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Forum topic by Elvin posted 962 days ago 778 views 0 times favorited 9 replies Add to Favorites Watch
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Elvin

55 posts in 1897 days


962 days ago

Don’t know if this is the right forum but I need some help. I am going to tap some new threads in an old iron oil pump to make a table lamp. Now the tap size I am going to use is 3/8 -24 teeth. Now I am trying to determine the size of the drill bit for this hole. I have looked on the internet at the charts they have available and they state to use a “Q” bit. I am unable to determine what exactly a “Q” bit is. If anyone has any knowledge on this subject I would appreciate any help available.
Thanks,
El

-- Elvin, Southern California, "How great would life be if we lived a little of it everyday"


9 replies so far

View Mickey Cassiba's profile

Mickey Cassiba

312 posts in 1530 days


#1 posted 962 days ago

Hi Elvin…here’s a link to a drill size chart. The Q is .332”
http://bobmay.astronomy.net/misc/drillchart.htm
HTH

-- One of these hammers oughta fix that...

View JJohnston's profile

JJohnston

1571 posts in 1790 days


#2 posted 962 days ago

Try McMaster-Carr (www.mcmaster.com). Search for “drill bit”, then narrow it down to size “Q” using the pulldown menus. They’re also in SoCal, so you might even be able to go there and pick it up.

-- The whole aim of practical politics is to keep the populace alarmed (and hence clamorous to be led to safety) by menacing it with an endless series of hobgoblins, all of them imaginary. - H.L. Mencken

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Grandpa

2976 posts in 1174 days


#3 posted 962 days ago

There are fractional drills, numbered drills and letter drills. Most of the number and letter drills are used for making holes to tap or something very precise. They are not expensive. For a lamp you might be able to substitute the next fractional size up. Do a test hole first. If this were something of strength then the letter drill would be used for sure.

View Arlin Eastman's profile

Arlin Eastman

1584 posts in 1060 days


#4 posted 962 days ago

+1 on what grandpa said, however, going up one size depends on the size going to. I would only go up afew thousands. You have to leave enough metal to thread with.
Arlin

-- It is always the right time, to do the right thing.

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Grandpa

2976 posts in 1174 days


#5 posted 961 days ago

That was what I was trying to say Arlin. I will cheat a little with a larger drill only if the dia. is close and the strength required is not great. Otherwise, go to the store and make the purchase. You should have it when the job is completed.

View crank49's profile (online now)

crank49

3239 posts in 1469 days


#6 posted 961 days ago

For what it’s worth, a 21/64” bit is .3281”, just a tad smaller than the “Q” bit. Might bind up on the tap.

And the 11/32” bit is 0.3437”, just a tad over size. This is what I’d use if the strength is not an issue. Your finished 3/8 threaded hole will be 0.375”, so you will still have some meat in the threads.

-- Michael :-{| Diapers and politicians both need to be changed often; and for the same reason.

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Dallas

2673 posts in 986 days


#7 posted 961 days ago

It’s for an oil lamp…. 3/8-24 would use a 5/16 bit. It’s not a precise fit or hardened steel. If you have a 21/64” bit, use it.

Make sure you tighten in a turn, back out a turn, tighten in a turn, back out a turn…. Keep the cutting edges clean as you go.

It’s not rocket surgery, so get as close to the size with the closest undersize that you own.

Good Luck, If they don’t find ya handsome at least they can find ya handy!

-- Improvise.... Adapt...... Overcome!

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Flyin636

57 posts in 992 days


#8 posted 959 days ago

Agree,not rocket science.Reason for post was that improper storage eats up more taps than actual usage.Throwin them in a drawer to bang around into each other will guarantee a dulled tap.Use compressed air to blow chips off tap,and put it back either in its box or;grab a nice block of wood(we use highly figure “drops)and drill a hole in top for taps along with their mated drills.Flyin636

View Elvin's profile

Elvin

55 posts in 1897 days


#9 posted 952 days ago

Thanks everyone. I couldn’t find a Q bit around town so I tried the 11/32” drill bit and it worked. I have a secure fit for the light and harp. Now I just have to finish the table. I will keep you posted.
Again thanks for taking the time to help.
El

-- Elvin, Southern California, "How great would life be if we lived a little of it everyday"

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