Advice on machining cover-story

[xperk]

I need some advice or ideas on how to approach a machinist workshop and not have them get the 'wrong' idea of what I want them to make.

Ideally my project would call for a barrel blank - however that is not an option due to regulation.

Now for the project at hand I would need a piece of 4140 round bar drilled, bored and threaded.. this obviously calls for a lathe, which I presently do not have at my disposal - hence the need for outside involvement.

I was thinking of ordering an 'adapter prototype', the 'adapter' I imagine would be needed in an either high stress environment requiring a high margin of safety. Of such places I can think of would be axles or connecting sections.

As the attached drawing illustrates the cover story for the project gets thinner as the adapter gets longer.

The cover story I could think of would embarrasingly be 'an adapter for a scuba tank' as this would explain the quality of the steel and tensile stress involved plus it would explain why heck I would be willing to pay to have one made. The precision of the internal diameter of the adapter would be required for optimal airflow. The thread specification would have to correlate to that of a scuba tank.
On the downside is the obvious problem of a guy wanting a corrosive metal adapter for scuba diving ...

This request for advice may seem premature, however I live in a small town, and the project being rejected at one machine shop would result in failure to get the device made locally.

Any experience related to approaching machine shop are welcome.

[Corona]

How about you ask them nicely? :-)

No, I'm serious. My point is, *don't* try to be creative with the truth, and don't try any BS with these people. In my experiance, these people can see right through you.

I think the biggest motivator is *repeat business*. The guys here know, I'm a regular customer for having tiny precision components machined. If I ever request them for the thing you want, they might raise an eyebrow, but they won't rat on me.

What matters to them is how good a customer you are and how mature you are. If they get the impression that you're out to dispatch someone using something THEY made.... well, thats that then, isn't it?

Remember... Don't try any BS. And be a good and regular customer for other items. You will not have any problems.

[xperk]

Corona,

I appreciate your comments, and I agree that to some extent 'a common understanding' with the machinist is preferrable to playing games.

However I feel that it is also somewhat of a balance between achieving a trust relationship and delievering too much information that may later compromise you. A trust relationship could also produce a complete production list of your various devices.

The advice about having several items made in advance of the project component is certainly a sound one and will go along way to achieve some of the things you recommend. And yes, I do get that the other items should be of unquestionable nature.

Still I would like some degree of official explanation as to the nature of the component as this would not only have value in relation to manufacture, but could also prove valuable at a later time. E.g storing or transporting a component that primarily serves legal functions, but remains available for other purposes.

Have others had adapters made or are you just all blessed with easy available barrels?

[zaibatsu]

Xperk,

While I don't agree that Corona's is the best idea for you, it does have some useful points. Why not slightly modify his idea, and instead say it is for an airgun? Airguns are legal is most of Europe, so I'm assuming they are in the Netherlands. Also, since this is going to be smoothbore, obviously accuracy isn't too much of a concern, so couldn't you just use an airgun barrel? I'm sure you could lap the airgun barrel to the required ID, although it may take a while.

[Corona]

A few thoughts and observations:

1. I live in Karachi with 13 million other people. I use 4 machinists for my regular work. They know me well and I can joke around with them. Of course, you can’t tell them everything… The way we do it is, we have developed an unspoken understanding… I don’t tell them what its for, and they don’t ask. THAT is the attitude repeat business creates for you. The machinist won’t pry.

2. I use precision parts for my work. So that nobody has the complete picture, I use.. like I said… 4 different machine shops. At one time I used 7.

3. People here like to get some work done and pay later or haggle about the price. Not me. I pay whatever the machinist asks me to pay for the service. I have found the prices to be reasonable, so it is okay. The guys appreciate this. Nobody likes a headache.

4. You are right though. There is a risk in saying too much, because the machinists are like a mafia. All of them know or have heard of every other machinist… or thats what it seems like to me. But over here, because of the competition in their line of business, they know the value of keeping customer confidentiality... even from the law.

5. These people have GREAT memories.

6. Also keep in mind that even though I have found machinists to be pretty bright.. a cop will always be a cop. Sub-intelligent monkey. Any good story will do and I think Zaibatsu's is the best.

7. And finally… You have a little brother? Or better yet.. a little sister? Less then 10 years old will be best. If not, then BORROW the kid from your neighbors or somewhere. Go with the kid. Seeing you with your little sister or little brother defuses any alarms going off. Human nature. Just makes your life that much easier.

Good luck.

[xperk]

zaibatsu,

the airgun barrel solution has crossed my mind and I might go for it for the early stage prototype - I acknowledge lapping will be needed.. and probably epoxying it into a DOM tube for safety as the airgun barrels I have previously played around with where scaringly easy to cut.

The machining story for an airgun barrel is quite good as a compressed air design a la 'Gunpower' design would require an adapter piece between the tank and the actual barrel. Thanks!

[JoeJablomy]

Corona: You live in PAKISTAN? I may be wrong, but I had the impression that gunsmithing was a widely practiced craft there; machinists and society in general are probably much less averse to guns that politically correct Europeans. Even in America, people look at big things and say "You could <I>hurt</I> someone with that," and in Europe the idea of making something specifically for threatening/hurting people might make business owners very uncomfortable. That's why PC-ness is detestable.

xperk: Even a long barrel blank would resemble some kind of cutting tool shaft or extender.
As for questions, you don't need good or detailed answers if you don't let them ask a whole bunch of questions. Walk in, tell them you need the part, give them a drawing, pay them, and leave. Just label the drawing "DRILL SHAFT" (for an old rock drill that you can't find new parts for) and look like you're not really interested in chatting. When they ask, the subject is boring, and isn't worth a definite, detailed answer that might lead them to more annoying questions. It might help if they are large and busy themselves.
Anyway, how do you plan on forming the chamber?

[xperk]

JoeJablomy,

hmm drill part might work..

I plan on forming the chamber using a chamber reamer from one of the parts shops online. I am unsure if that is the correct way to go about it.

hehe.. I actually visited Pakistan once, in one of the gunshops I was offered a 10 shot (!!) revolver.. I mean the drum was huge but talk about thin chamber walls :-)

[Bigfoot]

You're trying to build a vibration-free stand for your telescope...the part you need is for an air bearing housing. Hence close tolerances needed, esp. in the bore. If anyone there has ever made or seen an airbearing, he'll understand the need to have it lapped to precise tolerances. Spiral flutes running the length of the bore would also be part of an air bearing.
I was once tasked with assembling the device to cut flutes in the bore of an airbearing. It's essentially a rifling cutter, without the twist.

[xperk]

Bigfoot,

oh yeah now we're talking :-)
I took a look at around the web in the subject - seems like its the sort of hoovercraft of bearings right (pardon my ignorance).

So following my mickey mouse research on the subject of air bearings the device would be a spindle for an air bearing ..
Coupled with the astronomic need for precision I feel that we have a winner.

[megalomania]

Lets see, you could be building an airplane part, an automotive assembly, a air jet for your hot tub, a pneumatic machine assembly, a custom pressure washer attachment, or some vage component for a manufacturing machine like an injection molder or vacuum former. Just be consistent, but best not to mention anything gun - air or otherwise.