[thompson4433]

I'm trying to get started on a CNC project, I’m hoping you guys can help me out.

I’m a structural engineer, but I don’t have any experience with this sort of detailed machine work.

I would like to make some replacements of rare and expensive gun parts by reverse engineering the existing parts.

The gun I want to make parts for is very similar to the AR15, it's called the FN FNC. FN doesn't supply spare parts, so there are none at all.

So I have a few questions, any help or advice you can offer would be greatly appreciated.


1. Laser scanning

Suppose I wanted to have a part laser scanned for reverse engineering. Is there any company you might recommend? Cost is a consideration because the parts would be produced in low volume, say less than 25 pieces.


2. CAD software

At work we generally use Microstation and to a lesser degree AutoCAD. I don’t know how to use them, I make sketches and give them to a drafter.

I could probably get a copy one of them installed on my office computer from our work site license.

What program would you recommend?

Is there anyone I could send the existing parts to and have them create the CADD files?


3. Parts fabrication

Just so you know, I’m not going to do anything that breaks any BATFE laws, or any laws at all for that matter. I'm extremely careful about that sort of thing.

That having been said, are there any shops that could do a good job of producing parts? The part I’d like to do first would be similar to an AR15 upper or lower, maybe out of aircraft aluminum or better yet stainless steel. The lower for the gun I have in mind is flat sided and looks like it was carved out of a block of aluminum. I’d also like to replicate the folding stock and some small parts like hammers.

How about making prototype parts, maybe out of plastic? Any companies you can recommend?


THANK YOU very much, in advance, for any advice or help you can offer.

[awerby]

1. Laser scanning

Suppose I wanted to have a part laser scanned for reverse engineering. Is there any company you might recommend? Cost is a consideration because the parts would be produced in low volume, say less than 25 pieces.

[It will be difficult to make this work out economically, since scanning isn't cheap, and the reverse-engineering process is difficult, time-consuming, and requires expensive software. Machinists tend to charge more for small runs, too, since it often takes a few tries to get everything working correctly.]


2. CAD software

At work we generally use Microstation and to a lesser degree AutoCAD. I don’t know how to use them, I make sketches and give them to a drafter.

I could probably get a copy one of them installed on my office computer from our work site license.

What program would you recommend?

[The best software for reverse-engineering parts from laser scans is Rapidform XOR. You might be able to use your existing software to do it, but it would be more difficult, especially if you're not very good at using it.]

Is there anyone I could send the existing parts to and have them create the CADD files?

[Sure, but it might not be as cheap as you might want.]


3. Parts fabrication

Just so you know, I’m not going to do anything that breaks any BATFE laws, or any laws at all for that matter. I'm extremely careful about that sort of thing.

That having been said, are there any shops that could do a good job of producing parts? The part I’d like to do first would be similar to an AR15 upper or lower, maybe out of aircraft aluminum or better yet stainless steel. The lower for the gun I have in mind is flat sided and looks like it was carved out of a block of aluminum. I’d also like to replicate the folding stock and some small parts like hammers.

How about making prototype parts, maybe out of plastic? Any companies you can recommend?

[There are plenty of shops that can make plastic RP parts in plastic, but I'm not sure what good they would do you. You'd still need to do them in metal, using CNC machinery.]


Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[txcncman]

Ok. Let's walk through and and just toss some numbers at your ideas. Let's say you can get your parts reverse engineered for $100.00 per part. No idea how many different "spare parts" you actually want to make. But, take that number times $100.00. (Actual cost will probably be more in the $500.00 per part range, but I do not want to blow your idea out of the water yet. Once scanned or probed, still has to be converted into a model.)

Since you are getting your parts scanned, the only thing you will need CAD for is adding key dimensions and tolerances. Your available CAD software should be able to handle this, so, no extra cost there. Yes, there are companies (and some individuals) that can do the entire reverse engineering process for you. If you go this route, you are still looking at $100.00 or more per part.

You can also have parts 3D printed or machined from plastic, but if you are exactly replicating existing parts, what would be the point? Prototyping is for new designs. Yes, there are shops that can make these parts for you. Some types of parts should be done only through licensed sources. Others can probably be done by anyone. Check the appropriate laws for which is which.

[thompson4433]

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[thompson4433]

Ok. Let's walk through and and just toss some numbers at your ideas. Let's say you can get your parts reverse engineered for $100.00 per part. No idea how many different "spare parts" you actually want to make. But, take that number times $100.00. (Actual cost will probably be more in the $500.00 per part range, but I do not want to blow your idea out of the water yet. Once scanned or probed, still has to be converted into a model.)

Since you are getting your parts scanned, the only thing you will need CAD for is adding key dimensions and tolerances. Your available CAD software should be able to handle this, so, no extra cost there. Yes, there are companies (and some individuals) that can do the entire reverse engineering process for you. If you go this route, you are still looking at $100.00 or more per part.

You can also have parts 3D printed or machined from plastic, but if you are exactly replicating existing parts, what would be the point? Prototyping is for new designs. Yes, there are shops that can make these parts for you. Some types of parts should be done only through licensed sources. Others can probably be done by anyone. Check the appropriate laws for which is which.

