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Running the numbers

This topic contains 3 replies, has 4 voices, and was last updated by  Rob 2 years ago.

James L jamesl

Running the numbers

09/04/2016 at 14:05


I’d be interested to put together a little list to show the cost comparisons between buying chinese made plastic products from my local $1 store, and using a workshop like this to create some plastic products.

Is there anyone who could help with this?

For Precious Plastic workshop, I’m particularly interested in two numbers:

1) The total material cost of building a Precious Plastic workshop
2) a) The energy usage (e.g. kWh) of the Precious Plastic workshop to produce e.g. 1 watering can or one moulded plastic bowl
b) The energy usage of the Precious Plastic workshop as the production scales. How does it look for 100 or 10000 watering cans?

For the $1 plastic Chinese made item, I’m interested if anyone knows how to understand the externalities of this cost, e.g.

– Carbon usage to create the item and ship it
– Energy usage in China

I think it would be pretty healthy for this comparison to be really clear, see how big the gap is, and if Precious Plastic workshop is more expensive, how to close the gap.

Thanks 🙂


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In reply to: Running the numbers

18/04/2016 at 13:21

While I don’t have a workshop built for myself or all the numbers, I might be able to help for part of it. It is partially going to depend on how much electricity the motor for the shredder and the other parts that draw electricity actually use. It will also depend on the price of electricity in your area, or if you power it with other sources such as solar of wind. According to a quick internet search, a tipical oven draws around 2000 watts, or 2 kilowatts. A paper shredder shredder only draws about 150 watts but because we are using a plastic shredder I will make the assumption that it is 200 watts, or 0.2 kilowatts. In my area electricity costs about $.20 per kilowatts hour, or 20 cents to use one kilowatt for one hour. I live in Massachusetts and aparently the price of energy is relativly high in my area and i have hear it costing as little as $.1 per KWH in some other areas.So that means it costs about $.40 to run the oven for the compression molding for one hour and $.04 to run the shredder for 1 hour in my area based on the assumptions I made. I don’t know how many products you can make in an hour or if you need to use both machines constantly while working but it looks like the cost of electricity is less than $.50 an hour for operation. So one product sold for $1 would more than cover the operating cost of the equipment for 2 hours. So assuming your plastic is free any additional products you make in that 2 hour period would be profit.

I made a lot of assumptions for this calculation so it might be a little off but I hope this helps.

In reply to: Running the numbers

26/05/2016 at 13:31

you need a way heavier motor, if i’m not mistaking, dave used a 2 kW motor for the shredder… so that would almost double your costs.

you also need a mold and need to build your whole workshop, and you probably need to pay rent for the place you use. I am almost certain that even in the most beneficial situation, a product out of china would me much cheaper, because of mass production and all. If you live in a country that has a carbon-tax (some do) the Chinese product’s price sky-rockets due to the carbon pumped into the air during transport, and you might stand a chance with your workshop…

Dave himself already said in one of his instruction vids that this is in now way capable of beating the big boys, it’s meant for environment-saving stuff or working at a dumpyard-stuff, not beating the big guys-stuff

In reply to: Running the numbers

15/06/2016 at 04:00

I started a basic matrix over on the wiki. Have fun with this.

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