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Back up a few years. It's 2012 and myself and a buddy of mine decide that we want to build at least a pair of custom rifles.
Our final conversation on deciding what to make went something like this.
Well... we defiantly want rifles, and preferably something we can have as a semi-auto. So we're limited to roughly AR and AK platform constraints.
We want something subsonic because suppressors are fun and things that make loud booms (while fun) tend to make groundhogs run.
300 whisper? na.. plus who knows which will get standardized...
Some giant necked up .308 to .45 caliber? it'll fit in an AR 10 and chuck huge chunks of lead? (yes we almost made a .45 raptor 3 years ago) ... looks at AR 10 receivers (at the time) YIKES nope too pricey.
hmmm... what can we do with similar AK rounds. (I had built my AK 74 the previous year)
Look up the dimensions of a 7.62x39 case... what can we do with it?
Then a lightbulb went off in the back of my head. The Russians already make a subsonic round based on a 7.62x39mm. A 9x39mm
And the project went from there.
We did some research and found that there was more than just necking the case up.
as a comparison here's a 7.62x39
Ok great! now we know what we want to make the rifles in! Also we can use existing 7.62x39 parts kits and receivers as the base to all of it. We got an Egyptian parts kit from apexgunparts that October, and were getting drawings started on reamer dimensions for the chamber.
Then Sandy Hook happened and the project got shelved.
Fast forward to February 2014. I'm staring at my tax return check wondering what I want to do with it. Plop down in my computer chair. What haven't I played in a while?... I haven't played Call of Pripyat in a while I'll load up a new game. Play for a while, pick up a VSS vintorez. ... *pause game*... looks at screen... look at check... F it I'm taking the project back off of the shelf!
I call up Pacific Tool and Gauge and start working with them to get a reamer designed.
The result, this as a framed posted in my office.
After the reamers arrived I made a sizing die and then I realized this whole project would actually become a reality.
9x39 with a 286gr on the left. a Hornady 70gr 5.45x39 on the right.
What was next? getting designs for the whole front end rebuild of AK parts.
This is kind of a recap post that gets the project caught up to about a month ago. If there's anything you guys want more information on or additional photos of let me know and I'll see what I can do.
|# ¿ Nov 24, 2015 19:24|
|# ¿ Jul 28, 2021 11:53|
Those engineering drawings
ok *cracks knuckles*
M42 High Speed Steel. PTG uses M42 because it generally will hold a sharper edge and is tougher than M2 (much more common HSS)
What kind of steel are the reamers?
If I remember correctly they were only $130 each
How much did they cost you?
yes and no. They were done collaborating with Dave Kiff (THE reamer guy at PTG)
Are they your own design?
Do you fireform the casings, or are they custom made?
We don't have a functioning rifle yet. Those are 7.62x39 cases that are first sized into a straight walled case (even down through where the web starts), the upper 1/3 of the case is annealed, then the neck and shoulder are sized into shape. If you look really close there's a tiny wasp waist as an artifact to the forming process. That will be fireformed out the first time it's fired.
Did the reamers really need to be within 0.0004, or was that a preference/accuracy thing?
That's actually PTG's "normal" reamer tolerance. they make higher precision ones as well. (and note it's +0.0004 not + or -)
They need to be like that because for example what happens if the .3929 neck measurement is a thousands or two undersized? Your case neck will be grabbed and you're going to be wearing your bolt.
A little of both?
Are you using them for machine reaming, or are they going to be used for hand reaming?
the sizing die that I made from 4140 I machine reamed it *most* of the way then finished it by hand.
If memory serves I was running it at 53RPM. The feed was VERY slow (hand feeding via a lathe tailstock)
What kind of speeds and feeds do you run with them if they're machine reamers?
It's a chlorinated sulferized oil. Stinks but works great on steels
What kind of coolant/cutting oil are you using?
I never actually had heard that?
Why 9.3mm diameter bullets when the original was(reportedly) 9.25/9.26?
They're probably 9.3mm as that's a "relatively" common large game caliber in Europe. And on top of it 9.25mm comes out to 0.3642 inches and 9.3 comes out to 0.3661 inches. It's such a small difference that it wasn't worth us making custom bullet dies on top of everything else.
(comparatively that's very similar to the difference between a 9x19 bullet and one for a .38 spl or .357 mag.
Currently they're being held between the work and a spring loaded live center in the tailstock. Rotationally it's being held in place by a pretty large tap wrench.
What kind of toolholders are you using for the reamers?
