Spare Time Labs 2.0



jDraft 2.0




Ten-Buck Furnace

H8S Bootloader

Camera Calibration


Myford VFD

Fun with HC08


printf II

Java Goes Native





New Furnace

New Furnace
Part II

Linux 101



Gas Fired Furnace

Down Memory Lane


Wheel Patterns






JNA Benchmark

Contact Info
Created 6.12.2005

New Furnace

Come spring of -04 and I unearthed the furnace . Last melt of the previous autumn had manifested some problems, the burner tended to backfire and it took a long time to get to melt temperature. A litle investigation revealed that the furnace was totally clogged up by iron spills. Originally this furnace had no bottom (in fact it was a plain tube!) but I had added a bottom to improve insulation. This was probably futile as far as heat losses are concerned and stupid as far as spill are concerned, as there was no hole at the bottom and the bottom was unremovable. How unremovable it was, I soon found out. I tried to hammer (gently as you can with a 4 kg sledge) the bottom out, and the whole thing fell a part!

So, I was in for some furnace construction. Since I had the Gingery Building a Gas Fired Crucible Furnace I thought I'd have a go based on that design. A lot of people have have built it and have not reported problems so I figured it would be ok. On paper the desing seems great and has some nice features. The construction is very economical, it is difficult to see how it could be improved in that respect.

Note that this page is not a DIY instruction, if you want to build one to the Gingery design, go and buy the book. It is worth the dime and we should all engourage people like him to write more on the good stuff.

Having said that the brief discription of the furnace is as follows.

The furnace is made of three parts.

  • Base - a sort of flame whirl/vortex cage with the burner attached to it
  • Body - a lifting body structure that allows safe side access to the crucible
  • Lid - a side swinging lid that allows access to the crucible without lifting the body
  • This design has several good points to it: safer access to crucible because , small foot print, compact and economical construction, fast pour/recharge action, simple and inherently rather safe desing.

    All features you'll appreciate in a backyard foundry.

    The fine print: when above I write safe, it does not mean that the design or activity is safe, it simply means that it is safer than many other designs / practices. Make no mistake, this is dangerous activity. You and you alone will be responsible if you pursue these activities. Do your own risk assement and act accordingly.

    Because I was planning on casting some roof braces for our conservatory project I wanted to build a slightly larger furnace that could accomondate a larger crucible. So I needed to scale up the Gingery desing. This was a good way to test drive my 2D-CAD program, jDraft . On the left you can see the scaled up but basically 'standard' Gingery furnace, as captured from my screen. If you are a jDraft user you can down load the drawing which includes the dimensioning from here . If you are not a jDraft user you need to download jDraft first by visiting the jDraft home page. But you might want to read the whole story first.

    began the construction by cutting two circular holes to two pieces of plywood with my rooter. Amazing tool, even if you missposition the cutter so that you are effectively cutting with the stemp of the cutter only, it just burns away the wood! Mind you there is a lot of smoke. I also cut two circular discs to be used as the inside former supports. Actually, one of these discs was cut so that it was a ring so that I could get my hand into the inside of the former.

    I actually would have needed more of these but by doing the base, body and lid of the furnace each in turn I was able to recycle these parts.

    The inside former of the furnace body is made of 1 mm thick mild steep plate. Two small slots were cut into the inside discs' outer circumference and the end of the inside former plate was bent to angle so that the end of the plate would fit into the slot. Then I rolled the plate around the formers. Mild steel was pretty easy to form except that I was not able to form a perfect cylinder even with the help of some heavy pressure from load tying lines. Finally the former cylinder was secured with some M4 nuts and bolts and the ever so versatile duct tape.

    You can, just about, see the slot in the plywood ring and the angled plate edge in this picture if you look carefully.

    The outside former for the furnace body I made from similar steel plate. It was easier to get a good cylinder with plywood on the outside. Again the former was secured with M4 nuts and bolts, this time rather many of them about 50 mm appart, as these bolts are actually the king pins that hold the furnace body jacket together and prevent it from slipping out. And the body weights some 65 kg!

    The two pins that the furnace body rests on are made of M10 bolts weleded to and re-inforced with some 100 x 100 x 2 mm3 steel plates secured with four M4 nuts and bolts to the furnace body jacket.

    Inside view of furnace body jacket/outside former. BTW all the outside former plates are left in place ie they are part of the furnace lining jacket. A full metal jacket?

