Tapping thick aluminum with m12 1.75 tap 5

[BurningKrome]

I'm trying to hand tap 1.5cm thick aluminum with an m12 1.75 tap, but can't get it to tap more that two thread revolutions before turning it becomes impossible (I actually damaged the wrench attempting to get it to continue turning.)

I'm using a 10.2mm drill bit with cutting fluid to drill all the way through the aluminum. I then start manually tapping (also with cutting fluid) with the m12 1.75 tap. I get about two full thread rotations before I can't tap any further. I can successfully thread the bolt easily through the threads that do get cut. I just can't cut any further.

- Is tapping a sheet this thick unreasonable?
- Should I partially drill out the hole to clearance (13.5) and just thread a few millimeters?
- Is my tap just garbage (should I buy a better quality tap?)

 

[SwinnyGG]

Are you reversing the tap every 1/4 to 1/2 turn to break your chips?

 

[berkshire]

I would also look at your tap, if it is a 4 flute you may be better off with a 2 flute machine tap.
B.E.

You are judged not by what you know, but by what you can do.

 

[BurningKrome]

@SwinnyGG
I have been, but it didn't seem to help.

@berkshire
It's a four flute. I'll look into 2 flute.

 

[hendersdc]

My tap chart has 10.3mm pilot hole diameter for M12-1.75 and 75% thread and 10.9mm for 50% thread so at the very least I would increase from 10.2mm to 10.3mm drill. Depending on your application you could open it up even further.

Have you measured the pilot holes after drilling? Are they coming in at the expected size?

What type of tap are you using? A taper or plug tap would cut easier than a bottoming tap because of the increased lead in chamfer.

 

[3DDave]

According to

https://www.kennametal.com/us/en/re...alculators/tapping-torque-and-horsepower.html

the torque to tap metric threads in aluminum is a bit over 4N-m

Tapping depth is not a consideration - the amount of material being cut per turn is the same once the tap is fully engaged.

Running crooked will make tapping difficult. If it's a bottoming tap being hand turned, it will be harder to run straight. It doesn't take much. Tapered taps are easier to manage.

In a previous question about poor drilling capacity it turned out to be due to a poorly made drill bit - perhaps there is a problem with the tap - buy a new one from a reputable source.

 

[BurningKrome]

@3DDave

Based on looking at the camfer, I think it's a bottoming or plug tap. I've ordered some higher quality taps, as well as a 10.9 mm drill bit. I'll let people know what works. Thanks for the advice!

 

[BurningKrome]

OK. It was pretty simple. The tap was crap It was new, but I replaced it and the aluminum threaded like going through butter.

Thanks to all for the input and suggestions.

 

[racookpe1978]

Thank you for the feedback. Good to know it came out alright for you.