In May of 2006 I thought it might be fun to try and build, rather than buy, a turntable. The concept was as follows; Triangular plinth to accommodate 3 arms, each designed along different mechanical principles. Suspension, Pointed rather than sprung, with mechanical grounding of all components via large brass tiptoes. A platter using vacuum hold down rather than a center weight and ring clamp. Belt drive via 3 multi motor pods. Use of an epoxy/ lead matrix, where ever possible, to help dampen resonances. Implementation of an anti vibration device such as produced by Halcyonics, Vibraplane or Minus K Technologies. Last of all, build a dedicated, welded, tubular steel stand that would be filled with a lead shot / elastomeric material to reduce resonances. This stand would house the table, 3 electronic motor speed controllers, 3 phono head amps for 3 moving coil cartridges, and a high quality stereo pre amp to act as a switching device among the 3 cartridges. The pre amp would need balanced outputs so that I could locate the table anywhere within the listening room. The table is about 2 months from completion. The above photo, taken just before Christmas, shows most, but not all the design elements in place. This photo essay, along with brief descriptions of each step, may be of interest to anyone who ever deliberated the merits of the various table designs out there before making a final choice.
Since the triangular pedestal is the heart of the table, a pattern will be required in order to laminate the fiberglass mold into which the epoxy matrix will be poured. Shown is the MDF sheets being glued together from which the pattern will be fabricated. The dimensional stability and easy machinability of MDF makes this the material of choice. Note the table bearing well machined into the top 3 layers of MDF prior to gluing up step. The well side walls are tapered with a 3 % angle in order to facilitate demolding of the final part from the fiberglass mold.
The pattern shown includes 3
The accurate final assembly of the pods to the center pattern is accomplished by using biscuit joints and polyurethane glue. The black panels shown are the surfaces that have been laminated with slate textured, high pressure laminate.The remaining surfaces will be high gloss black. The contrast will not only be more attractive, but offer a more dimensional surface on which to mount the arms and levelers
Assembly of the 4 pattern pieces requires tight, accurate clamping. The irregular shape means typical clamps may not fit the bill. A band clamp on the bottom and pinch dogs on the top keep the parts from shifting when the pressure is applied.
- DIY MK 1 Pattern Coating Applied
After the clamps are removed, a decorative chamfer is machined around the top perimeter of the pattern. After the slate surfaces are masked, the pattern is sprayed with a polyester pattern coating. When the coating cures, the pattern can be sanded and polished prior to the production of the fiberglass mold.
- DIY MK 1 Lets Start Building A Mold
The finished pattern is mounted to a mold plate, prepared with multiple coats of mold release wax, then sprayed with a poly vinyl alcohol film forming barrier coat. The dry PVA film can be compared to sheet of saran wrap that will prevent any bond between the pattern an the mold surface about to be applied over the pattern.
- DIY MK 1 Surface Coat Applied First
Shown is the application of the metal filled surface being sprayed over the pattern. The surface coat will generate a mirror of surface of the pattern that will become the performance surface of the production mold. This surface coat is a 2 part, catalyzed material, as compared to an air dry, solvent based paint. Once cured, it will be impervious to the chemical attack generated when the final production pedestal is cast.
- DIY MK 1 Fiberglass Comes Next
Laminating fiberglass re-enforcemint will add strength and bulk to the thin layer of surface coat that has been sprayed over the pattern. Multiple layers, that add up to 1/4 inch in thickness, will be required before we can proceed to the next step. The dark areas around the corners and edges come from the paste made from ground glass, calcium carbonate and cotton flock that was brushed on prior to the first layer of fiberglass. It will eliminate any small air pockets that may result from the difficulty in getting stiff glass fibers to conform to sharp inside and outside corners.
- DIY MK 1 Rigidize The Laminate
Even though a 1'4 inch laminate of fiberglass has a great degree of strength, it must have a substrate of some thickness to maintain rigidity and dimensional stability. Panels of MDF are bonded to the flat surfaces in order to accomplish the desired result. Another layer of fiberglass will go over the MDF panels to effect a sandwich type of construction that will guarantee dimensional stability for years to come. A box will then be bonded to the back of the laminate to facilitate easy handling.
It's time to demold the pattern from the fiberglass mold. Shown at the top of the picture is the light gray pattern, with the darker gray fiberglass mold in the lower part of the picture.
