tap drill size

#7 bit.

I use my small cordless black&decker 3/8 drill in slip mode around 10 to drive the tap in, when it jams and the drill chatters, reverse it and then reenter. I do this all the time when making enclosure mounts etc..

P.S. If you don't have drill&tap oil around, use D-40 and use a start (tapered tip) tap not a bottom tap.

Jim Thompson wrote in news: snipped-for-privacy@4ax.com:

If you are doing through holes, what you really want is a "gun" tap. These push the chips out in front of the tap, so you don't have to do the "forward 3/4 turn, back up 1/4 turn" routine to bust off the chips. They just corkscrew out ahead of the tap.

A combination of:

1) lube

2) a guide block

3) a high quality gun tap

and you will be amazed at how easy it is to tap holes.

Doug White

That level of flexing is not normal. You risk snapping the tap off in the hole, which is a nuisance.

Lube, and, back the tap up a bit every half turn or so to break the chips (cuttings) loose as you go. That greatly reduces friction & cutting force. John's tapping block is another hot tip.

-- Cheers, James Arthur

Use lube. And back the tap up a quarter turn or so for every turn (once it starts cutting good thread) to clear the chips.

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1/4 - 20 through a mere 1/8 hole is too coarse a thread for that little thickness. Use a #10 or a metric.

Also, tapping a hole has a bit of art to it. If you do not know the limits of the metals the handles and taps, etc. are made of, you will not know the tricks of performing the task, like the one where you only turn a 1/4 turn or so at a time, and then back off and then go back in, and you slowly work the tap, not attempt to make the turns all in one fell swoop, and yes, some sort of lube is needed.

If you insist on the 1/4 - 20, then you can use the edges of the drill to open up the hole a little bit. Makes the tapped hole a bit looser as well, however.

Ideally, a panel that thin for a hole and subsequent bolt that size should get a boss welded onto the back side of the hole so that the number of threads is increased You should tap the boss first as it will harden up when welded, and then you chase the tap back down through the hole again after it has cooled.

1/4 - 20 can hold a pretty big load. Surely you could use a smaller fastener, like a #10 or such.

Here are the specs from the Morse Machinist's Practical Guide (1961) P.37: Size of screw 0.2500, body drill 17/64, size or number of drill for percent of full thread: 100% #13, 80% #8, 75% #7, 70% #6, 60% #4,

50% #3. Recommended sizes: for monel metal, high speed steel 50-60% #4; for bronze, tool steel, drop forged, stainless, nickel steel, copper, cast steel 60-70% #6; for mild steel, aluminum, cast brass, cast iron 70-75% #7; and for sheet brass, sheet nickel, duraluminum, fiber, babbit, white metal, hard rubber 75-80% #8.

#7 is 0.2010 which conforms to 75% of full thread from the chart above and seems to conform to the recommended size (mild steel). 13/64 _is_ "one step" higher at 0.2031, so i would say go another step to #6 0.2040 (next one is #5 0.2055 and then #4 0.2090).

I nominally use 2-56, 4-40, 6-32; sometimes 8-32, on rare occasion

10-32 then 10-24 and lastly 1/4-20 (been ages since i had to do a lot of work using 1/4-28 and it was in steel and i may have used 70% percent of full thread - over 40 years ago). On all of the common stuff mentioned, i use 75% percent of full thread since the hardest material i work with is aluminum.

Robert Baer wrote in news:hc2dndLbMsEPG0zXnZ2dnUVZ snipped-for-privacy@posted.localnet:

One note: 6-32 is the worst thread to tap. The ratio of the metal you are removing to the root diamter of the tap is the largest, and they are very easy to break if you aren't careful. A good tap block will help a lot. For 1/4-20, you can make your own. If you do a lot of tapping, do yourself a favor & get a commercial guide block or guided tap wrench. There are several to choose from. For electronics work where you frequently need to get into small spaces, I prefer one with removable sleeves, but the one I have doesn't appear to be available anymore. Here's a collection of tapping tools, including an inexpensive block:

Here's one that looks like it will work well in tight spots, and has a V- groove on the bottom for tapping round stock:

Doug White

For tapping blind holes there's another trick you can add to your toolbox.

Many years ago a TV science show demonstrated a new invention, plugs of wax like lubricant (a bit like glue stick) that you cut to length and push into a blind hole before running the tap in, as the tap runs into the hole it forces the lubricant out through the flutes - no part of the cutting edge escapes lubrication and the extruding lubricant pushes out the swarf.

A search on the web failed to find any examples so maybe the invention didn't catch on, but you can get a similar effect by injecting the blind hole with grease from a glue applicator syringe.

Probably a bit OTT for mild steel, but could be a life saver on tougher metals.

Can you get Taptite screws in that size?

That is a brand name, not a screw type. So, it is unfamiliar over here.

Here, we have PEMs, and KEPs and the like.

--
These work fine without welding:

http://www.pemnet.com/fastening_products/pdf/cldata.pdf

Drill, press, done!

JF

Well, a drill press, and usually a special press block to swage the union together.

But yes, I mentioned PEMs in this thread elsewhere. They are great, and the most common current solution employed.

Above a certain size though, you will still see welded bolsterings for holes. You can remove the temper by re-heating it with a torch after the weldment is done and letting it cool slowly.

6-32 is the size i work with the most; never had a problem. But i have broken a few 2-45 taps (they are delicate).

A search for "pem" comes up with punched in threaded inserts, "KEP" produces no relevant results.

Searching "taptite USA" finds a number of suppliers, sheet as thin as 1/8" might be a bit tricky with taptites, normal industry practice would be to drill the hole small and punch form the hole to the tapping size.

"KEP" Nuts have an attached lock washer... convenient for working in tight places. I always keep a box of 8-32 and 10-32 kep nuts on-hand.

Up one drill size plus cutting oil did the trick. All 24 holes now tapped ;-) ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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=A0 =A0 =A0...Jim Thompson

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you can also get pop rivets with threads inside, but they are probably hard to get flush with the surface

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or something like this

-Lasse

Jim Thompson scrobe on the papyrus:

. . .

I don't know if you can get these on your side of the pond, but I used to get through tens of thousands of them every year.

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If you\'re too open minded your brains will fall out.

Haven't seen them here quite like that, but those sure look nice! ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.