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I have two different holes on my 1972 Shovelhead that need the threads repaired, so in preparation for those repairs, I thought I would share a few important tips for tapping new threads.
Tapping new threads is considered a scary exercise by many amateur or novice mechanics – a task they simply don’t want to touch.
My recommendation is don’t be afraid. Tapping new threads can be a little stressful, but it is a skill all backyard wrenchers and weekend warriors should acquire. If you work on old bikes or even new bikes that have been mistreated a little, you will come across a damaged hole at some point – it isn’t a matter of if it will happen, but when.
Also, the only way to learn a new skill is to try and potentially fail. Life isn’t about fear.
Just keep in mind that when it comes to tapping new threads, doing a bad job isn’t irreparable. That said, take your time and give it your best shot on your first attempt
Tips for Tapping New Threads
-Follow the old adage of “Measure Twice, Cut Once.” Plan out the entire task from start to finish before taking the first step. Consider the depth of the hole, the type of thread that best suits the final application, and whether the potentially larger diameter hole will cause an issue with either of the parts to ultimately be fastened together.
-Match the drill bit size and tap size carefully. I like to purchase sets with matching bits and taps that way there can be no mistake. There are charts all over the Internet that can be used to match things up based on the desired ending bolt size.
-Buy quality taps – I prefer hss and made in America. The quality just tends to be better. You need taper or plug taps to start a hole.
-Use a proper tap handle. In order to be stronger than the metal they are cutting into, taps tend to be brittle. The chance of snapping a tap increases exponentially if you are trying to turn it with a set of pliers or grips.
-Taps generally can’t cut all the way to the bottom of a blind hole due to the taper of the first few tap threads. Keep this in mind when determining depth and overall number of threads required.
-Use a cutting lubricant, but done use WD-40. I use Magic Tap, which is reasonably priced off Amazon.
-Hold your tap in line with the hole, turning clockwise to cut. There might be a slight wobble or eccentricity on the first few turns, but after that things should straighten out nicely.
-Every few turns as it starts to get too difficult to turn, back the tap back out counterclockwise a little (quarter to half turn) to clear any chips or cuttings. You should feel the prior cutting break away. Do this more often the smaller the tap. Then proceed deeper.
-Once done cutting all of the threads, clean the hole up well and then re-run the tap over the new threads one more time. This finalizes the threads and cleans them up really good.
Okay, so off the top of my head, those are my 8 tips for tapping new threads.
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Also, forgive any typos or grammatical errors a I wrote this blog post from my phone.