- DIY MK 1 Making The Plinth
A few days later the mold has been sanded, polished and waxed. It's now ready to produce a final part. It will take some engineering to determine the size and shape of the aluminum plinth, along with the arm boards needed to accommodate the various tone arms and leveling vials. Because of these factors, it would be a good idea to laminate a trial horse off the mold to be used for experimentation. This photo shows the trial lamination, in black at the right, being demolded from the production mold,at the left, in light gray. This part is just a 1/4 inch thick fiberglass shell without any additional re-enforcement.
Trimming out a fiberglass part is never a fun job, but it doesn't take that long and it only itches for a little while.
- DIY MK 1 The Finished Plinth
With 2000 grit sandpaper and a little polishing , and it's as shiny as new money.
A mock up of the aluminum plinth plate, done in MDF makes it easy and inexpensive to work out the details before machining it in Aluminum.
- DIY MK 1 Plinth Plate Mock Up
Angles and measurements are accurately transferred to the MDF pattern, then cut to size.
With the vacuum platter on top, and the plinth plate on the bottom, things are taking shape. A few changes are made on the thickness and overall dimensions of the plinth plate, in order to maintain good proportions, and it's time for the next step.
Tip toes are mocked up in steel. Final parts to be in brass, but a thinner jam nut in brass is a must.
A Dynavector DV 507 MK II is shown ,sans head shell and counter weight, positioned on the first of three pods that each will accept a different type of tone arm.
The Kuzma Air Line, to be mounted at the rear of the pedestal, will make an impressive contribution, not only to the performance but to the overall looks of the project.
My intention in choosing arms was to utilize 3 very different arm types.The Tri Plainer Mk VII, mounted on the third pod of the table, will complement the other 2 choices.
The drive unit of choice is the VPI HRX twin motor drive. Utilizing a 15 lb stainless steel flywheel, the added mass will go a long way to maximize the speed stability of the table.
- VPI Industries SDS Controller
The VPI SDS electronic controller was the natural choice for the HRX motor drive. 3 separate SDS controllers will power the 3 HRX motor drive units powering the platter.
- DIY MK 1 Final Dimension Check
Shown is the pedestal with the plinth, platter and all 3 arms positioned correctly with respect to
The dimensions and angles of the mdf mock up of the plinth plate are transferred to a CNC machining center where the a 1- 1/2 inch thick aluminum slab is cut to the same dimensions, and the 1-1/2 fine threads are tapped to accept the tip toes.
A 3/4 inch thick aluminum arm board will be used to mount the various arms to the top of the pedestal. Note the inset vial level that will be used to continuously monitor the levelness of the table. A mock up tells me if my dimensions are correct before I proceed in aluminum.
- DIY MK 1 Aluminum Arm Board
The arm boards have been cut from 3/4 inch aluminum and the underside cored out removing almost 50 % of the aluminum. This cored area will then be filled in with a lead shot/ urethane elastomeric matrix that will dampen the resonance that might occur in a solid aluminum arm board.
- DIY MK 1 Final Machining- Arm Board
Additional machining on the top side includes a hole to access the top of the tip toe. Here a long T handle allen wrench can be inserted, fitting into the top of the tip toe, for easy adjustment of the pedestal height.
- DIY MK 1 Arm Boards, Final Location
Accurate location of the 4 mounting holes for the arm boards in the top of the plinth are laid out, along with the other holes for the arm cables, tip toe adjustment holes etc.
- DIY MK 1 Secondary Fittings Installed
Aluminum bars to accept the 10-32 threads for mounting of the arm boards , along with various pvc fittings to act as conduits for arm cables and tip toe adjustment, are epoxied in place.
- DIY MK 1 Aluminum Motor Bases
2 inch thick aluminum billet has been machined out to act as a bases for each of the 3 drive units. The drive units will be firmly bolted to these bases with a thin sheet of Isodamp in between for good contact. The chamfered edge has been maintained for continuity of the overall appearance of the unit.
- DIY MK 1 Motor Bases- Underside
As with the aluminum arm boards, the underside of the motor bases has been heavily cored out. This will then be filled with the same lead/ elastomeric matrix as used in the arm board. 3 holes are visible for the 1-1/2 dia threaded tip toes that will level and mechanically ground each motor drive unit.
- DIY MK 1 Threads And Holes
Threads for mounting the arm boards are tapped into the pedestal prior to it being filled with an epoxy / lead matrix. The holes for the signal cables and tip toe access are also drilled.
- DIY MK 1 Final Plinth Polishing
Final 2000 grit sanding and polishing of the plinth is done now. The next step will be to cast approximately 240 lbs of lead and epoxy fill into the underside. After that step it will be too heavy to handle for anything other than the final mounting on the aluminum plinth.