    The burner hole in the base part furnace molds was a fun excersize in geometric projection with the jDraft. I printed the ellipsoid shaped profile of the hole onto a paper that I placed on top of the steel plate and punched through to mark the hole outline.

    Amazingly the Black&Decker recip saw just crunched away the metal!

    Here the base mold is being tryed out.

    And here the furnace bottom mold is just before casting the refactory. The four square pieces of plywood were retracted as I rammed the refactory and the mold filled up.

    The lid mold was done pretty much like the other, I just bolted a piece of angle iron to function as a hinge and applied some zinc-coated wires across the lid. These are supposed to attache the frame band to the refactory and also prevent pieces falling out in case the lid cracks. BTW, as I said, the base, body and lid were done each in turn (so not in the sequence show here) so that I could re-use the plywood formers, like here underneat you can see the same plywood former that was used to hold the base and the body formers together.

    Unlike Gingery I prefer the commercial variety for my refactory lining. Not because I would not like to make this myself, I would, but because I feel this is a safety / furnace life time issue. An it is not THAT expensive.

    Mixing the stuff is rather hard work and boring. I used as litle water as possible, the constituency of the mixture was like porridge made from oat (but not corn ;-) flakes with too litle water.

    I just spooned the mixture into the mold a plastic-cup-full at a time and rammed it hard with a stick. Too hard as it turned out.

    After about an hour the body was filled to the rim.

    Compared to the body work the lid was a piece of cake, a pun-cake? (Sorr abot that)

    The base was first filled to the level of the furnace bottom. The pipe is there, of course, to leave a hole in the lining for the tangential burner insert. Note that there is a hole in the bottom to let spilled molten metal to flow out, it is just difficult to see in this picture as the plug that forms the hole is covered with white refractory stuff.

    Then the inside former was inserted and and centered with the afore mentioned pieces of plywood and the rest of the lining rammed in while the plywood pieces were retrackted.

    Here is the already hardened body being stripped down. The top outside former has already been removed, with help of a saw, as the cylinder turned out slightly concave, which prevented it from sliding away, so had to cut it free.

    All surplus refactory material was jammed (ha ha) into old strowberry jars to make flints and small pieces of plastic rod were pushed half way into the material, as show. These left four cavities that server to vent out an metal that spills on to the furnace floor.

    Like I said, rammed it too hard! The bottom plywood former shifted and the bottom of the furnace body was not orthogonal to the cylinder sides. Oh well, with a diamond disc and an angle crider it took less than ten minutes to put this right.

    And here is the flint, still upside down.

    The frame structure for the furnace was welded together from 30 x 30 x 3 mm angle iron, except for the vertical columns which are 40 x 40 x 5 mm.

    The wheels for the moving lifting mechanism were cut from a 40 mm dia Al block, turned and fitter with ball bearings.

    Here you see the rather small wheel base inherent in the Gingery design. How inheret, I'll tell you later.

    Here all the main parts of the furnace assemble meet together for the first time. The lift mechanism is still missing.

    And here the furnace is fully assembled, ready for action.

    For the fireworks I decided to try and see if an oil burner could be utilized. These are readily available as the companies that sell these are always urging old ladies and gentlemen that it would be a good time to change that old burner. Usually they (the burners) are good for another twenty years, so good second hand burners are easy to obtain. Here you can see the inlet mounted, ready to accept the burner.

    And here the complete furnace and burner assembly before firing up for the first time.

    Revers angle view; no I don't watch hockey. As you can see the burner is a neat package, the atomizing nozzle, high voltage ingniter, blower, high pressure oil pump, flame guard electronics all in one easy to mount piece. Just dip the hoses to a can of fuel and plug it in and with a press of a button it whoooms!

    The nice thing about oil firing is that it is rather safe. I accidentally un-screwed a plug hole while trying to adjust the burner which was in full blow. The fuel oil (not sure if that is the correct english term) bursted out and wetted my hands and the sand below before I could plug it again. But it never caught fire, as it does not burn readily!

    Finally, here is the result of one hour of oil heating. Bright read orange, but nowhere near what is required for casting iron. A dissapointment yes, but not a big deal, I've still got my MarkIV gas burner and that baby is hot! I do not think this is conclusive, but atleast with this burner it was not possible to get anything like the blue hot flame (some 1900 deg C) that any gass burner easily produces.

    All in all I was not totally happy with this new furnace, so, you guessed it, there have been developments since, but I think I'll leave that to another time and page, so tune in for New Furnace - Part II coming soon to a computer screen near you.

    cheers Kusti