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Why use a Pony Press to make Bio-Mass fire logs? It fund, easy to make and use, and it works.
The Pony press is also commonly called a “Book Press”
The basic principle is a “press screw”, which goes back to Roman and Greek times (and earlier) and was used for pressing olive oil and wine. Its use through the centuries included being part of the Gutenberg Press (which revolutionized how information was shared in society).
Putting weights on the end of the handles to use centrifugal force, this led to the use of “flywheels” for controlling the speed of steam engines, that powered the industrial revolution.
The conversion of rotational force to linear force provides a stunning amount of pressure, with or without a lever arm. BTW, The equations are a little daunting but if your interested search: “Press screw force equations”
There are lots of TH-cam designs for making sawdust fire logs (see here: sawdust fire logs), most of them are better thought out, better explained, and tested by actual engineers (Engineers Without Borders)
That being said, this approach is fast, cheap, easy to make, fun to use, and it works really well (plus it’s purple).
What I learned: Increasing the proportion of sawdust makes it burn longer, increasing paper makes it burn faster (at the start), and increasing coffee makes it burn hotter. This means you can tweak the mix so they will burn the way you want. For fragrance might want to add some mint or Sassafras leaves, or even mix some cedar sawdust in with the slurry.
Materials:
1 Nine inch Pony press screw
~ 18 $ US (veneer press clamp), I got mine from Grizzly Tools
4 - Three inch dry wall screws, or a few more if you're “unsecure”.
1 PVC pipe, Schedule 40, 3 inch diameter, 9 inches long
1 PVC Coupling collar, for 3 inch pipe
1 Three 3” hole cutter (for the end plugs)
1 wood (2”x4”) board about ~5 feet long
Total cost for materials is about 25$
Assembly:
Cut the PVC pipe in half, long-wise (any way you can, safely).
Cut the ends off of a 3” PVC pipe connector to make two rings that fit over the PVC pipe.
Cut the 2X4: Two 8 inch long and Two 15 inch long pieces
Screw the wood pieces together as shown in the diagram. I used an impact driver for the screws and some wood glue.
Drill a 1 1/8” hole in the top piece for the collar of the Press Screw. Drill two smaller holes, adjacent and intersecting the first hole, reverse and mount the collar (with it’s side ridges) upside down (see images). Bang (finesse) it into place.
Use a 3” hole saw to make end plugs. Bevel the top plug a little bit to make it seat easier, when placing it on the top of a filled cylinder.
Steps to make a fire log:
Make your slurry, let it soak for a day or two.
Have a “canning funnel” ready and a small scoop (keeps things neat).
Assemble the two part cylinder with bottom plug and outer rings.
Fill the cylinder with your slurry.
Give it a pre-press with a smaller diameter plug (with a string tied to it), and push it down with a stick. This smaller plug has the string tied to it, so you can pull it back up and out for a second “top-off”.
Place the slightly beveled top plug in the top of the filled cylinder.
Place the cylinder in the frame and turn the screw to compress the slush.
Take it all the way down, wait a few seconds then spin it back up.
Using thumbs for leverage, Slip off the rings, separate the two halves of the PVC pipe and push the log out with your thumbs.
Finally, stand your logs to dry.
FACTOIDS:
The logs take about a week to dry, on hot sunny days.
- Dried logs read about 15% - 20% on the moisture meter (mostly from atmosphere).
- They burn, and stay HOT, for about an hour.
- A cylindrical form (PVC) uniformly distributes the compressive force, try different sizes.
- You can make multiple short brickettes at one time, by separating them with plugs.
- I made an 8” radius turning lever, with two holes (see pictures), to avoid strain.
- Schedule_40 PVC rated at 261 PSI (distributed throughout the volume). - The volume of a 9 in tall cylinder is 64 cubic inches
- The volume of a compressed log is about 28 cubic inches ( 4” tall) - 1500 lbs of compressive force in 28 cubic inches, is safe at ~54 pounds per cubic inch
- Mechanical Advantage of a press screw (force Magnification) for a 9 inch Pony press screw, with standard Acme 4 Threads Per Inch (TPI), 11/16” diameter and a ¼ inch advance per turn, is about 8.6X (with no lever radius). If you add a lever arm with an 8” radius, then its about 201X. So as little as 10lbs of force on the lever-arm, gets about 1700 lbs.' of force, without much effort. That’s not bad, and it works really well.