# Drilling insulated firebrick



## jwmelvin (Apr 18, 2019)

I'm working on some forge projects and I'd like to drill some insulated firebrick. It is very soft, porous material made primary of silica and alumina (see info here). Thus it is abrasive but cracks very easily. I do not need much precision on the holes, but it will be a large number of high aspect-ratio holes. Say about 100 holes, 1/8" diameter, 2.5" deep. 

I'm guessing that a masonry bit is the best approach, and that clearing dust out will be key. I will not be doing this on my mill, I'll use a drill press and will have a shop vac running. I was wondering about using some sort of spade bit, even a shop-made one, just because the material is so soft. Any thoughts on best approach? With so many holes, I really want to avoid cracking the brick on my 87th hole or so. I will do some experiments but figure it's worth asking your collective wisdom.


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## ericc (Apr 18, 2019)

This kind of brick is just too friable for this kind of work.  It sounds like you are trying to make a ribbon burner.  Maybe just try a few experiments the more standard way?


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## jwmelvin (Apr 18, 2019)

Yes, making a ribbon burner. I will try casting one too but some people have reported success drilling so I figured it was worth a shot if I could optimize my approach.


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## JimDawson (Apr 18, 2019)

I think the masonry bit makes the most sense.


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## RJSakowski (Apr 18, 2019)

Because of the small diameter,m a carbide twist drill might be a better choice.  If using a masonry bit, I would dress the cutting edges.  The masonry bits that I have used have all had blunt edges out of the package and tended to bull their way through rather than cutting.


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## Cooter Brown (Apr 18, 2019)

Try a masonry bit in a cordless 1/4" impact gun.... and tape an air gun to it....


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## rwm (Apr 18, 2019)

This brick is really soft. Any drill will cut this stuff. You don't need an impact or hammer drill like you would for regular brick. I would experiment with several kinds or bits and see what gives the cleanest hole. You could even make a bit like a D type bit by just sharpening a rod. You could toughen the brick after shaping it by coating it with ITC 100.
Robert


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## francist (Apr 18, 2019)

I've used these type with good success on the softer ceramic and brick materials. They tend to be sharper than the standard masonry style of bit, so less pressure needed.

-frank


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## jwmelvin (Apr 18, 2019)

Thank you all, I will report back after I get a chance to try a few things.


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## Diecutter (Apr 18, 2019)

I replaced the soft firebrick in my small Paragon furnace a while ago, and it was very quick and easy.  Used a diy t-shaped bit (cut down from a spade bit) so the heating element could be retained in the wall without staples same as the original was. Definitely use a shop vac or you will be sorry. Finished job as good as original with no cracking. Try this company for inexpensive soft firebrick. It's first rate.  http://refwest.com/z-239straight9x45x252300fifb.aspx


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## Latinrascalrg1 (Apr 18, 2019)

That stuff is super easy to dril as in you could use a screw driver to manually drill a hole if needed although not recommended just an example showing how easily  worked they actually are.  When you start your project i would just be sure to have a sacrificial wood backing to fully support the back side which should help eliminate any "Break out" damage from happening. Also if drilling multiple holes like you stated i would probably use a predrilled wooden "jig" just to help keep things neat and Last but not Least If i remember correctly the Dust created from working those firebricks are not good to breathe so make sure you use a proper dust mask.


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## hman (Apr 18, 2019)

I think one of your main issues would be with dust packing the drill bit at increasing depths.  Whatever method you choose, be sure to lift out the bit frequently to clear the dust.


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## pontiac428 (Apr 18, 2019)

The dust in this case isn't too bad.  The crystalline fraction of the silica in the masonry is regulated now (2 years now for construction industry), and causes silicosis and cancer in people who are exposed to high levels daily over periods of decades.  For a small project, just vacuum up after yourself and you'll be fine.  You can also do your drilling wet to keep stuff out of the air.  A cute but effective trick for drilling holes in masonry is to put down a golf ball dollop of cheap shaving cream on the spot you're drilling, and go for it.  The dust ends up trapped in the cream, and you just rinse it off.


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## MontanaLon (Apr 18, 2019)

The shaving cream is a neat trick. I will have to remember that. 

That brick reminds me of florist foam in how it cuts


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## francist (Apr 18, 2019)

Oooh, I like that shaving cream idea too. That's going to come in handy for something, for sure!

-frank


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## pontiac428 (Apr 18, 2019)

It's actually an OSHA asbestos abatement trick, but with the new silica law in effect I've been including the shaving cream method in work instructions for masonry, too. You can do it on a wall, even works on the ceiling. Works with hole saws as well.


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## macardoso (Apr 18, 2019)

Hole saw?


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## francist (Apr 18, 2019)

pontiac428 said:


> It's actually an OSHA asbestos abatement trick, but with the new silica law in effect I've been including the shaving cream method in work instructions for masonry, too. You can do it on a wall, even works on the ceiling. Works with hole saws as well.




That's exactly where I was going to use it, although not so much for asbestos but rather lead paint, the latest workplace pariah. 

