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Foundry Sand Muller

This is my sand muller that I finished back on December 4 2015. It has two plows and a twenty-five pound roller made from the bottom of a five gallon pail and some concrete. I poured a bunch of scrap nails into the concrete to add weight. The plastic helps prevent sand from sticking. Since I’ve started doing a bit more casting, I wanted a muller to keep my sand conditioned better and faster. Prior to this, I had used a tiller attachment on my string trimmer. But I was afraid I was going to wear it out on my foundry sand, and the wife wouldn’t be too happy about that.

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The muller’s gear reduction began here. This is one of seven sectors of three-quarter inch plywood curved racks, and a three-tooth lantern gear that engages it. I used Matthias Wandell’s gear generator program to make these. There are 52 teeth in the big gear, which gives a seventeen and one third gear ratio. This, along with about a four-and-a-quarter to one ratio of the washing machine motor to pulley gives approximately a 74 to one ratio, taking a 1725 rpm motor down to about 23 rpm. The maytag motor I have is 2 speed, so I have a choice of 23 or 46 rpm.

UPDATE:  Here is a pdf of the sector shown above.  I cut out six of these with eight teeth, and one with four teeth to make a total of 52 teeth.  sandmuller_sectors.pdf

This lantern gear arrangement is a little bit noisy, but due to the ball bearings, there is practically no friction between the drive gear and the wood. I’ve run the muller quite a bit now, with no sign of wear or failure on this gear reduction.

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There’s a wooden arm made of scrap plywood, about four layers of it glued and screwed together, that carries the roller and its axle on some skate bearings. To allow the roller to move up and down as it rides over chunks of hard sand, there is a door hinge so the arm can move up and down.  The axis point of the hinge is low enough so the roller moves mostly straight up and down rather than at an angle, which would make it bind with the side of the barrel.

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Here’s the base frame, with a car wheel bearing and a maytag washing machine motor. The motor has a two-inch pulley which is not original. Then the eight and a half inch pulley is the maytag agitate and spin cycle drive pulley which I have mounted on a jackshaft made from a bolt going through a wheel assembly I got at tractor supply. The 3 tooth lantern gear is right on top of that pulley.

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In this shot, I have all the sectors glued and screwed to the bottom of this big MDF disk, which is also mounted to the car wheel bearing. The wheel bearing was from my 1999 Dodge Caravan, and was starting to get noisy, but is still very strong for a low-speed, low stress application such as this.

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Here’s the framework starting to take shape. It’s just built of scrap two-by-sixes I had laying around. I also drilled the 5 hole pattern in the bottom of the blue barrel section which is visible in the upper right.

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The muller isn’t quite finished here, but since I needed to quit for the day, I put the lid back on.  This 1/3 barrel full of fresh-smelling “dirt” is an irresistable temptation to our cats.  They would just love to get in here and do, well, you know what.  Since the muller is finished, I have a set of plywood covers that fit around the plow staves and other parts, to provide some cat-resistance.

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The muller actually worked and I used it for awhile just like this, with no roller. I would stomp the sand with my 8 pound splitting maul to break up the chunks. Those white flecks are sawdust, not sure how they got in there.

I let the concrete roller cure in a moist environment for about two weeks until finishing to this stage. The switch box on the side allows turning the muller on and off, as well as changing between high and low speed.

So I hope you enjoyed this, and gave you some ideas for your own sand muller build.  Here’s a youtube video:

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