Both terms mean practically the same thing, i.e., rough polishing, but "ashing" is usually done with wet pumice powder and "buffing" with one of the grease-bound buffing compounds. Ashing also includes the wearing-away of sharp corners and edges left by the machining operations.
The cheapest and probably the fastest method of doing this is with a "mud-wheel", which is a loose buffing wheel of 8" to 12" diameter, driven at a speed of from 1800 to 2500 R.P.M., by a one-quarter to two horsepower motor. At least a quarter horse-power is needed to make any speed. The buffing-wheel, if to be used with "mud", has a guard over it, and runs over a pan in which is kept a thick paste of 00 pumice and water, applied to the wheel from time to time with the hand or a trowel. (Plate 2S).
A cleaner and more convenient method is the use of cake buffing-compound (the proper grades are recommended or sold by the various plaitics companies) on a dry wheel of the same type. (Plate O) Given the proper type of wheel, the proper speed and sufficient power, and you can turn a rough unattractive surface into a glittering jewel with just a few passes on the wheel.
The wheel must be loose-stitched, and if you are unable to obtain this type, you can remove the rows of stitching from the ordinary type of wheel. Some professional operators remove all stitching, and insert smaller discs of heavy paper between each disc of muslin, thus opening up the wheel further. The purpose of this is two-fold—to guard against a "hot wheel" which would result in burning, and to enable the wheel to get down into cracks and carvings which otherwise it would not reach. Using small end-washers on the wheel also makes it "looser". Frequently it will be found that these deep grooves in carvings fill up with the buffing-compound—a sure sign that the bottom of the groove is not being polished. The remedy is a shallower groove, a looser wheel, or more power.
Other types of buffing compounds can be used, there being any number on the market, mostly using tripoli as an abrasive, and a trial will quickly show the efficacy of any particular type. Rouge is too fine and slow. All of the grease-bound compounds cause quite a "drag" on the wheel, which accounts for the considerable amount of power required, but in the long run this is perhaps the most convenient method for the home craftsman.
A caution in passing. You will get such an excellent polish on your plastics jobs with this buffing and polishing set-up that you may want to polish your tools, silverware or brass on the same wheel. If you do, you will blacken it and cause yourself considerable trouble when you return to plastics—keep another separate wheel handy for work on metal.
Regardless of the type of buffing or ashing abrasive used, be extremely liberal with it—it is the abrasive which does the work and not the muslin wheel. The wheel should be kept loaded at all times, and the cake of compound applied frequently during a job. After a while the wheel may become "caked up" at the edge from the use of so much compound. The quickest way to remove this excess is to construct a scraper consisting of a piece of wood about 12 inches long, 2 inches wide and a half-inch thick, thru which is driven a large number of small nails, projecting about a quarter-inch, and this is held against the wheel while it is revolving, removing the caked compound and cleaning the wheel.
Polishing The buffing operation is kept up until all sand-paper scratches are removed, which stage can easily be observed by the eye. When this is done, the object is ready for polishing. Before polishing, all traces of buffing-compound or ashing mud must be removed, either on a wheel kept for that purpose or by washing. If any of this compound gets on the polishing-wheel, it will prevent the latter from producing a perfect finish. The wheel used for polishing is the same type as that used for buffing, and must be kept clean for this purpose. Polishing compounds are usually a very fine grade of buffing-compound, bound in carnauba or other waxes, and occasionally the wax alone, or stearic acid, palmitic acid, etc., are used instead of the compound containing this fine abrasive. The latter however will produce better results for the average craftsman.
By the time the object reaches the polishing-wheel, it should be completely smooth and have no marks whatever visible to the eye. In fact, some cheaper grades of merchandise made of plastics never see the polishing wheel or drum, the finish left by the buffing being sufficiently smooth. Polishing merely adds the brilliance, or "glitter" that sets this material apart from all other crafts materials. The polish is caused by the heat and friction and to a minor degree by the very fine abrasive. The highest possible polish is obtained in the final buffing with no abrasive or wax, just a clean wheel. The wax contained in the polishing compound does not serve the same purpose in the case of plas-serves to fill up and level off the "pores" naturally found in the material. Plastics contains no "pores" or surface roughnesses of any kind, even microscopic, if properly finished. Polishing plastics does not mean adding anything to the surface, or giving it a coating, but merely removing all scratches and roughnesses —the final "finish" was there all the time, waiting merely to be uncovered.