Patience :P I hadn't done a lot of documentation of the processes up until now so I didn't have a lot of the photos of what I had done. Once we get caught up to now it'll be photo central.
Can we see a setup?
We're shooting for around 40~45ksi similar pressure to a 7.62x39mm
What are you estimating chamber pressure to be like?
nope... haven't done them because we don't know what the internal pressure will be exactly
Did you do hoop calculations/pressure in cylinder calcs for the chamber and barrel, and if so, can we see them?
What's the twist on the rifling going to be, and how deep?
so some math calculations we did we realized that a standard 9.3 barrel won't work... the twist rate is 1:12. Which will stablize a 285gr bullet down to (this is from memory so may not be 100% correct) about 1500fps?
Ideally we need a 1:9.5 but we're making the initial rifle as a 1:10 so we can buy an off the shelf barrel twist.
We actually didn't.
How did you calculate how much gas is going to be needed/used in the action?
We're taking an existing design and the powder volume should be comparable.
Can I print off those engineering drawing you made for the reamer and frame them above wherever I'm working as a reminder that machining is the coolest loving trade?
Go for it!
EDIT: Do you think the same maths and work could make a 9x39mm Cz858 possible?
There's a technical fiddiculty that we've encountered that I haven't discussed yet. Magazines will be your enemy.
|# ¿ Nov 24, 2015 21:00|
Double post because
Do they even make commercially available 9.25mm bullets?
Not to my knowledge?
*Have* to no actually... we found a very unexpected answer to it.
However we are because we want to have box magazines for it.
|# ¿ Nov 24, 2015 21:01|
Are you shoving this into an AK parts kit or attempting something cooler?
*mostly* the scope of hte project is to make an AK in 9x39
The part where a LOT of the machining comes in is anything that's attached to the barrel on an AK (rear sight block, gas block, front sight post) all have to be custom designed/made.
|# ¿ Nov 24, 2015 22:15|
Oh well. Not a home made VSS, but still cool.
We want to get the bugs out of a working 9x39 load and the AK's built.
Then it's paperwork time
|# ¿ Nov 24, 2015 23:29|
You're going to put a can on it, right? Let's not put the cart before the horse.
Are you crazy? of course we are!
|# ¿ Nov 25, 2015 03:08|
Any time is Pripyat Time
Not enough Vodka present
what's your estimated timeline on getting a gun that can shoot these right now? Do you have your own machine shop, and just farmed out the reamers for the tooling metallurgy, or are you making the drafts and having someone else make all the actual parts?
Currently it's late winter/early spring....ish? The biggest time wait right now will be the barrels. I've been scrambling around quite a bit at work and haven't gotten a hold of the one company that actually makes 1:10 twist 9.3 barrels off the shelf.
I currently run my own machine shop at a university. So I can do a good portion of the work myself. (just can't bring/work on receivers here) I also have a couple basement machine shops that I have limited but reliable access to for any receiver work.
I farmed out the reamers for a few reasons. I had never designed one so I had no idea which part needs to be 0.0005" and which can be + - accuracy of eyeball. It's always best to just ask the people who do this sort of thing for their living. Also I don't have a single piece of equipment that reliably hold the + 0.0004" tolerances needed on a round object. (let alone the equipment to check the compound tapers needed)
The drafts have been done for the parts I need to machine. I'm hoping to get a post out detailing that process either today or over the weekend. I'm definatly making all of these parts.
(yes everyone will get to see a different glimpse into the land of the black magic voodoo elves on the other side of the requisition button. Well... other than lathespin.gif he's already familiar with elf land.)
There's an order to these things. OTs-12 Tiss -> OTs-14 Groza -> VSS.
Pfft bullpups, bullpups, we don't need no stinking bullpups!
Actually it would be fun to design and build but right now it's not in the plans.
Teaser time for those who want to see chips/setups
shalafi4 fucked around with this message at 15:02 on Nov 25, 2015
|# ¿ Nov 25, 2015 14:51|
I did note the one-way tolerance. Undersizing would obviously have catastrophic effects.
The short version is they have a LOT more active contact surface than a traditional reamer.
normal reamers if you're cutting a straight hole the only part engaging is the front lead in chamfer and possibly the first 1/4 of the side walls are actually cutting (probably less than this if it is sharp)
A chamber reamer the ENTIRE cutter is engaged AND cutting
Edit: imagine the RPM on a pretty intricate lathe form tool compared to a single point tool... similar idea
shalafi4 fucked around with this message at 17:56 on Nov 26, 2015
|# ¿ Nov 26, 2015 17:54|
Okay, I was figuring it was something like that. In that case, is there a formula for figuring it out, or is it an approximate guess based on experience or experimentation?
