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© October  7, 2002 

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Tracer Lathes,
Set up and Uses

by Kap Pullen

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Tracer cutting a diesel horn

Over the years I have operated tracer lathes and found them to be very useful devices. As an apprentice I set up and operated tracer lathes. The shop where  I worked had ten L.& S. lathes in a row set up with Mimic hydraulic tracers. These machines finish machined seal housings for Pratt & Whitney, and GE Jet engines. The tolerances were tight and the materials nasty. That is where tracers earned my respect. The toolmaker made the templates for us operators, and apprentices. Tracer slides are generally set at 45 degrees and can only handle machining  in one “quadrant” at a time. The od could be cut, and a separate operation was required to finish the bore profiles. Separate operations were required for undercuts and features like snap ring grooves. A hundred parts could be cut by changing parts, and engaging the feeds. All shoulder and diameter dimensions were a function of the template and  adjustments on the valve housing.

CNCs multiple tool turrets, allowing roughing, and finishing, and undercutting in one operation, quickly made tracers obsolete

Tracers are somewhat limited to doing one operation at a time. Tracers are timesavers in hobby type work. I briefly had an American Lathe with a tracer later in life. I machined crowned pulleys for the cardboard box industry with this machine. For a year or so I’ve been looking on EBay for a tracer. Many have come and gone. Some too big, too small, too expensive, me too broke etc.. I kept remembering the one I had some years ago, which required a valve rebuild. That cost $750.  I can’t justify that now for hobby work. This Copy Master mechanical tracer appeared recently. The final selling price was $150.  It looked like a box of bolts blocks and slotted links.  The only reason I bid on it, was a blueprint in the description showing how the tracer  is to be setup and operated. As the machine is moved in one axis the spring holds the cutting head  (set at 45 degrees into the cut) against the template. When cutting, the cutting force also pushes the “stylus” against the template. The cutting head is trapped between the work piece, and template, and follows  the template contour, reproducing the shape on the part.

The tracer cutting a diesel horn. The round button on the left side is stationary, and stabilizes the template for the stylus. The stylus is shown against the contoured template side.

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The template holding setup. Two small “V”s mount on the ways holding the template holder. The whole unit is slotted to fit various size lathes. Cuts are taken using the crosslide dial for depth. Lengths must be adjusted with a double nutted ˝-20 threaded bar.

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When a lot of material must be taken off, the template will start at an angle but  must be straight with the ways when you approach finish diameter.  If the template is angled the cut will be distorted because the angle of the template  will change as the carriage progresses along the ways.

I set the tool at the finish diameter, with the stylus on the finish area of the template, and adjust the template holder so the template is straight in line with the ways.  

My templates are laid out, sawed, and sanded to shape. Proper templates should be  made of 1/8 inch steel but I’m using aluminum sheet because my quantities are small. A template can be laid out, rough sawed and sanded in a few minutes. The templates must be the inverse of the actual shape desired.  

For accurate work, the tool radius, and the stylus shape should be the same.  

Obviously I don’t take time to clean chips for photos.  Approaching finish diameter. Template is parallel with ways

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A parting tool is used for cutting undercuts after tracing. The template has an angular ramp to get  over the undercut area.  I usually mount a plunger type q.c. tool post for straight turning.

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Set up on my Machine World 13 X 40 lathe. This lathe has been a workhorse for the last 21years. This view shows the template holder setup.  I haven’t tried between center work. It should be possible using a long template to work around the center.

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The first cuts on the bell. Note the angle of the template. The template will be straight when finishing.

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Finish cuts on the bell od. That’s a good view of the stylus and tool at work.

The bell is drilled and tapped. This hole is to hold the bell in the pot fixture later.


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Home made boring tool adapter. The tool blocks have two mounting holes, and a curved  slot to allow height adjustments for various lathes.  The template is not yet engaged.

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The bell mounted in the pot fixture. Note the tool is upside down, cutting on the backside of the bore.

 This gives better visibility and the template can be setup on the front side.

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The finished bell and horn on a battery industrial “diesel” locomotive.

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The whole kit:

On the right side are the V blocks, above is the clamp bar, left is the spring loaded sliding tool block.

Below are the two slotted setup bars.

The horn template is shown in the top of the box. Note the ramp at the undercut location.

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Possible uses for this kit:

  • Diesel horns

  • Bells

  • Domes

  • Smokebox fronts

  • Marker light bodies

  • Wheel contours

  • Headlight Reflectors

  • Fittings

  • Lids

  • Smokestacks

  • Cylinder covers

  • Axle contours

  • Cannons and gun barrels.

Author: Kap Pullen




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