scratchedup
Well-known member
I just purchased these. Can someone explain how to read this chart?
Drill Bits & Tapping 101
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Buckgnarly
Well-known member
Top row tap size, next row down is for National Coarse threads in that tap size....next row tells what drill size to use.
Next two rows down are same except for fine thread (NF). Make sense?
Next two rows down are same except for fine thread (NF). Make sense?
Since this is 101 and not 102...
Rows 1, 3, & 5 are fractions. In other words, if you are seeing 8 rows, first combine rows 1/2, 4/5, 7/8 and look at them as 5 rows.
You have to drill a hole before tapping. Rows 1&2 or 1&4 combine for a desired tap thread, rows 3 or 5 tell you what hole to drill first.
Rows 1, 3, & 5 are fractions. In other words, if you are seeing 8 rows, first combine rows 1/2, 4/5, 7/8 and look at them as 5 rows.
You have to drill a hole before tapping. Rows 1&2 or 1&4 combine for a desired tap thread, rows 3 or 5 tell you what hole to drill first.
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I'm more of a learn by example type, so.
Ex. Say you want to tap something with a 1/4-20 thread, which is a 1/4" diameter NC (National Coarse) thread. You would select the 1/4" column, go down to the "20 (NC row)" and use the drill size below that, which would be a 13/64" drill bit.
Now say you wanted to tap something for a fine thread like 7/16-20. You would select the 7/16 column, go down to the "20" for the NF (National Fine) thread pitch row, and use the corresponding drill bit below that, which would be a 25/64" drill bit.
I've never seen a chart like that, is there a name on it?
Ex. Say you want to tap something with a 1/4-20 thread, which is a 1/4" diameter NC (National Coarse) thread. You would select the 1/4" column, go down to the "20 (NC row)" and use the drill size below that, which would be a 13/64" drill bit.
Now say you wanted to tap something for a fine thread like 7/16-20. You would select the 7/16 column, go down to the "20" for the NF (National Fine) thread pitch row, and use the corresponding drill bit below that, which would be a 25/64" drill bit.
I've never seen a chart like that, is there a name on it?
OP
scratchedup
Well-known member
Thanks I get it now.
Question 2-
The set came with sizes 1/16" through 1/2". Since they were helpful enough to include tap sizes for 1/4 - 1/2 why did they not include sizes screw 2, 4, 6, 10...?
"I've never seen a chart like that, is there a name on it?"
I splurged---
I'm ready for 102!
Question 2-
The set came with sizes 1/16" through 1/2". Since they were helpful enough to include tap sizes for 1/4 - 1/2 why did they not include sizes screw 2, 4, 6, 10...?
"I've never seen a chart like that, is there a name on it?"
I splurged---
I'm ready for 102!
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woody 73
Well-known member
Yes I was thinking along the same lines; but then I did not want to scare the **** out of the op now he has to go out and buy more drill bit sets...
http://www.guhring.com/documents/Tech/Charts/CutTapDrill.pdf
Study the above chart to get a bit more understanding. Some tapped holes call out a number or letter drill bit. If you also understand percent thread then you can start to learn how to fudge a bit on tap drill size. There is a whole science behind tapped holes in different materials and threaded joints.
Also spend a bit of time on the guhring site and you can learn a lot
http://www.guhring.com/ELearning/Category/?cat=8
lg
no neat sig line
Study the above chart to get a bit more understanding. Some tapped holes call out a number or letter drill bit. If you also understand percent thread then you can start to learn how to fudge a bit on tap drill size. There is a whole science behind tapped holes in different materials and threaded joints.
Also spend a bit of time on the guhring site and you can learn a lot
http://www.guhring.com/ELearning/Category/?cat=8
lg
no neat sig line
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MotoDave
Well-known member
One of my favorite Drill/Tap charts: http://littlemachineshop.com/Reference/TapDrillSizes.pdf
Wamsutta
Well-known member
For a 1/4-20 tap use 13/64 drill
For a 1/4-28 tap use 7/32 drill
For a 1/4-28 tap use 7/32 drill
Matt Irvine
Well-known member
For anyone who was interested in the chart, my Huot index also has the same chart in it.
Also here is a Starrett tap drill chart:
http://www.brokenbolt.com/drill-tap-chart.php
Some places that sell machine tools and measuring instruments will give away a wallet-sized, laminated card that has all this info on it. They can also get a bigger version that you can hang on the wall.
http://www.brokenbolt.com/drill-tap-chart.php
Some places that sell machine tools and measuring instruments will give away a wallet-sized, laminated card that has all this info on it. They can also get a bigger version that you can hang on the wall.
woody 73
Well-known member
Now you guys went and did it, scaring the **** out of the op...poor guy only wants to drill a few holes and soon we will convinced him that now he needs a drill press.
