Making a Fire Grate

Making a fire grate from a solid piece of cast iron. I wasn’t going to be able to buy one of these and I don’t have the kit to cast one. So, my only option was to machine from from cast iron.

clamping support for a round part

I needed something to allow me to hold the disc of cast iron without damaging it. This would become more critical after machining one side. After machining one side the part would be more prone to fracture.

I machined a 3mm deep recess into a square piece of aluminium. The recess was machined at exactly 42mm in diameter so it was a tight fit onto the cast iron blank.

The slot was cut after the recess was machined. This slot allows the aluminium to be clamped in the parallel jaws of the mill vice and for this then to impart a clamping force on the cast iron.

blank cast iron round disc

Cast iron disc 42mm in diameter and 8.5mm thick. This fits perfectly into the aluminium jig.

The 8.5mm thickness will allow for me to machine the grate bars 4mm deep and then the stays will be machined 4.75mm deep from the other side.

The tope side of the grate was machined first. This was done using a 3mm slot drill. This is a carbide slot drill from Rennie Tools. The bars are also 3mm wide and 4mm deep,

machining the grate
top of grate machined

Top of the grate machined. Note that one bar is in the centre of the disc.

Depending on the bar width, gap and disc diameter you might have to decide if it is best to have a gap in the centre or a bar. This sizing worked best with a bar.

grate machined one side

Machining the Stays

machining the supports

Once turned over I machined the support stays 4mm wide with 6mm gaps. Here I used a Milling Cutter Store 3 flute carbide bit.

You can now see why I made the aluminium jig. I needed something that could grip the grate bars and apply an even pressure when clamped.

20 degree milling bit

I machined an angle on the sides of the stays using a 20° carving bit. This is carbide, but such a simple cutter that is not designed for use on metal.

After about 10 cuts it broke and I decided to finish the shaping of the stays with a file. They actually need a bit of unevenness so as to look at bit more authentic.

finished fire grate

Making a fire grate was actually quite rewarding. Of course I need to see how well it works. For that I need to finish the small vertical boiler.

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