[Stoves] 100 technologies under $100

Tue Feb 2 19:06:34 CST 2016

Dear Rebecca

>…But let me start with the simple STOVE INSERT called Mewar Angithi (MA).  I would like to try this insert in my eco-kalan stove to see how much more improvement I can get from my stove by simply replacing the clay parilla with  the metal MA.  

>Can this grate be made readily from an ordinary machine shop?  What special tools will be required?

Sorry for the shortage of time to answer just this question.  The grate is an insert and it is expected that there will be a floor of some kind. To make a grate insert (which implies that the stove was not intended to have one, and it must support itself) I suggest the following:

1.      If it is accessible, purchase perforated metal sheets. They are quite common or can be ordered from sheet metal suppliers. They look like this:

2.      It is far easier to buy sheets to make hundreds than to punch your own holes.  If you want to make a few to try, it is best to use a manual punch. There are many sources for such punches but basically they look like this:

Home-made manual punch <http://www.search.alot.com/landing?slk=manual+punch+press&nid=2&cid=10163569038&kwid=21069054402&akwd=manual%20punch%20press&dmt=b&bmt=bb&dist=s&uq=manual%20punch%20mubea&device=c&ismobile=false&msclkid=41fad85b4ad64549b4eb4246611ee150&accid=35000652&campid=61724902&agid=4082679782&vx=0> :

Or you can buy similar things from multiple sources. 

3.      There are manually pumped hydraulic ones that are far more powerful if you want to punch thicker steel.

4.      If you punch holes it is about 1/10th the cost of drilling them, maybe 1/20th.  So for any level of production you want to be punching the holes, not drilling them

5.      The function of an inserted grate is to get the fire off the floor. This can be done with a U-shaped sheet – i.e. a flat platform for the fire and two sides bent down. They do not have to be parallel sides, the grate can have some tilt. I suggest that the tilt be upwards at the back, that is, a marble will roll out of the front of the stove if placed on the grate.

6.      Don’t punch holes you don’t need. Punch first then bend afterwards. The holes should not be very large – maybe 8 to 10mm. Generally speaking grates for wood burning are far too coarse. People do that to save material but it wastes fuel. If you make a parallel bar grate make the gaps 4 to 5mm. Not 20.

7.      If you order sheets pre-cut to the size you want to punch then bend, it is much cheaper to order them pre-cut by a company that specialises in that trade. They usually charge by the kg. Supposed you wanted 2.2 tons of material pre-cut to 280 x 340. It would be produced from a coil, not sheets, and it would add something like $0.10 a kg or less to cut it perfectly to that size, which would be done by a fully automatic slitting guillotine in a few minutes. With 1.6mm material it would yield about 1500 parts.

8.      With the right jigging, small holes such as you want can be punched at a rate of 10-15 per minute. You need oil.

9.      In medium quantities the holes should also be CNC punched by a service. Then you bend them, but they can probably do that pretty cheaply too. In large quantities you have a punching tool made to do all of them at once. 

10.   Have a look at the sheets of punched material if you have to buy new sheets. If you are using recycled material (offcuts) you are ahead to punch them yourself using a manual machine. There are many sizes so get the smallest one that will make the biggest hole you will need. Smaller means faster because the arm is shorter.

I hope it goes well.

Crispin

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