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Forum topic by Elvin posted 08-28-2011 04:11 AM 868 views 0 times favorited 9 replies Add to Favorites Watch
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Elvin

62 posts in 2152 days


08-28-2011 04:11 AM

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 1785 days


#1 posted 08-28-2011 04:20 AM

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

1602 posts in 2045 days


#2 posted 08-28-2011 04:27 AM

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.

-- "A man may conduct himself well in both adversity and good fortune, but if you want to test his character, give him power." - Abraham Lincoln

View Grandpa's profile

Grandpa

3212 posts in 1429 days


#3 posted 08-28-2011 04:31 AM

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

2250 posts in 1315 days


#4 posted 08-28-2011 04:43 AM

+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

3212 posts in 1429 days


#5 posted 08-29-2011 08:37 PM

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

crank49

3524 posts in 1724 days


#6 posted 08-29-2011 09:11 PM

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 :-{| “If you tell a big enough lie and tell it frequently enough, it will be believed.” ― A H

View Dallas's profile

Dallas

3217 posts in 1241 days


#7 posted 08-29-2011 09:56 PM

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!

View Flyin636's profile

Flyin636

57 posts in 1247 days


#8 posted 08-31-2011 10:59 AM

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

62 posts in 2152 days


#9 posted 09-07-2011 11:13 PM

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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