If there's a specific formula I'm not aware of it? Just from experience reamers that have any real kind of profile to them I try to run around 100 rpm for a 0.5" ish reamer
|# ¿ Nov 27, 2015 02:10|
Batshit crazy idea: $16 (beer)
Super awesome tech drawings: $30
Shiny weird shaped precision cutty thingies: $275
Realizing the black hole of the project has opened up: priceless
So... to recap we have a plan, reamers, go/ no-go gauges, and a sizing die made.
Not pictured is the sizing die. I'll get some photos of it once I'm back home. For an expanded ball/decapping pin I ordered an RCBS spare parts stem with .366 sizer.
here's where the project started spreading out in the scope of it.
We knew that we are using AK actions.
For those who are not familiar with them down to every nut and bolt enjoy. (I'll be referring to this drawing for a while)
Take a couple minutes to really look at it. Specifically everything that touches the barrel and the gas system.
There's a lot there... take another look.
OK, First thing to note on for our project. Nearly everything is pinned onto the barrel. The only one that is labeled on the drawing is the Barrel pin. However you can see 5 other pins if you look closely.
1 on the rear sight base
2 on the gas block
2 on the front sight post
So these will need to be completely redesigned.
Alright so we need to remake at least 3 part for our mutant AK.
Time to sit down and start designing.
There are pretty drat near an infinite number of ways to go about designing parts.
Many are better than others but here is a glimpse into the crazy process that I go through.
What does each part do?
Rear sight: Holds the rear sight. Helps guide the gas piston during cycling. (Possibly help hold the hand guard? )
Gas block: Ports and directs vent gas to the gas piston. Fully supports the Gas piston when at rest.
Front sight: Holds the front sight. (in some AK designs also holds the threads for any muzzle device)
Are there any hard restrictions ?
To me hard restrictions include:
New parts having to fit into other non modifiable parts. Fixed existing lengths.
Basically dimensions that can't or shouldn't be changed.
OK for all of you who just skim through these pages and like to armchair general it's
How many hard restrictions/constraints are there for the parts I've been talking about? Remember that we are making a new barrel the MUST have a larger OD than the existing one.
I'll answer general questions but not ones that directly answer any of the constraints.
Answers to be posted on the next main update.
shalafi4 fucked around with this message at 15:55 on Nov 30, 2015
|# ¿ Nov 30, 2015 15:36|
For the record you guys are no fun.
The answer is 5
I also apologize for this one it's going to be more a wall o'text than usual. I'm going to try to walk through the whole designing process.
So our restrictions are.
Diameter of the front trunion.
The 9x39 round is so close in dimensions to a 7.62x39 that we don't need to modify/make a new trunnion.
Length of the gas piston.
We need that to set where our new gas block will be positioned on the barrel
Diameter of the gas piston.
If we make our gas block too small, bad news. If it's too large we'll probably bleed too much gas around the piston and it may not cycle.
Centerline distance from the bore of the barrel to the center of the gas piston.
If that's off a little bit the bolt carrier will tilt as it cycles. Not normally an issue with an AK but it *can* cause premature wear on the receiver.
Barrel can't be too thin
This one is a little more nebulous. Intuitively it makes sense but there is not a specific "The answer is this specific number" type of problem to solve.
(well without pretty massive amount of computer modeling and a crapton of equipment and time that I don't have)
So we have our constraints. Now what?
We have 4 hard constraints and a "squishy" one.
I started with the "squishy" one since everything attaches onto the barrel I figured determining it's outer diameter would probably be a good start.
This one I pretty much solved empirically rather than in CAD or by experience. Ideally I wanted to try and keep the attachment pieces under 1" thick to help save on stock costs but I wouldn't know until I had a barrel diameter determined.
I'm sure I looked like a doofus walking around Cabela's one day. I went around with a set of calipers and measured every 9.3x57 or 9.3x62 mauser I could find.
They were all hunting rifles so the barrel profiles were pretty thin.
Most came out around 5/8" give or take. so I figured that .650" would be an absolute MINIMUM outer diameter.
So now I have a lower limit to my "squishy" tolerance. Time to figure out the maximum.
