[CNC] Self-reversing Tapping Head On Cnc, Experience?

[FLguy]

With a thread form tap drill to 55% effective thd. dia. and make sure your form tape can vent. This thread will be stronger than, if I remember correctly a 72% effective thd..

 

[Country_Bubba]

"0-80 is .0600" major diameter, almost exactly half the diameter of your 3 mm threads. CNC in titanium?"

Not sure as I have done neither, but I have broken a lot of hand taps doing deep threading of Al and Steel in sizes ranging from 2-56 to 6-32 and recently even a 1/4-20.
I have always read that side forces break more taps than anything and if your doing power tapping on a cnc, then there should be no side force and that should help.
Good Luck.

 

[Jamespvill]

If your mill has rigid tapping capability you don't need a tapping head. Whether you go with rigid tapping or a tapping head a 0-80 tap is going to be a dicey undertaking.

Tom S.

No rigid tapping for the Pm45 CNC. At least, I cannot image in has the capacity to. So far, I have never managed to break an 0-80 tap. I do most of my tapping with my little 12v Ridgid gun. Dicey just about sums up an 0-80 thread...

 

[Jamespvill]

Your luck sounds like mine. From good to bad.
0-80 in Ti?
Step 1: Buy a big wheelbarrow load of taps.
Step 2: make sure you have no blind holes or at least a way to those broken taps out.
Step 3: Remove all time constraints from the contract or P.O.

This i going to be a process.
In Al, it would be an undertaking. Not just because of the size, but because of the setup. The rigidity of your tooling and machine will matter. The accuracy of your motor will matter. You will probably want to "sneak up" on the holes from the same direction each time to preload the bearings (yes, it's a thing).
Then when you get to Ti, everything is amplified; every shortcoming comes up worse. And everything that took minutes to do now will seemingly take hours.
Don't count on this running automatically. This will need plenty of babysitting, IMO.


Wrat

This sounds like it's going to be a fun one...and potentially expensive. The good news is that it is a personal project, so no time constraints, just sanity limitations. I've also got a blind hole that has about 4.5 threads worth of engagement- I'm not particularly looking forward to that one.

Thank you for the tips on the bearing preload, I've heard that before, and my machine isn't exactly the tightest to start with- so I'll need all the help I can get. Titanium is in the future, so I (should) have plenty of time to get ahold of the aluminum and copper first. Thanks for the pointers, I appreciate it!

 

[Jamespvill]

Hi,
I got one of the generic ones when I was building my router. I had 50 3mm holes to tap in 1/2" aluminum.
I broke a tap in the third hole, but that was due to my not having the parameters set properly in my cam. Once I figured that part out,the rest went with absolutely no problems. I figure it did a much better job than I could have trying to hold the tap straight by hand:{)

I don't use it often, but sure is nice to have when I need it. IIRC it is a Taco brand made in India I think, not sure where I got it but it might have been from Enco.

Awesome, my hopes are that I will be able to tune it in without too much hassle, then the rest will all my on me and my CAM skills, which I can work with!

 

[Jamespvill]

With a thread form tap drill to 55% effective thd. dia. and make sure your form tape can vent. This thread will be stronger than, if I remember correctly a 72% effective thd..

Think a blind hole is going to give me issues? I had always thought the "flute" on a form tap was to vent the pressure?

 

[Bob Korves]

The form tap should help a lot with the blind hole issues. I think what you really need is the best possible quality tap and the best possible threading lube for the job, not to mention tight control of the tap, Keeping it in line with the hole and letting it slip in the driver if the loading exceeds a safe load -- and some good luck! Also, as suggested above, consider a larger hole and lower percentage thread depth.

 

[derf]

The tapping heads I use rely on down pressure to keep the clutch engaged and are self feeding via hand pressure and feel, which would mean that using one on a cnc mill, one would have to have the feed rate almost spot on.

 

[Country_Bubba]

There is some allowance between jamming the tap at the top and before the clutch will disengage on mine. I believe there is .150 " of travel. My cam then recommends underfeeding the rpm of the spindle feed slightly to compensate for feed rate (in/rev) possibly not being correct. If the tap outruns the feed, it simply stops. If the feed were to outrun the tap, it would jam at the top of the travel and bad things surely would happen. As I stated earlier, once I got my parameters properly set with a 3mm tap, did about 47 holes full depth in 1/2" 6061 with no problems.

 

[Jamespvill]

The form tap should help a lot with the blind hole issues. I think what you really need is the best possible quality tap and the best possible threading lube for the job, not to mention tight control of the tap, Keeping it in line with the hole and letting it slip in the driver if the loading exceeds a safe load -- and some good luck! Also, as suggested above, consider a larger hole and lower percentage thread depth.

Gotcha, There are plenty of screw holes so I can get away with a lower percentage thread. I'll also buck up and buy the most expensive tap and fluid (presumably also the best quality).