The following are my demonstration handouts for the “Cast and Threaded Pewter Collar and Finial” demonstration presented at the 2013 AAW Symposium in Tampa, FL.
Pewter is a non-ferrous metal alloy primarily made up of tin (85 to 99%), with the remainder consisting of copper, antimony, bismuth and lead. Modern pewter’s contain no lead and are actually Britannia metal. One noteworthy use of pewter is the Oscar statuettes. They are made of Britannia metal plated with gold. The melting point of pewter is approximately 375 degree Fahrenheit (190 degrees Celsius). The low melting point and non-ferrous nature make pewter a great candidate for incorporating it into turned pieces. A regular propane torch can melt it and it can be cut, drilled and turned with regular woodworking and woodturning tools.
Pewter can be purchased from online metal stores where you can expect to pay around $20 per pound. The frugal among us can also find it sold in ingot form on eBay, where you can typically win with a bid of about $12 per pound. The eBay sellers are normally selling melted down pewter mugs, plates etc. As such you take your chances regarding the lead content, although many claim the pewter is lead free and include pictures of test results.
While pewter can be melted in a metal ladle, I use a small electric furnace or melting pot made by Lee Precision. This is the same pot used for reloading or casting fishing weights. They cost around $60 and are available from most hunting or sporting goods websites. One of the advantages of using this melting pot, aside from not having open flames in the workshop, is the pot is a “bottom pour”. Molten pewter contains a fair amount of “dross”. These impurities float to the top of the mix. With a “bottom pour” pot, when you lift a handle the molten metal flows from the bottom of the pot into your mold, leaving the “dross” in the pot. I have found the spout clogs occasionally, so I keep a propane torch on hand to melt the solid pewter clogging the spout. A casting thermometer is also very useful.
Molds can be made from a variety of materials. I use both wood and silicone to make molds. The silicone I use is sold by Smooth-On. It is called Heat Resistant Mold Max® 60 Silicone. I use this when I have spent time and effort creating a master and want to be able to cast a number of collars from the same mold. For one off collars I will typically just make a wooden mold. They are cheap, quick and easy to make and the collars poured in them can easily be embellished at the lathe. The wooden molds have a limited life span as the heat from the molten pewter causes them to warp. I use kiln dried maple for my wooden molds. The moisture content of the wood needs to be low in order to minimize the possibility of it turning into steam and expanding.
When casting and pouring the pewter make sure you take all safety precautions.
- Never leave the melting pot unattended while plugged in.
- Place the melting pot on a ceramic tile.
- Wear thick gloves and safety glasses.
- Allow the pewter to cool fully before trying to de-mold it. Sometimes it can appear solid on the surface but still be liquid inside.
I typically make my collars between 2 and 2 1/2” in diameter. This size works well for a hollow form from six to 12 inches tall. More important it allows me to easily mount the poured collar in my chuck for further work on the lathe. The first step is to drill a ¾” hole through the collar using a Jacobs chuck in the tailstock. Technically, for the size tap I use the hole should be 47/64”, but a ¾” drill bit is more readily available and being off by 1/64” doesn’t seem to make much difference.
Once the hole is drilled I use a NPS 1/2-14 tap to tap the threads in the collar.
Side note: NPS refers to Nominal Pipe Size. This is different to NPT which will produce a tapered thread. The ½” description can be a bit confusing as well, especially as we have just drilled a ¾” hole! It refers to the internal diameter of the schedule 40 pipe that this size thread is used on. The 14 refers to the threads per inch.
The tap is held on the lathe by means of a Lathe Tap Holder. These are available for purchase, but they are relatively easy to make. I made mine from a section of 1 1/8” aluminum rod which I drilled on the lathe. The idea behind threading on the lathe is to keep everything centered on the centerline axis of the lathe. The first collar I threaded, I did by hand holding the collar in the vise on my workbench. When I put the collar on the hollow form the finial was not plumb and stood at an angle!
It is important to use some form of lubrication when threading or tapping metal. Although the pewter is a soft metal and threads/taps very easily, you will get a far better finished surface using lubricating oil. In lieu of actual threading oil I just use some regular 3 in One oil.
