DIY Slanted Cabbing Lap for Under $200

Commercial lapidary equipment is expensive, but with a little resourcefulness and tinkering, I made a DIY slanted cabbing lap that turned out awesomely.

Why I Built A Home-Brew Lapidary Wheel

My partner Jenna is a hiking and rock-finding badass, and for years she’s been amassing hundreds of rocks, minerals, and gemstones from all over the world. Sadly, like most normal people she’s never been able to afford the INSANELY EXPENSIVE lapidary equipment that would allow her collection to really shine.

We’ve looked together into buying used equipment, but even the second-hand gear (at least here in Seattle, WA) is crazy expensive. Considering the machinery is fundamentally basic—a motor, a power controller, some diamonds and a water circuit—I was pretty confident I could build one.

I found very few resources online for building a DIY lapidary / cabbing grinder, so I mostly made this project up as I went along. At each step, I tried to design for modularity, servicability, and low costs.

My brainstorm started with the idea of using a standard flat 9″ cake pan, but this quickly morphed into using a 10″ tube cake pan because of the center stem.

Once I had the idea of using a tube cake pan, the rest of the pieces all seemed to fall into place. My initial plan looked something like this:

Wooden Base

The base of the unit is made of 3/4″ MDF scrap that I had leftover from another project. All I knew was that I wanted the motor held at 45-degrees, so I cut a base, added some wedges, and started there. I then stapled a few other scraps to the base plate to create a holding surface for the wheel pan and water nozzle.


Before I gave the wood a rough paint job, I test fit the major pieces. Shown below are my first (and later rejected) concepts for the wheel pan and water tube. Both were later replaced with more refined iterations.

Once I ensured the major bits fit, I gave the MDF wood two coats of “high solids” enamel paint. I didn’t sand the MDF prior to or between coats, and instead relied on a heavy-handed spray (times two coats) to seal up the pores of the MDF. Because this is a work tool, I’m not highly concerned about aesthetic looks—just durability & functionality.

Wheel Pan

Preparing The Tube Pan

Using an angle grinder, I quickly cut the aluminum tube pan neck to length, about 2.25″. Because I was wingin’ the design, I didn’t get the first tube pan right and had to make a more refined second edition. The first one (silver) wasn’t watertight, and had holes in the wrong places.

I used caulk and flexible adhesive to join and seal the two parts of the pan. Using silicone tubing sliced down its centerline, I added a bumper for the sharp edges of the pan stem.

Flex-Sealing The WHOLE Thing

This was my first time using a sprayable flexible rubber sealant and I’ve learned that for all things water, flex-seal is the answer. This stuff is amazing and I can’t believe what a good job it did filling all the gaps. It provides a durable, waterproof surface for the wheel pan, and might be the sturdiest part of the whole contraption.

Splash Guard

A splash guard wasn’t part of my initial plan, but I quickly learned that 1750 RPM throws water EVERYWHERE. I was able to use some 20mil PVC sheeting (from the local fabric store) and rare earth magnets to create a flexible “collar” for the wheel pan.

This solution does a great job containing the mist, but a great future upgrade would be to 3D print a hard, more easily removable, cleanable, & replaceable collar.

Electronics

Forming The Switchplate

The switchplate was formed out of a scrap sheet of KSM .018″ stainless steel. It was easy enough to cut with large snips, and drilled well on my drill press.

I roughly placed the electronics, marked their diameters, and drilled holes accordingly. Using clamps and scrap wood, I made a DIY press brake to bend a 90-degree knee in the sheet.

Wiring Up Components

The machine is wired with 16AWG hookup wire, and all metal components are grounded to a 1/4-20 threaded insert & screw to provide a GFCI-protected common ground to ALL of the energized and metal parts.

WARNING

Electricity is hazardous and this project requires expertise. Know your limits—don’t be a dummy.

The 3-position terminal block holds AC-NEUTRAL / AC-HOT-VARIABLE / AC-HOT-SWITCHED and allows variable control of the motor and switched control of the water pump. Feeding the water pump, I cannibalized a spare wall wart adapter that I had laying around. This allows the pump to be easily replaced when it inevitably fails due to grist in the impeller.

Shown below, you can see the common grounding lug and basic wire path from mains > into toggle switch > into variable speed control > into neon indicator lamp > out to motor and pump.

The GFCI plug is the MVP of this project, and the ONLY reason I feel okay tinkering with water and 120 VAC in the same project. Especially considering that my partner Jenna will be its primary user, I want to make this device as safe as I possibly can.

In the event water comes in contact with any electricity, this device will instantly interrupt power and prevent harm.

Finished Photos

First Cuts

The instant I presented the wheel to Jenna, she wanted to grind things, so we raided one of my rock stashes and found a few different stones to test.

We used 5-minute epoxy and dowels for this first try, but down the road she intends to use dopping wax. Only time will tell which one proves more optimal.

It works—it works! I’m totally thrilled the machine works! Not only would it have been a pretty lame gift if the machine didn’t produce results, but it worked faster, more effectively, and with less mess/splashing/dust than I was expecting.

Cost Breakdown

Wood Base & Wheel Pan

ITEM COST SOURCE/NOTES
3/4″ MDF Wood <$5 I used scrap, probably less than 3sf (.28m²)
1/4-20 T-Nuts (x4) 50¢
1/4-20 Screw Feet (x4) $3 I used felt feet, but next time I’d choose rubber.
1/4-20 Threaded Inserts (x7) $2 (4) for motor (2) for wheel pan, (1) grounding lug.
1/4-20 Threaded Stud Knob (x6) $7 (4) for motor (2) for wheel pan.
Tube Cake Pan, Used $3 Purchased from Goodwill
$20.50 Minus Time & Tools

Key Tools 10″ Bosch jobsite table saw ($350), Bostich Pneumatic Fastener Kit ($200), WEN Benchtop drill press ($120), wood glue.

Electrical

ITEM COST SOURCE/NOTES
1/2HP Induction Motor Salvaged Recovered from a dead Harbor Freight bench sander.
GFCI Plug $14 Super sturdy plastic & solid gaskets.
Recirculating Water Pump $8
Silicone Tubing $1.50 I used less than 2′ of the 16 on this roll.
Articulating Nozzle $5
Barrier Strip, 3 Position $1.50
120V Neon Indicator Light $2
2000W Motor Speed Control $5
20A Toggle Switch $2.50
$44.50 (plus a surplus motor)

Grinding Components

ITEM COST SOURCE/NOTES
Threaded Arbor, 1/2-20 $9 This one fits 1/2″ and 5/8″ shafts.
8″x1/2″ Master Lap, Aluminum $37 Adds a valuable amount of mass & momentum.
100 Grit Diamond Wheel, 8″ $18
320 Grit Diamond Wheel, 8″ $16
600 Grit Diamond Wheel, 8″ $15
1000 Grit Diamond Wheel, 8″ $15
$95 $160 Project Total

Full Disclosure This page links to products I’ve bought at full price & use myself. Buying from a link on this page earns me a few pennies to help pay for my cheap-and-completely-okay web hosting.


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