A final touch on a clean dry wheel with nothing on it frequently adds to the polish, and leaves a surface which will not show finger-marks as a wax-covered surface would.
Comments on finishing-methods using a small electric handgrinder have already made in the chapter on Carving, and hand-polishing with felt-covered sticks is described in Chapter Two. How to Make a Tumbling Barrel
Two classes of amateur craftsmen or small home manufacturers want a tumbling-barrel, judging from my correspondence, and their desires are so insistent that even though I disagree with the necessity for such a device in small shops, I am furnishing a compromise design here which is quite simple in construction and inexpensive, yet which will handle a considerable volume of work in a professional manner.
The two classes of craftsmen referred to are the ones who fail to sand or semi-finish their work completely enough, making their buffing unnecessarily difficult and tiresome, or who try to buff carving too deep on a wheel that is too stiff or not powerful enough, and the type of small home manufacturer who feels he can compete with the chain stores if he only had a tumbling-barrel, whereas my advice in another chapter is, not to try to compete with chain-store merchandise, but to go after the quality lines where the profit is greater and you are on an equal footing with the biggest shops in the country, except that you have less expense.
However, here is the design, patterned after professional equipment such as that shown in Plate 2T. In a large professional shop there are usually at least three barrels, one for each of the compounds used, and frequently these are gang-mounted, such as the two shown one above the other in the back of the picture, to save space and facilitate loading. These are usually made of sheet metal, lined with maple 1 1/2" thick, which must be renewed from time to time as the cutting compound wears them away from the inside, and nothing must touch the plastics in the presence of the abrasive which is any harder than the plastics itself.
Reducing this design to its utmost simplicity, one barrel could be used, emptied and carefully wiped out between each operation, but a good compromise would be to make one longer barrel, with two partitions inside, making three sections in all, one for each step.
The barrel itself is a simple construction job, consisting of the two octagonal end-pieces at least 18" across the flats, the two octagonal center divisions, and the covers. The covers must be ripped or shaped to the proper angle to make a tight fit, and the entire job assembled with screws, using plastic wood or some other material between all joints to prevent leakage of the powder, especially around the partitions. The length of the covers should be at least 45 inches. The spindle can run all the way through, but a better and easier assembly is to mount stub spindles on either end, making sure they are strong and straight. Ya." shafting is strong enough, running in conventional shaft-hangers, pillow-blocks, or roller-bearings if you have them to save on power.
Fig. 21. Details of the Tumbling Barrel. Speed required is only 30-35 R.P.M., driving-pnlley dimensions being arranged accordingly.
One panel should be left off during the assembly. The next step is to line one of the end chambers with felt, glued or cemented on; this is to be the final polishing-chamber, where even the wood might scar the material in the presence of abrasives. This felt will need replacing occasionally. The panel left off becomes the door by which the chambers are loaded and unloaded, and can either be made in one piece or three. Three is better, as in that case one chamber at a time can be dumped— otherwise all three will open up at once. In either event, the joints around the door MUST be lined with felt, rubber or weather-stripping, to prevent leakage of abrasive, especially into the polishing-chamber. The door can be hinged, or mounted with the type of clamp shown in the sketch Figure 21. In any event it must be tight and vibration-proof.
The barrel is next mounted on a sort of trestle, high enough from the floor so that the trap-door can be opened up and taken off, and the contents dumped into a tray about 4" larger all around than the door-opening, and covered with a screen having openings a little smaller than the smallest objects that are to be polished in the barrel. Some shops use a double-layer tray, the bottom half having a solid bottom, to catch the pegs and compound, and the upper half having the screen bottom, to catch the articles being polished. This is a very convenient set-up, if you have enough work to require it.
The next problem is the drive. Comparatively little power is required, since the speed is so low. From 30 to 40 R.P.M. is sufficient, as any higher speed would bring in a centrifugal action which would prevent the contents from "tumbling" properly. This speed can be arrived at by a double pulley drive and countershaft, as illustrated in Figure 21, For this size barrel, an eighth horsepower motor provides ample power, and the job could possibly be done with a smaller motor.