# Needing some math...



## SDB777 (Apr 11, 2016)

I tried doing a search, 'words to common' were deleted leaving me with nothing I was looking for....strange enough, but so am I


My question(s):

#1: What is the *outside* diameter of material you leave before using a die?
{example:  M12x.75 single start die}

**Is it 12mm plus the .75mm equaling 12.75mm(0.50195 inch)(or as close as humanly possible using a wood lathe and free-handing tools)?

**Just 12mm(.4724 inch)?

**Or something else?


I have nice clean threads using a 7/16ths(.4375 inch) drill bit and my M12x.75 tap, but I'm constantly ending up with way too tight to fit, or way too loose to engage threads....either is acceptable(at least for me).


It would be really awesome if someone had a search engine that would give me the chart for all my taps?  But I haven't found much information about the outside diameter of anything.....anywhere.





Scott (maybe whiskey and math is a better idea) B


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## Carl Fisher (Apr 11, 2016)

For OD before using a die, I typically turn down just under the major diameter.

So for an M12 die I'll turn to about 11.8 +/-  There are charts out there that will give you exact targets for percentage of thread depth, etc... but I find for pen making you don't have to be that exact.

For the drill hole for your tapping internal threads, the starting point is usually the size minus the pitch.  So M12x0.8 would put you at 11.2mm as a starting point. You can adjust to your taste.


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## Phillip Kelley (Apr 11, 2016)

*Scott:  Try this for a copy of a Starrett Chart*

Drill Tap Chart | BrokenBolt.com


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## SDB777 (Apr 11, 2016)

Phillip Kelley said:


> Drill Tap Chart | BrokenBolt.com


 

All good for tapping stuff...but it doesn't say anything about how big to leave the outside of something before twisting your die onto it.

Guess I'll need to load the 'fail' body onto photobucket and let y'all shed a tear for me(them blanks are awesomeness).




Scott (no one else has fails....I've looked) B


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## SDB777 (Apr 11, 2016)

Outside diameter of this was 11.8mm before using a M12x.75....thread were barely noticeable.  And no, they did not break off.

Now the other possibility is that the M12x.75 die is 'bad', but I purchased it so long ago, it'd be a 'problematic' trying to convince the place I bought it from.



Scott (purty fail) B


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## Carl Fisher (Apr 11, 2016)

This will sound silly, but make sure you're starting with the die facing the right way. The text on the die should be face out as there is typically a lead in taper that will center up the die on the tenon.  I've left "threads" like yours if I accidentally tried to run the die backwards.


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## SDB777 (Apr 11, 2016)

I shall make sure to 'face them', but I do think the lettering was towards the cut.  But like everything else.....the more you think about it, the less you remember.

Maybe I need to start tossing a GoPro onto a clamp and filming everything I do(that could become embarrassing though)....certainly would bore the masses on youtube!




Scott (was it or wasn't it) B


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## Phillip Kelley (Apr 11, 2016)

*Another chart:*

Millimeter to Inch Chart

Scott:  It looks like 12MM = .472  so is your tap 12mm x .75 or 1.75??
It has been my experience in metal work  to make the DIA for outside threading to turn to the desired OD of your thread.  I am working with a section as well & the tap & die that I am having to use is 12mm x 1.75


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## BRobbins629 (Apr 11, 2016)

Some dies are also split, allowing for some adjustment with a set screw.  Not sure yours are, but its another way to adjust.  I've found there is no good diameter for all material.  Each one reacts a little different.  Either that, or my measurements are sometimes off.  No photobucket, but a big fail bucket here.  Write everything down is a good idea - not what I do, but what I say.


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## SDB777 (Apr 11, 2016)

Phillip Kelley said:


> Millimeter to Inch Chart
> 
> Scott:  It looks like 12MM = .472  so is your tap 12mm x .75 or 1.75??
> It has been my experience in metal work  to make the DIA for outside threading to turn to the desired OD of your thread.  I am working with a section as well & the tap & die that I am having to use is 12mm x 1.75


 

I didn't realize there was a 1.75?  I have the .75 'stuff', with exception to the feed taps I have here.



Scott (just order bottoming taps the other day too) B


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## Dalecamino (Apr 11, 2016)

Scott, I may be late on this and, haven't read every post. But, here's what I've used from the start and, works well for me. Drill bit 7/16ths and .465" for the tenon. Easy-Peasy :wink::biggrin:


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## Joey-Nieves (Apr 12, 2016)

try this calculator Guhring, Inc. - Tap-Drill
it tells you what bit to use for a tight or a loose fit.


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## Carl Fisher (Apr 12, 2016)

This can also happen if your are out of round on your tenon or offset on your die. 

11.8 is definitely the sweet spot for me though. Did 2 more last night.


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## More4dan (Apr 12, 2016)

What I do when sitting at the lathe and don't feel like looking it up i just measure the tap I will be using and make the OD just slightly under. The starting OD for metric threads should be same as the nominal. 12mm x whatever pitch should be 12mm OD.  By measuring your tap the male threads will fit the threads you tap each time.  No math required.


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