# Just a few things I've picked up over my 2-year Machining Studies



## benmychree (Mar 6, 2018)

The general rule for pipe tapping is to leave 3 - 5  threads showing on the tap,  The best thing for reaming dowel pin holes is to buy an over and undersize set of dowel pin reamers; it will give you a tight fit for the stationary fit and a snug slip fir for the removable part.


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## cathead (Mar 6, 2018)

benmychree said:


> The general rule for pipe tapping is to leave 3 - 5  threads showing on the tap,  The best thing for reaming dowel pin holes is to buy an over and undersize set of dowel pin reamers; it will give you a tight fit for the stationary fit and a snug slip fir for the removable part.



How about on a die, John?


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## benmychree (Mar 6, 2018)

cathead said:


> How about on a die, John?


When I am using an automatic die, I just fit the thread to a female fitting; I have made a lot of parts with 1/16" pipe thread, for that I made a thread ring gage with a std. pipe tap and sized it so the finished thread was flush with the small end of the gage, this is the practice with pipe ring gages.  With solid dies, I thread the die on until the small end is flush with the die or chasers in a regular ratchet type pipe die.  I also have a pipe threading machine, a Toledo 999, same thing with it, open the dies when they are flush at the small end.   For making many parts to be interchangeable, best is to have a ring and plug gage.  I found the ones that I had on e bay for the most part.


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## Silverbullet (Mar 6, 2018)

Dies I usually go about three threads past the die but it's not all the same with different die sizes you have to Ck the fit. I use to buy a pipe connector in the size needed then Ck on both ends that will put you in the right spot . Most use Teflon to seal connections . Dope or tape.


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## jwmay (Mar 9, 2018)

According to the formula, rpm for an 1/8 endmill is like 30,560 in steel. Did you happen to add a zero, or omit a decimal point?  Or perhaps I’ve just showcased my poor mathematics abilities. I’ve got (1000/.125)•3.82=30560 rpm

According to the other cheat charts I have, it should be 3056 rpm.


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## Bob Korves (Mar 9, 2018)

jwmay said:


> According to the formula, rpm for an 1/8 endmill is like 30,560 in steel. Did you happen to add a zero, or omit a decimal point?  Or perhaps I’ve just showcased my poor mathematics abilities. I’ve got (1000/.125)•3.82=30560 rpm
> 
> According to the other cheat charts I have, it should be 3056 rpm.


The cutting speed in steel is not 1000 SFPM, but more like 50-100 SFPM, depending on the steel, and assuming HSS tools.  Also, the formula I use is
SFPM X 3.82
cutter diameter in inches   =   RPM

80 X 3.82
.125                 =     2445 RPM

Using carbide tools, you could multiply the speed (SFPM) by as much as 5 times, ~12000 rpm


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## jwmay (Mar 10, 2018)

Thanks Bob Korves. Our math works out the same, except you didn’t use 100 like I did. Which I’m sure you realize. I had considered that the OPs numbers were specific to Cnc milling with insert tooling, but you’ve corrected that as well. Thank you very much.


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## jlsmithseven (Mar 10, 2018)

Yeah I guess mine are for insert cutters rather than manual stuff. I believe my max RPM was 2800 on the Prototrak so if it went over that, I just ran it near max and it worked.


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## Bob Korves (Mar 10, 2018)

If you round the 3.82 up to 4, then the equation is simple enough to do in your head.  1/2" HSS end mill on mild steel, 90 x 4 is 360, divided by 1/2 = 720 rpm.


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