tapping aluminum - tap clogging

[RobertB]

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.

 

[dansawyer]

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.

 

[projectnut]

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.

 

[Mitch Alsup]

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.

 

[savarin]

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.

 

[Mitch Alsup]

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.

 

[cathead]

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.

 

[Illinoyance]

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.

 

[pontiac428]

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