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HomeAircraftHelicopterCAD - Engineering - Technical › Sloppy tapped holes
10-22-2004 03:10 AM  13 years agoPost 1


Toms River, NJ

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When I tap a 3.0 x 0.5mm thread, it seems that the threaded hole is a bit *sloppy* compared to 3mm holes that I'm use to in *manufactured* kits and parts. I'm using a 3/32 tap drill as oppoped to a 4.3mm drill, the 8 tenths shouldn't be any great concern as far as I think. I'm using Alum-Tap as a fluid, tapping 2024 or 6064 basically. Do the manufactures ues a different class of tap to make their holes fit better? A lot of times I'm tapping round stock in a lathe and use the tail-stock to drill and start the tap.


10-22-2004 05:00 AM  13 years agoPost 2


Cookeville, TN

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Most likely what is happening is that you are wallowing out the hole when you tap it. The Alum tap is good, that's what I use but the .093 tap drill hole is too small. Technically the tap drill size should be 2.5mm or .098" for a 75% thread depth. I tend to go .002" smaller for a tight thread fit and no more.

If you are using a cheap tap, like one from Sears or some other supplier you might be better served if you buy a quality tap. Most of the vendors that I will use are:

Cleveland Twist Drill
Metal Removal

The trick is to use a good tap for the intended application.


10-22-2004 10:15 AM  13 years agoPost 3



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Are you doing it by hand..??

Stay tuned fore more happy days

10-22-2004 04:16 PM  13 years agoPost 4


Pasadena, Texas

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I agree with Terry, most likely your problem is your tap. A good tapping compound specifically for aluminum is a must. Most cheap taps are carbon steel a good High Speed Steel tap and a cutting fluid will solve your problem. If you can't find a cutting fluid you can use WD-40 but the result may not be as good. The aluminum sticks to the tap (more so on carbon than high speed steel) and causes the threads to cut oversize. The cutting fluid I use for aluminum is A-9 and should be available at most industrial supply companies. If you correct these problems I think you be happy with your results.

If God meant man to fly, He'd have given him more money

10-22-2004 07:39 PM  13 years agoPost 5


Long Beach, CA

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dubro sells metric taps. your LHS may have them. i recently bought a set of five taps and drills for $25 - 2mm, 2.5mm, 3mm, 4mm, 5mm. the drills that come with the taps are decent quality, and the right size for the tap. they also sell individual tap/drill sets.

i use A-9 for tapping alum. works well, and i like the smell for some reason

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