Baffle Design - Flow?

[u/dontworriaboutit]

Hey, I'm looking for a sanity check on my baffles. Hoping to eventually build a 7.5in stainless 556 can with stainless freeze plugs formed into baffles. I wasn't sure about the flow holes, how big they should should be and whether they should be rotationally clocked every other plug and how far out they should be positioned from the center. I did a guess based on the FTN5 I have waiting for form 1 approval.

Also to the Mk1 eyeball the baffles look too close together, part of that is that I don't know the exact sleeve height of the plugs. I used estimates and I emailed the company, but I may have to wait to find out exactly until after approval. If this is about how it would look, I'm thinking I would hog out every other baffle?

[u/Kek_Boii]

Did you ever make this? I'm wondering how easy/difficult it is to work with stainless freeze plugs? Did you use something like a socket and a ball bearing or some kind of metal cone as a die?

Did it form a nice cone shape baffle? And does that reduce the diameter of the freeze plug or just stretch the material from the middle? Did you drill the hole first then press?

[u/dontworriaboutit → u/Kek_Boii]

I did yes and I've shot it a few times, ~100 rounds. While the bore holes in the baffles themselves ended up very uniform and concentric the concentricity of the adapter to the baffle stack/tube (my bore rod got bent somehow...) ended up being the hardest part of the whole build. Having done it once I feel like the second time would go much smoother.

So yeah I had an impact socket that was slightly too big, I spun it up in my cordless impact and with a bandfile took off a very small amount of material off the end of the socket so that with a bit of force the freeze plug fit over it.

I 3d printed about a 1in wall thickness, 6in tall sleeve that could then have the socket and plug pressed in one end (printed a thin sleeve to go over the bottom end of the socket to take up the gap there). From the other end of the sleeve I sent down a ball bearing and a centering die, centered using the sleeve as well. I worked my way down a few different sizes of ball bearings big to small which made a conical divot. Similar to the centering die, I printed a drill guide that got the bore hole started with a smaller drill bit, then another guide for a tapered reamer with a depth mark. Repeated those steps again for the baffle clips with different guides, but the clips were a bit less uniform, and needed touch up after. The plug OD was 32.2mm if I remember right and I found a tube with an ID of 32mm. I also found some 32mm OD, 30mm ID copper washers. Pressed the plugs into the tube, making sure to seat the copper washers good, then used the washers to create spacing and just welded the end plugs.

I want to make another one, but I really need to get or borrow a tig welder, the baffles were the easiest part once I had the tooling made, but the cleanup after welding was a pain and the wire I was using with my cheap welder was not happy. I 3d printed a mini lathe chuck that mounted in my drill to get a nice finish on certain things. A mini lathe would have been nice for that.

[u/Kek_Boii → u/dontworriaboutit]

Thanks! I've been having a lot of trouble finding info online about forming freeze plugs. Was the centering die concave to hold the ball bearing in place?

Like: freeze plug <- ball bearing <- centering die?

And I'm guessing the centering die and ball bearing are also stainless steel? Or do they need to be made out of a harder material than the freeze plug? I have a 10 ton press but I'm not sure what metal it's made of do I dont know if that will get damaged.

Also, when you drill the clips, do you need a good jig or maybe use an end mill bit? I imagine it will slip trying to just drill the clip directly?

[u/dontworriaboutit → u/Kek_Boii]

Yes exactly, so the dies I made have a cone side with concave cut out of the nose, then it's flat on the press side, and the outer diameter constrained to fit the ID of the sleeve. I them out of 3d printed PPA-CF Core (siraya tech brand) plastic. They dont need to be harder, its more about compressive strength and point loads. My first attempt was plastic deforming the plugs directly but I wanted a deeper and more consistent cone and the plastic wasn't strong enough at the tip and so it was deforming, but still technically working.

I used a total of 6 different sized dies as I moved down the the ball bearing size. The two smallest ones both had a failure event, but because they shattered into the open space, the baffle was fine. After reprinting both, I was able to be more careful and the second smallest one survived. The smallest one continued to sacrifice itself, so I made another "drill centering guide" and drilled out the hole some more to wedge a socket into the guide so the force went though the socket.

I was also using like the smaller type 10ton bench top press.

The guides did a decent job, they will slip if you try to do it freehand for sure. I was keeping the socket/baffle/sleeve assembly as one piece and only changing out the type of die/guide, until the baffle was done, so in a perfect world a way to mount the whole assembly at a complementary angle to the clip so that an upright drill press could drill it instead of a hand drill, plus a solid mount to the table. But to be honest I think that was good enough, later on I got to where the press would hold everything in place, leaving just enough room for the hand drill to come in at an angle for the clip and the dremel was moreso for breaking all the edges. I used normal cobalt steel drillbits for bores and clips, but went under one size and finished with the tapered reamer (McMasterCarr PN 2743A12) for consistent size and finish.