Now that the collar is tapped, wipe it down and soak it in some acetone or denatured alcohol to get rid of the excess oil. We now need to mount it to the lathe in order to turn a tenon on the underside and shape the top. I use a “27 cent chuck” I get from the hardware store to do this. A ½” PVC male adapter is held in my chuck and then the collar is threaded onto this.
I turn the underside of the tenon first. I turn a tenon which is slightly larger than the hole in the hollow form. (I find it is easier to size the hole in the hollow form to the tenon than the other way around.) I then reduce the bulk of the collar by shaping the underside. Because the collar is held to the lathe by means of a PVC adaptor, I can cut right to the threads and into the PVC collar without worrying about damaging the gouge.
I then remove the collar from the PVC adapter and rotate it so I can turn the top. Wear gloves when removing the collar from the PVC adapter! The collar will have become pretty tight on the adaptor and the metal edges can cut you. Once the top of the collar is shaped it needs to be sanded/polished before embellish. Any embellishing tool you would use on a box top or spinning top can be used on the pewter. Chatter tools, Wagner texture tool, Sorby spiral tool and the Decorating Elf can be used, and the embellishments outlined with the tip of a skew chisel. These embellishments can also be further enhanced by applying India Ink, allowing it to dry before wiping it off.
When I turn the hollow form I use a faceplate and I do not part the hollow form off initially. I typically hollow end grain and so do not experience a lot of movement as the piece dries. Now that the collar is complete I mount the hollow form back on the lathe and size the opening to fit the lathe. Once I have achieved a snug fit, I attach the collar to the hollow form while it is still on the lathe. I use 5 minute epoxy and put it around the opening of the hollow form. I then insert the collar and lightly clamp it using a 60 degree live center in the tailstock.
The next step is turn finish turning the bottom of the hollow form. Ideally I will allow the epoxy to cure overnight, but if you are careful the epoxy is strong enough to allow the next step within about half an hour. After removing the faceplate from the hollow form, mount the ½” PVC adapter in the chuck and then screw the hollow form onto it. Place a live center in the tailstock and bring it up to support the hollow form. Part the hollow form almost through, just leaving a little nub. Shape the underside of the hollow form and sand. Slow the lathe down and cut through the last of the nub. If you have allowed the epoxy time to cure the hollow form will be secure enough on the PVC adapter that you can finish sanding the underside. Keep the lathe speed slow though!
We now need to turn the finial and attach a threaded ring to it. A simple mold for the pewter ring can be made by drilling a 7/8” hole in a block off wood a couple of inches deep. The pewter is then poured into that. Allow the pewter time to cool. This might take a while as it is a pretty large volume of pewter. To remove the pewter from the mold, drill a hole in the block of wood from the underside and use the knock out bar from your lathe to knock the pewter free. It is then mounted in pin jaws in the chuck; drilled with a ½” drill, turned to 53/64” diameter and then threaded using a Round NPS ½-14 Die held in a Lathe Die Holder. Don’t forget to use some form of lubrication.
You will not be able to thread the entire column as the die will stop at the pin jaws, but thread at least ¾”. What is not used can always be melted and used again. Turn the exposed end of the column true and then part off ½” of the threaded column.
The base of the finial needs to be at least 7/8” diameter or it will just screw right into the hollow form! I leave a tenon on the finial which is about ¾” long and exactly 1/2” diameter before parting it off. The threaded pewter ring is then attached to the tenon on the finial using 5 minute epoxy. Apply the tenon to the inside of the pewter ring and not to the finial tenon. By doing so any excess will get pushed out the ring where it will be turned away later.
The final step is to clean up the underside of the tenon on finial. I do this by mounting a length of 2” PVC pipe using my chuck jaws in expansion mode. In the open end of the PVC pipe I place a piece of scrap wood with an appropriately sized tenon. The wooden insert has been drilled and threaded in the center so that the finial can be screwed into it. It helps if you cut a slit with a bandsaw from the edge of the wood to the center, making a “collet” chuck. The wood is then friction fit into the PVC pipe with the finial inside the pipe and the underside of the tenon exposed allowing you to turn it true.