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Engraving vs. milling requirements

tmmill

Plastic
Joined
Nov 9, 2009
Location
california, usa
I've looked and searched and inquired but not finding what I'd like to hear so here it is.
I'd like a machine that will engrave/mill aluminum to the specs required for aluminum and plastic AR lowers (yes, California) - that is, reasonably sized lettering and needing at least .003" depth. I found machines made in China and also elsewhere all in price ranges you would expect. The problem is everyone has a different take on what's needed for rigidity and power at the spindle along with what's considered milling or engraving.

So what's the general consensus about what's needed to cut text into 6061 or 7075 material. I'm thinking that multiple passes would require some accuracy in the machine but a single cut might be better with more power. There are conversions from wattage to horsepower for spindle motors but where is the 'breakpoint' between scratching the surface for engraving and cutting a bit deeper? 1/2hp, 1hp or more or .8kw, 1.5kw or 2.2kw. What are the capabilities?

Thanks for the info in advance.

TM
 
I've pondered this myself, but mainly just as a "can I do this, for me, with the gear I already have?" sort of question.

The short form is at that kind of depth, it comes down to RPM more than anything else. You're only going .005" deep, with an acute point tool, which won't put any real side load on the system. So it's all about max RMP, unless you want to use a diamond point for drag engraving. Which still won't put any real load on the servos. So look for something with a very high RPM, like 20K, or more.

If they're hard ano'd first, you may have trouble, just from the hardness of the ano versus the very teeny tip of the tool, but with some tweaking, you should be able to iron out the right speeds & feeds to make that work.

Just FYI, as I understand it, plastic lowers have to be serialized on a piece of metal that's cast into, or otherwise permanently integrated into the lower. You can't just engrave the plastic. (Look at how Glocks are serialized.)

Best of luck, but you may be better served finding someone local with a fiber laser to just blast the numbers in for you. Quick, painless, and a whole lot cheaper than buying a whole mini-mill just to put on a few numbers.

You could also look for an old jewelry engraving machine. Those'll do it too, and can be found reasonably cheaply.

FWIW,
Brian
 
You can buy Letter/Number punches and a Hammer at HF. Very reasonable pricing, I hear. You could scratch Awl them, or use an electric Engraving tool. I know Chisels seem a little old skool, but I think it's important to experience the work.

What makes my mind tingle, is obviously you aren't building aftermarket Lowers (which is a stupid description BTW), but your willing to ask on a public forum how to Serialize them???? A little shady, but shady doesn't mean anything.

You're going to have a tough time getting answers about Arms manufacturing on this site. We are professional and we are careful.

Robert
 
You can buy Letter/Number punches and a Hammer at HF. Very reasonable pricing, I hear. You could scratch Awl them, or use an electric Engraving tool. I know Chisels seem a little old skool, but I think it's important to experience the work.

What makes my mind tingle, is obviously you aren't building aftermarket Lowers (which is a stupid description BTW), but your willing to ask on a public forum how to Serialize them???? A little shady, but shady doesn't mean anything.

You're going to have a tough time getting answers about Arms manufacturing on this site. We are professional and we are careful.

Robert

Robert,
Welcome to California.
As of ?1/1/18? I think, or some point reasonably recently, 80% lowers here *must* be serialized with a Cali-DOJ assigned serial number. They're still legal to build, as I understand it, so long as you apply for the serial first, and jump through whatever hoops they want you to. Which may or may not be actually possible, but at least in theory, that's the game.
So he may just be asking about what's required to deal with the new rules.
If he were doing anything seriously untoward, I don't figure he'd be asking about how to serialize the things.

Cheers-
Brian
 
I've pondered this myself, but mainly just as a "can I do this, for me, with the gear I already have?" sort of question.

The short form is at that kind of depth, it comes down to RPM more than anything else. You're only going .005" deep, with an acute point tool, which won't put any real side load on the system. So it's all about max RMP, unless you want to use a diamond point for drag engraving. Which still won't put any real load on the servos. So look for something with a very high RPM, like 20K, or more.

