Buzzkill

I’ve been tinkering around with naturally aspirated ribbon burners for a few years now. In that time I’ve tried quite a few different configurations regarding the number, diameter, and length of the ports. There are a few generalizations I’ve gleaned in that time, but I wanted to zero in on the specifics a little better. Recently I’ve learned enough CAD to emulate AFB’s vortex inducer, so I started looking for a good combination of that inducer and a burner block that gives me good results. Specifically the characteristics I’m after are as follows: Able to reach forge welding temperatures in a reasonable amount of time. Relatively quiet. I like to be able to have a conversation near the forge while it's running. Can turn down to low pressure after forge welding without backfiring or burning in the plenum. At least as fuel efficient as a single port burner with the same mixing tube diameter. Everything I’ve made and tested recently has been cast using Tabcast 94. It’s not bad, but there is a fair amount of aggregate material in it (similar to Kastolite), which makes vibrating the castings pretty much a necessity. The finish is not quite as smooth as I’d like either. A couple minutes after firing up the first burner option I decided to set up a type K thermocouple to monitor temperatures. All of these are using an AFB inspired vortex inducer of the appropriate size for the mixing tube. The first one tested employed a .030 MIG tip for the jet. The ports are 3/16” in diameter and 1.5” long. I forgot to record the number of ports, but I can provide that if anyone is interested. The PSI shown is what I set it to at the time listed to the left. I recorded the temperature in degrees Celsius because my PID controller only displays degrees C. Time Temp (C) PSI Dragon’s Breath 13:20 70 5 Minor 13:30 960 10 No change 13:40 1170 15 No significant change 13:45 1252 5 Minor 13:50 1203 3 Backfire/burning in plenum immediately At this point I switched to a 0.6 mm 3d printer nozzle for the jet, but left everything else the same. There was no dragon’s breath at any pressure, and it was so far from being acceptable that I just recorded the temperature at max pressure. Time Temp (C) PSI Dragon’s Breath 1109 21 None Switched to a ½” mixing tube with appropriate inducer, but still with the 0.6 mm 3d printer nozzle. Again, no dragon’s breath observed and it was not suitable for further testing. Time Temp (C) PSI Dragon’s Breath 1063 21 None Changed to a 0.8mm 3d printer nozzle with ¾” mixing tube. Time Temp (C) PSI Dragon’s Breath 14:30 490 5 None 14:35 940 10 None 14:40 1051 15 None 14:45 1145 20 minor 14:50 1235 5 barely visible 14:55 1165 N/A Backfired immediately when pressure dropped below 5 psi At this point I decided to try a different plenum/burner block combination that had given me unsatisfactory results previously. I ran a rod through all the full length ports to ensure they were clear before testing this time. Originally there were 189 ports, but due to the fragility of the 3d prints I had fewer full length ports. I believe I still have about 185 functional ports which are 1/8” in diameter and about 3” long. The info below was gathered using the same vortex inducer, 0.8mm 3d printer nozzle, and ¾” mixing tube. Time Temp (C) PSI Dragon’s Breath 15:10 545 5 None 15:15 905 10 Barely visible 15:20 1030 15 Slight 15:25 1126 20 Small/moderate 15:30 1201 20 No change 15:35 1235 20 No change 15:40 1260 20 No change 15:45 1280 5 Slight 15:50 1229 2 small/lazy 15:55 1150 1 no change 16:00 1099 0 forge off 16:05 814 For those that don’t want to do the conversions, 1260 degrees C is 2300 degrees F. That combination of inducer and burner block has provided the results I was looking for, so I’m not sure how much more experimenting I’ll do at this time. However, to satisfy my own curiosity I may run the last burner setup again with a Frosty T setup instead of a vortex inducer to see if there is much of a difference for NARB’s. I may also run it again using a single port configuration with the vortex inducer. I suspect a single port will get hotter faster than the ribbon burner.

Whenever I see a break like that on something that is built that stout I always have to question why it cracked in the first place. Was it normal wear and tear fatigue or is that possibly an indicator of other issues? The last thing you want to do is spend the time, energy, and money fixing the ram guide only to have it break again as soon as you try to use it.

That's looking pretty good! It might just be a combination of the light and the grind marks, but on what will be the cutting edge just above the glare in the middle of the blade it appears as though there might be some small cracks. I could only see them when enlarging the photo, and it might be nothing, but I can tell you from experience how deflating it is to spend hours on a blade only to have it fail at the quench. Hopefully it's nothing to worry about and we'll soon get to see the finished blade.