Again, ideally I wanted to make the front and rear sights and gas block out of 1" bar stock. I figured if we were making them out of steel a minimum dimension of around 1/16" around the barrel should be strong enough (assuming there's some extra bulk around where the pins go)
So assuming that the "max" barrel OD would be about 0.875 (1" - 0.625*2)
Ok so we have a barrel OD range of about 0.650" ~ 0.875"
Time to pull in one of the hard constraints to check and see if it would work.
Will the trunion bore size cause any issues with a barrel that big? *checks a couple trunions* NOPE! we're good The couple AK trunions I have are 0.917" YYYEEEEEYYYY I should be able to make my parts out of 1" stock!
I go back to talk with my friend who essentially is the customer for the 2nd one of these. We both want to make a fairly heavy barreled version at least for our prototype.
So 0.875 is the "max" we could go... I want to give myself some wiggle room in case the bar stock is undersized so I figured make it 0.866. Yes it'll be chunky but having a quarter inch thick barrel I KNOW that I'm well into the safety zone on pressures. (and don't have to go through the calculations on them in detail)
To wrap up, we know our constraints and have a rough barrel design hammered out (I dont' have a CAD model of it) Basically it's 0.917" for the trunion segment and then rolls down to 0.866" OD the entire length of the barrel.
Next up the first really fiddly bit and wrapping up the rest of those constraints.
As always feel free to ask questions on anything. The worst that'll happen is I'll give you a stupid answer
|# ¿ Dec 2, 2015 16:17|
I don't have a lot to add but this is genuinely one of the best threads I've seen in years and I'm really interested to see how it all comes out.
Even if you don't think you have much to add feel free to join in when I ask questions! Everyone might learn something from it!
|# ¿ Dec 2, 2015 17:47|
This is really neato. It's also interesting to peek at the design process for metal work. I have zero metalworking experience (except for a welding class that was ) in myself or friends or relations so it's neat to see the design process insides which are so different from my usual "head straight to the workbench for a quick proof of concept" that I do with electronics.
Completely understand. The electronics deity that has the office beside me said something pretty similar a few weeks ago.
|# ¿ Dec 2, 2015 18:10|
You may want to trade notes with BFG Cartridges. They even call their .358 Gremlin the 9x39 USA. Their cartridge is meant to be legal for deer hunting in Indiana rather than for suppressed shooting, and I'm not sure how close the dimensions are for the two rounds. Also, they only offer their cartridge in bolt-action rifles, so if you get an AK to cooperate with yours, you'll be way ahead of what they've been able to do. I only know of the Gremlin from seeing it in Cartridges of the World.
This is going off of memory.
The dimensions are pretty close? The 358 Gremlin if I remember correctly is simply a necked up 7.62x39 and the shoulder angle is modified. The 9x39 has the case body angle changed much straighter as well.
The 358 gremlin guys also are going for a completely different goal. They are making (comparatively) high velocity hunting rounds where as we're going the subsonic route.
That being said the cases are close enough that it would work perfectly fine in the AK we're building.
I should see if it's in my giant book of reamer tech drawings. I could see a lot more definitively on the differences.
I was wondering about the availability of 358 bullets vs. 366 but apparently 9.3mm is a big huge thing I'd never heard of until looking for it so there's plenty of options.
yea the 9.3's are common in Europe but never really took off here in the US. (45-70 supremacy)
And I can defiantly make some dummy rounds
I can make some now although they have a tiny wasp waist to them since I haven't made an expander that fits the case web profile yet.
|# ¿ Dec 3, 2015 01:00|
Kind of a "drr" question, I guess, but any idea how this sort of cartridge would fare in a full-auto gun? More recoil, more stresses to contain, etcetera?
It should do fine in a full auto. Most if not all of the actual Russian military rifles chambered in it are capable of full auto fire.
*educated guess time*
It probably has a bit more felt recoil? The stresses on the bolt/recoiling assembly *should* be pretty comparable to a normal AK 47 so that shouldn't be an issue.
fundamentally it's an AK47 that's chucking about 2 1/2 bullets worth of weight out at a lot lower velocity.
|# ¿ Dec 3, 2015 01:35|
At least from what I've read about it's kind of a yes and no at the same time on whether they are or not.
The biggest "issue" that people seem to complain about are the blow down ports directly behind the gas block.
on the left image at the top you can see some small holes around where the gas piston would sit.
apparently those have people complaining that they make noise and spit excessive amounts of gas out when suppressed. I don't have any direct experience with a suppressed AK so I can't say for sure much past that.