If they're hard ano'd first, you may have trouble, just from the hardness of the ano versus the very teeny tip of the tool, but with some tweaking, you should be able to iron out the right speeds & feeds to make that work.

Just FYI, as I understand it, plastic lowers have to be serialized on a piece of metal that's cast into, or otherwise permanently integrated into the lower. You can't just engrave the plastic. (Look at how Glocks are serialized.)

Best of luck, but you may be better served finding someone local with a fiber laser to just blast the numbers in for you. Quick, painless, and a whole lot cheaper than buying a whole mini-mill just to put on a few numbers.

You could also look for an old jewelry engraving machine. Those'll do it too, and can be found reasonably cheaply.

FWIW,
Brian

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i would use a cnc mill to engrave. i have even used a Prototrak mill to engrave but you have to raise and lower manually for each letter. not much different than a manual engraving machine. of course you can engrave on 3 axis cnc. you do not need higher than 3000 rpm. just use a lower feed like 1 to 5 ipm feed
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software some like millwrite which can select 2 axis text. that keeps gcode smaller as many Prototrak have a 200-300 gcode line limit. not like you going to write a book with it.
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i used a sharpie marker holder with a slip on brass bushing for guidance and some weight. i would write what i engrave first to confirm spelling
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some materials throw up a burr. yes you can recut .001 just be aware still might have a slight burr. some use wood tongue depressor or craft sticks to rub off burr.
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if you do not engrave .010 deep but shallow like .003 if piece in vice uneven .002 if will show up as uneven engraving. if you do not use a cutter but a drag diamond or tungsten carbide engraver if piece uneven it really will be uneven unless it is a spring loaded engraver. they do sell spring loaded engraving tool holders
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to be honest many engraving jobs are done by laser now. usually it looks very good. but its not deep so it can wear off eventually.
 
Thanks for the replies and the suggestions. Sort of confirms what I already had in mind.
There's absolutely nothing illegal suggested or proposed here, only compliance with the current and upcoming legislation.

The intention is to use a small cnc type engraver/router for other stuff, too, but the capability to cut just a little deeper than normal engraving would be a plus. A little more research is needed and I'll post any decisions and results for future reference. I really need to find someone within driving distance who has one of these table-top cnc engravers/routers to see one in person. I may just purchase a reasonable cheap unit and install a more powerful spindle motor and see what happens. Wouldn't be the first piece of equipment I modded and trashed. It'd be nice if it wasn't the last.

I'm sure it would be a lot cheaper and probably faster and with less headache to send parts out for engraving but what fun is that?

I also considered laser as an option but to get .003" depth into metal, even aluminum, requires some power that's too far outside my budget limit. 150 watt laser cutters in the sub-$5K range won't do it, I'm told. The makerspace at the local college has a 130 watt machine. Someone tried to etch a piece of stainless and the resulting heat shattered the glass in the top cover. Don't know the exact details of that operation.

TM
 
To engrave a sharp point .003" deep you don't need much power, but you need SPEED. The point is at a theoretical 0 SFPM so the faster the better. I use an air motor spindle held in a stationary toolholder in a VMC to engrave .015"+ deep with no difficulty. When we first tried it at 4000 rpm we struggled mightily. Adding the 50,000 rpm air spindle made it a breeze to engrave with a single flute 60° engraver. Just about any device, including a hobby cnc will engrave OK if it creates sufficciently attractive toolpath and has a high spindle speed.
 
To engrave a sharp point .003" deep you don't need much power, but you need SPEED. The point is at a theoretical 0 SFPM so the faster the better. I use an air motor spindle held in a stationary toolholder in a VMC to engrave .015"+ deep with no difficulty. When we first tried it at 4000 rpm we struggled mightily. Adding the 50,000 rpm air spindle made it a breeze to engrave with a single flute 60° engraver. Just about any device, including a hobby cnc will engrave OK if it creates sufficciently attractive toolpath and has a high spindle speed.

