Tapping, quick and cheap

Tricks of the trade

Tapping, quick and cheap

Postby Doug Coulter » Thu Jul 15, 2010 12:56 pm

When making things, I love tapped holes, as there is no nut to lose, but until I learned this trick, I hated the actual tapping process itself.
I'm sure most of the folks here have had experience with a dull "True Value" or Chinese tap and breaking little ones off in the hole, sometimes ruining the whole workpiece, which is both expensive and frustrating.

So, here's how I do it without tears, expensive gear and a lot of time wasted.

Step one:

Get the right sized hole! This will vary with material and use of course, the little guide on the back of the hardware store taps doesn't get all the information you need there. Neither does the attached file, but it's a great place to begin. I have one of those 115 piece drill bit sets that is used only for precise holes for things like this, and don't use it for knock around the shop kinds of things -- that alone is a pretty serious help. Some materials "upset" or flow into the space between the tap fins more than others, and those materials need a larger hole in the first place if tapping is to be easy. Some just cut clean, so you can use a smaller hole for those. In other words, for "goopy" things like copper or plastic, use a drill size for "60%" threads, but if cutting holes in something that machines like 12L14 steel, use the right drill for 75% or more tapping (eg a smaller hole).

Step two:

Make a special loose tap holder. I took a hardware store one, removed the cross bar, and ground three flats on it so I could chuck into my Makita or Ryobi battery drills. You want a little play here, so you won't as easily break off the tap if you hold the drill a little crooked. You can then see how to hold to get a straight tapping job as it goes along.

Step three:

Tap the hole, using the drill's screw driving torque limiter to prevent twisting the tap off it if jams. On metals, I use Moly-Dee lube (better than hardware store tapping oil), on other things, I just do it dry. For deep blind holes, nothing beats backing the tap out a time or two and cleaning both the hole and the tap with compressed air, something that's worth it for many shops to have. If you don't, I suppose a can of it would do as well, at more expense on a per-hole basis.

As luck would have it, my 1/2" Makita (which I use in first gear for this) has a clutch setting that matches most taps just right, eg use "4" for 4-40, and "10" for 10-32 and you'll never break a tap that way. All this is a little touchy-feely -- you don't hold the drill real tight or run it real fast, especially as you learn this. Let the tap decide how to guide the drill, and let your hands have a little give in case the tap jams. At that point, you've not broken it yet, so back it back out, clean things off, and go again.

Attached find a file of drill sizes correlated to taps, and a picture of the "special" tap holder that makes this all work. Since the taps have a square end, I don't tighten them into the tap holder all that tight -- you can usually pull the drill/holder right off a stuck tap with no damage to anything. A little play is what makes this trick work. That is a 10-32 TiNC coated tap there -- don't use a TiN coated tap on Al, it will bind -- use the carbo-nitride or plain tool steel for grabby stuff like aluminum.

Always get really good taps at McMaster-Carr (or other trustworthy vendor in this business, I like McMaster fine) -- they will save you both money and frustration over those in the stores. They are often offered in sets of 3 for long taper, normal, and blind hole tapping to close to the bottom.

This isn't as good as, but is faster and cheaper than, a tapping head on a milling machine, for example, and for nearly everything -- plenty good enough.
QuickTapper.jpg
Picture of quick tapper tool
QuickTapper.jpg (38.05 KiB) Viewed 7215 times
Attachments
Drillsort.pdf
Print me and stick me to the wall in the shop
(33.34 KiB) Downloaded 558 times
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Doug Coulter
 
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Re: Tapping, quick and cheap

Postby Doug Coulter » Thu Jul 15, 2010 1:41 pm

Here is the drillsort file as raw text so you and edit it in your desktop publishing scheme and repost it for all....
No two systems seem to have the same tab settings, sigh -- this belongs in a word or open office table format.


