Thoughts on peck tapping holes in steel

[CC]

Good morning all
i'm looking for thoughts on tapping steel welded fabricated housings on a cnc mill.
We presently use spiral point taps (3/8" to 1") for threading holes in mostly a36 and some really hard a514.
We typically tap drill holes 1/64" over standard tap drill size. We typically tap the holes 2-3 tap diameters deep.
Some holes are blind and others are through. Tap breakage is minimal but happens regularly.
We rigid peck tap every hole, no matter what, retracting the tap completely out of the hole and then go back in.
The mills do not have coolant thru spindle, just a nozzle directed in the vicinity.
I'm just looking for comments regarding peck tapping vs in/out/done.....

Thanks for your time!
For what it's worth.....The main reason for the post is the enormous amount of wasted time going in and out and in and out....

 

[Booze Daily]

I only peck tap on unusually deep holes. 8-32 x .75 deep, 6-32 x .625 deep.
I also peck tap NPT holes. Seems to eliminate ripped threads.

 

[Cole2534]

If you can rigid tap you can threadmill?

Are the broken taps in a particular size or location? How good is your mill? Maybe a floating tap holder would help if its sync issues causing breakage.

What about skipping the pecks and going to a spiral flute tap on the blind holes?

Half the burden of tapping, hell just machining in general, is chip evac. I don't see how peck tapping blind holes would be at all beneficial in this regard.

Broken taps suck ass.

Programmed via Mazatrol

 

[Gordon Heaton]

I rigid tap on a manual mill. For me, pecking with a spiral-point tap is asking for trouble. The chips don't behave if you retract before you're finished. I use spiral-point on blind holes if I can drill deep enough to provide chip space, then pick it out afterward.

 

[gregormarwick]

Spiral point taps are not intended for pecking, but they also are not for blind holes...

 

[Cole2534]

I rigid tap on a manual mill. For me, pecking with a spiral-point tap is asking for trouble. The chips don't behave if you retract before you're finished. I use spiral-point on blind holes if I can drill deep enough to provide chip space, then pick it out afterward.

Likewise. I prefer that to spiral flute taps if I can make it work.

 

[eKretz]

Likewise. I prefer that to spiral flute taps if I can make it work.

Add me to the list as well. Most of the shops I've worked in only had spiral point taps. But those were mostly manual machines.

 

[Cole2534]

Add me to the list as well. Most of the shops I've worked in only had spiral point taps. But those were mostly manual machines.

There's also the panic inducing sound of chips crunching and then the inevitable...TINK.

Programmed via Mazatrol

 

[doug925]

We use Vega brand, spiral flute, bottom taps to peck tap 1 & 1.5" thick A514
For non welded material, we use XHP, and when going through weld, we use the XEN style.
The majority of the threads are 1/2-13 & 5/8-11
Tapping SFM is low: IIRC 25 for weldments and 35 sfm for non welded A514.

I will drill / mill for the top of the minor (-0.002") when needed.
If the parts/ customer allows, I will go a tad beyond minor limitations.

Through holes are easy as pie, using spiral taps. We peck at 1.75 -2.5 x dia. depending on the tap size.

Doug.

 

[Bill D]

As a boy, hand tapping only, I was told to reverse the tap every turn or two to break the chip then continue. Only to remove it all the way if the chips packed too tight and it may break.
Bill D

 

[CC]

What is your reasoning for peck tapping?

 

[edwin dirnbeck]

Spiral point taps are not intended for pecking, but they also are not for blind holes...

Yea,BUT EVERYONE DOES IT because they are the freest cutting and longest lasting taps. period.I always try to chop off the useless front end of the taps that the tap makers leave on the front of the taps because they are to lazy or stupid to remove.Edwin Dirnbeck

 

[gregormarwick]

Yea,BUT EVERYONE DOES IT because they are the freest cutting and longest lasting taps. period.I always try to chop off the useless front end of the taps that the tap makers leave on the front of the taps because they are to lazy or stupid to remove.Edwin Dirnbeck

Sure, if they don't care about the depth of the hole or the additional time required to get the compacted chips out of the bottom of the hole.

Nothing wrong with it. I do it sometimes when I am not constrained like that.

But if it's a production part where you don't want to quadruple the production time by digging chips out of holes, or there is a constrained hole depth, then you use the proper tool for the job, which is a spiral flute tap, or a roll tap, not a spiral point tap.

 

[ViktorS]

Just my experience but I have found that spiral point taps are really no good at all to reverse out of a hole without going completely through with the cutting edges to break of the chip.

Seems like they are not ground to break or push the stringy chips at the back of the flutes and chips will get jammed between the material and tap, which results in broken tap when reversing out of the hole.

Had a job that was about 6000 of M6 holes, both blind and through, and trying to use spiral point only resulted in about 1/3rd tap life, and the tap always broke when reversing. After a while i overcame my laziness and set up a second tap with spiral flutes for the blind holes, and the job went smooth as silk from there on out.

EDIT: I'm stupid and wrote through holes in the last sentance.

 

[BT Fabrication]

don't peck tap! thats how you mess things up and break taps.

also dont go too slow. most go too slow which allows the tap to torque and twist slightly, allowing the threads behind it to bind. needs to be fast enough to break the chip, but slow enough not to break the tap. 3/4" tap i feed about 500 rpms.

 

[AARONT]

I wouldn't peck tap those. What's your coolant concentration look like?