Another Vertical forge thread

Discussion in 'Knife Maker Shop Talk' started by springer82, Mar 17, 2017.

  1. springer82

    springer82 Well-Known Member

    I have found many threads on how to make a vertical forge. Some with pics and some just text. There is a lot of information out there. With that said I still can't find the answers to my questions. I'm going to open this up with the hopes of a little help from the lady's and gentlemen here.

    The rough tub is 12" dia x18" long. I will put 2" of Inswool HTZ on all sides topped off with some satanite and ITC-100. Just the basic forge. Now for my questions.

    After reading the FAQ at High Temp I see this stuff is bad for you. For the top lid, is it better to seal it or go with the kaowool that is ok not to seal. I am concerned about sealing between the sides and top if it all has satanite on it. It might not sit flat enough.

    I know the inlet pipe has to be off center. Should it also be tipped up ??? 10°/15° or ?? to help in the movement of heat.

    The 4x4" inlet window will start 4" down from the top. With the Inswool going 2" down from the top that leaves 2" to the start of the opening. Is that enough??

    This is my first forge. I truly appreciate any help or suggestions you can offer. Thank you very much for your time.
  2. EdCaffreyMS

    EdCaffreyMS Forum Owner - Moderator

    I assume you are talking about the ceramic fiber blanket? If so, the answer is yes, it's "bad" to breath the fibers from UNCOATED ceramic fiber. The coatings used on ceramic fiber insulators are there for basically two purposes.... 1. To MINIMIZE the amount of fibers floating around in the air and reducing the chances of breathing them in. 2. With SOME of the coatings, they not only help keep fibers from floating around in check, but they add a degree of insulating/heat reflection value (ITC100).

    If you're burner is placed at/near the bottom of the forge, it is more important to correctly place the tangent of the burner to follow the curvature of the forge interior. If the burner is placed near the bottom, there is no need for it to be "tipped" in either direction (up or down), and in some cases doing so can be detrimental. Heat/flame is naturally going to travel up. When I built my last vertical/welding forge, I used a form to "cast" a channel approx. 2/3 of the way around the bottom of the forge, and it works just as I intended.

    Personally, if you're going to do anything other then very light/occassional welding, ceramic fiber isn't a good choice for insulation....especially if you're using doesn't matter what coating(s) you use, the ceramic fiber will quickly get wrecked with flux in the mix. I am also NOT a fan of using 2" thick ceramic fiber. The common thinking is that if 1" is good, then 2" must be better.....that's not the case. 2" of ceramic fiber takes more fuel and time to come to temp, and more fuel to maintain that temp then the same forge with 1" of ceramic fiber (assuming both the 1" & 2" ceramic fiber are #8 density).

    I'm not fully certain of what you're saying/asking there....bit it sounds to me like you are saying there isn't any insulation for a 2" space? Or, is there just 2" from the top of the opening to the top of the forge? Due to the fact that heat always travels up, a vertical forge is always naturally SLIGHTLY hotter near the top, then it is near the bottom. Probably one of the biggest things that fools those who are just starting out with their first forge is understanding that placing steel or a billet directly in the burner's flame IS NOT a good thing. As long as you can position the steel or billet where it's not directly in the burner's flame, you're going to be OK.

    Finally, and most importantly, DO NOT build a forge body that is "tightly sealed". Any forge works best, and is most controllable if it's able to "breathe". To that end, don't worry about tightly sealing the openings or the "lid". Use firebricks to "block up" any openings on the front or back, and a simple "gasket" of ceramic fiber for the lid....that will give you enough of a "seal"....but not too much.
    Last edited: Mar 19, 2017
  3. springer82

    springer82 Well-Known Member

    Vertical Forge Plans 1.jpg

    Thank you Ed for the help.

    When I posted the thread I was thinking of sinking the inswool 2" down inside the forge body. That would leave 2" to the top of the inlet door. That is different from my original plans. That would have put the top resting on the upper surface. My idea was to cut the working area down to save on heat. I like the idea of the concentric pipes. I don't want my forge to sound like a F16. I much prefer a A10. lol,,,, Your forge is much larger then the one I will build. I think a 1" inlet pipe should be find. I will go to Home Depot and see what I can find to fit inside.

    I cant begin to tell you how many searches I have done on vertical forges. I will say that the link you gave me is much appreciated. In all my searches I have net seen that one until now. I guess it all depends on how you word your search. In many of the plans I have seen if they say anything it will be put 2" of kaowool in. Oh well. The inswool is on its was as I write this along with a 5lb bag of satanite. If at some time I weld more then a few blades I will consider building one like yours. But smaller!! :drool:

    I ordered a blower like the one you are using. Again,, but smaller. Your lucky you had it sitting around. My 65cfm ran more then a few bucks over what yours cost you. With NO experience in forge building it is easy for me to tell you that by tipping the inlet pipe up 15*+ would only add to the tornado effect inside the forge. I would have thought that was a good thing. Once again,,, ignorance is bliss. Thank you again for your time and sharing your knowledge.
  4. CMS3900

