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# Picatinny Rails?

#15
10-01-2013, 03:53 PM
 Bronze Member Join Date: Apr 2008 Posts: 36
Re: Picatinny Rails?

Thanks, but my question was not about wiggle room, it was pure geometry of the MIL-STD as shown in every image on th net, but I probably couldn't explain it precise enough.

The way it's drawn it can't be machined, cause some of the dimensions seem to be "over-defined", meaning there are 3 specific dimensions where if 2 are made right, the third can't be the value specified.

If you look at the drawing I'm sure you can follow. The heart of the rail is in the middle of the rail profile, datum C, which is a rectangle .748 +/- 0.002 wide, and exactly 0.108 high. On both sides, the corners of this datum C are touching 45° lines, these lines intersect in a 0.835 +/- 0.005 width (rail width), without any chamfer.

The vertical sides of datum C and the 2x45° lines form two little triangles on both edges of the rail. The base of those triangles is the side of datum C, which must be 0.108. Perpendicular to this vertical base, the "height" of those triangles (on the image it's actually horizontal, and isn't drawn) from the middle of the base to opposite corner of triangle is obviously half of the difference between datum C width and rail width (0.835 - 0.748) / 2 = 0.0435.

Now in a symmethrical triangle, if the height (which is 0.0435 here) is not equal to half of the base length (0.108/2=0.054 here), then the angle of the triangle sides can not be 2x45°, it's geometrically impossible. So, back to the MIL-STD drawing, if you require datum C to have the drawn dimensions, AND require the side angles to be 2x45°, then rail width can not be 0.835. From those 3 conditions, only 2 can be met at a time.

So which one of the required dimensions must not be met so strict in your opinion to still have a match between rail and any proper mount?
#16
10-01-2013, 06:33 PM
 Platinum Member Join Date: Feb 2011 Location: Cincinnati, Ohio Posts: 2,480
Re: Picatinny Rails?

So what if the drawing isnt totally complete or for that matter 100% accurate? You trying to MAKE a rail from the drawing or just buzzing someone else' s ass about it.
#17
10-02-2013, 12:40 AM
 Bronze Member Join Date: Apr 2008 Posts: 36
Re: Picatinny Rails?

I don't do CAD drawings for fun, of course I want to make it on machine. But if you can’t do it on paper first, based on the drwaing’s dimensions, you can’t do it on machine eighter. That's why drawing are for. Your question shows you didn’t even try to understand the geometry problem, and ask me about wanting to buzz someone’s? Have you tried making it maybe?

Regards

Last edited by Razor18; 10-02-2013 at 02:07 AM.
#18
10-02-2013, 05:14 AM
 Platinum Member Join Date: Feb 2011 Location: Cincinnati, Ohio Posts: 2,480
Re: Picatinny Rails?

Quote:
 Originally Posted by Razor18 I don't do CAD drawings for fun, of course I want to make it on machine. But if you can’t do it on paper first, based on the drwaing’s dimensions, you can’t do it on machine eighter. That's why drawing are for. Your question shows you didn’t even try to understand the geometry problem, and ask me about wanting to buzz someone’s? Have you tried making it maybe? Regards
I designed jet engine hardware for 37 years partner...and what you say isnt true. Look up the term "Kellering" and then try and decipher how you would draw it! And dont tell me jack squat about CAD drawings either....thats what I used from 1974 till 2004
#19
10-02-2013, 05:35 AM
 Bronze Member Join Date: Apr 2008 Posts: 36
Re: Picatinny Rails?

If this is the case, I honestly don't understand your first answer. Wouldn't take too much for you to start drawing datum C (0.748 x 0.108), put the 45° lines onto the corners of datum C. Then just measure if the width of the 2x45° edges can ever be 0.835. No, it will be 0.856. If you find, how to machine it for 0.835, I would really happy to know it, honestly. I want to make it, but can't, till this question is solved, or the rail won't fit. I really didn't try to ask here for nit-picking.

Last edited by Razor18; 10-02-2013 at 06:31 AM.
#20
10-02-2013, 12:28 PM
 Silver Member Join Date: Oct 2012 Location: Windsor, VA (but heading for the Rockies) Posts: 427
Re: Picatinny Rails?

Quote:
 Originally Posted by Hunter02 I appreciate you teaching me something new (about air guns) Thanks for that. Thanks, hope you have a great weekend. Respect is earned, not something you are entitled too. Happy shootin'
Respect, like dignity and integrity are always implied until one is found unworthy, young sir. Perhaps you should be a bit more humble and accepting of advice and mentorship when it is freely offered. Arrogance goes hand in hand with the ignorance of youth whom believe that they are worthy because they have watched a video or two.

The gentleman whom you so disrespectfully offended is a long time member and mentor of many on this site, a respected machinist, designer, engineer, business owner whom has probably held more weapons in his life than most professional soldiers. He is one of the many on this site who have 'been there, done that', made the mistake, and then shared the lesson with us.

You will be surprised to learn that there ARE actual rocket scientists, ballistic engineers, master gunsmiths, world champion marksmen, optics engineers, and genuine experts. Perhaps a bit of humility on your part will earn you the respect that you are so quick to deny others of.

Please enjoy the site, learn from others here, and remember only liberals use insults when they are loosing arguments!

Another ole'timer...

DocB
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http://www.heaven-scent-rescue.org

"History does not long trust the care of freedom to the weak or timid" Dwight David Eisenhower
Sic Semper Tyrannis...Veritas et Aequitas

#21
10-05-2013, 06:29 PM
 Platinum Member Join Date: May 2011 Location: Ventura CA Posts: 1,106
Re: Picatinny Rails?

Quote:
 Originally Posted by Hunter02 ...Respect is earned, not something you are entitled too...
I disagree. I think we earned it when we were born. We're all entitled to it.

And thank you DocB. Good to see you're still kicking. I'm still looking forward to sharing a beer when you get back. Keep the photos coming.

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