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The Offcial Machinist Thread: Revised 01/04/2014

A place to ask general spud cannon related questions.
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Unread postAuthor: Technician1002 » Sat Jul 07, 2012 6:00 pm

technology was expensive


Have you seen the budget for technology development lately? Look for Research and Development. Number is in Millions.

http://www.google.com/finance?q=NASDAQ:INTC&fstype=ii

One 13 week quarter; 2,401.00
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Unread postAuthor: Lockednloaded » Fri Aug 24, 2012 10:23 pm

I don't really know if this belongs here, but I was wondering if I could get some wooden air-gun parts made? The gun has a plastic grip and plastic stock that I want replicated in wood. They have to match the current ones so that they fit on the gun, so I need a pretty skilled craftsman
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I love lamp
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Unread postAuthor: Zeus » Fri Aug 24, 2012 10:28 pm

It's not that difficult to inlet and shape wood, just takes some practice. Ask a gunsmith for some two piece blanks.
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/sarcasm, /hyperbole
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Unread postAuthor: PaperNinja » Fri Aug 24, 2012 10:53 pm

Ok. I know some of my other posts were unclear or unreasonable, but here's my current part I need :).

I don't really care what material it's made out of. It's not gonna be taking any pressure, so it doesn't matter too much. Brass or stainless steel would be best.

It's basically a .55" OD metal rod, about .783" in length. On one end is tapped 1/4" BSPP threads that go in about .2". If it's easier to go in farther, go ahead but the min is .2". In the middle there is a hex bolt thing, this doesn't need to be wide, just about 1/8" wide. On the other end is 3/8"-24 UNF threads, going in at least .27". The taper of the size of the hole between the two threads can be as gradual as you like.

Here's a picture:

Image

Also note that I don't know the real size of 3/8"-24 UNF... so if the hole size taper should be going the other way... :roll: well I'm an idiot then, but I think this is right.

The tolerance doesn't have to be too small... uhm idk maybe .002"?

Please get a quote, including shipping to area code 03301 (USA).

I'm VERY sorry if I've messed up again, and something is unclear or unfeasible. PLEASE if I've done something noobish or bad or unclear or unworkwithable, just pm me and ask me to clarify, I'll also edit this post.

Thank you.
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Unread postAuthor: dewey-1 » Sat Aug 25, 2012 11:18 am

Are you sure you want BSPP and not BSPT?

If you want BSPP buy McMaster 4860K152.
Cut of the Male NPT end, drill a .332 hole (size Q) and tap 3/8-24.
A lot cheaper than all that machining !!!
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Unread postAuthor: PaperNinja » Sat Aug 25, 2012 2:51 pm

Yes it's BSPP. Not that it really matters, the other end is going to be on a custom part as well.

The problem with that is I really need to lengths to be accurate.

About how much would it cost otherwise?
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Unread postAuthor: dewey-1 » Sat Aug 25, 2012 3:37 pm

The fitting is $7.65.
If you have somone machine this from raw materials (brass) you cannot afford it. Way to much machining time.

If this McMaster fitting was used and modified you may be able to afford it.
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Unread postAuthor: PaperNinja » Sat Aug 25, 2012 3:43 pm

Hmm I'll try and understand these diagrams. As long as the total length is the same, and the threads go at least as far in as I specified it should be fine. Thanks! :)

Btw I don't know how long it took, but I really appreciate the well-made drawings :)


It seems to me that the inside of the 1/4" NPT is too large for the 3/8 - 24 UNF. I'm probably wrong, but just a concern.

If you can guarantee that this will work, how much would this cost?
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Unread postAuthor: DYI » Sat Aug 25, 2012 4:26 pm

Dewey may be overestimating the difficulty of making this part. I could, if not for going back to school very soon, make this for $90-$100, materials included, assuming the tolerance does not apply to the lengths of the female threaded holes (which your post implies it does not). I don't charge $70/hour like a machine shop would, but I'm also not as fast as they are.

In response to Dewey - you're not going to hold .002" on the external lengths without using machine tools.

@PaperNinja: why do you need the lengths so accurate?
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Unread postAuthor: PaperNinja » Sat Aug 25, 2012 4:42 pm

Well honestly they don't need to be.

I didn't realize how expensive a little part would be when I asked for it, if it would make it cheaper much larger tolerances would be acceptable, even up to .01"

I need it reasonably accurate, I'm going to use this to mount an air cylinder to use to reload a semi-auto gun. If the lengths aren't right, the loading piston won't press and seal against the hole in the barrel, greatly reducing power & efficiency.

I chose .002" because it is the tolerance I WILL need in another part I haven't written the plans for yet, and I figured I may as well have the tolerance uniform.
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Unread postAuthor: DYI » Sat Aug 25, 2012 4:55 pm

What diameter does the hex need to be, Ninja? I assumed it was a standard diameter you could buy hex rod in. What are the diameter tolerances on the OD? If all the tolerances are large enough that the part can be made with no measuring instruments apart from dial caliper, you could probably have it made, materials (~$15) included for $50-$60 (at the rate I work at right now, I estimate it would take me about 45 minutes to make this part. A skilled machinist could do it in less).
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Unread postAuthor: dewey-1 » Sat Aug 25, 2012 4:55 pm

DYI wrote:Dewey may be overestimating the difficulty of making this part.

I am simply stating a $7.65 part modified is one hell of a lot cheaper than your $90 estimate.

Cut off, drill and tap and your done! 15 to 20 minutes tops.

In response to Dewey - you're not going to hold .002" on the external lengths without using machine tools.

I never said .002" tolerance. He can get away with .005"

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Unread postAuthor: PaperNinja » Sat Aug 25, 2012 5:10 pm

Ok I think I may be able to do this modification.

I have a 21/64" drill bit - will work as Q

A 3/8 - 24 tap is another $7

I have a drill.

My only problem is, I don't know if it'll be the right length when I cut off the male NPT. I don't want to have to cut through the thick part :/. Even if I have to, I worry that while making it that short, there won't be enough room to thread far enough in...

Oh well... If I'm saving $60, I'll make it work. I am worried though that the hole will be to large for the tap after I cut off the male threads.
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Unread postAuthor: Goats spudz » Sat Aug 25, 2012 5:55 pm

PaperNinja wrote:I am worried though that the hole will be to large for the tap after I cut off the male threads.
:banghead: Why do you need such tight tolerances for a reducer anyway?
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Unread postAuthor: PaperNinja » Sat Aug 25, 2012 6:32 pm

PaperNinja wrote:I didn't realize how expensive a little part would be when I asked for it, if it would make it cheaper much larger tolerances would be acceptable, even up to .01"

I need it reasonably accurate, I'm going to use this to mount an air cylinder to use to reload a semi-auto gun. If the lengths aren't right, the loading piston won't press and seal against the hole in the barrel, greatly reducing power & efficiency.

I chose .002" because it is the tolerance I WILL need in another part I haven't written the plans for yet, and I figured I may as well have the tolerance uniform.



Look up :wink:
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