I went with the ratios illustrated somewhere in this thread, and shown on the top right of the screen under posted images: 3 times the mixing tube diameter for the funnel entrance and twice the mixing tube diameter for the height of the funnel. For the curve between the funnel opening and the the mixing tube I just played with it until it looked right to me. I'd call it more of a trumpet shape. I may not have all the dimensions optimal, but I was impressed with the unrefined results.

John, Have you ever tempered an item by watching the colors run and quenching at the right color? How much time was there at temperature if you did? Technically it requires enough time to alter the structure, but that can be measured in seconds in some cases. Regardless, the statement that it is MORE a function of temperature than time is still accurate to the best of my knowledge. In this instance I believe either Rogue misunderstands the tempering process or I'm not understanding what he's saying. To the best of my knowledge there is no risk of losing the hardness of an item by tempering for a longer period of time at the appropriate temperature, or multiple temper cycles at the appropriate temperature.

Generally speaking, the effectiveness of tempering is more a function of temperature than time. We hold a temperature for a time to ensure an even temperature throughout the entire item. As with normalizing, multiple tempers can improve the characteristics of the steel, but there are diminishing returns. The first one has the largest impact by far. Subsequent temper cycles have less of an impact. So, when you say if you temper for a couple hours it would have no hardness whatsoever, what do you mean? If you were to temper at 200 degrees F, I would expect it to have very little impact on the steel even if you held the temperature for a full day. On the other hand if you were to temper at 1000 degrees F for an hour I would expect the steel to lose most of the gained hardness (assuming a simple steel alloy).

I finally got around to learning enough to mess around a bit on FreeCAD. After gleaning pertinent information and looking at the pics posted here I was able to create a reasonable facsimile of AFB's inducer. AFB was kind enough to look over my file to see if there were any glaring errors as well. I've been using NARBs for the past several years, and I like them a lot. My idea was to marry the inducer with a a multiport burner. So far I haven't done much testing, but I have found that a burner block that is about 3 inches deep with 180+ nozzlettes is extremely quiet, doesn't burn back into the plenum ever - even when shutting the fuel off- but unfortunately doesn't seem to reach the temps I'm looking for. Just to be sure the burner block was the issue, I removed the inducer/mixing tube from the NARB and aimed it at a glowing forge interior. Wow! The performance characteristics are amazing to me. It functions under 1 psi without burning back into the mixing tube and I was able to easily reach forge welding temps in a few minutes using less than 10 psi. This was with a 3/4" mixing tube and a 0.30 mig tip - and my first attempt with no fine tuning and no flared nozzle on the end. I still want to see if I can find a combination of this inducer and a multiport burner that function well together, so to that end I've designed a NARB body which should allow me to swap out burner face blocks so I can try different diameters, lengths, and numbers of holes using the same inducer, mixing tube, plenum, burner body, and forge. Fortunately I can design and print plastic mold forms now. If I come up with anything that I think is worthwhile I'll probably post it over on one of the NARB threads.

I agree. However, with the tools you have you could have done some sculpting. It would be easiest before attaching the guard to the knife. A simple curve on the handle side of the guard would go a long way towards making it look better. To do this use a magic marker or something similar and draw the curve on the side of the guard until you like the profile. Since you have a tool rest on your grinder you can hold the guard with vice grips and lay the narrow edge on the tool rest. Then just use the edge of the belt to take off small amounts until the curve matches what you have drawn. You can then use the "shoeshine" technique with strips of sandpaper to take the sharp edges off and make if feel comfortable in your hand. If you have a drill and small drum sanders you can also accomplish the same thing, but it's slower and side pressure on drills can wear them out faster than drilling holes.

Fair enough. It's not just the oven though. The machines in the background tell a story of their own.

After seeing the pictures of your oven construction I'm not buying that for a second!

So, if I understand this correctly, the correct (or at least lowest error) way to wire this would be with a matching yellow plug and wiring that connects directly to the SSR (no splices or other types of connections).

I am truly amazed at what some of the competitors have done in 40 hours of work. I've spent that much on far smaller blades. However, I'd really like to see what some of them could do if given 2 or 3 times as much time on the final challenge. Frequently the last round ends up with competitors barely getting something done within parameters rather than their best work. I hear what you are saying about working under pressure, but that show is mostly "you can barely get it done if you make no mistakes and everything goes as you planned" type of pressure. How often have you heard competitors say something like, "If I was at home this knife would go into the scrap pile."?

