+++ #18078 From: calbru@a... Subject: Re: tapping question It appears that on the QB fuselage two holes will have to be tapped for 3/8's fine thread bolts and two for 5/16th fine thread bolts. (for the reat seat attatchment) Can anyone tell me the official size that the holes should be pilot drilled prior to tapping. (I'm a carpenter, not a metal guy!) This question comes as a result of my breaking of a 5/16 course thread tap (to fit my eye bolt) in the aft most hole earlier tonight. (maybe I should not have been using a ratchet with a pipe on it??) Ideas on how to remove the remainder of the tap--it broke off flush with the top.... Thanks, Cal B +++ #18082 From: "Bruce A. Frank" Subject: Re: tapping question The proper drill size for 3/8-24 (NF) is a Q bit (.3320" dia). With plenty of good lubrication and care you can do it with a 21/64" bit (.3281" diameter). As for removing the broken tap...you know that you have a problem. If it were a lower carbon bolt you could place a nut over the hole and use 7018 stick electrode to strike the arc on the bolt, let the rod build up in the center for a few seconds then move the rod in a circular motion to incorporate the nut. Let it cool for a minute or two, then take a wrench to the nut and the bolt will come out. BUT, and this is a very big BUT, that will not work on a tap (if stuck tightly), the weld will be too brittle and the weld will just shear off when you begin to twist the nut. Now it can be done and done easily with the correct welding rod. With the proper rod the arc is struck through the center of the nut and the rod allowed to consume itself to fill the nut. The flux flows to the edge of the hole and protects the thread and prevents the contact between the tap and the edge of the hole from getting welded together. As the nut fills up with weld and flux, begin to move the rod to incorporate the nut. When things cool some it will back out just like a lower carbon bolt would. I sell the rod (stick electrode) that is specifically designed to extract bolts and taps that way. There are similar products from other companies. And I will say they may work for you, but my product is the best. The competition brands are MG Industries and the rod is MG 600. Another is Rockmont and the rod is called Brutus. My product is Cronatron 333. I have used them all side by side. If you cannot find a rep in your area for any of these rods, someone who will just give you one rod, let me know and I will mail you one. Another method: if the hole is a through one then a fine nozzle cutting torch can be used to blow the center mass of the tap out of the hole. With the oxygen just eat away as much of the tap as possible without getting into the hole threads. Don't dwell too long because if the edge of the hole starts to get red hot the oxygen jet's swirls and burbles can cut there just as easily as it cuts the tap. Let things cool some and go after the remaining tap material in the hole with screw drivers and small chisels; driving the material towards the open center of the hole. Bruce A. Frank +++ #18090 From: Russ and Penny Erb Subject: RE: tapping question OW! OW! OW! Must we talk of this kind of open carnage!? I'd rather face Pat's (formerly) damaged elevator than a broken tap! The side of my 3/8-24 tap says to use a 21/64 drill. The side of my 5/16-24 says to use a 17/64 drill. Bruce mentioned a letter drill which I have seen in some references. Go to http://www.mcmaster.com and search for hand taps. In the table of taps you can buy it will tell you the proper drill size. I haven't had any formal training in tapping, but here is what I've been able to pick up (I have a whole mess of successfully tapped holes to show for it): 1. If you can't turn the tap by hand using the leverage available on a standard tap wrench (two 3" or one 5" lever arm) then STOP!!! Something is WRONG! More torque will only mess up the threads, or worse--break the tap (YUCK!) 2. a. The best way to remove a broken tap is not to break it in the first place (after tapping a few holes, you will develop the feel for what the proper amount of torque is. If that amount of torque isn't working, STOP and fix what is wrong). b. The next best way to remove a broken tap is to throw the part away and make a new one. c. If you have to actually remove the tap, you'll have to do something like Bruce suggested. Remember the tap cuts because it is much harder than the part. Because it is so hard, it is as hard or harder than drill bits, so you can't drill it out. Generally you have to burn it out. As for attaching to it with weld rod--just remember how hard you turned it to break it--you'll probably have to turn it that hard to back it out. 3. Use a proper cutting/tapping oil. I use Relton Rapid-Tap cutting fluid, available at my local hardware store and through the Avery Tools catalog. Motor oil won't work--the viscosity is too high. I started out tapping holes using motor oil with poor results--no noticeable difference from tapping dry. When I switched to proper cutting fluid, there was a very noticeable reduction in the torque required to turn the tap. I was surprised--I didn't think it would make that much difference. I've been sold on it ever since. I use it for drilling 4130 also. 4. In steel, after turning the tap forward one turn or so (you'll feel the torque required increase), stop and back the tap up about a quarter to half turn to break off the chips (you'll feel them break off). Then continue forward. If the tap is still harder to turn after doing this (such as when you're down deep--such as 1/2" to 3/4" in a hole), back it all of the way out and blow the chips off the tap and out of the hole. Reapply cutting oil and continue. (Note--the forward-back procedure may not be required in softer materials, such as plastics) Using these procedures I have tapped 3/8-24 and 5/16-24 holes to the full depth of the tap (just over 1 to 1.25 inches) in 4130 with no problems. I did notice that by the time I was using the 3/8-24 tap on the seventh full depth hole that the tap was getting tired (dull--getting harder to turn) and bought another one. To re-emphasize--DON'T FORCE A TAP!!!!!!!!!!!!!! There are very few things worse than dealing with a broken tap. Russ "Broken Tap-a-phobic" Erb +++ #18099 From: Bob Romanko Subject: RE: tapping question I can't believe no one has mentioned using a Walton Tap Extractor. These are slick...and usually work on taps that were broken "gently". If you tap a hole with a 4 foot breaker bar these don't always work. 'Course...if someone's dim enough to do something like that, they desearve a stuck tap. http://www.waltontools.com/products/extractr.htm Another neat thing is partial sets are usually on eBay on the cheap. Planter "Can full of broken taps..right next to my breaker bar" Bob +++ $Id: 3.1-ToolUsage,v 1.1 2003/05/22 03:47:30 bentonh Exp $