Gromit Posted October 4, 2007 Share Posted October 4, 2007 I've to tap a hole for an EGT probe. The fitting is 1/8" NTP. So I drill an 8.5 mm hole and tap it. I've been out playing with it on some bits of steel ; I've a few questions. I've a starter and finisher tap. I assume the starter is the one with a longer smooth taper on it. What does the finisher do that the starter doesn't? What's the best lubricant to use while tapping? Paraffin? As the tap is tapered, I'm a bit confused about how far into the hole I should run the tap(s). Sorry for the basic questions, but this is all completely new to me Quote Link to comment Share on other sites More sharing options...
western Posted October 4, 2007 Share Posted October 4, 2007 (edited) This should help using taps & dies to cut threads drill sizes for thread tapping scroll down to the 3rd table for NPT threads Edited October 4, 2007 by western Quote Link to comment Share on other sites More sharing options...
Gromit Posted October 4, 2007 Author Share Posted October 4, 2007 This should help using taps & dies to cut threads Yeah, I was reading that when my brain when on strike :wacko: Quote Link to comment Share on other sites More sharing options...
western Posted October 4, 2007 Share Posted October 4, 2007 Yeah, I was reading that when my brain when on strike :wacko: time for a coffee break then Quote Link to comment Share on other sites More sharing options...
Gromit Posted October 4, 2007 Author Share Posted October 4, 2007 time for a coffee break then After coffee, found these 2 articles on good old Wiki which helped. Tap Wrench Taps and dies Still haven't found answers to my questions though.... Quote Link to comment Share on other sites More sharing options...
kiall Posted October 4, 2007 Share Posted October 4, 2007 the taper tap starts the thread more easily for u , then u go for the plug tap with squares the hole of do that u get a gd hold on it , u get a cutting compond for tapping but i use grease at work , when your tapping work the tap back and forth ie 1/2 forword 1/2 back then 1 turn forward so that u clear it out , just go slow and do ti right , no bother trying to rush it youll only break the tap , Quote Link to comment Share on other sites More sharing options...
houd Posted October 4, 2007 Share Posted October 4, 2007 ... What does the finisher do that the starter doesn't? If you are threading through a piece of flat strap or similar, nothing. However, if you were cutting a 'blind' hole, i.e. not right through, you need the finisher to cut the thread properly right down the hole. What's the best lubricant to use while tapping? Paraffin? Trefolex, because it stays put, rather than dribbling away. As the tap is tapered, I'm a bit confused about how far into the hole I should run the tap(s). See answer above; right through if it's possible, or to just short of the base in a blind hole, then the same with the finisher - snapping a hardened steel tool in the hole is bad news .... Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted October 5, 2007 Share Posted October 5, 2007 Kiall's advice is good - a turn or so, then back off 1/2 a turn to break the swarf off before carrying on. Good quality taps help, I'm guessing if you have a starter and finisher they're not from the 50p shop anyway. I used grease last time I did any tapping as I was trying not to get swarf in my axle casing, seemed to work nicely. Quote Link to comment Share on other sites More sharing options...
kiall Posted October 5, 2007 Share Posted October 5, 2007 impervia grease i used at work , and to grease any bolts as its thick and water proof, although we have expensive taps they still do break as they dont like that much torque, although as mentioned above the finisher tap may still be tapered so if your going to tap a blind hole u may need a actuall plug tap which is square all the way to the bottom. a good tool also to get it s a ratching dwang ie, link (no flaming , i make my living wiv them) Quote Link to comment Share on other sites More sharing options...
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