Tapping Aluminum

Rex Smith

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I am about to tap a bunch of 10/32 x 3/4" blind holes in aluminum. I have some good quality HSS 2-flute taps and a floating tapping head that I got for the occasion. I've studied the procedure and think I know how to approach it. I looked up the feeds and speeds on the CNC zone calculator and am suspicious they are too high. I know that the speed and feed need to be compatible with the thread pitch, but the speed it's giving me is over 32 ipm. Does that make sense? I'm visualizing the tap breaking at that speed in aluminum as the tap gets galled. I don't seem to have a pecking option. I'll be using Hangsterfer's coolant in the process.
thanks, rex
 
Rex,
I just checked GWizard and got 891 RPM with a feed of 27.6 ipm. This is the conservative setting. The aggressive setting is 905 RPM and 29 ipm.
Regards,
 
Rex,
You didn't say, but you are using spiral flute taps for the tapping, head I hope. Standard hand taps are not meant to be used for machine tapping. :)
GWizard also calls for flood or mist use during the operation.

Marty
 
I have a Hertel 2 flute spiral point tap. Same thing? It says it's good for thru and blind holes.
I have misting on the machine. Sounds like I'm good to go?
 
You have the right tap but I would slow down to approx. 500rpm. Put some fluid in the blind hole.
 
That's what I was wondering about the speed. It seems to me that GWizard is a little too aggressive. It doesn't offer speeds that low for this configuration.
 
Is there a good reference about tapping feeds and speeds, so I can understand the logic?
 
use a express tap or also called shrinker tap for aluminum, they don't cut but extrude the metal. I used to work for Besly tap co.
 
I sense a disturbance in the force. A spiral TIP tap is for through holes, since it moves the chips forward. In a blind hole, this is a not-good thing. A spiral FLUTE tap, OTOH, is for blind holes, since it pulls the chip backwards.

Look at page 3: https://www.yamawa.com/en/support/catalog/pdf/understanding-the-basics-of-spiral-fluted-taps.pdf

I wanted to like your post, but LIKE is not showing up for some reason, so ... I totally agree with what you said, sprial is for through, spiral flute is for blind, or through.
 
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