How to Engine Turn | CRATEX Abrasives

How to Engine Turn Aluminum with CRATEX stick

@_craftyb_ Kirk Brown owner of Crafty B Nostalgic Speed, builder of the worlds coolest gas caps.

This chapter is going to deliver some Engine Turning 101 – main steps to follow and some basic instructions and points you should consider. You’re going to need: a metal sheet, pencil and a ruler, CRATEX abrasive rods, drill press and some protective gear.

Step 1: Safety first

One of the first and most important things to remember is to always wear eye protection and never permit anyone to view the operation without the proper eye protection. Since you’re going to be working with a drill press, it is a good idea to protect your hands with from sharp metal edges with safety gloves. Be careful particularly when using tools abrasive pads on steel as powdered metal will get blown directly into your face. Unless you want to spend days blowing gray from your nose into tissues, we suggest you wear a mask.

Step 2: Clean and polish surface

After you get geared up, you’ll need to clean the work surface. The surface needs to be completely clean, polished and flat. The best results will be obtained if engine turning is conducted on a flat piece of metal, so in case you need to work on a curved piece, make sure to flatten it for applying decoration and then simply reshape it after you’re done.

Depending on the project, you’ll need to mill or grind the surface off first, or just use a sand paper or hand rotary tool with fine abrasives to smooth down the surface and remove any imperfections that would show through engine turning and ruin the finish. It is a misconception that the patterns will hide all irregularities on the surface of your project, and make sure you don’t use a file or coarse sanding paper to polish the surface, because those could leave deeper scratches which will also show through the swirl and will ruin the design. Important lesson here is: the smoother the surface, the better the engine turning pattern will look.

You can clean the surface with alcohol after you’re done to remove any fragments occurred during the process.

Step 3: Mark out lines

The next step would be to mark out the lines for engine turning (some even use digital readouts and spreadsheets of X and Y positions for supreme accuracy). First, you should measure the width of your piece and draw lines to guide you through the process. You can start with the center line drawn with the help of a 90-degree ruler. Next, you’ll measure the rubber abrasive diameter and determine the degree of overlaps. Now grab a ruler and start drawing lines parallel to the center line based on the determined overlap spacings (you can mark the spacings with small hash lines both horizontally and vertically). In the end, you should get a net with identical square fields and the rod should be pressed down on each cross.   

You can also use a tape or a lead pencil, just make sure you never use a permanent marker or sharp objects to scribe the working surface for guidance.

Step 4: Chuck rubber abrasive stick to the drill press

CRATEX sticks should be cut into 1-1/2 to 2” parts and placed into the drill press chuck with about 1” part or less exposed as it will provide the best precision. The longer the exposed part, the greater the chance of developing a wiping type action that will result in larger spins, but the longer piece tends to flex more easily and that way you’ll lose accuracy.

Always be careful not to over tighten the abrasive stick after placing it in the rotating device as it will eventually snap off if tighten too tightly. The best rotating speed is between 900 and 1400 rpm, but it’s best to start slower and then adjust the speed as you’re getting the hang of it.

Important safety tip: Always make sure that your drill press is securely attached to a flat, stable surface.

Step 5: Apply drill press against the surface

After completing the machine preparation, the next step would be to execute initial testing on a scrap piece of metal until the desired spin depth is achieved. You should also experiment with the lapping compound on a scrap metal first before using it on real workpiece.

To determine the spin depth also means to determine the desired cycle time or the time the rotating abrasive stick is supposed to be pressed down on the surface and the pressure. After a few tries, the same pressure and pressure time should be applied during every cycle. Pressure should be light as strong pressure will cause the end of the abrasive stick to roll out to mushroom and cause inconsistent patters sizes. Some use digital scale, which reliefs you from worrying about the pressure, while you’ll still need to be focused on the contact point each time you’re about to apply pressure.

Precision is not that important here, especially when starting out, but uniformity of spacing is crucial. Consistency is what will contribute to the professional look of the design. Correct pressure will prevent you from destroying your piece of work, so give yourself some time. Note that a very light pressure is needed when using CRATEX rods on a drill press, and the slower the speed, the less compound you get flying all over the place.

Typically, the overlap of the swirly decoration is done by half the diameter of the abrasive, but that is now a strict rule – so 1/2, 1/3 or 1/4 the size of the swirl – it’s up to you. The circles can overlap more or less and can be pressed in straight lines or at an angle. Some machinists have their own way of pressing the decorations, which eventually becomes their signature. Moreover, many old-school craftsmen prefer working on a drill press, as their goal is to achieve a more hand-made look and a less CNC look and despite drill-press work being a lot more physically intense, especially when you’re working on larger pieces, like firewalls.

After you’re done, apply a clear coat to strengthen the abrasion resistance.

Tips (maintenance)

From time to time CRATEX abrasive stick may become embedded with metal particles and will need to be dressed back to expose fresh abrasive. Standard CRATEX dressing block or a fine grit sand paper can be used for this purpose, just make sure very light pressure is applied for a few seconds against the dressing material.