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# Picatinny Rails?

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#22
10-05-2013, 07:34 PM
 Platinum Member Join Date: Jul 2011 Location: Near Napoleon,MI Posts: 1,192
Re: Picatinny Rails?

Ok, I am not a professional cad jocky but I am an engineer and do about 90% of my own CAD work except for loading them in SAP.

I'm trying to understand your issue with drawing this section.

If we assume that the 0.748 dimension is the "gauge" distance for the dovetail and that the 0.108 gauge height is centered on the 90 degree corner, then working outwards the dimension to the theoretical corner intersection is 0.748 + 2x(0.108/2) = 0.856.

So the fact that the print shows a dimension (which appears to be corner to corner) of 0.835" suggests that the rail does not have a sharp corner but in fact has a small flat which is (0.0105^2*2)^0.5*2 = 0.0297" wide (vertically).

If you think about it, it is never good engineering practice to put a sharp corner on something which is going to fit into an outer part. That is because no-one can make a tool that cuts a true square corner (at least not for very long). So cutting tools have a radius on the edge and the part that fits into the feature needs a flat or chamfer to clear the radius so that it can be properly seated on the 2 45 degree faces as intended.

I was going to write you a description of how to draw it, but I don't think you need it now ? All clear ?

I will add that a good print would show a detail of that corner feature so you could see the 0.030" flat, but this was probably done a long time ago and they were probably initially cut by artisans who understood how things needed to be made to fit together and not by operators hired off the street who were shown where to push the button.

I will tell you that the hardest thing one ever has to accomplish as an engineer is to get artisans to trust your work. The problem being that the work they get from about 90% of the engineers is incapable of fitting together and the shop gets blamed for delays at the end when it does not go together... The day that guys from the shop floor walk in your door with suggestions about how to make your work better (instead of WTF is this sh&\$%t ?) you have "arrived".

Quote:
 Originally Posted by Razor18 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.
#23
10-05-2013, 07:56 PM
 Platinum Member Join Date: Feb 2011 Location: Cincinnati, Ohio Posts: 2,480
Re: Picatinny Rails?

Quote:
 Originally Posted by bruce_ventura 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.

Ive got to disagree. Being born is a biological incident...nothing more. Becoming respected is via your actions over time and your interface with others on this planet
#24
10-05-2013, 08:22 PM
 Platinum Member Join Date: May 2011 Location: Ventura CA Posts: 1,106
I completely respect your opinion, which I would do even if we were total strangers.
#25
10-05-2013, 08:25 PM
 Junior Member Join Date: Jun 2013 Posts: 14
Re: Picatinny Rails?

Alright. So I regret what I said to sideflipcar and apologize. I wish I had never said it. I didn't realize the thread was older than dirt. And I should have responded to his comment how I did. His comment about my dad (that I never had) pissed me off as well. I did feel his original comment was disrespectful and I overreacted.

There are young people out there that do know a dcnt amount about shooting, and I commonly see them shot down, soley because they soley because they are young.

I am on here to learn and help people out that have questions.

I have no hard feelings, and will take it a a learning experience.
Sorry to those of you I offeneded. Hopefully we can accept each other differences and call it a day.

Happy shootin
#26
10-05-2013, 10:09 PM
 Silver Member Join Date: Oct 2012 Location: Windsor, VA (but heading for the Rockies) Posts: 427
Re: Picatinny Rails?

Quote:
 Originally Posted by bruce_ventura 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.
Hey Bruce!

I'm telling ya, a nice cold Sam Adams or two would be great right now! lol.. That's for sure.

Yep, still over here kicking rocks and dirt clods around, my incoming count is up to 894! lol.. I just wish these guys would behave.

Thanks for doing what you do sir, I'm sure that I've met a few of your 'students' over here where I am, they're 'fair' shots! lol!!!

There's a reason that Dignity, Honor, Respect, and Integrity are the values instilled in all recruits, they are the bedrock of men becoming MEN.

Watch out for all those whacky liberals out there on the 'left coast' Bruce! We'll get together and share a few, talk about horses and shooting someday soon!

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

#27
10-06-2013, 11:42 AM
 Bronze Member Join Date: Apr 2008 Posts: 36
Re: Picatinny Rails?

Quote:
 Originally Posted by westcliffe01 . If we assume that the 0.748 dimension is the "gauge" distance for the dovetail and that the 0.108 gauge height is centered on the 90 degree corner, then working outwards the dimension to the theoretical corner intersection is 0.748 + 2x(0.108/2) = 0.856. So the fact that the print shows a dimension (which appears to be corner to corner) of 0.835" suggests that the rail does not have a sharp corner but in fact has a small flat which is (0.0105^2*2)^0.5*2 = 0.0297" wide (vertically).
Dear westcliife01,

THANK YOU, this is exactly the kind of answer I was looking for from Someone who tries to understand the question instead of answering some nonsense, like "the drawing is not perfect, so what?" (let alone from someone who's been engineer, claiming to have "been there done that" on jet engines for decades...). Drawings are invented to show how to do something, and if something isn't on the drawing, how could anyone expect it to be done right?

Yes, I got the same answer from another credible source too: the edge-to-edge dimension of 0.835 is in fact the distance of the "chamfering" after cutting the 2x45° edges, and not the edges themselves, as drawn. With this additional information the drawing is perfectly enough to mill a rail, but on the drawing there is no sign of any chamfering, so again, the drawing is simply wrong, and no rail can be done based on that without this additional information, which is missing from the drawing. Would like to watch the jet engineer try to mill it by the original drawing to make him understand.

Thanks, I appreciate your approach to the problem.
#28
10-06-2013, 04:02 PM
 Platinum Member Join Date: Feb 2011 Location: Cincinnati, Ohio Posts: 2,480
Re: Picatinny Rails?

Quote:
 Originally Posted by Razor18 Dear westcliife01, THANK YOU, this is exactly the kind of answer I was looking for from Someone who tries to understand the question instead of answering some nonsense, like "the drawing is not perfect, so what?" (let alone from someone who's been engineer, claiming to have "been there done that" on jet engines for decades...). Drawings are invented to show how to do something, and if something isn't on the drawing, how could anyone expect it to be done right? Yes, I got the same answer from another credible source too: the edge-to-edge dimension of 0.835 is in fact the distance of the "chamfering" after cutting the 2x45° edges, and not the edges themselves, as drawn. With this additional information the drawing is perfectly enough to mill a rail, but on the drawing there is no sign of any chamfering, so again, the drawing is simply wrong, and no rail can be done based on that without this additional information, which is missing from the drawing. Would like to watch the jet engineer try to mill it by the original drawing to make him understand. Thanks, I appreciate your approach to the problem.
If you are referring to ME...I never said I was a jet engine ENGINEER now did I? I said I DESIGNED engine hardware ( basically for the military group of engines) for my whole career.. And if you were SMART ENOUGH to get a copy of spec SI-212,010 or PITF3 CL-A you would see that INTERPRETATION OF DWG states that not every little thing has to be specifically dimensioned because many are FALL OUT edges , surfaces. The resultant of other actually dimensioned surfaces being machined and whats left is whats left.

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