Need Some Tapping Help

[dconder]

Hey all. I need some advice in the worst way. First off, this is a new problem that has developed on some parts we run all the time. The material is aluminum. We are drilling and tapping around 30 holes, m5 x .8 and 1/2" thread depth. Our problem is all the sudden over the past couple of weeks, we will have a random hole or two or three out of 30 that the no go gauge goes in to. We can run 200 holes with no problems and then all the sudden 1 or 2 bad holes pop up. We have tried different RPM and feedrates with no succes. Different taps and drills as well. . We are running these on Haas VF4 machines and have the same issue on more than one machine. I have even tried it on my old VF2 and it will still get a bad hole once in a while. A bad hole scraps that part and the material alone is quite costly. I am using rigid tapping with the tap and have tried different collet holders to make sure the holder is not running out. I am about at my wits end. Anyone have any suggestions?? Thanks all.

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[Jim Dawson]

I would take a look at the coolant. It could be that you are welding a bit to the tap and that's what is causing the oversize. The other possibility is occasionally a chip gets stuck in the tap and makes an oversize hole. Maybe an air blast to blow off tap and the part to make sure they are clear? Is it possible to use a forming tap rather than a cutting tap?

Is it possible to use a heli-coil to save the part?

EDIT: I had another thought. Are the hole sizes on the offending holes correct? One of the old tricks to oversize a drilled hole was to drill through a rag, you can do the same thing with a tap. Some of the rag fibers would be pulled into the holes with the drill bit and would cause a slight oversize, a chip stuck in the drill bit might cause the same problem.

[DruMor]

Have you checked your coolant concentration? Years ago, we had some problems with aluminum galling into the flutes of the tap, and when the tap came out it would tear the threads up. Upped the coolant concentration and the problem went away. Since you had the problem in 2 machines, which obviously use 2 different coolant sumps, that may not be your issue but it is worth looking at.

[Machineit]

You really don't give enough information here. Are the holes oversize or undersized? What RPM are you tapping at? I tap everything at 1000 rpm. Do not use slow rpm as that is not good. What type of tap, what is the material, etc. etc.

Mike

[Kool Parts]

Most would cringe at the added cycle time, but when tapping multiple holes I always start 1 inch up. That give the coolant time to blast the chips from the hole before.
If you are peck tapping then maybe 2 inch would be advisable.
Like has been said if you have a chip hung on the tap and drive it down into the next..not good. Coolant concentration, more is better
Gary

[ProToZyKo]

Might not be the tap at fault here, the drill can also be the cause.

[Ksorensen69]

Might not be the tap at fault here, the drill can also be the cause.

Try using a thread hob. They are made for that small of hole and are fast if you get the multiple flute type. Another option is get an acid brush and straight coolant or cutting oil and hand apply while machine is in a slower rapid mode or single block state. Have your air handy and blow chips as you go. Water soluble coolant just sucks after water is added, for tapping anyways.

Sent from my Moto G (5S) Plus using Tapatalk

[Machineit]

Use a form tap.