(personally the amount of gas barfed into your face from a suppressed AR with a badly fitting charging handle is probably worse... that I DO have experience with)
One thought that I did have and I'm not sure on if we would do it or not is to have the blowdown ports on the actual gas tube its self and maybe have a sliding sleeve that could cover them. I don't have all of the gas port specifics ironed out as of yet.
If anyone has any experience with one please feel free to chime in.
shalafi4 fucked around with this message at 05:33 on Dec 3, 2015
|# ¿ Dec 3, 2015 05:31|
So I figured I would try to get into the late 90's and make a thing
|# ¿ Dec 3, 2015 16:17|
Last time we figured out our barrel dimensions and were ready to continue designing the front end parts.
To recap we have a trunnion end diameter of 0.917 and we figured out a barrel diameter of 0.866 would work fine.
Now to tie up the other constraints.
Center line distance between the gas piston and the bore.
Diameter of the gas block socket.
Length of the gas piston
Ok... length of the gas piston we'll deal with when we attach the gas block to the barrel. It's a pretty simple matter of lock the bolt&bolt carrier into the trunion. Measure to the proper length and mark appropriately.
The diameter of the gas block socket (I couldn't come up with a better name for it)
For this I just did a direct measurement of both of the existing gas blocks from the parts kits. Which came out to about 0.650" (oddly round number for something designed in metric) You'll also notice a pretty heavy taper leading into the socket. I took a little creative license with this. It is close to the normal dimension but it is tweeked a tiny bit deeper than normal.
The center line distance I also took direct measurements off of. (unfortunately I don't have a photo of the setup... someone bug me to take another photo of the setup later)
Picture two precision pins socketed into the holes in the gas block.
I know the dimensions of both of the pins.
Measure the outer dimension of the pins.
Subtract the radii of each pin.
Volia center line distance
With that out of the way I got the gas block mocked up and all of the detail work done.
With that however for our front and rear sight block we have another constraint that we didn't have before.
The tops of the sight blocks need to clear the gas block.
It also brought up another question. How are we going to attach sights to this?
I was pondering for the better part of a week on how I was going to retrofit AK sights onto the project. Cut and weld? machine new ones? cannibalize some parts but not others?
Myself and the other guy in the project were talking about it and after probably close to 2 hours of debating and contemplating my friend asks.
"Why don't we just put a front and rear rail on it like an AR? "
After some tinkering with solidworks
Meet Front block
And Rear block
And after looking up the specs for mil spec rails the whole family is done.
bonus points to the person who figures out what feature is missing on the rear block. (other than pin holes)
|# ¿ Dec 7, 2015 16:11|
Don't you need to have some method to lock in / remove the gas tube ?
That wasn't the one I was thinking of but that is absent on the drawings.
Due to something I was planning on talking about in the next installment we're actually welding the gas tube in place. All of the front end blocks are going to be Stainless. (the rails are something else however)
|# ¿ Dec 7, 2015 16:37|
Any reason why you didn't just merge the gas block and front sight mount into a single part?
It would only give something like an 8" sight radius
we thought about it but figured might as well make proper front sights for it in case we want it.
|# ¿ Dec 7, 2015 19:52|
My guess is that if it even goes off, it will look something like this:
It would *probably* go off since the section right in front of the case head is the same dimensions as a 7.62x39.
However I doubt it would actually fireform like that. The case would probably rupture down most of its length and the bullet would probably ooze out of the barrel since the bore is significantly larger.
Closest comparison I can think of would be drop a .357 sig into a 10mm chamber. Some flash, some noise and a lot of WTF just happened
|# ¿ Dec 8, 2015 02:15|
Would that kind of discharge damage the ID of the barrel?
If you did it all the time? probably.
once or twice? I doubt it.
|# ¿ Dec 8, 2015 02:58|
Just wanted to say I've been waiting for this thread to pop up for ages, hell yes this is the Good poo poo
If you have any input on setups/what to show everyone feel free to chime in.
|# ¿ Dec 8, 2015 15:09|
Ahhh the smell of burning coolant in the morning
|# ¿ Dec 11, 2015 17:13|
Do you have to make a bunch of additional cuts so that your new parts play nice with furniture?
just a few.... dozen... yea....
Here's a repost of the .gif that has the tool paths for the front sight block. The other parts have similar paths.
How long does something like that take to cut? And how much baby sitting (watching carefully, swapping bits, etc)
Actual cutting time on that one was only around 12 minutes?
