Breaking 6-32 taps

Tapping a bunch of 6-32 blind hole in 6061, spotted and drilling 2.8mm .110" x .750" deep with carbide coolant through drill. Breaking taps when spindle reverses, taps are 2 flute straight 3-4 pitch taper going .550" deep. Can not find the manufacture on the tap but probably a greenfield as we do not buy crappy tools. Tap is in a ER 20 collet holder.

Here is the code Okuma 300 control;

N8 (6-32 UNC-2B TAP)
N9 G116 TOOL=68
N11 G15H1
N12 G0 X0.3 Y0.25 M03 S1000
N13 G00 G56 Z0.5 H68 M08
N14 G00 X0.3 Y0.25 Z0.5
N15 G71 Z0.5
N16 G84 Z-0.55 R0.3 F31.3 M53
N17 X1.05
N18 X2.05
N19 X2.8
N20 X3.8
N21 X4.55
N22 X5.55
N23 X6.3
N24 G0
N25 G00 Z0.5

I usually roll tap 6-32, any reason you can't do that? Those taps are a little stronger.

btw I hate 6-32 for this reason. That's kind of an aggressive pitch for the diameter. Wish 6-40 was used more.

I just noticed that in CAM the pitch was 3 decimal places not 4, eited that and it changed the feed rate to 31.25 instead of 31.3 so we'll see if that makes a difference.

Yes, form tap #6's if at all possible. Have form tapped 10's of 1000's of #6-32 in 6061, est. 2000 holes tapped per tap.

Regards.

Mike

Your feed maybe a little off F31.25
I always use feed per rev G95 in tapping cycle.

Form tap, and life will be better.

Captdave said:

taps are 2 flute straight 3-4 pitch taper

Click to expand...

Sounds like an ignorant "hand" tap to me. Common as housefly poop, but the wrong one for this task. Chips will jam on the back-out. Nearly always. By hand, one rocks them, eyeballs them, babies them, "feels" the way back safely.

CNC? Guess you could program at least SOME of that, but far better to just use a more suitable tap.

2CW

I meant to say 5 decimal places, Changing feed rate to 31.25 still breaking on reverse.

Does the machine have peck tapping?

Captdave said:

I meant to say 5 decimal places, Changing feed rate to 31.25 still breaking on reverse.

Click to expand...

Spiral flute or spiral point tap?

Regards.

Mike

Hi Captdave:
Volitan has it; 6:32 is a shitty design; too coarse for its diameter.
Having got that off my chest, that doesn't help you at all.

One thing you may try if you haven't already: I find editing the spindle speed until the feedrate is an even number sometimes does magic.
Your feedrate of 31.3 is not quite synchronous with the tap pitch at 1000 RPM; it's been rounded up from 31.25.
So by the time you're at the bottom of a 0.550" deep hole your pitch error is almost a thou and that's probably enough to torque the tap and break it when the load is suddenly reversed.

I don't know if your Okuma will accept feedrates to two decimal places or if your spindle encoder is accurate enough to hold oddball speeds accurately, but on my Haas the edit I suggested above has sometimes done the trick for me.

Another thing you can try if you cannot roll tap or threadmill, is to peck tap.
It's a last resort if you're trying to make time on it, because it's so SLOOOOW, but it sometimes is a bacon saver.
Then there's the old standby of drilling the holes up a bit and, of course, buying the best aluminum specific taps you can get your mitts on.
There's also the magic of Moly Dee and other exotic tapping fluids; but none of this is going to be revelational news to you.

As another last resort, a floating tap holder can sometimes do the trick too, but it's a PITA, and most shops don't bother to keep these things around anymore; they expect to rigid tap everything successfully and with anything other than these skinny coarse pitch taps that's a perfectly reasonable expectation.

Obviously there are no great solutions for this intrinsically crappy problem; going that deep with a tap that fragile is bound to give you fits, so it's not something you're doing wrong; rather you're approaching the limits of what's possible to do.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com

Edit; lots of typers WAY faster than me.
Cheers

MC

Monarchist said:

Sounds like an ignorant "hand" tap to me. Common as housefly poop, but the wrong one for this task. Chips will jam on the back-out. Nearly always. By hand, one rocks them, eyeballs them, babies them, "feels" the way back safely.

CNC? Guess you could program at least SOME of that, but far better to just use a more suitable tap.

2CW

Click to expand...

Since we already have carbide coolant drills we're stuck with cut taps. What would you recommend then?


No. 6–32 UNC, 3 Flute, Bright Finish, Cobalt Spiral Flute Tap – Modified Bottoming Chamfer, or a 2 flute?

Not had much success with spiral flute taps when this small as the web is so thin but I'm open to any ideas.

I know they say Bright Finish for aluminum but I've always preferred TiN coated.

Captdave said:

Since we already have carbide coolant drills we're stuck with cut taps.

Click to expand...

Izzat a Federal Law? Or just the State of Georgia? Could get around it by moving to Nawth Carolina, perhaps?

A third flute is gonna make it worse. Everyone is right that a 6-32 form tap is the best method. You must have a .125 carbide drill kicking around no? The decrease in broken tools will easily pay for a couple on them and your costs would be quickly offset

Captdave said:

Since we already have carbide coolant drills we're stuck with cut taps. What would you recommend then?


No. 6–32 UNC, 3 Flute, Bright Finish, Cobalt Spiral Flute Tap – Modified Bottoming Chamfer, or a 2 flute?

Not had much success with spiral flute taps when this small as the web is so thin but I'm open to any ideas.

Click to expand...

OK here is my best OSG spiral flute taps no coating ( bright finish) 2 flute.

Your not using Chinese 6061 are you? I cut tap that deep in 6061 with a 6-32 on a CNC Swiss all the time and I think I am using the same tap I bought on my 16th birthday and I am in my mid 50's.

MSC is the closet tool supplier so sent a runner after these as they do not have OSG in stock.

No. 6-32 UNC, 2 Flute, Bright Finish, Cobalt 63268999 - MSC

Dualkit said:

I think I am using the same tap I bought on my 16th birthday and I am in my mid 50's.

Click to expand...

6-32?

That's probably more of a signal your memory has gone walkabout than anything to do with tapping holes...