[philld]

this is not a recent problem happened about a month ago. had to tap M12x1.75 3/4 deep in A-36 plate steel (through hole), they were burnouts machined all over. the tl-1 did the turning and the tm-1 the holes and tapping. i have a tension holder for the tap so i programed the feed of the tap and slowed it down a bit to let the holder do it's job it tapped one hole and the on the second stopped dead in it's tracks! spindle load pegged and the machine just stopped. so i reset and got the tap out and it didn't look too good chipped cutting edges so i got a new tap installed it and same thing first hole didn't go over 50% spindle load second hole no dice! (tap also looked chipped on the edges)

i'm using a cleveland spiral point gun tap and plenty of coolant. i know this machine will do this from the first hole. my question is: is this material known to be hit or miss on its consistancy of hardness? i've tapped the same plate with the same taps and every thing went fine before. just seems once and awhile these burnouts come in harder than others.

also any suggestions for different taps that will hold up to this material?

thanks, phill

[pugsley]

One thing you can try is to use a 10.5mm drill instead of a 10.2 which is the correct size tat will ease the tap.
As m12 is a fairly corse pitch (1.75) you will still have a good thread,i have used this in stainless before with no problems.
Also try a spiral flut tap(dormer) that may help.
Also i do not know how you are programming try using g95 in the line above the tapping cycle.
eg
95
G84 S50 Z-??? R? F1.75
G80
G94
This will take out any varys in the rpm.
(Do not forget to change back to g94 after)

[Ken_Shea]

Phil,
My tapping experience suddenly became a lot more pleasant when I started following this advice from another. Maybe they may be of help to you.

1) Stopped using coolant as a lube and started using Tap-Magic, this can slow things down but not as much as a broken tap.

2) Slowed down my RPM to 200rpm or so.

3) Stopped using the spiral flute, It seems a lot of guys swear by them and the other half swear at them.

4) Peck tapping, while I am using Rigid Tapping I cant see why this would not work out with a tapping head, but I do not know, the rigid peck tapping post mod was done by another.

If you are using a Tapping head then you probably do not have the Rigid Tapping function turned on within your TM-1. If you purchased new within the last few years the you have 200 hours available free, assuming you have not used it already.

Rigid tapping could be the best $1000 you ever spent.


Ken

[pugsley]

I agree if you have not got rigid tapping on your tm1 turn it on and try it,My tm2 has rigid tap and it is worth every penny.
Make sure your coolant is also the right consistancy for tapping and not to weak.

[scbeer]

1. Are these blind holes? If so the spiral point tap is pushing the chip in front of the tap, filling the hole with chip.

2. You say there are burnouts all over the part! These create hard spots in the material.

3. I would second the suggestion that you step up to the next size drill, then use a spiral flute tap without coolant, but with a tapping fluid. At the shop I work at we run into this all the time. Especialy in stainless weldments using small taps. I cringe at the anticipation of the sound of taps breaking. Ruins a hole shift drillig out broken taps.

4. Worst case is you start tap with a spiral point tap (they tend to be beefier in design) then hand tap to depth. I know this negates the whole point of using a cnc mill, but some times it is unavoidable.

[philld]

thanks for the repleis, the holes are through holes. i'm thinking the material has been hardened by being burned out. next time we get this job i'm going to buy a better tap (coated) and i'll try drilling the holes a little bigger the machine does have rigid tapping but i never checked to see if it was turned on! it taps smaller size taps great, but on bigger ones the theads didn't look to good so i started using the floating holder. thanks again guys!!

[HuFlungDung]

FWIW, I think that coolant makes a poor tapping fluid in tough materials. Sulferized cutting oil (or equivalent) seems to be very good. I even used SafeTap for a while, tapping A36, but the tap life was still not as good as sulferized cutting oil.

If your tap is chipping, it might indicate too high of a speed, too much heat is generated, and then the watery coolant shocks the tap and cracks the tips of the teeth. Another reason cutting oil is better is that it provides a less severe quench effect and lubricates much better than most coolants I have seen.

Hopefully your part setup allows the through moving chips room to evacuate.

It is true that some A36 plate is a bit harder. If you have a real troublesome batch, tapping in two steps might even be of some benefit. If you've hand tapped a few holes, you'll appreciate that 3/4" is a long way to drive a tap, when the lube oil is hand applied, because the tap is getting pretty dry by the time it gets to the bottom of the hole.

[scbeer]

Yeah, What Hu Flung Dung said! Slowing down the tapping speeds and feeds, plus using a tapping fluid does work.
We generaly don't have problems with with thread quality until we get above 1"(Slow down). The small taps usually just break! :cheers: