Tapping for 10-32

I would use a roll tap for this - no chips, stronger threads.
 
I would also suggest using a good-quality tap. It doesn't need to break the bank, but something better than hardware store variety. I can buy Norseman taps here as well as Widia (sp?) from my local industrial supply in the individual sizes I use frequently. Using one of them compared to my El-Cheapo Canuck Tire "104 piece set" that I purchased years ago is night and day. Cheaper taps (and dies too for that matter) just don't cut as nicely and it's really noticeable, especially in smaller sizes where you're already concerned about maybe breaking one. 10-32 in aluminum should not be an effort. And yes, some form of cutting fluid (kerosene, WD40, cutting oil, etc) will also ease the process.

-frank
 
You can always try one size larger , 3/16, and see what you think. Seems aluminum shouldnt be to hard to tap though.. but the extra room would probably make it easier, should still get good threads... only 1/32 inch differece. Have you tried a little wd40 while tapping?

3/16" is approximately the major diameter of a #10 machine screw. A 10-32 tap would barely scratch it, even if it drilled perfectly on size.
 
My tap chart contains the following information for 10-32 cut threads.
Drill size...…………………………………………….Theoretical % of thread
5/32……………………………………………………..83
22....……………………………………………………..81
21....……………………………………………………..76
20....……………………………………………………..71
19....…………………………………………………….59

For roll form threads 10-32
#16
 
If the drawing has a thread class call out such as 10-32 3B stick with the Maximum Minor Dia. allowed by the ANSI standards, if a 2B use the MMD for this thread which will be larger and easier to tap.
Above all do not use hardware store taps, a far more expensive tap will last longer and tap with less force and chance of leaving it in the part.

This is a decent resource that I use when to lazy to go through 60 pages of MH thread data charts, just enter the thread diameter, lead and the class and it will tell you the max. minor diameter and use that for the hole size. If the customer is going to gauge it all bets are off, it takes very little error for a 3B NG gauge to go in the hole and fail inspection.

If you are just putting parts on your motorcycle/bicycle/BBQ grill use the 2B thread data.

https://www.amesweb.info/Screws/AsmeUnifiedInchScrewThread.aspx
 
I will give a try to different size drill mentioned, thanks to all

BTW I always use wd40 when tapping / drilling

The tapping is for both through / blind holes

I buy my taps from KBC Tools in Ontario
 
I buy from KBC as well, I think their quality is pretty good. At least I'm pleased with them.

-frank
 
As usual for me, a day late and a dollar short........ My two cents worth, or is it a nickle now?
First off, a Nr 10 machine screw is 0.190" (060+(.013x10))
Next, a 3/16" stove bolt is 0.1875" (2-1/2 thou smaller)
Threads for 32TPI are 1/32 (0.03125") less than that to tap.
That yeilds 0.15875 as the optimum drill size. Use the closest larger drill for tapping. I don't have handy a chart, but the closest drill may well be metric. Who knows?
I could lecture on aluminium as being tenaceous, but I won't. I do remember breaking more taps in it than in steel. Panel steel was gauge 11, call it 2mm. Aluminium was 3mm, m/l. In my experience, 10-24 was a much more usable size in aluminium. Hanging electrical components....... Of course, troubleshooters usually had some 10-24s in their pockets. Only the electronics guys kept extra 10-32s.
Bill Hudson​
 
32 pitch has a nominal thread depth of 0.0192, and doubling that would yield 0.0384. Nominal major diameter is 0.1900, so in basic dimensions, the minor should be 0.1900 - 0.0384 or 0.1516. Recommended (for 75% engagement IIRC) hole size is 0.1590.
 
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