-f


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## jwmelvin (Apr 18, 2019)

I drilled a couple ~4 mm holes with a bit like francist recommended and it seemed to do well. I would definitely want to use a drill jig to at least start the holes. It didn’t make much mess just pecking with the shop vac right there. I am, however, questioning whether I want to drill an array of ~100 holes. I suspect I will have a hard time keeping everything neat. I may still give it a shot. But I’m also working on a 3D printed core to burn out after casting refractory around it.


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## Diecutter (Apr 19, 2019)

For slots to receive a heating element, I first cut a straight slot with the drill press and a router bit, then used the T shaped bit. This eliminated excessive packed dust around the bit.


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## Eddyde (Apr 19, 2019)

I have used common spade bits designed for wood to counterbore cast iron, I bet they would do well in fire brick.


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## Latinrascalrg1 (Apr 19, 2019)

jwmelvin said:


> But I’m also working on a 3D printed core to burn out after casting refractory around it.



In the past ive used cheap crayons and candles sized as needed so that I could melt them out at a later point in the project like you are talking about with the 3d printed jig.  Anyway a piece of styrofoam, a big box of crayons and a few pieces of wood and you have yourself very quick and easy and effective mold jig to cast the ribbon burner.


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## jwmelvin (Apr 19, 2019)

Latinrascalrg1 said:


> In the past ive used cheap crayons and candles sized as needed so that I could melt them out at a later point in the project like you are talking about with the 3d printed jig.  Anyway a piece of styrofoam, a big box of crayons and a few pieces of wood and you have yourself very quick and easy and effective mold jig to cast the ribbon burner.


Yea, it seems like there are a variety of possible ways to do it. Here is a picture of the couple test holes I drilled in the firebrick:


They were full depth of that bit, which I think would work but I'd have to resaw the firebrick down from 2.5" to maybe 1.5". Possible, but that's what led me to design this core for a molded nozzle (138 nozzles, 4 mm dia., 8"x2.5" opening):



I'm excited to get my castable refractory and see if I can make a nozzle.


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## rwm (Apr 19, 2019)

That 3D print is awesome! That should work great! What refractory will you use?
Robert


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## jwmelvin (Apr 19, 2019)

rwm said:


> That 3D print is awesome! That should work great! What refractory will you use?
> Robert



Thanks, I’m looking forward to it. I ordered mystery refractory #2 from Wayne Coe Forge. I also have Kast-O-Lite 30.


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## rwm (Apr 19, 2019)

I like Kastolite but its kind of brittle and flaky for this application. Can't wait to see how it turns out. 
Robert


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## Latinrascalrg1 (Apr 19, 2019)

Do you plan on casting directly onto the metal part of the burner or do you have a different option for connecting the 2 pieces together?


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## jwmelvin (Apr 19, 2019)

Latinrascalrg1 said:


> Do you plan on casting directly onto the metal part of the burner...



That was my plan. Unless you suggest otherwise?


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## Latinrascalrg1 (Apr 19, 2019)

Nope that's what i was going to suggest.


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## rwm (Apr 20, 2019)

Keep in mind that metal and ceramic have differing thermal expansion. You need some way to hold the ceramic that can account for this. If they are rigidly attached the metal will stretch the ceramic and crack it. Of course some cracking may be inevitable.
Robert


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## jwmelvin (Apr 20, 2019)

rwm said:


> Keep in mind that metal and ceramic have differing thermal expansion. You need some way to hold the ceramic that can account for this. If they are rigidly attached the metal will stretch the ceramic and crack it. Of course some cracking may be inevitable.
> Robert



Thanks. My plan was to have the metal extend into the ceramic from the outside, just a planar interface parallel to the front of the burner. Perhaps it would be good to use some mold release or paper coating on the metal?


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## rwm (Apr 20, 2019)

That sounds like a great plan. I don't think mold release would be necessary. I was going to suggest several smooth pins sticking into the ceramic from the edge. A lot of furnace lids are done that way. That might be technically easier?
Robert


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## jwmelvin (Apr 20, 2019)

rwm said:


> That might be technically easier?


I like that idea thank you.


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## jwmelvin (May 4, 2019)

I printed a mold with integral cores for the nozzles and cast a first burner today. It will be a while before I can fire it to burn the core out but the casting went pretty well. Easier than drilling I think. 










For retention of the refractory I bent four tabs in on the front edge of the metal shell.


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## jwmelvin (May 6, 2019)

Today I got my forge working (fired the refractory lining and installed a burner), so I was able to burn out the PLA core of my casting. Part of installing the burner involved drilling an insulated fire brick, which I figured I would take a picture of in case someone searches this thread some day. It was super easy on the drill press with a hole saw (no pilot) and a shop vac:


The forge appears to be a success so far:


And here is the burned-out casting for the ribbon burner (the approach I am taking instead of drilling as I initial though about), ready to finish integrating with a plenum and try in the forge:


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## jwmelvin (May 18, 2019)

I know this is out of band for this forum and even off topic for this thread but I am happy to report that my ribbon-burner prototype (what motivated this thread) appears to work. It will benefit from some tuning but I’m excited. I made a sheet metal diffuser to expand the inducer flow to the nozzle bock:




And I’m getting a pretty reasonable flame:


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## bfd (May 19, 2019)

instead of compressed air hold a reduced dia vacuum as you drill each hole bill


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