# tapping aluminum - tap clogging



## dansawyer (Sep 1, 2019)

I am trying to tap 1/2 inch deep 10-32 holes in T6061. The holes are drilled with a #21 drill and I am attempting to tap the first one. The tap is aligned well. The tapping was strange compared to steel from the beginning. The steel technique is to tap forward until build up is felt then to reverse and break up the build up. There was no sense of build up and release as the tapping proceeded. Tapping just got harder and harder. Reversing did not release any buildup. 
When I removed the tap it was heavily clogged. There were no identifiable chips. The aluminum was pressed into both teeth and into the grooves. 
Did I choose a too fine a thread? Should I switch to 10-24? (#21 is already large for 10-24) 
Should I drill the holes out a few more thousands? 
Is there a lubricant that will help>


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## gradient (Sep 1, 2019)

Try a lube such as Tap magic or WD-40.  You may have to back the tap out after a couple of turns and clear the threads.  You could also try a spiral flute tap.  They tend to have more space in the flutes.  Usually used for CNC machines but can be hand tapped.


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## bluechips (Sep 1, 2019)

How about when the tap starts to feel harder to turn you back tap out and clear the chips from the tap and hole.  Clear hole with compressed air and a rag to put around hole to catch debris...  Re-start tap and count the number of turns of tap till you reach the same sense of snug as the first time and repeat above.  Clear chips and go back in until you reach desired thread depth.   You're wearing eye protection right?

Just how I would do it.


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## MarkDavis (Sep 1, 2019)

I have been using form taps in aluminum.  They do not leave chips, and the threads are stronger. Choose your drill size specifically for form taps, and lube is good, as mentioned, WD-40,  Tap magic, kerosene, also is good for aluminum lube.


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## RJSakowski (Sep 1, 2019)

Dry tapping aluminum is asking for trouble.  It doesn't take much for aluminum the stick to steel cutting tools with an almost weld-like bond.  WD 40 or some of the tapping fluids specifically designed for aluminum like AlumTap or Tapmatic for Aluminum work well at preventing galling.


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## Canus (Sep 2, 2019)

Make sure the tapping fluid you use is for Aluminum.  The older tapmatic for steel will destroy aluminum,


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## gradient (Sep 2, 2019)

According to GWizard, the #21 tap drill is giving you a 76% thread.  You could open it up just a bit with a #20 drill and still get a 71% thread. Plenty of thread for aluminum and it would tap just a bit easier.


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## ezduzit (Sep 2, 2019)

Use a sharp, quality tap. WD-40 for lube and to wash the chips out of the tap. #21 drill is fine.


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## markba633csi (Sep 2, 2019)

Agree with all above- I remove the tap every so often and use an old toothbrush to clean the tap. Aluminum is somewhat "gummy"
Liquid wrench makes a good emergency tapping/cutting fluid for aluminum
mark


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## epanzella (Sep 2, 2019)

You didn't say what the threads look like in the hole.  Are they there or wiped out?


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## RobertB (Sep 2, 2019)

Another thing to consider is to counter bore the hole a bit. 1/2" is pretty deep for 10-32. If you don't need the entire depth threaded it will make it easier.


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## dansawyer (Sep 2, 2019)

Quick update: First, thank you all for the advice and encouragement. The 10-32 tap had nearly 'welded' aluminum to the tap. I decided to switch to 10-24 threads. The number 21 drill made taping a breeze. WD 40 and slow and steady worked very well.


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## projectnut (Sep 2, 2019)

You might consider using a spiral flute tap with plenty of cutting fluid.  They look like this:









						Widia GTD Spiral Flute Tap 3/8"-16 UNC x 2-15/16" 3FL HSS 19642   | eBay
					

Find many great new & used options and get the best deals for Widia GTD Spiral Flute Tap 3/8"-16 UNC x 2-15/16" 3FL HSS 19642  at the best online prices at eBay! Free shipping for many products!



					www.ebay.com
				




Rather than push the chips forward like a spiral point (gun) tap, the chips come out the entrance hole in a long line like swarf from a lathe cut.  They're used mainly for blind holes to keep the chips from packing into the bottom of the hole, but they also work well on gummy material where chips tend o stick to the tap.

You might also want to use a cutting fluid formulated specifically for use on aluminum. Tap Matic and other manufacturers make several different formulas that will work on aluminum:








						TAP MAGIC Aluminum Tapping Drilling Milling 4 oz 20004A Cutting Fluid  | eBay
					

Precision is always excellent and the finish is always superb.



					www.ebay.com
				




On Edit:
I thought this post went out at about 8:30 this morning.  When I cam back to see if there were any responses I saw it still waiting to be submitted.  Glad to hear all worked out.  Just a little information for future reference.


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## Mitch Alsup (Sep 2, 2019)

I tap a bunch of 4-40 through 1/4" 6061T6 plate.
I have found that sulphur based cutting fluid works better than WD-40 for tapping.


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## savarin (Sep 2, 2019)

Was it a new or well used tap?
I have found that the older used taps of mine a bit harder to cut nicely but I've never seen the gumming although I use any oil to hand.


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## Mitch Alsup (Sep 2, 2019)

savarin said:


> Was it a new or well used tap?



Both, I had a 4-40 tap that had about 300 tappings (old) and a new one, and they both respond about the same.

Also note, when tapping 1/4" 6061T6 (today) I had to remove the tap from the hole at least 3 times to get the chips out of the way.
I would think in a 1/2" 10/32 that you would have to remove tap to clean chips at least 6 times.


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## cathead (Sep 3, 2019)

Tap technology is very interesting.  Some taps lift the spirals out and some in for one thing.  A lot of taps are designed for
one type of metal or operation.  Then we have starter taps and bottoming taps etc to confuse the issue.  I have a lot of taps
and have found that if the going is difficult for some reason, it is a good idea to try another similar or possibly different tap permutation.    
It is wise to take a good look the tap and select a geometry that will fit the application and use an appropriate lube.


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## Illinoyance (Sep 3, 2019)

You might also consider a spiral point tap for through holes.
Aluminum will usually weld to the tool unless lubricant is used.  WD 40 is a popular lube.


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## pontiac428 (Sep 3, 2019)

Careful with tap coatings.  Ti-N will do fine in aluminum, but Ti-Al-N will cold weld to aluminum.


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