The first one takes significantly longer because I babysit it from start to finish to watch for any coding fuckups. After that once the part is set correctly press play and walk away (it's only one tool)
that being said ALL of the operations in the gif (on the computer side) says it's going to take an hour and 58 minutes @ 100% feed and that's just cutting time not counting the changes between the 5 other tools and re orientating the part.
shalafi4 fucked around with this message at 22:04 on Dec 11, 2015
|# ¿ Dec 11, 2015 22:01|
Have some machining Pr0n to hold yourself over until I get the time to write the next full update
Also click to biggify and you can see the tool paths in the block.
|# ¿ Dec 22, 2015 17:06|
Hnnnngggg I can't wait to see the finished product. Have you mocked up what the full rifle might look like, with furniture and everything? Or is it too early to tell what will and won't work out
It'll look like a goofy AK with rails for the rear and front sights. We're not trying to reinvent the wheel, just make less drag
|# ¿ Dec 22, 2015 17:46|
I always wondered how weird profiles like that got machined, neat! Would something like this be possible without CNC?
oh it defiantly could be done without CNC. IF I start making a bunch of these and I still don't have CNC access I'd probably rough cast them and machine the critical surfaces.
It'd be readily possible without CNC, but it'd probably take a whole gently caress of a lot longer. I've got a somewhat related question: How many bloody passes is that, and what kind of tool were you using? Looks like it was just a small endmill, and a fuckload of passes. Also, are those 3/4" drill parallels? Why not use actual milling parallels? Would the extra width get in the way of something? How long did it take to program the procedure and finish the cutting on the part?
# of passes? ummmm yes
0.250" dia 5 flute 0.015" radius bullnose endmill
They're 1/8" thick parallels. Typically I use 1/32" thick ones but I was lazy.
The wider ones would be fine for the application but the majority of the projects in the shop are smaller/are ran by students. If we had wider parallels they would wind up with holes in them.
Programming wise I think I have about 45 minutes in plotting the CAMM for the entire part (not just this face) The total run time once I tweeked the speeds some was about 55 minutes (most of which is the fluff detail finishing)
|# ¿ Dec 23, 2015 03:10|
Remember kids, no friction welding in the machine shop.
|# ¿ Dec 30, 2015 02:39|
No matter what a stripper says?
I don't wanna know how much chafing it takes to friction weld.
Press fits however are encouraged.
|# ¿ Dec 30, 2015 02:52|
Unless I am mistaken that would appear to be what's left of a center drill, originally used for popping center holes for lathe workholding, but in reality mostly used for making an accurate starting hole for drilling so the next bit doesn't wander...
Very very close. I was using one of these with the central web thinned out instead of a center drill.
I got incredibly lucky.
It actually got hot enough to weld/melt the point off. (under full flood coolant) Between the heat and the spotting drill acting like a blender the spot underneath was actually fairly soft. I poked at it with a scribe a little to see if I could figure out where the point was and it had dispersed across the hole pretty uniformly. To get it out/drill through it I started with a carbide end mill plunging down to see if it had been buried under the surface. Still squishy. Switched out to my 1/2" drill bit and crossed fingers I wouldn't find a hard spot. Only ran into one small spot and it was off center enough that the drill bit popped it out without taking too much damage.
(put the decimal place in the wrong spot and drove the bit into the part 10 times faster than it should have been)
Normally it'll make this kind of soft hissing sound as the bit plunges in. It did that, and then sounded about like pouring a cup of water into a cast iron skillet that's really hot. And then it was done, and glowing...
shalafi4 fucked around with this message at 07:06 on Jan 3, 2016
|# ¿ Jan 3, 2016 07:04|
Alright. Back to it.
Apologies on the long hiatus I had to scramble to finish all of the CNC machining before the 1st of January. Short version, I left my job on the 1st and have been wrapping up lots of loose ends and personal things that were put off over the holidays. BUT, the parts are done.
Now... where were we.
So we have CAD models of all the parts. Yippee! Now to do the role of the man behind the curtain and make them.
First choice, what to make them out of?
We have the bottom pieces and the rails. One thought was to make them all out of Aluminum. That got axed pretty early on. While it would probably work, these are prototypes and we'd rather have them built like tanks.
That narrowed our options down quite a bit. We didn't want to go with a low or medium alloy steel because we didn't want to mess with bluing or Parkerizing them.
That pretty much left Stainless steels and Titanium.
*looks up the price of a bar of Titanium big enough to make 3 sets of the lower parts*
OK then Stainless it is.
We wound up choosing 304 alloy Stainless for our parts. (If people want me to go into the reasoning that lead us to that let me know)
Fast forward a week and a half and a hunk of stainless arrives.
Laying out the parts.
