagement will make up for the fact that your hole was 0.002" larger in diameter. 72% engagement rather than 75% is no problem unless it that's enough to make your flying machine fall out of the air. Yes, as you get into smaller and smaller sizes things get fussier, but for say, 3/16" (5mm ish) and upwards there is generally wiggle room.

I do have number and letter drills, and use them, but sometimes it's easier to just grab one that's "close enough". Regular imperial size drills can be had for pennies at yard sale and places like the Habitat For Humanity Restore, and resharpened - possibly cut down to a length you are happy with. And if you are sharpening them anyway, you can make the point whatever angle you need.

That is what I do..... I have a good set of Dormers that I keep for special occasions, and everything thing else comes out of a tobacco can of extras for everyday hand drill use.....

 

[Susquatch]

Also, intuitively at least, if you are able make your threaded hole a few threads deeper that extra engagement will make up for the fact that your hole was 0.002" larger in diameter.

Fundamentally, I like your post and agree with most of your comments. I approach deeper tbreads a wee bit differently.

Although it seems intuitive that deeper threads can make up for loose fits, it ain't necessarily true. In this case, there are limits. As a threaded fastenener is tightened with increasing torque, the male threaded shaft stretches and the female threaded hole compresses. The stretching starts at one end and then "grows" toward the other end as torque increases. There comes a point in the length of the fastener after which the threaded portions no longer stretch or compress and any extra threads in the extra length are just there for the ride. Also, as the threads stretch, they can reach their yield strength and start failing. When this happens, subsequent threads will take up some load but there is only so much they can take until things start to break and the threads strip or the bolt breaks off.

Different materials have different properties, steel requires fewer threads than aluminium. Even more problems arise when the male and female parts have different material properties.

Lastly, every situation is different. Whole books have been written on the subject. Ideally, a fellow would analyse and test each situation to determine the best solution.

Most of us don't have the luxury of being able to do that. That's why I like your thoughts on this.

Generally speaking, I think it's preferable to strive for a good fit for the requisite length than to make the threaded connection longer.

 

[mbond]

the shape of the thread roots matters a lot when considering a failure of this kind.

 

[slow-poke]

Great chat and options for drill bits.... Yes the ones that Mike is referring to are a high quality Morse brand (Made in USA) and are typically sold into production applications.

I do have available a wide variety of sets in a number of quality ranges:

ProCut - Import
Rapidkut - USA Generic
Morse, Precision Twist, Chicago-Latrobe - Premium

If price was the same which of the premium ones would you choose?

 

[SkookumRob]

If price was the same which of the premium ones would you choose?

Great question... I have favored Morse Cutting Tools as my "go-to" premium drill bit, however that decision was more based off business relations than value/quality assessment. I honestly have not really heard any great differences between the premium brands, so it typically goes to "personal preference" or inventory availability (some supply quicker than others). Even the "Rapidkut" which could come from a number of different USA manufacturers (not divulged to us which one - but I have my suspicions!) can often be of similar quality.

So the short answer is "I" would typically choose Morse or if I am finding the pricing just too high, I would go with RapidKut. But really there is not a poor choice in the bunch!

 

[buckbrush]

I have used both inch and metric screw machine drill sets from KBC, they work well. For sizes I use a lot, I buy multiples of higher quality screw machine bits. I have found Walther and Guring (both German made) to last the longest and only drill .002 thou oversized on my machines.