Matt Todd

An update: I opened the mold and sprayed the tops and edges with water. Then re-covered in plastic again for another 24 hrs. The top edges that got squirted from both exposed top and sides seemed to have firmed up a bit. The bottom edges were still awful soft (dry/powdery) so when I took a wire brush to all the edges, the bottom edges gave up more and exposed some aggregate. A metal scraper knocked off any loose aggregate.

No idea why those bottom edges were so dry. The soy wax I used was plenty thick and souldn't have robbed moisture. But the bottom face is nice and smooth at least.

Now they're suspended over a dehumidifier to begin the drying process. I think I'll keep playing with these and not count them as a 100% loss just yet. I will do the gradual heating ramp up curing and see how they look and feel after all that.

thomas rubino wrote:
I was warned, possibly by Fox, who has vast experience vibrating cast items, to be careful "Not" to over-vibrate!

I took the warnings not to over vibrate or over water too far!

So now I'll put these slabs through a torture test just for fun. And probably end up re-casting (a $100 mistake.)

Or I could sandwich the slab in kiln shelves. I could have used kiln shelf from the get-go but that's more expensive and I wanted the thick cast refractory slab for mass since the top of the firebox will be the bottom of a white oven.

But on the bright side, sharing failures is what helps other succeed!  

thomas rubino wrote:
I used a variable-speed saws- all with no blade. My forms were sitting on plywood with a tire bolted to it.

I very much appreciated and studied that post before I made this attempt, but I suppose I was unclear on how you used the saw to vibrate the form.
So the form was sitting on a tire which allowed the whole thing to "jiggle" more than it ever could sitting on a solid surface (my first mistake.)

How did you use the saw though? Just pressed the front of the saw against the table and pulling the trigger engaged the piston inside enough to vibrate the table?

Here is my first attempt at casting refractory cement. Product is called Meeco's Red Devil Castable Refractory. This is for the firebox roof in a Shorty core, which I split into two parts because one continuous slab would be over 60 lbs, which seemed unreasonable to cure and handle.
I made the form 2.5 inches tall and coated it in wax for form release.
I dry mixed the refractory, and then carefully added the appropriate amount of water and mixed for about 7 minutes (instructions said I should mix for between 3 and 6 minutes but I needed more time.)

From there I packed it tightly into the form. Then I TRIED to vibrate, and this is where things started to feel off. I had 2 massage guns and an oscillating tool on hand and tried them all but the cement did not visibly settle much at all and no water rose to the top as I'd seen in videos of this process. I figured I'd just packed it well enough. I sprayed the top with a squirt bottle and covered it in plastic.

48 hours later I released the form and I'm seeing dry cement around the edges that brushes right off. Also seeing some cavities.

I sprayed down the dry areas and covered it back up, hoping they absorb and firm up.

But... did I totally botch this attempt???

thomas rubino wrote:Hi Matt;
Gerry did all the welding on the airframe itself.
I built the door while he worked on that.

11-gauge steel plate, 3/8" square stock , 1/2" gasket stuffed tight, 1/2" rod as the handle.
The window glass is 8x8", and the opening is 7x7",  I cut it with a skinny wheel on a side grinder, and a jig saw.

Thanks for the details! That 3/8" square stock made the plate steel look thicker than it actually is. 11 gauge is manageable and I like how the 3/8" track makes room for the gasket and reinforces the door.

Hey Gerry, great info on the air-frame!  But what about the door itself?
How thick is that door metal (looks BEEFY) ?
How did you cut it and the window hole inside?
Trying to figure out if I can do that bit myself or if maybe paying the metal shop to plasma cut it would be easier.

I now have my floor braced and plan to start fabricating the metal parts soon!

Hey Glenn, what did you use to "seal" the top of the firebrick ceiling?
Or another way of phrasing the question: what is between your firebricks and clay bricks in the ceiling?
I see where you had spread something on top of your firebricks in the development thread.

thomas rubino wrote:
I am very happy to report the highest temps my arch has risen to are just over 400F!!!  (Success!)

Do you have any measurement on what your core exhaust temperature is reading?
Reason I ask is, I'M BUILDING A SHORTY IN A BRICK BELL TOO!

One final detail I'm working out is the internal chimney. Planning to do the "plunger tube" style of chimney into the bell. But my Shorty core will flip the exhaust to shoot out the back wall of the riser stub so I can put an oven on top of the firebox. The potential issue being hot exhaust shooting horizontally right at my plunger tube. My DSR2 build has a black stove pipe plunger tube and I intend to do the same here. Just a little worried about it being directly in the exhaust path.

Guess I could wrap it in superwool and hope for the best. Or spend an extra $300ish to continue stainless double wall pipe inside the bell. Any thoughts on this scenario?

Peter van den Berg wrote:

Matt Todd wrote:@Peter van den Berg  
Do you think it would be alright to put the final exhaust opening on the BACK side of the riser instead of the front?

Yes, Glenn is right, it can be done. The lower riser part should be different, the pictures of the French bench build are quite clear how it should be done, in my opinion.

Alright, so a simple matter of moving the "riser liner" to the back wall instead of the front. I was afraid that this decrease in port depth would have an effect on the design, but I see now that you have tested this and found it satisfactory. The flames still enter a square space to form the vortex before expanding in the wider top half of the riser. Thanks for confirming!

@Peter van den Berg  
Do you think it would be alright to put the final exhaust opening on the BACK side of the riser instead of the front?

I'm thinking of putting an oven on top of the firebox. Which would only work if the exhaust could shoot out the back of the riser into a bell.