    CMS3900 Well-Known Member

    Ed's right on as usual with his advice. After looking at your drawing the only thing I want to add is that its common in vertical forges with wool linings to put cat litter in the bottom instead of refractory wool as a sacrificial "insulation" to catch flux. My vertical forge I built has the top welded to the tube with a lifting eye, and it sits on a steel plate. I can put a cup through the forge opening and fill the base with cat litter to the right height, and use the lifting eye to lift the whole thing off the plate to replace it. 2" of wool will take longer to get to temp, but I don't know how the efficiency of 1" with ITC vs 2" with ITC works out. What I do know is that after I made my forge out of 2" wool I found a thread that talked about using 2 1" blankets over 1 2" blanket. This allowed for only having to rip out the outer blanket when relining the forge instead of all the lining. However, if I have to make another forge for welding I feel I will go Ed's route and make the whole thing out of cast-able refractory.
  5. springer82

    springer82 Well-Known Member

    I have seen threads that talked about cat litter in the bottom of the forge. I assumed that went in over the wool and refractory. How much do you put in. A few inches?
  6. CMS3900

    CMS3900 Well-Known Member

    Yea a couple inches, usually up to just under the burner area. The plate the forge sits on is set up on hard fire brick on top of a steel plate topped table to reduce any heat transfer or fire hazard.
  7. EdCaffreyMS

    EdCaffreyMS Forum Owner - Moderator

    Just make sure you use "plain old" cat Tidy Cat.....WITHOUT any of the fancy order reducers or anything or the other "stuff". Just plain old clay cat litter. The idea being that the heat more or less softens the clay, and it essentially acts like a sponge in the bottom of the forge, soaking up flux. When it cools its like a layer of glass on the bottom of the forge. Once it builds up, you simply chip it out, and most of the time the bottom of the forge is unharmed.....then just add more kitty litter and keep forging until it needs cleaned out again. That's one of the reasons I always make the floor of a welding forge out of castable refratory.
  8. springer82

    springer82 Well-Known Member

    Would I be better off leaving about a 1/2" gap around the openings and fill that space with satanite? I can only assume the inswool is something like asbestos.
  9. springer82

    springer82 Well-Known Member

    The forge is done. I have about 1/4" of Satanite. I fired it up at 1200° for about 5 minutes. The same at 1500° twice. Then 2000°. Each time letting cool completely. Is it normal to get small cracks in the Satanite? Should I do one more thin coat to fill the cracks. Fire it up at maybe 500° and let it cool down. I would like to get the ITC-100 on this weekend if possible. Thanks!!
  10. EdCaffreyMS

    EdCaffreyMS Forum Owner - Moderator

    Coatings don't work well like that..... heating them in an attempt to make them cure faster, dramatically shortens their use life. The only way to make the coatings last for longer then just a few firings is to allow them to cure NATURALLY. What you've seen with the "small cracks" will only get worse, and it will start falling off in short order.

    I know it's not what you want to hear, but allowing castable refractory, or any of the refractory coatings to cure naturally...until they are FULLY dry/cured, is the only way to make them last for any length of time. I learned my lesson a long time ago....when I built my first castable refractory forge, I thought the same thing about "helping" the curing after "pouring" the castable, I pulled the forms the next day, and the following day I did the same thing you did....fired it several times, allowing it to cool between firings, and increasing the temp with each firing. After a couple of days of doing that, it no longer steamed when hot, so I though it was ready to go....I fired it ONE time, built a couple billets of damascus and shut it down. The next day I went to the shop and started to fire it up again.... the castable was cracked like crazy, and several big junks had fallen out! $250 worth of castable (that was over 20 years ago) wasted.

    The last forge I built was a castable refractory welding forge, with a slurry coat of ITC-100..... it took over 2 months for the castable to cure, and another 2 weeks after that for the ITC slurry to cure. About the only method I have seen/used that will SLIGHTLY speed up the curing process without weakening/destroying everything is to put a heat lamp/bulb inside and leave it. I have also set smaller forges on top of a wood stove, but even that takes weeks.

    The bottom line is....if you see any cracking in the refractory or coatings, you've already messed up. A way to try to save what you have is to spritz the inside with water (spray it out of an old windex bottle or something similar) then make a slurry of the coating that's about the consistency of latex paint, and brush it on to fill the cracks. Then leave it alone until it's cured, otherwise you'll be back in the same spot.
  11. Jammer Six

    Jammer Six Well-Known Member


    Note to self: let it cure. Let it cure. Let it cure.
  12. springer82

    springer82 Well-Known Member

    Ed,,,,, I let it set and cure for over a week. I know now that was not long enough. I heated it up like that because I found it ????? on this site or another knife site. I have looked at so much info I don't know where I got it from anymore. What would help is a "Sticky" on forge making. The do's and the don'ts and what were you thinking when you did that!! lol,,, I will mix up some thin mud and give it a shot. Thanks
  13. EdCaffreyMS

    EdCaffreyMS Forum Owner - Moderator

    I feel your pain! It's tough to say just exactly how long it takes things to cure....just way too many variables..... heat, humidity, how thick or thin the refractory/coatings are, etc, etc. What I do know it that any more then a heat bulb inside the forge, or setting it in/on a warm place is too much, too fast. I know the next time I build a castable forge, it's gona be at least 6 months ahead of when I think I wanna use it. :)

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