The sensitive part on this particular firearm is the upper receiver assembly, BATFE issued a letter saying that the upper would be considered the "registered firearm" similar to the FN FAL.

That makes everything else on the gun just a misc. part, including the lower. The letter was issued specifically to allow people to machine the lower without any legal restrictions.

Of course I'll check on all this with BATFE before proceeding. I know it's not a deal killer, there are plenty of guys machining all kind of parts for guns legally.

Parts for this particular firearm are so scarce, a $5 hammer sells for upwards of $125.

So there is plenty of $$ room in there for product development.

The point of getting part made from plastic would be to insure that is fits properly before making the final finished part. Is that not needed?

I've seen all kinds of parts being made for guns on the internet, I'm just not familiar with the process and what would be the best way to proceed.

[awerby]

It's good if you (and everybody working for you) don't get arrested for making these parts. It would be nice if you got a lawyer experienced in this realm to confirm your thoughts on these matters - one never knows...

But let's look at your numbers. This is a good test case, since these are rare parts that would theoretically be worth producing in small quantities, considering that there is a market for them which seems relatively unsatisfied. The problem is, that you have to do a lot of work on each part before you can make any. The question is, how big a batch do you have to have to justify the cost of doing them?

Let's assume that you want to produce those $5 hammers you mentioned. Let's assume that they really retail for $125 each. That means that as a manufacturer, you can get about half that for producing them: $63 each, times your part run of 25, which equals $1575, which represents all your costs and profit for doing this part.

Txcncman gave you quite an optimistic estimate of the cost of 3D scanning and reverse-engineering to create an accurate CAD model. Considering the price of the hardware and software and the level of expertise required, I don't see you getting from a physical part to a CAD model that retrieves its original design intent for anywhere near $100. Add a zero and you might be getting close.

Once you've got a good model, I suppose you could send it out to an RP shop for a plastic model. Figure $200+ for that. It would give you a rough idea of whether the part would fit, or if it has major problems. But it wouldn't tell you much about how the parts that need to be machined will actually turn out. For that, you'd need to hire a CNC-capable machine shop with a qualified machinist, have that person analyze your part and figure out what fixtures to build that would hold onto it while the various machining strategies necessary to producing something mechanically functional are performed. This is another highly-skilled person you need to enlist, since that's who the whole reputation of your venture is ultimately going to rest on.

Once the fixtures have been built and the toolpaths have been posted to G-code, it's simply a matter of procuring a blank of tool steel in an annealed state, setting it up in the VMC, cutting the part using a series of tool changes, hardening, tempering, finishing, bluing, and voila! But it's hard to see anybody going through all that for much less than about $1000 per model, plus a certain amount per part. Once you've run enough of them, the initial labor is amortized, but on a part run of 25 it will loom large.

I don't want to discourage you, but it will be very difficult to justify all that work for such small part runs, at least if you have to pay to get it done. Maybe you could learn to do it all yourself, and purchase the machinery and software required. Or perhaps you could partner with some gun-nut who had all that stuff and knew how to use it, and was looking for a challenge. Who knows, there might even be someone like that here on the 'Zone...

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[thompson4433]

First of all, thanks for the responses so far, very helpful.

Making gun parts is a common thing, there is a lot information on the BATFE website about it.

ATF Online - Firearms - Frequently Asked Questions - General

Q: Does the GCA control the sale of firearms parts?
No, except that frames or receivers of firearms are “firearms” as defined in the law and subject to the same controls as complete firearms. Silencer parts are also firearms under the GCA, as well as under the National Firearms Act (NFA). Certain machine gun parts, such as conversion parts or kits, are also subject to the NFA.

[18 U.S.C. 921(a)(3) and (24), 26 U.S.C. 5845, 27 CFR 478.11 and 479.11]



Based on what I've read here, it doesn't seem completely unrealistic to get parts made.

If the setup cost $2000 for the CAD model and $2,000 for setting up the CNC, if you made a run of 50 parts, the setup costs would be $80 a part.

So you figure you'd have to make a run of 50 parts minimum and the setup costs would be $40 each for a small part and $80 for a big part.

And the per part cost on top of it.

[awerby]

Based on what I've read here, it doesn't seem completely unrealistic to get parts made.

If the setup cost $2000 for the CAD model and $2,000 for setting up the CNC, if you made a run of 50 parts, the setup costs would be $80 a part.

So you figure you'd have to make a run of 50 parts minimum and the setup costs would be $40 each for a small part and $80 for a big part.

And the per part cost on top of it.[/QUOTE]

[Right, except that a small part isn't necessarily going to cost any less to set up than a big one. It's more to do with the complexity of the part, the fixtures necessary to hold onto it, and the number of machining operations necessary to produce it. The per-part cost is more likely to be higher on a big part than a little one, though. A part run of 50 makes twice as much sense as a part run of 25. And making 100 at a time would be even better. ]

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software