What size drill bit?

[Ellen Benkin]

With the understanding that there are no dumb questions -- here's one

I am drilling holes in several pieces of mahogany to insert a 10-24 threaded rod. I've experimented and found that I can thread them through a 13/64 hole but it is very tight. The next size up 7/32 is too lose. I have borrowed a set of metric bits and will try them next. Any suggestions? I have a lot to do so I would be willing to purchase an odd size bit.

Thanks.

Ellen

[Dave Richards]

Are you sure it's 10-24 rod? If it is, it should have a major diameter of 0.190". A #11 drill would be 0.1910" dia., #10, 0.1935" dia. and 5mm, 0.1969" dia.

13/64" is 0.2031" and 12-24 would have a major diameter of 0.2160" which I would expect would have to be threaded in to get it through a 13/64" hole.

If you have #12 rod, a 5.5mm drill might be the ticket at 0.2165.

[Greg R Bradley]

A #3 is 0.01" larger than 13/64" but still 0.05" smaller than 7/32".

This doesn't quite add up as a tight clearance for 10/24 is #9 and a free fit is #7. Even the #7 is a tiny bit smaller than the 13-64" you say is too tight.

I added a nice chart that shows the progression of drill sizes including Number, Letter, Fractional, and Metric: tap drill chart 03.pdf

[Jim Becker]

As an aside, I will add that a digital caliper is an invaluable tool in the shop, including for things like this. Most have the ability to switch between inch decimal and metric and some also have inch fractional. (mine does) While I originally bought mine in support of my CNC for measuring material thickness, I'm using it an incredible lot for all kinds of projects including determining clearance hole size for fasteners like this. The brand I have is from iGuaging and I'm very pleased with it for the $30 or so it cost. Don't buy a really cheap "plastic" one...the often miss a digit of precision and I found out the hard way they were not quite accurate, either.

[Ray Newman]

This might help: Tap and drill size chart -- https://www.imperialsupplies.com/pdf...DrillChart.pdf

[Bill Dufour]

This might help: Tap and drill size chart -- https://www.imperialsupplies.com/pdf...DrillChart.pdf

My chart says #9 for close fit #7 for loose fit.#9 make sense because that is the next size up from #10.

[John K Jordan]

This chart has "close" and "free" fit drill sizes for common machine screw sizes.
https://pages.mtu.edu/~suits/misc/tapsizes.html

Maybe describe in more detail what you need to do.
- How deep are the holes?
- In side grain such as through a board or in end grain?
- Do you just need to insert the threaded rod or do you need for it to be able to slide freely but without slop? If the 13/64 is too tight in side grain, could it be that fibers on the inside are making the fit too tight? Maybe the drill bit is not sharp enough. I've used beeswax as lubricant. If fibers are suspected you might try dousing the inside of the hole with sanding sealer then redrilling after it's dry.

To slightly enlarge a hole in wood I've made "reamers" from a steel rod. I slightly flattened and widened a section near the end of a rod a bit with a hammer, filed a few grooves to help cut then spun the rod along the hole. Mostly the insides of the wooden holes were burnished to a slightly larger size.

If the threaded rod needs to slide freely without slop for some mechanical reason, I might consider drilling a larger hole and gluing in a bushing, perhaps a piece of tubing if I could find one that fit or make a bushing by drilling brass, aluminum, or HDPE or Delrin or something.

JKJ

With the understanding that there are no dumb questions -- here's one

I am drilling holes in several pieces of mahogany to insert a 10-24 threaded rod. I've experimented and found that I can thread them through a 13/64 hole but it is very tight. The next size up 7/32 is too lose. I have borrowed a set of metric bits and will try them next. Any suggestions? I have a lot to do so I would be willing to purchase an odd size bit.

Thanks.

Ellen

[Ellen Benkin]

Thanks everyone. I did want the rod to slide without either binding or slop. It turns out that a 5mm bit works well.

Yes, Jim, accurate measuring would help but I use the measuring device so infrequently that the battery is always dead. And trial and error is so much more fun.

[Jim Becker]

The unit I mentioned has auto-off, so the battery life is substantial. It comes with a second battery in the package, too. You will likely use one more than you think!

[John K Jordan]

...measuring would help but I use the measuring device so infrequently that the battery is always dead.

My favorite calipers for the shop, especially at the lathe and when sizing for drilling. I like this so much I bought a second in case I accidentally set one down somewhere.
The batteries are guaranteed to last an eternity.

caliper_fractions.jpg caliper_fractions_CU.jpg
https://www.amazon.com/gp/product/B005FRGF1Q

The scale is 64ths and 100ths but the eye can get much closer when needed.

JKJ

[Greg R Bradley]

Thanks everyone. I did want the rod to slide without either binding or slop. It turns out that a 5mm bit works well.

Yes, Jim, accurate measuring would help but I use the measuring device so infrequently that the battery is always dead. And trial and error is so much more fun.

As I said in the beginning, something doesn't add up.

The 5mm working confirms that something is wrong. It is smaller than the the 13/64" you said was too tight. Now if you had calipers so you could measure the supposed 13/64" bit and determine its actual size .................

[Greg R Bradley]

My favorite calipers for the shop, especially at the lathe and when sizing for drilling. I like this so much I bought a second in case I accidentally set one down somewhere.
The batteries are guaranteed to last an eternity.

caliper_fractions.jpg caliper_fractions_CU.jpg
https://www.amazon.com/gp/product/B005FRGF1Q

The scale is 64ths and 100ths but the eye can get much closer when needed.

JKJ

That is a brilliant idea. Another example of where analog beats digital. OR, where metric beats imperial

[Dave Richards]

As I said in the beginning, something doesn't add up.

The 5mm working confirms that something is wrong. It is smaller than the the 13/64" you said was too tight. Now if you had calipers so you could measure the supposed 13/64" bit and determine its actual size .................

I suspect the "13/64 in." isn't really 13/64 in. probably a smaller one that ended up in the wrong hole in the drill index.

[bill tindall]

Every woodworker needs a set of number drills for just such occasions as this one. Surprisingly many woodworkers have never heard of number drills. Splurge and get a set of letter drills too.

[John K Jordan]

Every woodworker needs a set of number drills for just such occasions as this one. Surprisingly many woodworkers have never heard of number drills. Splurge and get a set of letter drills too.

This is the type of set I've had in my drilling and tapping tool cabinet for a bunch of years:
drill_bit_set.jpg

Here's one:
https://www.amazon.com/dp/B00S1PZK2E

These sets typically have 115 bits with fractional (in 64ths), letter, and numbered bits.
So far I've always been able to find the bit I need for special clearance or for an odd-sized tap.
Get a good set and it will last a lifetime.

JKJ