Help! 1/4-18 NPT in D2!

Hi all, Another on-topic post for your expert consideration: I gotta job here that uses a 1/4-18 NPT tap in D2. I'd rather not go to thread milling because of the tooling expense and greater cycle time. This is a mill turn machine with rigid tapping. I have ER tapping collets and nice beefy holders. The set up is solid. Has anyone ever done this or or something comparable? Can anyone give me some tap recommendations? That is, style of tap, manufacturers you have used and can recommend, tap materials, coatings etc? The machine has water based coolant, but using an M00 stop (actually 2 or 3, depending) & adding tap goop is in fact an option. In the case of a D2 job with 1/8-27NPT I got away with standard taps in water base, and was able to go all the way to depth (this is a non-negotiable requirement in my book) but the 1/4-18 NPT is proving to be way more of a breakage problem. Thanx,


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Get, and use, a pipe tap reamer in the hole to prep it.

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John R. Carroll

What he said.

D2 tears kind of easy. Use a generous dose of Castrol Moly Dee tapping oil (in the hole and on the tool) with OSG HY-PRO taps.

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Black Dragon

Rigid tapping, you can tap halfway to depth. Stop, clear the chips, add more lube and then retap to full depth. If you don't have the tapered reamer, you can rough the taper in steps by circlemilling. That said, I usually threadmill because it can be done unattended. Fred

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