The red is called Layout Dye. It's a super fast drying paint essentially. It allows the scribe marks on the bar to show up MUCH clearer. (silver on red vs slightly shiny silver on silver)
Here's all the parts laid out.
The Black sharpie corner is a reference corner. I do it out of habit but on some high tolerance parts and some materials (*cough*Ti 555*cough*) you need to know the orientation of each part to account for stress relief as you're machining.
Horizontal Band saw GOOOO
Slow and steady is generally the name of the game in Stainless. A LOT of machinists despise the stuff but as long as you stay in it's "happy zone" and don't try to push it your tools will be fine.
About ~3 min in .... My minions at the time hadn't ever really delt with stainless before and they were really surprised how long it takes to cut. (95% of their stuff is out of Aluminum)
Different angle on another cut.
Cleaning up one of the ends.
Up next we'll start making them actually square.
|# ¿ Jan 22, 2016 20:03|
Modern bandsaw blades are usually HSS teeth on a tempered carbon steel band, same tech as 'bi-metal' hacksaw blades. Tungsten carbide toothed blades are also available but $$$$$. You probably won't run into a plain carbon steel blade anymore unless you buy the cheapest poo poo you can find.
Yup it was a bi-metal blade.
Gnawing through stainless is a really good description.
Also speaking of crazy warp speed SFM materials, look up Renshape 460.
Generally as long as your blade is sharp it'll go through Stainless pretty easy. It's when you try to push the envelope of where it's happy to cut is when issues crop up.
|# ¿ Jan 22, 2016 22:46|
... roughing @ 2,500 SFM?! what the fuuuuuuuuuuuuuuuck
The stuff it crazy to play with though on the spec sheet the "roughing" speeds it called for was something like 5000 rpm with a 1" end mill. The crazy part is it called for full engagement with it. (normally you only engage at most 1/2 ~ 5/8 of an end mill's width assuming a perfect setup)
|# ¿ Jan 22, 2016 23:52|
I'll bite, I'm curious why you went with 304 over a more free machining stainless such as 440 or 416? the small amount of 300 series SS I've played with has been befuddlingly difficult to machine, and after doing some research, is apparently the poster child for "why people don't like working with stainless"
YEY someone asked!
(pulled from wiki because )
SAE 304 stainless steel, also known as A2 stainless steel (not the same as A2 tool steel) or 18/8 stainless steel, European norm 1.4301, is the most common stainless steel. The steel contains both chromium (usually 18%) and nickel (usually 8%) metals as the main non-iron constituents. It is an austenite steel. It is not very electrically or thermally conductive, and is non-magnetic. It has a higher corrosion resistance than regular steel and is widely used because of the ease in which it is formed into various shapes. It contains 17.5-20% Chromium, 8-11% Nickel, and less than 0.08% Carbon, 2% Manganese, 1% Silicon, 0.045% Phosphorus, and 0.03% Sulfur .
304 Stainless Steel has excellent resistance to a wide range of atmospheric environments and many corrosive media. It is subject to pitting and crevice corrosion in warm chloride environments, and to stress corrosion cracking above about 60°C. It is considered resistant to potable water with up to about 200mg/L chlorides at ambient temperatures, reducing to about 150mg/L at 60°C.
304 stainless steel is used for a variety of household and industrial applications such as screws, machinery parts, car headers, and food handling equipment.
You're probably thinking, OK great.. it doesn't rust. That tells us nothing on why you picked it.
We're going to go deep into the metallurgy sperg rabbit hole so go grab some coffee or beer.
I'm going to write this like I'm writing it as a metallurgy paper. If there's terms that I forget to say what they are please point them out.
Stainless steels generally come in 3 types. (there's a 4th but not getting into that group)
Ferritic, Austenitic and Martensitic
For "normal" household items Austenitic and Martensitic are the most common. Ferritic stainless steels are "generally" used in more wide scope projects to save money.
So, some details about each,
Martensitic stainless steels
Generally these are your 4xx series steels. Martensite is a BCC crystal phase type that can be formed in steels with a high enough carbon content. The short version is Martensite is what can make steel hard. Knives, chisels, drill bits, endmills are all Martensitc steels (albiet except for knives rarely stainless)
It's generally formed by heating a part up, cooling it quickly (quenching) then tempering it afterwards. (without the tempering it can be incredibly brittle) I always tell people when they ask why tool steels need tempered that when they're fully hardened they're more akin to a coffee cup than "steel" that everyone knows.
