not how they teach you to do it in school

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liveaboard
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not how they teach you to do it in school

Post by liveaboard »

I need to tap a whole lot of 12mm holes in my new worktops.

I ordered a nice German tap 2 weeks ago but it still hasn't made it to my house with no number on a road with no name...
So I'm using a cheapo tap from a set I once got at a flea market. It might break before I'm done.
I just added the reversing switch to the drill press

I don't think this is how they teach you to tap holes in engineering school; but since I never went to school I wouldn't know.
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John Hasler
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Re: not how they teach you to do it in school

Post by John Hasler »

If I relied only on my engineering school education I wouldn't know what a tap was.
LIALLEGHENY
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Re: not how they teach you to do it in school

Post by LIALLEGHENY »

Are you asking if this is an acceptable method of tapping? The answer is yes and no. Power tapping is acceptable using the correct taps, don't use a hand tap. Are the holes through the material or blind? You also don't want your RPM to high. Some drill presses don't run slow enough.

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Steggy
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Re: not how they teach you to do it in school

Post by Steggy »

liveaboard wrote: Fri Jun 22, 2018 1:19 pm I need to tap a whole lot of 12mm holes in my new worktops.

I ordered a nice German tap 2 weeks ago but it still hasn't made it to my house with no number on a road with no name...
So I'm using a cheapo tap from a set I once got at a flea market. It might break before I'm done.
I just added the reversing switch to the drill press

I don't think this is how they teach you to tap holes in engineering school; but since I never went to school I wouldn't know.
Power tapping in a drill press is okay—I do it all the time without using a reversing tapping head (although I do have one). Be sure to use a spiral point tap, aka "gun" tap, not a hand tap like sold in the hardware store. Also, be generous with cutting oil and don't run the tap too fast.

Spiral point ("gun") tap
Spiral point ("gun") tap
Spiral point ("gun") tap
Spiral point ("gun") tap
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Harold_V
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Re: not how they teach you to do it in school

Post by Harold_V »

What BDD said. Power tapping demands a tap that deals with chips, so they don't remain in the flutes. A straight flute without a lead at the cutting edge (like a hand tap) lacks that feature.

When one attempts to power tap with a hand tap, if the material isn't quite thin, chips accumulate in the flutes to the point where they begin to bind the tap in the hole. Once that happens, you have little chance of finishing the hole before the tap seizes and breaks.

Spiral fluted taps draw the chips outward, but my experience with using them dictates that they are quite easy to break as compared to the gun tap design. For that reason, I use gun taps even for blind holes, assuming I can drill the hole deep enough to allow for chips to accumulate. Even if they get compressed, they're usually reasonably easy to remove by using a needle point air hose.

H
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liveaboard
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Re: not how they teach you to do it in school

Post by liveaboard »

These are though holes in 10mm [3/8"] mild steel plate.

Hand tap is all I have; engineering supplies are a bit thin on the ground where I live, the only shop that sold those things went belly up during the financial crisis. When I was in town last, I couldn't get ANY 12mm tap [out of stock], never mind a particular type.

The clutch [aka drive belt] on the drill press has been keeping the cheap Chinese tap alive so far. At first it went through in one pass, then it started jamming and needed to be pulled out once, then twice as (I assume) the tap gets duller. The chuck disengages in reverse so I have to remove by hand, which is probably a good thing.
I have about 20 holes left to thread.

Thanks for the lessons, guys; I'll let you know how it goes.
Magicniner
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Re: not how they teach you to do it in school

Post by Magicniner »

You can sharpen a tap by, with skill and judgement, relieving the leading edge with a diamond file or hone, once you have it down pat you can use a diamond tipped tool in a Dremel-like tool to get back to a sharp edge.
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Re: not how they teach you to do it in school

Post by choprboy »

Better than a spiral point (gun tap), is a spiral flute tap. I do 12mm power taps in the drill chuck of my mill all the time. Takes a bit of experience, but get everything lined up and make sure you have enough quill length for the hole, turn on the motor and let the tap gently drop into the workpiece and self feed, shut off the motor part just as you are starting or part way thru (depending on tap depth) and let the machine coast thru the hole tapping (possibly use the spindle brake to prevent going to far). The main thing is don't over drive and don't try to start in the tapped hole, always back out and try a new run if you don't make it all the way.
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Steggy
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Re: not how they teach you to do it in school

Post by Steggy »

Harold_V wrote: Fri Jun 22, 2018 3:59 pmWhen one attempts to power tap with a hand tap, if the material isn't quite thin, chips accumulate in the flutes to the point where they begin to bind the tap in the hole. Once that happens, you have little chance of finishing the hole before the tap seizes and breaks.
In the old days, we called that "crowding the tap." Dunno what term is now used to describe the tap-breaking process to apprentice machinists.
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Steggy
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Re: not how they teach you to do it in school

Post by Steggy »

choprboy wrote: Fri Jun 22, 2018 9:13 pmBetter than a spiral point (gun tap), is a spiral flute tap.
Some 55 years of experience makes me disagree. As Harold noted, spiral flute taps are relatively fragile, mostly due to their small cross-section. I'd rather spend a bit of extra time clearing chips from a blind hole that was tapped with a gun tap than extracting a broken spiral flute tap from a piece that has many hours of work in it.
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Magicniner
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Re: not how they teach you to do it in school

Post by Magicniner »

BigDumbDinosaur wrote: Sat Jun 23, 2018 4:29 am
choprboy wrote: Fri Jun 22, 2018 9:13 pmBetter than a spiral point (gun tap), is a spiral flute tap.
Some 55 years of experience makes me disagree. As Harold noted, spiral flute taps are relatively fragile, mostly due to their small cross-section. I'd rather spend a bit of extra time clearing chips from a blind hole that was tapped with a gun tap than extracting a broken spiral flute tap from a piece that has many hours of work in it.
It's a use, judgement and experience thing, I use spiral flute taps down to M3 with a battery drill and haven't broken one that way yet, I suppose if you're cack-handed you could bust one every time with any machine though :lol:
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liveaboard
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Re: not how they teach you to do it in school

Post by liveaboard »

I finally got my new taps from Germany; I had some mail trouble and the first order got lost.

What a difference, it cuts like butter. Just slides right through the 3/8" steel plate.
vokel tap.jpg
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