Plansifter Project

I built a planetary sifter, or plansifter, this month to replace the bolting reel sifter I had been using for the past few years.  The bolting reel had trouble in the collection system, where flour would pile up underneath the reel and then get pushed over into the bran chute.  The problem was not acute, but it always bothered me that some of the flour was going out with the bran.  Hence the plansifter project.

A plansifter is a box filled with sifting trays.  The box hangs on flexible canes, and a motor with an intentionally out-of-balance counterweight causes the whole things to move in a circle.  The target is a gyration of 240-250 rpm, and a gyration of 62-65 mm.  See https://www.millingsystems.com/wnewsdisp.php?id=4040 for more information.

My unit is running at 250 rpm but the gyration is only around 40 mm.  I wish it were more but I'm afraid to put more counterweight on.  Right now I have 18 lbs of counterweight flying around about 6" from the shaft, which is already quite terrifying to me.  So for the time being I'll keep things as is.  However, the flour did not really move at all until I was well over 12 lbs of counterweight.  So if I ever need the unit to move more flour I will add more counterweight.

Here is the formula for gyration (thank you https://forum.bulk-online.com/showthread.php?20776-Counter-Weight-Problem):

The weight of the counterweights required will be equal to:
m = (M x r) / R

where
m = required total weight of all counterweights in pounds
M = total vibrating weight of screen (basket + mechanism + effective material load) in pounds
r = the required radius of vibration in inches
R = the radius from centre line of the mechanism shaft to the centre of gravity of the counterweight in inches

My plansifter is a simple two-part separation.  I built two screens, which I think have more than enough capacity for my 200 lb/hr mill.  The box is nominally 24" x 24" x 12".   I built the box a little taller than needed in case I want more screens at some point.  My target is 95% extraction and I currently use a 28 mesh stainless steel screen with an opening around 700 microns.

The new plansifter as installed.  I use a shop dust collector to create a slight negative pressure in the unit, which keeps my mill room remarkably dust free.  Flour comes out on the left and bran on the right.  The flour enters at the top right and is dumped directly onto the top screen.  Anything that falls through the screen gets pushed off to the side by the tray cleaners and falls to the bottom of the box.  The bran flows to the left and then drops down to a second screen, where it starts flowing to the right.  Anything that goes through the second screen also falls to the bottom of the box and out the left spout.  Basically you just have to seal up and baffle everything so that there is no choice about what media ends up where.  The constant shaking of the plansifter ensures that product will continue to flow.

Startup of the plansifter is a little dicey.  If it bumps the mill the unit will bounce hard and possibly cause damage.  But once it is up and running the unit is rock solid and stays put.  Apparently stable startups are an issue with commercial units as well.  See https://www.gwmfg.com/Pages/HS-tru-balance-drive.htm.

Leveling things off during the installation.  The wooden clamps I made for the canes worked so-so.  The top is held down with four bolts.  Prior to putting the top on, I add shims so that the tray stack is firmly clamped together.  The trays have ordinary wool felt strips between them to seal things off.  Of course, there needs to be a flexible connection for flour going in and out, since the whole thing is going to be shaking at 250 rpm.  I use an old long-sleeve shirt as a gasket between the mill and sifter.

Installing the plansifter.  It hangs from the ceiling on four 3/8" fiberglass fence posts.

Here is my first sifter tray with tray cleaners and screen installed.  This style does not use backwire.  The bottom of the tray is perfectly flat.  The screen cleaners bounce around, keeping the screen clean and pushing the flour off to the sides.  Cleaners were easily purchased after contacting the folks at Filip in Germany: https://filip-gmbh.com/en/products/for-plansifter-sieves-without-backwire/.  The wood strips on the side are slotted so the flour can slide off.  See https://www.youtube.com/watch?v=-zrWWhUPOzE

Trial fitting.

Gluing up a shield for the counterweight. Ultimately I glued it into place and it became part of the bracing for the counterweight shaft.  There is a nice stave calculator at https://uniontownlabs.org/tools/stave/.  Those weights being used to hold it down for gluing are the counterweights.  They are held in place on two 3/8" by 6" bolts off of the steel 3/4" shaft.

The reduction drive and counterweight shaft.  I had to use a 15" pulley to get down to the target of 240-250 rpm for the counterweight.  This size pulley weighs more than the motor, which is unfortunate.  The heavier the unit, the heavier the counterweight needs to be.  Ideally I would start out with a 1200 rpm motor which would make the reduction easier and lighter.

Machining the keyway on a harbor freight drill press.  Not very precise work, but good enough for a keyway.  I wanted everything to be as strong as possible, not knowing exactly where things would be stressed.

Here is the final motor and counterweight installation.  It's a 3/4" shaft.  I found two 3/4" gear hubs, which I drilled and tapped to accept a 3/8" bolt.  The hubs are held to the shaft with a square key and set screws.  The counterweights just bolt into the hubs.  Spacers are some thick-wall steel tubing.  The motor is an 1800 rpm 1/4 or 1/3 hp unit with an adjustable pulley to tweak the shaft speed.

Here is what it looked like the first time I fitted up a sifting frame.  Everything is perfectly flat, with the exception of the box floor.  If you look close at the bottom of the photo you can see where I am missing baffling.  I figured this out after the first run when I found flour coming out with the bran.

The plansifter needs to be strong--it will undergo a great deal of strain as it is being gyrated.  I chose to make corners with outside hardwood reinforcers.  Everything is glued and screwed.  The reinforcing stringers on one end will help support the counterweight shaft and bracketing.

First frame going together.  The side pieces have some space underneath to allow the flour to fall through.  I used a dado head on a radial arm saw to make the corner joints.  After gluing the frame up, I nailed a piece of 3/16" plywood to the bottom.