Ferritic stainless steels
Generally used in more large scale projects to help on cost. Ferritic stainless steels *generally* have lower amounts of alloying agents (primary ones in stainlesses are Chromium and Nickel) which in turn starts to affect their corrosion resistance slightly. The one textbook example used in metallurgy classes. Everyone's seen a stainless handrail that's been outside that has flecks of rust on it? Those are Ferritic stainless steels. They fall under the "It'll work for its intended purpose but may wind up with cosmetic rust after while"
(Also to help confuse the @#$@ out of people... some martinsitic stainlesses are ALSO listed as Ferritic... 416 is one of these.... Technically a Martensitic stainless is Ferritic until it's heat treated. But not all ferritic stainless steels can be Martinsitic. It's one of those not all rectangles are square but all squares are rectangles things. )
Austinitic stainless steels
These are generally the 3xx series stainless steels. Austinitic stainless steels are FCC crystal structured steels. They're generally the highest alloyed of the stainlesses and also have the highest corrosion resistance of them. 304 and 316 stainless steels are the poster children of Austinitic stainless steels. They cannot be hardened via heat treatment due to their crystal structure. (see tje beginning of the post for the info on 304, most of that info holds for the 3xx series just with varying alloying elements)
ok so why pick 304 vs 416 vs 440?
Both 416 and 440 are Martensitic stainless.
Easier to Machine
Easier on Tooling
Not as corrosion resistant as 3xx
very sensitive to welding due to being heat treatable. (416 has an additional issue I"ll address in a minute)
more corrosion resistant
welds without filler metal
OM NOM NOM tools
So some of the machinists are probably going why not use 303? It's the "easier to machine" version of 304?
The only difference between 303 and 304 stainless is about 0.75~1.0% sulfur. The 303 stainless has a tiny bit of sulfur added to it that interferes with 304's workharding issues it's notorious for. (416 also has sulfer added for the same reason)
As we were going through I realized that I really DIDN'T want to try and machine the gas tube. So instead we're going to weld a stainless one in place. So 4xx series ones become trickier to weld (they generally require filler metals) So we wanted to go 3xx series as it welds much better.
Back to the 303 vs 304 (and 316 as well)
That tiny bit of Sulfur added to 303 that makes it easier to machine? That makes welding a complete bitch to do. The sulfur likes to segregate out into weld areas and makes them crack like crazy.
Since I"m mediocre at welding we're back to 304 vs 316. (316 is a smudge more difficult to cut but they're about on par) From there it came down to the 304 was a little cheaper than the 316.
If there's questions you know the drill
Also this does a pretty good job of going into all of the different types
shalafi4 fucked around with this message at 03:05 on Jan 24, 2016
|# ¿ Jan 24, 2016 03:02|
Ah, VERY cool, that actually makes a ton of sense. I presume that without the need for filler metal, TIG process welding will be how you go about affixing the gas tube etc? Also, what are some of your tricks for cutting the 3xx series stainless, anything more than just feeds & speeds (& carbide & lube) ?
You are correct. All TIG all the time. (I actually have the inverse to what's "Normal" welding experience wise. a shitton of TIG and hardly any MIG or stick)
Other than STAY in your feed/speed range and don't push it. flood coolant is your friend, Stainless barely conducts heat so all of the heat generated by cutting goes into your tool which can make for a bad day.
Actually, unless I'm doing multiple parts or production runs. I prefer M42 cobalt HSS for doing small Stainless parts. The sharper edge than the carbide helps with the work hardening issues that come up with Stainless.
|# ¿ Jan 24, 2016 05:16|
Project isn't dead I've just been too busy to get another effort post done up.
I may try to get one made up tomorrow in between studying for "how to read sound waves in metals"
|# ¿ Feb 28, 2016 07:38|
Please also do an effortpost on reading sound waves in metals tia
Actually I might... I have a non destructive weld evaluation exam on Wednesday and It goes over Ultrasonic testing of welds. Might be a good way to wrap everything together
|# ¿ Feb 29, 2016 19:13|
Double post for extra lack of effort.
Here's the tldr; version of the sound effort post.
Click to make readable
|# ¿ Mar 1, 2016 15:52|
|# ¿ Jul 28, 2021 11:53|
I am so glad the only stainless I'm cutting on for my suppressor build is a 1/16" or less thick freeze plug, the rest is ordinary carbon steel.
They're alright quality wise. In the proper machining world they kinda crap but if you're not doing full production work you'll be fine.
What diameter are they?
|# ¿ Mar 3, 2016 03:47|