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i have engraved at least 500 parts just fine at 3000 rpm, sure feed is more like F1. or F2. but it always works ok for me
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depth .003 to .010" deep. depends on how wide you want the lines. if close space ruler type lines then they are normally .005 or less.
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many times i engrave .010 to .015" deep cause part later gets precision ground where .005" is often ground off
 
It won't take much to engrave. I only have 6k rpm available and have no problems. I use 2L Inc engravers, which are inexpensive and work exceptionally well. They have multiple point types, or you can use a small ball end mill. It just all depends on the look you want. You don't need much HP, but more spindle speed will help you engrave faster. For what you want, even a basic 440 Tormach would work fine. Lasers work well too and can get way more intricate with less setup, I'm guessing you were using the wrong one for your application. You don't need 150W to engrave metal with the correct laser.

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24457858757_5a64eab77d_z.jpg
 
Fiber laser, all the way!

I used to engrave NFA parts for a friend's company. He would arrive with lowers, can parts, etc, and wait while I engraved them.
Typical time to wait was about an hour....

Oh yeah, and this same customer had purchased a Chinese, CNC engraver..... it never worked, or never worked well enough....

With my laser Fiber laser, that time is 5 minutes (or less) from start to finish. (assuming the laser is already powered on...lol)

Given the versatility in fonts, barcodes, etc, you cannot really compare a laser to a mill, as they are apples to oranges.

Just my $.02
Doug.
 
I agree, if all you want to do is engrave, fiber galvo head laser. The huge 'advantage' of a 'mill' (even lightweight) is a little more flexibility. There are plenty of dudes that make good livings just doing laser engraving. Fiber lasers kick ass and you just flat out won't beat the setup and engraving. Not to mention not having to buy tools, little to no fixturing and it's pretty easy to learn the basics if you're relatively computer savvy. If you are already familiar with something like Photoshop or some other art type program, you could learn to be lasering nice serials and even logos in under 30 minutes.
 
Fiber laser, all the way!

I used to engrave NFA parts for a friend's company. He would arrive with lowers, can parts, etc, and wait while I engraved them.
Typical time to wait was about an hour....

Oh yeah, and this same customer had purchased a Chinese, CNC engraver..... it never worked, or never worked well enough....

With my laser Fiber laser, that time is 5 minutes (or less) from start to finish. (assuming the laser is already powered on...lol)

Given the versatility in fonts, barcodes, etc, you cannot really compare a laser to a mill, as they are apples to oranges.

Just my $.02
Doug.

This also sound interesting although it's outside my pricing limits. But what laser power levels are we talking about for a laser that'll do this type of marking?

TM
 
Your main problem will be flatness. Forged lowers aren't very flat, so your .005" deep engraving with a V shaped mill will leave different line widths everywhere, completely disapearing in low spots. No cheap mill or cheap software will be able to probe and compensate for it.

Having cosmetically engraved one of my own lowers I can tell you it takes a surprising amount of time to get it to look good. Machine power is not an issue.
 
Again, thanks for the tips, recommendations and information. Some good points have been made that directly affect the decision on what to buy.
Still waiting for some requests for information from a few inquiries I've made.

TM
 
Your main problem will be flatness. Forged lowers aren't very flat, so your .005" deep engraving with a V shaped mill will leave different line widths everywhere, completely disapearing in low spots. No cheap mill or cheap software will be able to probe and compensate for it.

Having cosmetically engraved one of my own lowers I can tell you it takes a surprising amount of time to get it to look good. Machine power is not an issue.

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i agree if part only .001 or .002" not flat and engraving a shallow .005" you will see the difference. if drag engraving with a diamond. .002" not flat can break tip off.
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they sell spring loaded engraving tool holders that are often recommended for shallow depth engraving. my experience is with normal size lettering .2 to .4" tall letters is about .010" to .015" deep. usually width of engraved lines is about 1/8 (min 10% wide) the height of letters so .2" letters about .02 wide minimum give or take.
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i agree to make engraving look good it can be time consuming. nothing worse than making a spelling error too.
 








 
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