This article first appeared in
Studio Potter Network Newsletter, Volume 3, Number 2 (Fall 1990).
Copyright © 1998 by Studio Potter. All rights reserved.
Tired of once again cleaning out the barrel and plunger of my large Bailey extruder for a short run of mug handles, I decided one day about twelve years ago to make a smaller, easier-to-clean version. Within an hour I had sketched plans for an 11" gas pipe extruder made of parts available in any hardware store. This tool may be a blessing to almost anyone, and a necessity as well to those who have arthritis in their hands, as I do. Next to my wheel and pugmill, it is my most valuable piece of equipment.
Note: All materials can be purchased at your local plumbing supply outlet and hardware store. You may have some on hand, and feel free to make substitutions.
You will need:
You will need an electric drill, drill bits (3/16", 1/4"), a vise, a pipe wrench or vise grips, and a metal punch. Two types of files are needed: a 10" medium tooth mill bastard file, (used for removing burrs from edges of holes drilled through metal), and an 8" medium-tooth rat-tail file (for removing burrs inside holes drilled in metal or wood). A coping saw, screwdrivers, and emery paper are also necessary. A Dremel Moto-tool is useful, but not necessary. (This is a small hand-held electrical tool, available at Sears and hardware stores, with a large assortment of high-speed cutters useful in making the bevel on the dies.) One job will have to be done at a machine shop; all others can be done in your studio with the tools listed.
Larger version of diagram.
Larger version of diagram.
Larger version of diagram.
Before starting to assemble the stand, take the 2 1/2" cap to your local machine shop and have them mill out the bottom of the cap, leaving only a 1/8" lip (for the dies to rest on: see bottom of drawing #5).
Next, take one of your 1/2" x 12" pipes. Starting 1/2" down from top of pipe, drill a series of 13 holes 3/4" apart using a 3/16" drill bit, going through both sides of pipe. (See left side of drawing #5). Be sure to file off all burrs.
Referring to drawings #1 and #2, assemble the stand that holds the barrel. Be sure holes in 12" pipe are parallel to base, and that the 2 "Ts" are facing forward to hold the barrel evenly. Slip on the two rubber tips (floor protectors) as shown on bottom of drawing #2. These will level the stand and keep it from slipping.
Position the barrel on the stand against the "Ts." Using the adjustable band clamps, secure it as shown in drawings #1 and #2, with a 10" clearance between the base of the barrel and the bottom of the stand. Be sure it is clamped tightly at areas where the "Ts" meet the barrel as shown in drawing #1. Be careful here, as this area will take all the force being exerted on the clay, which is considerable. (Note: I have never had any problems with the barrel moving out of alignment.)
Note: Try to be as accurate as possible with this assembly, as it is critical to the smooth operation of the extruder.
First, take the two 1/8" x 3/4" x 4 1/2" pieces of aluminum bars. Measuring 1/2" from one end, punch mark (make a slight indentation using a nail, awl or metal punch) the first hole. Make the second punch mark 2" from the first, and the third 1" from the second. Please refer to drawing #7 to clarify. Clamp the bars in a vise or secure them with masking tape. Using a 1/4" bit, drill each pair of holes.
Next, take the two 1/8" x 3/4" x 3 3/4" aluminum bars and again measuring 1/2" from the end, punch mark the first hole. The next punch mark will be 1 1/4" from the first and the third mark will be 1 1/4" from the second. Again referring to drawing #7, drill these holes with a 1/4" drill bit, as you did the other bars.
Now take the large 1" x 30" pipe handle and drill a 1/4" hole through both sides of the pipe 1/2" from the end. Drill the next hole 1" from the first, through both sides of pipe. Refer to drawings #5 and #7, top. At this point, assemble the handle and bars as shown in drawings #1, #5, and #6, using the 1/4" x 1 1/2" and 1/4" x 2" bolts and nuts and also using the 1/4" x 1/2" washers as spacers. Use lock washers to secure the nuts. Remember to use the 1/4" x 2" bolts and nuts on the vertical aluminum bars, #B in drawing #5, which will hold the plunger and enable it to work freely in coordination with the handle.
