Finishing a Ring Casting
|This is a 14-karat palladium white gold rough ring casting. It has been cast, pickled, rinsed and magnetic pin finished. The ring has a rough surface. Here are the bench top equipment, materials and procedures I used to expedite this finishing job: |
| ||This image shows: |
- An expandable rubber mandrel designed to hold 1/2 x 1 inch abrasive drums with a 1/4 inch shaft.
- A collet holder designed to hold a variety of collet sizes in order to accommodate a variety of mandrel shaft sizes. For this project, I use a 1/4 inch collet to hold the mandrel (A). Foredom’s part number is CHA-5.
- A 1/2X1 inch 3M Diamond Flex abrasive drum. These diamond abrasive drums come in 5 abrasive grades ranging from 60 to 800 grit.
- A 1/2X1 inch 3M Ceramic Purple abrasive drum. These ceramic abrasive drums come in 4 abrasive grades ranging from 60 to 220 grits.
- A 1/2X1 inch 3M Trizact abrasive drum. These abrasive drums come in 5 abrasive grades ranging from 220 to 2500 grits.
| ||I removed the right tapered spindle and replaced it with the CHA-5 collet holder (B). I’ve mounted the expandable rubber 1/2 by 1 inch abrasive drum holder. Here I’m placing a 220 grit 3M Trizact band on the mandrel. After putting it in place, I hold the knurled side with one hand and screw the rubber portion with my other hand. This expands the rubber portion and secures the drum to the mandrel. |
| ||With the assembly ready, I begin sanding the inside of the ring. I use each of the grits to produce a dead flat smooth surface inside the ring. Notice the sorting tray I use for my 1 inch abrasive bands. Each of the grits are identified and clearly marked, making it quick and easy to change from one to another. |
| ||For the final step prior to rouge polishing inside the ring, I insert a 3mm collet into the collet holder and then mount a 1/2X1 inch rubberized silicone drum. These mandrels are also available in 1/8 inch size and would be used with a 1/8 inch collet. |
| ||With the silicone drum mounted on the bench lathe, I adjust the motor to a medium/full speed and quickly complete the pre-polishing work. |
| ||I use the 3M FX Polishing wheels on the flat and semi-rounded surfaces on the outside portion of the ring shank. The FX wheels can be grooved or shaped for repetitive work on like pieces with rounded shapes. I have found a slow to medium speed and minimal pressure between the work piece and wheel produces best results. FX wheels come in 5 abrasive grades ranging from 240 to 3000 grit. Water can be used on pieces being worked by the FX wheels to reduce heating if necessary. They generate minimal waste. I use each abrasive grade wheel on each project, starting with the one that is appropriate and progressing to the finest wheel. I use these wheels for most everything, including repair work. |
| ||For the recessed contoured portions of the ring, I use the series of 3 inch 3M Radial Bristle Discs. This step shows the last step prior to rouge polishing. |
| ||I polished the ring using Foredom’s Platinum Blue and White compounds. The white compound is 8000 grit and produces a super color and luster. |
| ||Using the Foredom BL Lathe directly on my bench top, I pre-finish an assortment of 14-karat yellow gold pendant and earring rough castings. Two of the pendants have flat surfaces. I remove the tapered spindle from the bench top motor from the right side and install the collet holder (Foredom part No. CHA-5). Next I insert a 3" disc mandrel (Foredom part No. M34). I use both the 3 and 2" disc mandrels for a variety of applications and abrasive materials. The red arrow indicates the 2" disc mandrel (Foredom part number M33). Both mandrels have 1/4" shanks. They are designed to be used with abrasive discs that have PSA (pressure sensitive adhesive) backing. |
| ||I have installed a 3M Ceramic Purple Coated abrasive disc. These discs are available in 60, 80, 120 and 220 grit and are aggressive to moderately aggressive. I am using the 80 grit disc to remove the remainder of the gate from the cast piece prior to sanding the bottoms. (A kit of ceramic purple sanding discs contains a disc of each grit in the system. It is Foredom part No. 5690 or they can be ordered separately.) |
| ||3M Ceramic Purple Coated abrasives come in discs and bands of varying sizes. They are made of 3M’s patented Cubitron [trademark symbol] ceramic aluminum oxide mineral that sharpens itself with use. As grinding wears the grain, it fractures along the micro-cracks creating new cutting edges. I have found these ceramic coated abrasives to last longer than traditional aluminum oxide abrasives and their sustained cutting ability provides faster stock removal with less heat and loading. I use both the discs and bands. |