All in good fun hope you learned a few things today.
All in good fun hope you learned a few things today.
OP
scratchedup
Well-known member
Like I said I splurged...I bought all 3 full sets USA made.
I assume its covered in the provided links but but now maybe the simple stamped guide chart is not so accurate...it assumes one only has a fractional set???
Scared is good...it keeps me from making as many mistakes
I assume its covered in the provided links but but now maybe the simple stamped guide chart is not so accurate...it assumes one only has a fractional set???
Scared is good...it keeps me from making as many mistakes
OP
scratchedup
Well-known member
I think this may be 'Masters Level" work...
Its a wow
There is a lot more to tapping a hole than making a hole and putting some ridges in it. The above is the minimum you should understand if your are serious about what you are doing.
lg
no neat sig line
woody 73
Well-known member
It took me years to understand we all have been in your shoes at one time or another; The following youtube video is from a shop teacher that does a very good job of explaining things for you, although you might need need to start with his first video on the subject of tapping.
MFolks
Well-known member
Make sure, when drilling holes in metal, to use a coolant. Dark Sulfur oil for drilling and tapping for steel, or Rapid Tap cutting fluid, Aluminum can use WD-40 spray, or Aluma tap cutting fluid.
For me, preferred taps are the two flute "Gun" taps, for open, or through holes, as it forced the chip out as threads are being cut. If the hole is closed, or "Blind", then a bottoming tap is needed.
The typical hardware store tap, is usually the 4 flute type, requiring you to start the cutting action, stop, turn back, and then turn to the right again to keep cutting. Repeating this action until the hole is tapped. It takes a certain "Feel" doing this, as taps will break if forced being brittle.
To ensure the tap is starting at 90 degrees to the drilled hole, I advise getting a tapping block: http://littlemachineshop.com/products/product_view.php?ProductID=2571 Once a tap starts, do not try to "Straighten it out", if it's going crooked, almost a certainty of breaking.
For me, preferred taps are the two flute "Gun" taps, for open, or through holes, as it forced the chip out as threads are being cut. If the hole is closed, or "Blind", then a bottoming tap is needed.
The typical hardware store tap, is usually the 4 flute type, requiring you to start the cutting action, stop, turn back, and then turn to the right again to keep cutting. Repeating this action until the hole is tapped. It takes a certain "Feel" doing this, as taps will break if forced being brittle.
To ensure the tap is starting at 90 degrees to the drilled hole, I advise getting a tapping block: http://littlemachineshop.com/products/product_view.php?ProductID=2571 Once a tap starts, do not try to "Straighten it out", if it's going crooked, almost a certainty of breaking.
OP
scratchedup
Well-known member
Thanks...all this has really helped.
Think you guys are reading too much into this. For stuff in the range of 1/4" to 1/2", I just drill two drill sizes smaller. That will get you into the range for good enough threads for any home workshop type job.
Have never owned lettered or numbered bits, except those teeny ones, for orifice drilling/cleanout use.
Have never owned lettered or numbered bits, except those teeny ones, for orifice drilling/cleanout use.
Not all of us come from a home workshop point of view. Items I've had a hand in building items that have gone into space... Two sizes smaller will not cut it.
Just curious, what is the size of a drill bit two sizes smaller than a 1/2"?
lg
no neat sig line
I don't think we are overthinking this. You have decided to oversimplify something that is quite simple already. Why deviate from accepted standards and compromise the end result?
The op was specifically asking what the chart was actually stating. You basically told him to forget it and use your rule of thumb. He has a 115 piece drill set so why not use the correct bit? Because it's too difficult to find it? It's in the case.
softailgarage
Well-known member
Now you guys went and did it, scaring the **** out of the op...poor guy only wants to drill a few holes and soon we will convinced him that now he needs a drill press.
All in good fun hope you learned a few things today.
OK, so now you've mastered the Drill/Tap charts. In order to be completely educated you MUST buy a drill press.
He would recommend 15/32 with his rule of thumb. This is .46875.
1/2-13 calls for .4219 for 75% thread.
1/2-13 calls for .4531 for 50% thread.
1/2-20 calls for .4531 for 75% thread.
1/2-20 calls for .4688 for 50% thread.
Sounds like his rule of thumb is spot on for 50% thread in 1/2 nf. And for the other stuff, pretty dam loose no?
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OK, so now you've mastered the Drill/Tap charts. In order to be completely educated you MUST buy a drill press.