Take the 1/8" x 3" x 3" aluminum plate. Carefully measure the interior diameter of the 2 1/2" x 11" extruder barrel, and cut the plate to fit inside the barrel, allowing 1/32" clearance in circumference. Drill a 3/16" hole through the center of the disk you have made and attach it to one end of the 1" x 10" wood dowel, using the 2" x 3/16" round head screw (see bottom of drawing #5). Now round off other end of the dowel (see drawing #5), and attach it to the 1/8" x 3/4" x 3 3/4" aluminum bars as shown on top of drawing #5, using the 1/4" x 2" bolts and nuts. Be sure to leave enough clearance at top of dowel for it to work freely in tandem with the handle (refer to top of drawing #5). Drill your first 1/4" hole down 1/2" from the end of dowel, then line up the two bars evenly and drill the other 1/4" hole. You are drilling through holes previously drilled. Be accurate and careful with all measurements and assembly.
You may now assemble and tighten the entire plunger and handle assembly as shown in drawings #1, #5 and #6, using the remaining 1/4" bolts, nuts, washers and lock washers. Minor adjustments may be made, using the washers as spacers, so that the plunger works easily up and down in the barrel. It is wise not to tighten the bolts and nuts too securely until the plunger works freely. When this happens, tighten. (After 12 years of hard use I have never had to make an adjustment to any part of my extruder.)
Make up several 1/4" tempered masonite dies to use in your extruder. If your masonite is the dark brown type, it is helpful to give your design surface a spray coat of white acrylic paint to make it easier to see and to draw the design on the die. On drawings #3 and #4 I show two designs I find most useful for mugs, casseroles and lids. The designs can be almost any shape, and are limited only by your needs and imagination. Don't forget to form a 45-degree angle/bevel from the top of the die to the bottom exit area to aid in compressing the clay as it flows from the die. I usually try to design my dies so I can use an electric drill with various size bits to make the rounded contours. Then I cut out the remaining material with a coping saw or jigsaw.
Finish up the die's beveled areas with a Dremel Moto-Tool, or cut it with a utility knife, followed by medium and fine sandpaper. The exit area of your dies should be very smooth; finish it off by hand using a small rolled up coil of fine emery paper.
It is also advisable at this point to give both sides of your dies a spray coat of lacquer. This will prevent the moisture in the clay from warping or watersoaking the die.
Now make your support dies, which are placed under the main die to prevent it from "bulging" downwards, especially if the clay is overfirm. The support die (see very bottom of drawing #5) is a regular size die with a large circle cut out of the center to within 1/2" of the edge. I also have one that is oval shaped, to use under the wider strap handle type dies. These dies should also be thoroughly coated with Crystal Glaze or lacquer spray.
Roll out a coil of clay about 2" thick and 9" long. After placing your die in the barrel cap and screwing it onto the barrel bottom, drop the clay down into the top of the barrel. Take your plunger and handle assembly and guide the disk end of the plunger into the top of the barrel. Fit the very end of the assembly down over the vertical pipe stand (with the holes - see drawings #1, #5 and #6), and pushing down as hard as you can, compress the clay somewhat and slide the 3/16" "L" hook into the top hole and pull down on the handle. The resistance of the clay will force the end of the assembly up against the hook, and the plunger will force the clay downward. Repeat the procedure and keep moving the "L" hook downward and cut off the extruded clay as needed. To remove the plunger, reverse the procedure.
Your clay should be plastic, and about throwing consistency. I have found that "old used clay" tears and chatters through the die and will not exit smoothly. After some experience with the extruder you will find the best consistency for your use. I have also found that clay containing a lot of grog will be more likely to produce scoring, scratching and pitting on the faces of the extrusion. I have 38 dies made over the years; the fact that the dies are made from masonite, rather than metal or plastic, encourages one to try all kinds of extrusion shapes. You are limited only by your creativity and imagination.