Taps, 2 vs. 4 flute, spiral vs. straight flute

What a great link Techno!

I must add, that a tap purchased from a hardware store will be just a basic 'run of the mill' bulk standard cheap tap that will cut a thread of whatever size you want but without the accuracy or the repeatability of a quality tap designed for a specific application! A tap designed for mild steel will not be of the same cutting geometry as that made for bronze or iron! Same can be said for blind holes or through holes! The strength of a thread can also be improved by thread forming/rolling instead of cutting (or chasing). It all depends on your application and setup! The physical size of the thread can also play a part due to the manufacturing process. I guess the table above is a good starting place for Bruce!

Always remember, A sharp tool is a happy tool and a clean machine is a happy machine!

Words of wisdom from a Toolmaker called Dick who had hands the size of plates and could coax a lathe to dance the tango!

I agree, great link.

I have not yet made it through the other information at your link (http://www.precisiondormer.com/) but I hope they also have the "class of fit" information.

Part of the comment from Mr. Truman Brain has me a little confused. I can see from the precisiondormer link how flat bottom, taper point and spiral/straight come into play. But, does "A tap designed for mild steel will not be of the same cutting geometry as that made for bronze or iron" mean that the actual thread profile and thread depth on a "top of the line" tap would be different based upon the material that the tap is made for?

The thread will be the same size but, how it was cut will be different! The cutting geometry of the tap is tailored to suit the material it is going to cut!

Thread profile will remain the same, however the clearance angle, back rake angle, level of finish quality, amount of room for accumulated chips, tap material (such as high carbon steel, high speed steel, or cobalt), and coatings ( such as TIN, TIAIN, Daimond PVD) can all be different depending on the material to be cut or formed.

Wow, that is a lot for me to think about. I'll go back through my MSC and McMaster Carr catalogs and see how well I can extract the truth from what the marketeers put in print.

Thank you,

Bruce

If you have any expensive taps/dies that become dull you can re-sharpen them by either giving them to a grinding machine shop or get a set of round sharpening stones and do it by hand.

Hope this helps.

Duck.

Buy your tap from local industrial supplier. You can buy tap for all the specific class. They can assist you on what kind of tap that fit your need best.

For precision fit use undersize tap and lap the threads.

For bronze use HSS. Do not use coated.

If you are using alike metals then the diametre of the threaded bolt determines the depth of the tapped hole. The strength of the metal bolt does not increase with the amount of thread it is inserted into.

There are drills that are graduated into .010" increments used in the precision optics industry.

I find the combined drill and tap to the best for general use.

I've also noticed that the combined drill and tap hold up better then the four fluke taps, it might have something to do with their being more material in the length of the tap but I've had far fewer combined drill and taps break then with the four fluke taps.

Another advantage of the combined drill and tap is that it's easer to run the tap through a second time to clean the threads, where as with the four fluke there is more of a tendency of the tap to start cutting into the already existing threads.

I've also found that taps with a narrowing shank hold up better then the taps where the shank and the fluked cutting portion are the same diameter.

That's just my experience. We used both types and I would get one with the narrow shank and keep it to myself and have it last me a good while.

Material I primarily worked with are Stainless Steel, Mild Steel, Aluminum and UHMW.

I've never had to tap bronze.

Thank you for the information on the drill-tap combinations. As we purchase new vehicles, I am tasked with mounting the equipment carried on them. I would guess 300 holes drilled,then tapped. Most are 1/4x20 and into aluminum. A few are into galvaneel (galvanized steel) I have been averaging about 1 tap per truck. I long ago gave up and just stuck the tap into the cordless reversible drill. Last week I bought a set of drill-tap combos just to not have to do two separate steps. I think they are from Greenlee. I have never used them before, and feared they were just a crappy gimmick. Now I have more hope. Thanks again.