My main complaint with FIF is that it has turned into a gimmicky forge welding/time management competition for the most part with the knife making portion being of secondary or tertiary importance. If you want it to be an actual knife making competition then give people enough time to make a halfway decent knife rather than pile a bunch of extraneous stuff on them and then complain that the handle isn't comfortable. IMO a competition should be a test of someone's best work against other people's best work. FIF is definitely not that.

You could also make the real distinction between the UV type of radiation that exists in sunlight, along with the IR radiation, compared to pretty much "IR only" radiation that would be emitted from fire or glowing metal.

I don't think it would be possible to super heat water anywhere near forging temperatures - even at extreme pressures. Water turns to steam at 212 F. We're generally forging steel in the 1400 to 1800 F range for simple steels, and we forge weld around 2300 F. I'm not sure how you'd work it into your story, but one possibility that doesn't involve fire is induction. Essentially these are strong localized electromagnetic fields which are capable of heating steel quickly. However, there is one glaring problem you still have -- steel heated to the temperatures required for forging or welding glows brightly. We risk eye damage if we look into the fire at the temps we use to move or weld steel for too long. Steel left in a propane or coal forge will reach the same temperature, which produces the same glow. It would be as unbearable to look at the heated steel as it would be to look at what heated it. Perhaps a better solution would be for the underground smiths to have found a volcanic glass material that is translucent. They could make eye wear that blocks much of the light and allows them to work the metal. You could even build into the story that these metal workers typically go completely blind after a number of years even with the eye protection.

Based on the pictures, you have succeeded. If they perform anywhere nearly as well as they look any woodworker would be proud to own and use those tools.

I figured it was just a clever marketing name, but I was truly surprised at the difference Tap Magic made when cutting threads or drilling in certain materials.

It's from the movie "The Princess Bride"

You keep using that word. I do not think it means what you think it means.

I'm fairly sure it reads "E W Bliss Co No. 3 Brooklyn, NY USA"

Sounds like Scott from Kentucky Ballistics.

We had a 20 pound Monster Maul with an oval hollow steel handle for splitting wood I used quite a bit as a teenager. I think the wood absorbed enough of the shock that it wasn't horrible on the hands. If you did end up missing your mark and caught the wood on the handle it would definitely send a jolt up through the arms. We also had a knock off brand with a round handle that vibrated a bit on the strikes, so they are not all created equal. The chainsaws always bothered my hands more than mauls though. I'd sometimes have to pry my fingers open after using one of the chainsaws without a dampening frame all day long.

Looks good to me. It's not uncommon to put at least one 90 degree elbow in between the point where you introduce the fuel and the burner to help mix the fuel and air. The great thing about forced air burners is you can control the forge atmosphere easily by adjusting the amount of air flow or fuel. It looks like you have plenty of blower power to go with the large fuel orifice, so you shouldn't experience any limitations in that regard. Looking forward to see what you mount it in.

Kind of. I see what you are getting at, but the thickness of a piece of steel when quenched significantly affects the rate at which it cools. Therefore, grinding away portions to check the hardness at certain depths does not give you the same information as quenching different thicknesses of steel. If they had started with 1/8" thick test coupons the results would be nearly identical for some alloys, but most likely significantly different for others. Usually for knives you can get away with one step slower quench than the manufacturer recommends. That's because they give their recommendations based on inches of thickness rather than portions of an inch. So, something that normally specifies a water quench can be properly hardened in a fast oil if it's a thin cross section. I've had a couple blades made from O1 air harden. Similarly, you could expect different results than shown for 1/4" thick pieces if you are quenching thinner pieces. Most of my blades are between 1/8" and 1/4" when quenched, so I would expect slightly different results than shown on the chart you posted earlier. Like you said though, you can try different quench mediums for yourself and see how they perform. I highly recommend doing this - and breaking the test pieces to observe the grain structure. This can really help you figure out what works best for a specific alloy and what quenchants you have available to you.

No. That is a chart of hardness of 1084 with different quenchants at the same thickness (1/4") and quench temperature. That was probably the worst showing for canola oil in all of the tests. Fortunately you've said you'll be able to get some quality quench oil, so that renders the canola oil issue moot. My preference is in the 58 to 61 hardness range (after tempering) for most blades. You can usually get good edge retention, reasonable toughness, and still be able to sharpen the blades using traditional means in that range. I like 80CrV2 quite a bit myself. One word of caution though - it can develop a thicker decarb layer than other simple steels. Sometimes this might lead you to believe a quench failed to harden the blade if you just do a quick file test. To check it properly let it cool close to room temperature and grind away a thin layer before testing.