| ||The PSA backing on the reverse side of the grit disc has prolonged holding capability. This is an advantage for removal and replacement of these discs through a progressive pre-finishing process. When I remove abrasive discs, I replace the original protective backing on the disc for storage. In this image, I removed the final ceramic purple abrasive disc and I’m placing a 3M Diamond Polishing disc on the disc mandrel. |
| ||The 3M Diamond Polishing Cloth disc’s come in 7 abrasive grits ranging from 220 (coarse) to 50,000 (extra fine). These diamond polishing discs are ideal for very fine finishing and are available individually. Other discs available from Foredom that work exceptionally well with the BL Lathe are 3M’s Flexible Diamond discs and Trizact disc products. All the products are available in 1, 2 and 3 ” diameters. |
| ||The next step in the pre-finishing of these earrings and pendants is to remove wax mold parting lines. For that, I’m using Foredom’s MetalMaster [trademark symbol] rubberized abrasive polishing wheels and rods. The wheels are 7/8" x 1/8" thick and the rods are 1/4" x 7/8" and both can be shaped according to the job-at-hand. I use multiple Foredom Rotating Bur Holders (Foredom part No. 10081) to sort and organize a variety of pre-finishing and polishing accessories. |
| ||MetalMaster wheels and rods are superior rubber bonded abrasives. They hold their shape better and last longer than other rubber bonded abrasives. MetalMaster accessories are available in 3 color coded grits; brown (coarse 120 grit), black (medium 180 girt) and green (fine 220 grit). They are available in 3 different kits (Foredom part Nos. AK710, AK700 or AK713). I use these wheels and rods with my Foredom Series SR flexshaft and No. 20 quick change handpiece. They are ideal wheels to use prior to Foredom’s CW Series Ceramic Impregnated Polishing Wheels. |
| ||With the bottom surfaces pre-finished and the parting lines removed, I use 3M’s Radial Bristle Disc system prior to final polishing. They are ideal for these castings because they reach areas that rubberized abrasives and polishing wheels would have difficulty accessing in a timely manner. |
| ||I remove the tapered spindle from the left side and the collet holder from the right side and install Foredom Wheel Mandrel’s (Foredom part Nos. WM-5 and WM-6). The wheel mandrels hold abrasive wheels (up to 3" in diameter), sanding drums, brushes and other accessories with 1/4" mounting holes. Shown in this image is a 3M EXL Unitized Wheel mounted on the left side and I’m mounting a 1 1/2" grinding wheel on the right side. |
| ||To install the wheel mandrel, the spindle is removed by loosening 2 allen screws and pulling it off. The wheel mandrel is put on the motor shaft and the 2 allen screws are tightened. The 5/16" shaft from the motor has a flat portion that the allen screws are lined up with prior to tightening. I regularly change between the tapered spindles, collet holder and wheel mandrel and find changing to be quick, easy and secure. |
| ||I set the BL Lathe to a medium speed using the variable speed dial and I remove most of the remaining portion of the gate that wasn’t cut after casting on this wedding set using the small grinding wheel. |
| ||Next I use 3M Scotch-Brite EXL Unitized Wheels to remove the remainder of the gate and to partially blend it into the shank. EXL wheels come in 3 diameters, 3 thicknesses and have 3 different arbor holes. They are available in soft to hard densities, and are made from aluminum oxide or silicon carbide in coarse, medium and fine grits. They work well for decorative finishing, cleaning and conditioning, pre-finishing (as shown), oxide removal, deburring, blending and polishing. |
| ||The BL Lathe also serves as a bench top buffing and polishing motor. Since this process generates significant waste and debris, I use the Foredom Dust Hood (Foredom part No. DCH-1). The hood has a dust collector attachment on the back and can be used with or without a dust collecting unit. The hood can be used at the bench to catch general debris or with a light duty dust collection system attached – like a standard shop vacuum. Shown in this image, I’m using an inside ring mandrel and Foredom’s platinum white compound (Foredom part No. 4006) to bring out the final luster on a palladium and diamond ring. The compound is 8000 grit and is fantastic for all precious metals, especially palladium and platinum. |
| ||I prefer doing regular buffing and polishing away from my bench top and with a heavy duty dust collection system. Using PVC pipe and fittings purchased at a hardware store, I made a dust collection system that would hold and draw significantly from 2 hoods. I hooked it to a heavy duty dust collection unit. Shown are a variety of buffing and polishing supplies available from Foredom. |