Drill Size Tap info
#60 .0400
#59 .0410
#58 .0420
#57 .0430
#56 .0465
#55 .0520
#54 .0550
#53 .0595
1/16 .0625
#52 .0635
#51 .0670
#50 .0700
#49 .0730
#48 .0760
5/64 .0781
#47 .0785 3-48 75%
#46 .0810
#45 .0820 3-48 60%, 3-56 75%
#44 .0860 3-56 60%, 4-36 75%
#43 .0890 4-36 60%, 4-40 75%
#42 .0935 4-40 60%, 4-48 75%
3/32 .0938
#41 .0960 4-48 60%
#40 .0980
#39 .0995
#38 .1015 5-40 75%
#37 .1040 5-40 60%, 5-44 75%
#36 .1065 5-44 60%, 6-32 75%
7/64 .1094
#35 .1100
#34 .1110
#33 .1130 6-32 60%, 6-40 75%
#32 .1160 6-48 soft/thin
#31 .1200 6-40 60%, 6-48rd
1/8 .1250
#30 .1285 8-40 soft/thin
#29 .1360 8-32 75% 8-40rd
#28 .1405 8-36 75%
9/64 .1406 8-32 60%
#27 .1440 8-36 60%
#26 .1470 10-24 75%
#25 .1495
#24 .1520
#23 .1540
5/32 .1563
#22 .1570 10-24 60%, 10-32 75%
#21 .1590
#20 .1610
#19 .1660 10-32 60%
#18 .1695
11/64 .1719
#17 .1730
#16 .1770 12-24 75%
#15 .1800
#14 .1820 12-28 75%
#13 .1850
3/16 .1875 12-28 60%
#9 .1960
#8 .1990
#7 .2010 1/4-20 75%
#12 .1890
#11 .1910
#10 .1935
13/64 .2031
#6 .2040
#5 .2055
#4 .2090 1/4-20 60%
#3 .2130 1/4-28 75%
7/32 .2188
#2 .2210 1/4-28 60%
#1 .2280
A .2340
15/64 .2344
B .2380
C .2420
D .2460
E .2500
1/4 .2500
F .2570 5/16-18 75%
G .2610
17/64 .2656
H .2660 5/16-18 60%
I .2720 5/16-24 75%
J .2770
K .2810 5/16-24 60%
9/32 .2813
L .2900
M .2950
19/64 .2969
N .3020
5/16 .3125 3/8-16 75%
O .3160
P .3230
21/64 .3281 3/8-16 60%, 1/8-27 NPT 75%
Q .3320 3/8-24 75%
R .3390 3/8-24 60%
11/32 .3438 1/8-27 NPT 60%
S .3480
T .3580
23/64 .3594
U .3680 7/16-14 75%
3/8 .3750
V .3770
W .3860 7/16-14 60%
25/64 .3906 7/16-20 75%
X .3970 7/16-20 60%
Y .4040
13/32 .4063
Z .4130
27/64 .4219 1/2-13 75%
7/16 .4375 1/2-13 60%
29/64 .4531 1/2-20 75%
15/32 .4688
31/64 .4844
1/2 .5000
9/16 .5625
5/8 .6250
11/16 .6875
3/4 .7500
13/16 .8125
7/8 .8750
15/16 .9375
1 1.000
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Tapping, quick and cheap

Postby Jerry » Tue Jul 20, 2010 12:19 am

I find myself buying more and more thread forming taps. Instead of cutting like normal taps these form the threads through plastic deformation of the material. They can be a little spendy (Around $8 for a 8-32 Balax) but they are much stronger than a regular tap since there are no flutes. Also the threads formed are harder and have a better surface finish. Form taps do not use the same drill size at thread cutting taps. The manufacturer will have a chart in their catalog. Often the drill sized turn out to be metric so you may need to buy a drill when you get the tap.

Do not use cutting fluid with these taps! These need lubricant. Way lube works as well as the stick waxes.

I have used these taps from 2-56 in Titanium to 1/4"-20 in Aluminum and Stainless.

One thing that Doug mentioned and I cannot stress enough is buy good brand named taps. OSG, Balax, etc. When I was working at TechShop in Portland I had a member that was building a flycutter. I tried to stress to him that he needed to buy good cutting tools. Pleading poverty he bought a cheap chinese 1/4-28 tap for the set screw holes. He must have spent a half hour trying to get the tap started. He brought it to me and I looked at the tap ant the first row of teeth were gone! I walked to my cage and grabbed a nice OSG gun point tap and proceeded to tap all three hole in about 1 minute as he watched slack jawed. He never bought chinese cutting tools again! ;) Of course that tap cost over $20...
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Re: Tapping, quick and cheap

Postby solar_dave » Fri Aug 31, 2012 11:36 am

Lets not forget that if you are heat treating tapped materials a 5% oversize tap is a life saver after heat treat. They are harder to find but over the years I have accumulated a pretty good supply.
Dave Shiels

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Re: Tapping, quick and cheap

Postby chrismb » Fri Aug 31, 2012 11:50 am

The issue with Chinese tools is the variability. They can certainly make the right tools right, but you run a lottery which you buy them. I bought a real cheap tap set from 'Aldi' (which is a German supermarket chain that has some stores here in UK and they sell their regular lines here). I can't really tell if these are German or not, but suspect Chinese as cheap (yet well made) - this is about quality control, so wherever they sourced them from it looks like they did a good job at ensuring product quality. Either that, or I was just lucky!

(Similarly I bought some cheap hole punches off ebay. When I got them they were pretty blunt but metal-wise they seemed good quality and well-hardened. Had a friend in a local machine shop sharpen them and he was really surprised at the quality of the hardened finish for such cheap tools. Shame they didn't arrive properly prepared, but they're a good set of tools now with the finish my friend put on them - not too sharp, but just sharp enough for a robust, reliable cutting edge.)
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