Bolt Holes

[iyermihir]

Hello,
I am designing a drive train and I want to use 1/4-20 bolts for some connections. I am not sure how big the holes should be. I was also wondering if there is a way to know what hole size to use for different size bolts.
Thanks

[Madison]

A hole size chart is indispensable.

See:
http://www.stanford.edu/~jwodin/holes.html

[Brandon Holley]

Originally Posted by Madison

A hole size chart is indispensable.

See:
http://www.stanford.edu/~jwodin/holes.html

This thing is bookmarked on just about every browser/computer I've ever used.

[Ninja_Bait]

Originally Posted by topgun

I wouldn't consider that useful advice.

Why not? If you find a bolt that you want to use, for whatever reason, and you don't know what size it is (let's say you dug it out of a bin of unsorted machine screws of various practically indistinguishable sizes), testing it in the holes in a drill index or a drill gauge could easily tell you what hole size you need.

Of course, a chart or a rule of thumb like FrankJ's is always better, especially when you know exactly what you're doing, and I did not intend to present this as replacement for the precise way. But for a quick and unimportant fix, I see nothing wrong with the above method.

[Gary Dillard]

Originally Posted by Ninja_Bait

Why not? If you find a bolt that you want to use, for whatever reason, and you don't know what size it is (let's say you dug it out of a bin of unsorted machine screws of various practically indistinguishable sizes), testing it in the holes in a drill index or a drill gauge could easily tell you what hole size you need.

What does that tell you? The hole in a drill guide are oversized quite a bit, so it's easy to put the bits in and out. Probably if you put a 1/4 inch bolt in the hole for a 1/4 inch drill bit, it would fit in really loose because the hole is larger. If you then used the 1/4 inch bit to drill your holes as you suggest, you wouldn't be able to assemble the parts because of tolerances. You may not even get 1 in since the bit wears down.

[Ninja_Bait]

Originally Posted by Gary Dillard

What does that tell you? The hole in a drill guide are oversized quite a bit, so it's easy to put the bits in and out. Probably if you put a 1/4 inch bolt in the hole for a 1/4 inch drill bit, it would fit in really loose because the hole is larger. If you then used the 1/4 inch bit to drill your holes as you suggest, you wouldn't be able to assemble the parts because of tolerances. You may not even get 1 in since the bit wears down.

Ah, I understand the ire now. I knew it wasn't a GOOD method, but I was suggesting it as a LAZY method. I'm sorry I have encouraged laziness in the FIRST community, and will recant my previous two posts on this thread.

(Though if I'm tired and frustrated around week four of build season, I may choose to use a drill gauge on a bolt. I'm sorry, I just can't stop myself. )

[EricH]

Originally Posted by Ninja_Bait

Ah, I understand the ire now. I knew it wasn't a GOOD method, but I was suggesting it as a LAZY method. I'm sorry I have encouraged laziness in the FIRST community, and will recant my previous two posts on this thread.

(Though if I'm tired and frustrated around week four of build season, I may choose to use a drill gauge on a bolt. I'm sorry, I just can't stop myself. )

There is a "better" lazy method. Compare the screw to the drill bit shank, right next to each other. If the shank matches the screw size, then you should be all set. If the hole is too small, find the next drill size larger (or a non-working student or mentor with a rat-tail file or similar device) and make the hole large enough for the bolt.

Can't tell how many times I've used that to find the drill bit that best fits small screws used to attach servo stuff to R/C airplanes...

[PAR_WIG1350]

Calipers work too, just use the flat parts, not the tapered portion which could slip in between threads and give an inaccurate measurement.

[Retired Starman]

There are other reasons to drill holes larger than necessary for the bolt in question. A 14-20 bolt will easily fit in a 1/4 in. hole, but if the hole is in aluminum, once you have tightened the bolt, you have deformed the hole so that the bolt will be difficult to remove and reinsert the next time.

In different applications, hole clearance varies. For precision machines, specified clearance is less than for architectural use, for instance.

Use of a good, appropriate chart is suggested.

Dr. Bob

[JB987]

Just Google "through hole size chart" and you will come up with many great charts like the one from this link...

http://www.stanford.edu/~jwodin/holes.html

Madison beat me to it, guess my old fingers don't fly fast enough!

[Gray Adams]

If you're using Inventor (and probably SolidWorks too, but I wouldn't swear to it), you can define clearance holes for various bolt sizes with the hole tool.

[Ankit S.]

Also, just in case you did not know this, the first number in a two-number bolt number is the diameter of the screw, while the second number is the threads per inch.
i.e. 10-32= #10 diameter (this is where the chart comes in handy) and 32 threads per inch.

[Ninja_Bait]

You can also just take a drill index and stick bolts in it until you find the right hole size.

[IndySam]

I use a droid app to tell me such things.

[topgun]

Originally Posted by Ninja_Bait

You can also just take a drill index and stick bolts in it until you find the right hole size.

I wouldn't consider that useful advice.

Both SAE and Metric are located here:
http://littlemachineshop.com/Referen...DrillSizes.pdf

Print this and put one copy by your CAD workstation, one by your mechanical toolbox and one by your electrical toolbox, or wherever you will be drilling holes for tapping or clearance.