Yes, drill press is a must. Someone is going to come along and say that we have made it too difficult and that a hand drill is good enough.
justme-
Well-known member
FWIw, my old Craftsman large index as well as my houts have a similar chart in them. Important to note tho is the charts should be related to the index they are in- a fractional index will list fractional size bits where a numeric index will have numeric ones. this differs in vintage cases where my Craftsman (60's era) lists correct sizes, both numerical, alphabetical and fractional for the specific tap yet the index is fractional.
I prefer a drill press for tapping whenever I can simply because it ensures a 90* hole and thread (providing the press is straight and setup). I'm going to have to get a tapping guide...never seen one of those before. Thanks!
I prefer a drill press for tapping whenever I can simply because it ensures a 90* hole and thread (providing the press is straight and setup). I'm going to have to get a tapping guide...never seen one of those before. Thanks!
Well jeeze with that attitude, all we should own is a adjustable wrench, flip flop screwdriver and a claw hammer? Ain't you ever heard the phrase, close enough is only applicable in horseshoes and hand grenades?
Test Question:
Not so fast. First answer this test question:
Does a worn drill bit produce a larger hole or a smaller hole?
(dont' read too much into this- forget temperature or the nominal drill size).
Yes, drill press is a must. Someone is going to come along and say that we have made it too difficult and that a hand drill is good enough.
Not so fast. First answer this test question:
Does a worn drill bit produce a larger hole or a smaller hole?
(dont' read too much into this- forget temperature or the nominal drill size).
Fretters
Well-known member
Re: Test Question:
Some of you do take things way too seriously.
Larger, if it's the tip which is off kilter.
Some of you do take things way too seriously.
Larger, if it's the tip which is off kilter.
davethorik
Well-known member
i think some of you guys should see power tapping on a cnc machine. blind holes? No sweat, use a spiral flute tap and the chips come out the top (3 long coiled strings).
Re: Test Question:
Correct answer. Drill bits wear at the tip and "walk". As they get worn, the tip follows a noncircular path, resulting in a larger, and sometimes non-round hold.
So step one, you should develop a way to sharpen drill bits. I have a Drill Doctor, but you can learn to do it by hand as well. I envy those who can do a good job sharpening by hand.
Once you have a way of sharpening drill bits THEN you need a drill press so you can drill square to your work piece. Hopefully the drill has little run-out (wobble due to lack of concentricity).
Once you can produce good quality holes, then you can tap them and produce good strong threads. I have a little spring loaded device for a drill chuck that allows you to tap the hole using your drill press quill as a guide for square.
Some of you do take things way too seriously.
Larger, if it's the tip which is off kilter.
Correct answer. Drill bits wear at the tip and "walk". As they get worn, the tip follows a noncircular path, resulting in a larger, and sometimes non-round hold.
So step one, you should develop a way to sharpen drill bits. I have a Drill Doctor, but you can learn to do it by hand as well. I envy those who can do a good job sharpening by hand.
Once you have a way of sharpening drill bits THEN you need a drill press so you can drill square to your work piece. Hopefully the drill has little run-out (wobble due to lack of concentricity).
Once you can produce good quality holes, then you can tap them and produce good strong threads. I have a little spring loaded device for a drill chuck that allows you to tap the hole using your drill press quill as a guide for square.
OP
scratchedup
Well-known member
CAN SOMEONE SELL ME A DRILL PRESS...FAST!
Well I have one but its kind of a cheapie Rikon.
Well I have one but its kind of a cheapie Rikon.
A cheap drill press is better than none. If it is not worn out and does not have excessive runout then it should work OK. Be sure to check out the youtube video up in post #17. He gives some alternatives to the drill press that may work for you. I really liked the method of counterboring a slightly larger hole to guide the tap alignment, should work well enough for most threaded holes.
woody 73
Well-known member
I have created a "MONSTER"...
http://jacksonville.craigslist.org/tls/4593793183.html
Lord help me out.
http://jacksonville.craigslist.org/tls/4593793183.html
Lord help me out.
OP
scratchedup
Well-known member
that actually looks pretty cool and its not $500!
davethorik
Well-known member
Re: Test Question:
I forgot about this, I know a few older machinists who have all had to make one in their apprenticeship. I decided to take the easy route and get the Fisher Micro Tap Guide. Made in USA
http://fishermachine.com/index.php?content=buyproducts&cat=6
I forgot about this, I know a few older machinists who have all had to make one in their apprenticeship. I decided to take the easy route and get the Fisher Micro Tap Guide. Made in USA
http://fishermachine.com/index.php?content=buyproducts&cat=6
Your assuming that he has a set of bits that graduates in 1/64" increments.
lg
no neat sig line
OP
scratchedup
Well-known member
Are these available as a set? That would be a lot O bits.
Look close and you'll find your 29 piece graduates in 64 ths. Out little discussion has a 1/2"=32/64" two sizes smaller is 30/64" or 15/32".
lg
no neat sig line