Why Does a Rigid Tap Sometimes Strip a Hole in Titanium Even When Speeds and Feeds Look Correct?

A rigid tap strips in titanium most often because the tap drill left too little material for the flank to shear cleanly, not because the spindle speed or feed rate was wrong. Titanium's low thermal conductivity and its tendency to gall against cutting edges mean the failure mode looks like a speeds-and-feeds problem but is usually a hole-prep or lubrication problem instead.

Why titanium behaves differently here

Most tapping charts are built around steel and aluminum, where heat generated at the cutting edge dissipates into the surrounding material fast enough that the tap keeps cutting cleanly. Titanium holds heat at the cutting zone instead of carrying it away, so the tap's leading edges run hotter than the same speed would produce in steel. Hot, work-hardening titanium chips weld to the tap flank instead of shearing off, and a tap that's picking up material behaves like a dull tap: it pushes rather than cuts, and the threads it forms come out shallow or torn.

That's the mechanism behind a "stripped" thread. It's not that the tap broke or that the hole came out oversized on a gauge check. The thread crest tears because the tap was plowing partially-welded material instead of cleanly shearing it, and the resulting thread doesn't hold full engagement even though the tap drill diameter and program numbers all check out.

What actually goes wrong

• Tap drill percentage too aggressive. A drill sized for 75% thread engagement, which is standard practice in steel, leaves titanium too little clearance to shed the heat and chip load the material generates. Titanium often wants a slightly larger tap drill, sacrificing some thread engagement percentage for a cooler, cleaner cut.
• Lubrication and coolant delivery. Flood coolant that doesn't actually reach the flutes at the bottom of a blind hole does nothing for the galling tendency. Through-tool coolant or a tapping fluid specifically rated for titanium matters more here than in steel or aluminum, where a general-purpose cutting oil gets by fine.
• Tap coating and geometry. A tap ground and coated for steel doesn't necessarily resist galling in titanium. This is a tooling selection issue as much as a process parameter one.
• Peck or chip-clearing strategy in a blind hole. Titanium chips don't break as cleanly as steel chips at the same feed, and a rigid tap cycle without adequate chip evacuation packs material back into the flutes, which increases friction and heat on every subsequent pass.

What to do about it

Start by loosening the tap drill percentage rather than chasing spindle speed. A slightly larger tap drill trades a small amount of thread strength for a tap that isn't fighting to shear excess material.

For most fastener applications, that strength loss is well within what the joint needs.

Confirm the tap and coating are actually rated for titanium rather than assuming a general-purpose tap works the same across alloys, and make sure coolant is reaching the cut, not just running nearby.

If a hole keeps stripping after those changes, look at chip evacuation in the specific hole depth you're running. A blind hole that packs chips behaves differently than a through hole with the same nominal parameters, and titanium punishes that difference more than steel does.