Homemade Faceting Machine

Introduction

Building your own faceting machine is a challenge but it can be done. You need to be able to make parts using a lathe and milling machine. I used a table top Sherline lathe with a milling attachment. With a light touch and care I was able to deal with some very large chunks of metal. Most of the parts and materials were sourced from surplus stores and e-bay. Tools and other parts were purchased from Enco (not in business anymore) and McMaster-Carr.

This write-up is meant to be a documentation of how my machine went together and not a step by step set of instructions,  instead it is more of a guide.  A lot of the dimensions of things were the result of what I could scrounge and adapt to the project.

 

The Mast Assembly

The mast is 1” diameter by 12” long. This must be a piece of precision ground stainless steel.  The mast base is 1/2” thick aluminum which I lightly machined on the bottom and where the mast seated to insure that the base was perfectly flat and parallel (this might have been over-kill). The mast is attached to the base with a countersunk 5/16” stainless machine screw.  It is critical that the end of the shaft be turned and bored to be exactly 90 degrees to the length of the shaft. For the final assembly after making sure that the mast was at 90 degrees, I put epoxy on the mast end and machine screw to ensure that the joint would be rigid (again maybe overkill but it couldn't hurt). The coarse height adjustment clamp is turned from UHMW plastic or nylon and consists of a 1” thick base, a 5/16” threaded rod with a knob and a top cap.  Use a nylon or plastic pellet at the end of the rod as a pressure pad so that the rod doesn't damage the surface of the mast. There is a thin circular roller thrust bearing between the clamp base and the top cap piece.  

 

The Yoke Assembly

The bearing block of the yoke is milled so that the sides are perfectly parallel and the top and bottom are parallel. Bore a hole to fit a 1” ID linear/radial ball bearing or a linear sleeve bearing.  In a perfect world this would be a pressure fit. I bored it as close as I could get to a pressure fit and then drilled and threaded a 1/4” hole to fit a machine screw in the back of the block to secure the bearing.  The arms of the yoke are made from 1/4” aluminum. When making matching parts like this, I glue them together with super glue (sandwich a piece of thick paper between them to help get them apart) then drill and machine them both at the same time to ensure that they are exactly the same. Heat them with a torch to weaken the glue to separate them. I used 3/8” ID x 1/4” thick bearings for the spindle axles, again bored close to pressure fit and fastened in place with set screws from the bottom. Take care tightening the set screws, if over tightened you can distort and damage the bearings.

 

The Spindle Block Assembly

The spindle block is milled so all the surfaces are trued up. A hole is drilled lengthwise that is slightly larger than 1/2”dia., bore a recess in each end to fit 1/2” ID bearings. Use precision bearings here. I used grade 8 ceramic skate board bearings (e-bay).  Again, set screws to secure if necessary. Cross bore a hole in the block to fit the axles on each side.  The axles are turned from 1/2” brass rod.  Turn them down to 3/8” leaving a flange that will fit between the spindle block and the inside of the yoke arms. The axles are secured with set screws from the bottom. File flat areas on the axles where the set screws are. There is a lot of pressure here so the flats are needed to keep the axles from turning (use thread locker).

 

The Spindle Itself

This is the most critical part of the whole deal. This is the part that drove me to learn machining. On my first machine (an Ultra Tec ) the dop chuck was 1/32” off-center making it impossible to transfer a stone and have a level girdle without massive swings of the cheater. You must use precision ground 1/2” dia. stainless steel. The lathe set-up must be as perfect as you can get it, with the spindle rod spinning perfectly centered. Bore the hole for the dop slightly less than 1/4” and then ream the hole to exactly .25” using a new carbide reamer. I use dops made from precision ground stainless rod. They fit so closely that the dop is like a piston pushing against the air pressure. The dop is attached with a set screw in the collar on the end of the spindle. The collar is held in place with a set screw on the bottom side of the spindle. The dop set screw is threaded in the collar and then passes through a slightly larger hole in the spindle to press against the dop. I use three equally spaced dop set screws to put equal pressure on all sides of the dop (not shown on the photos). This is probably overkill as it doesn't seem to make much difference to dop centering because they already fit so precisely,  but it helps keep the dop from slipping from the torque when cutting large stones. A note about the set screws used; the screws used to hold the dops and the index gears must have a brass tip to prevent the set screws from cutting circles and gouges into them. You can buy these, but I filed the end of the set screw flat and soldered on a piece of brass rod.  Also, the set screws used to adjust the pressure on the threaded adjustment rods and the height adjustment clamp must have a small pellet of nylon or plastic in front of the screw to act as a pressure pad that won't damage the threads or the mast.

