This is Part III in the series of articles covering mechanical rebuilding of a 1914 Simplex 50 h.p. Model “F” long-stroke Speed Car from the Collier Collection at the The Revs Institute, located in Naples, FL. As a part of planning the job, a thorough inspection of the rest of the car was conducted before the engine rebuild was begun. One issue that turned up was a bent foot brake drum and a worn jackshaft (shaft between the differential and sprocket) bearing.
- The lead photo shows one of two new finished brake drums for the Simplex.
- A side-view illustration of an earlier Simplex short stroke 50 h.p. chassis shows an identical layout of the two separate braking systems. The differential brakes (inboard) operated by the foot pedal, can be seen just inside of the frame side rail behind the front chain sprocket. The hand brakes are located on the rear wheels.
The Simplex differential brakes are operated by the foot pedal and are what is referred to as an external-contracting brake. This type of brake can work well but suffers from a few drawbacks: road dirt between the lining and drums causes severe scoring and wear in time, during wet weather water that gets between the two surfaces causes an almost complete loss of braking.
The differential brake drum friction surface on the Simplex and other chain drive cars of the period that share this system are usually extremely worn and ineffective after a normal service life. On the other hand the rear wheel internal-expanding brakes (and parking brake) work very well and are operated by hand with a long lever next to the shifter and are used for the majority of all braking.
- A brake drum with its heavy cast iron or steel brake shoes and linings.
To salvage this set of brake drums and those on many other Simplex cars, early restorer Ralph Buckley first machined off the complete outer drum surface. He then welded steel tubing to the spokes and machined the outer surfaces and sides to run true. This did work well with one exemption – steel has a lower coefficient of friction than cast iron, which reduces the brakes efficiency.
At some point afterwards, one of the drums must have gotten hit and bent by something, as it was running out, side-to-side by a 1/4 of an inch and a lesser amount out-of-round. Straightening this would be very difficult, and require bending the brittle cast iron spokes. Having to re-bend them a second time would likely have caused the spokes to either crack or fail in use and cause a large amount of damage which is unacceptable. A set of new brake drums was put on the list of things to do.
- The two sections of wood that meet in the center with the outside surface cut on a two-degree angle are glued onto the drum with body filler. The angle on each piece ends up producing a peak in the center. After curing another set of angled wooden pieces, are also attached to the inside.
We have made casting patterns for many other items and worked with pattern makers in the past for complex casings. Parts that have been sent out to have cast in iron include small parts, brake drums, and cylinder blocks. We work with the Henry Perkins and Co., a foundry in Bridgewater, MA, that is family run and was first opened in the 1850s
To make or have a pattern maker produce a match plate pattern for this job could cost as much as $3000. Since only two were going to cast, the “loose pattern” method was chosen as the cost would end up being only 25-30 percent of a production style of pattern.
Two requirements are necessary for a pattern of this type. All of the round areas must be built up to provide for enough extra material needed to compensate for shrinkage (1/8″ per foot) during cooling. In addition, an extra amount that will allow the casting to be machined to the correct size is needed. The round surfaces also need to have a 1 to 3-degree draft angle added on the outside round surfaces to allow the pattern to be pulled out of the molds cleanly without damage to the sand.
- This image shows both wooden surfaces finished off with an added layer of filler. A 1/8-inch thick piece of dense paperboard was glued on to each side of the drum and on either side of the hub. A layer of green masking tape has been applied to the hub to serve as a guide for filling it in.
- The finished and painted pattern, with the draft angle now visible on the side of the hub. The same added angle is also seen on the inside surface of the drum. Painting makes the surface smoother so the pattern will be able to be pulled out of the sand without damaging it.
This video, taken at the Miller Foundry in Santa Ana, CA, demonstrates all the steps involved in setting a loose pattern, followed by the actual casting process. Viewing this video first will help you to understand how the brake drum pattern is set. Courtesy of Mrvideoer.
To use the brake drum pattern in this manner, exactly one half of it is set horizontally in the drag (bottom half of the mold) on top of hardened baked casting sand supports under it to locate it. Next molding sand is packed under and around it. The sand is then compacted and leveled to a perfectly flat finish.
- Diagram illustrating a completed mold ready for pouring. Picture the brake drum pattern positioned horizontally in place of the one shown. Image courtesy of what-when-how.
The second part of the operation involves placing parting sand on top of the mold in the drag. The cope is then placed on top of it with two dowels that will leave shafts in the sand for the riser and sprue when removed. The cope is then filled with sand that is compacted and leveled off. The riser dowels are removed, and the cope is carefully lifted off so as not to disturb the sand around the pattern.
Finally, the gates that feed the molten metal into the two halves of the mold are placed in the sand on the top surface of the drag, and the pattern is then carefully removed. The cope is then placed back on top of the drag and the mold is ready for the pour.
You can look back at Parts I and II of the series here.
- The finished castings after shot blasting and grinding off flash, ready for the machining operations.