Alot of these weird drill sizes were probably developed during the WWII years. Heli-coil thread inserts were invented during WWII for our warbirds.
I like to back up the tap a quarter turn after every turn, just enough to feel the chip break. Haven't broken a tap in a long time.
Not to mention a lot of different styles of RIVET...or maybe it WAS just to fuck with us in the future...
This is the best piece of advice yet said. I would go one step further and back up after every ½ turn. And use the best cutting fluid you can buy...no cheap crap. .
I think alot of guys braek taps from using dull taps, no lubrication, and not backing the tap out a 1/4 to 1/2 turn to break the chip. I also believe there are so many sizes of drills because of the many aplications. Like you don't use a 1/4" drill when you are going to use a 1/4" reamer. Becarefull taping that king pin boss it is hardend, just go slow and use a lubricant that is oil based. I worked in one shop that made you feel like you were in the 30's and the owner was 74. He used bacon lard as a lube. Matt
LOL! This comes straight from the bible itself: <O Tap drill size limits for a 5/16 18 UNC internal 2B and 3B fit inclusive: <O .252 minimum, .265 maximum. <O I know many machinists are experts at the off center sharpening and .002 oversize when using a ¼ drill is probable especially by hand. <O
I actually do it every 1/2 myself, but I thought it was overkill; I am usually a little over cautious.
Believe it or not tapping holes is kind of a science. You may get away with tight holes for awhile, and yes, I've done it. One hole at a time may work with little clearance but try a 1000 holes power tapping. When you start pitching $200 castings you may check your charts for % of thread. A lot depends on the material, aluminum is way more forgiving, too tight of a % of thread in stainless steel could make you really unhappy. On stainless I use 65%. Just remember what it is for, if it's holding a railroad car over your head, which I've done, or a bracket on your throttle linkage which most of us have done, what are the risks? Do it right. I'll be throwing out some tech here shortly on the general info all Hot Rodders should know about drilling, milling, and tapping. Nothing over the top, just tips that I use every day. Dashman's Hot Rod & Speed Parts www.dashman.net Just as a side point, all my taps are two flute.
i have had to tap a bunch of holes in 4140 and I have to back off 1/4 turn for every 1/4 or 1/2 turn, its tough stuff when the hole is only 0.091 and the taps are so small. i have found that spiral fluted taps seem to work well, but when we are tapping in the machine, it really will tear up just about any tap you can throw at it
I'm a little surprised no one has brought up the phenomenon of $40 115-piece drill bit sets (Titanium coated!) that are sold by all kinds of cut-rate outlets (HeartlandAmerica, among many others, perhaps even Harbor Freight and Northern Tool) that have numbered sets (1-60), lettered sets (A-Z), as well as fractional sets PLUS! a handy dandy chart, "Decimal Equivalents of Drill Sizes". They're undoubtedly made in China but imho belong in every shade tree mechanics workshop. Cheers -- Gary The darkest hour in any man's life is when he sits down to plan how to get money without earning it.--Horace Greely
I bought individual sets, Fractions, Numbers, Letters. All Dormer/SKF. I think the least expensive of the three was over $80 on sale 25 years ago. Cheapshit Imported tools SUCK. When a crappy imported tool breaks, ruining a part, you just wasted a bunch of time and material, to try and save a couple bucks. The Titanium Coating on quality cutting tools makes a difference, and is priced accordingly, the Cheapshit coating is just that, cheap shit.
Thanks, I need to set up a better deal for those on the Hamb, just waiting for Ryan to get back to me. In the classified I've given free shipping on all our stuff. Unfortunately it doesn't always work out too great for me, it can equate to 35% off by the time I ship, ah but you guys are worth it! Just remember, on tooling, often you get what you pay for. Some poor quality stuff I'm still paying for! Dashman's Hot Rod & Speed Parts www.dashman.net
I have one of those cheap-ass sets(or half a set, so many are broken) that I keep next to the drill press for my friends to abuse when they are over here working on stuff. I keep my good USA made bits WELL hidden.
That is something I want to touch on, often it is the speeds and feeds of the bit that will give you the biggest headache, no matter what you spend on a bit. Nothings more frustrating than breaking off a $.99 bit or a $1200.00 bit in a hole of a one up part. It's aggravating at any level. Dashman's Hot Rod & Speed Parts www.dashman.net
If you have no drill/tap chart quickly available, the calculation for a simple UNC assembly thread is; Major diameter - thread pitch. Pitch is equal to; 1/ number of threads per inch. Unless you are a admitted hacker please don't waste your money on cheap drill bits, even the coated ones. Your best invetment is a good quality HSS drill set. They will last through your grandchildren's lifetime if properly maintained. Your projects deserve it!
in my shop i placed a conversion chart for inches to metric & tap to hole size chart above my drill press on the wall. handy good luck DoozCoop
Here's a quick simple formula to convert metric to fractional: (mm) divided by 25.4 = .000" 8mm divided by 25.4 = .3149" This is pretty close to 5/16" This can help you to determine the size of a hole, for "close enough" jobs or to use those metric drills that are sitting on the shelf. Dashman's Hot Rod & Speed Parts www.dashman.net
i found out years ago that different metals have different requirements for drill sizes... when in to buy taps for my 1st nitrous install... the counter man asked me what material i was tapping into ... i told him both aluminum&steel >he then gave me 2 different drills for each tap i bought.....today unless you are buying from a machine shop supply house they donot know enough about this to be off any help......
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