The bearing ID and the precision ground spindle should result in a pressure fit. I greased up the spindle rod and tapped the bearings into place. I removed a small amount of metal in the area on the spindle between the bearing locations to make seating the front bearing a little easier. A narrow groove for a retaining ring (e-clip) is turned in front of the front bearing to keep the index gear from being pushed right up against the spindle block. There is a small notch filed at the end of the spindle to align the table adapter.

 

The Index Lever and Cheater Assembly

I used brass for this part because it machines nicely and it can be soldered. I used 1.6 mm brass sheet to fabricated the frame. The side pieces were cut slightly over sized, super glued together and filed to shape. The pieces are soldered together. The axle is 5/6” dia. in the center and threaded to the width of the inside of the frame and then turned down to 1/4” dia. to fit the miniature bearings and threaded on the ends to accept the cheater knob and the end collar. The cheater knob needs to be fastened securely to prevent it from unscrewing in use. I used non-removable thread locker on that end only. The frame is attached in position on the spindle block with 2 cap screws. The critical thing about this assembly is determining the position of the indexing rocker and the index gear. The rocker should be level when engaged on the index gear and be able to pivot up and down from that level position. I used the gear diameter of ultratec gears (from my first machine) to determine this distance.  On a side note,  I disassembled an old HP inkjet printer scrounging for parts and found 2 gears with 96 teeth, a plastic one and a metal one that were the exact diameter of ultratec gears.  I attached them to an aluminum center with a 1/2” bore and glued on a printed and plastic laminated tooth number dial. The free rotation pin assembly threads into the side of the frame. Locate it so that when the index rocker is lifted up the pin can be pushed under the rocker to keep it in the raised position. The pin return spring (from a ball point pen) will push the pin out when the pressure from the rocker is released.

 

The Angle Protractor

I installed an optical encoder which makes a super accurate protractor with a lighted display.  The details for using an encoder can be found in Amateur Gemstone Faceting Volume 2 by Tom Herbst  (www.facetingbook.com,  both vol. 1 & vol. 2 are great books and should be on every facetors bookshelf).  Alternately you can adapt a $25.00 digital protractor. I originally had one installed on my machine (I have included a photo of it for reference) it did the job but it was a little hard to read and calibrate.  My machine is a 'left' hand design so I can't say if there would be problems adapting an inexpensive digital protractor on a right hand machine (the lcd would be upside down).

 

The Machine Base Assembly

The surface of the base needs to be smooth and perfectly flat. I used a slab of 5/8” phenolitic plastic (gariolite). This was kind of pricey but I needed a material that I could saw holes, drill and cut using woodworking tools. I found a suitable arbor for the platen, a 90 volt DC motor and a speed control from a surplus store. The arbor I used was a lawn mower spindle that had a flange with mounting holes. I replaced the spindle shaft with a 1/2” dia. shaft that was long enough to mount the lap platen on one end and a pulley on the other.  I shaped the platen and press fit it on the shaft and then mounted the shaft in the lathe and re-machined the top surface to be at 90 degrees to the shaft with no run-out. The platen arbor needs to be mounted so the platen (and lap) can be calibrated to be perfectly parallel to the base surface. I mounted the platen arbor on a circular piece of 1/4” aluminum with 3 equally spaced threaded holes for upside down bolts that act like feet and 3 equally spaced mounting bolt holes in the disc and through the base. Adjust the feet to calibrate the lap to the base and then lock it down with the three mounting bolts.

The splash pan is made from two plastic buckets from a dollar store that nest inside each other. The buckets have a cut-out to allow for the dop to be horizontal for cutting the stone  girdle. When not in use, the top bucket rotates around and covers the cut-out and blocks the splash. A length of tubing is attached to drain the pan. The inner wall of the pan is another plastic bowl from the dollar store that is fastened with rivets and sealed with goop sealant. The water tank is a plastic kitchen canister.

 

Optional Upper Mast Clamp

When cutting low angle facets with the spindle nearing vertical (5 to 10 degree angles) it is possible to force the faceting head to slide up on the mast if you are heavy handed (like I tend to be). I added a clamp made from uhmw plastic that rides free on the linear bearing most of the time and then clamped as needed when cutting low angle facets.

 

 

Alternate protractor fashioned from a $25 digital protractor.  This works on  a left handed machine.  It must be calibrated to zero degrees with the spindle vertical.

 

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