Modification of Carl Professional Rotary Trimmer to improve operator interface


Requested Project

A Carl Professional Rotary Trimmer, Model RT0200, has been used by Hills and Dales to cut labels to size.  This trimmer requires the operator to slide the rotary blade assembly along a rail while exerting enough downward force to overcome springs to lower the blade and clamp the paper.  Most clients are not able to consistently apply the force necessary to cleanly cut the labels.  A modification is desired that will make it easier to achieve good cuts without the degree of downward pressure that is currently required.

Design Notes

Modification of Carl Professional Rotary Trimmer, Model RT0200

The rotary trimmer has a two stage spring arrangement associated with the cutter head.  Weak springs support a cutter guide/paper clamp off of the platen so paper can be inserted beneath the blade assembly.  The cutter assembly is also spring loaded with a stronger spring that also keeps the cutter blade off of the work surface until it is needed.  In use, the operator presses down on the blade assembly, first causing the paper clamp to lower and pin the paper in place.  Further force then lowers the cutting blade to engage the work.  Successful operation requires consistent pressure on a palm grip on the cutter head while the blade assembly is pushed along the line of the cut.  This modification is intended to eliminate the need for the operator to apply downward pressure while moving the cutter head.

Some repairs were also required on the assembly as received. The sliding cutter bar is held in place by small plastic tabs at each end.  Both tabs were broken on one end and one on the other.  These tabs were replaced by a small metal bracket secured by the end-cap mounting screws.

The modification provides a linear cam followed by a roller mounted to the blade assembly.  As the blade is drawn across the work, the cam forces the blade downward into the work.  Consequently, the operator only has to push or pull on the sliding cutter to make the cut, no downward pressure is necessary.

For the following sections, please refer to the included pictures to assist in visualizing the fabrication and assembly process.

The linear cam is fabricated from extruded  ?? square aluminum tube.  The overall length of the cam is 17 1/8?.  The height of the square tube is reduce to 7/16? for a 2? long section at each end.  Then over a 1 ?? length the cam is tapered up to its full depth of ??.  The profiles at each end are accomplished by leaving the top and bottom surfaces of the tube intact while removing material at the sides to make the desired shape.  A band saw works well to make these cuts.  The lower edge of each end of the cam is then bent to conform to the side contour noted above and aluminum brazing material is used to seal the joint.  Avoid excessive material buildup on the sides as a nylon slider contacts the sides of the cam.

The rotary cutter as obtained from Hills & Dales had been mounted on a piece of Plexiglas about 18? square.  The extension of this panel beyond the ends of the rotary trimmer provide an area to place posts which support the cam at each end.  The posts are fabricated from 7/8? dowels and each post is 3 5/16? long.  The posts are center drilled to accept mounting screws from the bottom and screws to hold the cam on top.  The cam is then mounted to the posts with 1 ?? round head brass wood screws having an unthreaded section beneath the head of about 5/8? long.  A tapered spring, of a type used in Delta faucet repair kits is place under each screw head so the cam can move slightly up and down as the pressure on the cam changes.

The operator handle and roller follower for the cam is fabricated from plastic pipe parts.  Two 1? Tees, a short section of 1? plastic pipe and a 4? to 3? reducing coupling are required.

The original palm grip provided on the rotary trimmer is attached to the blade and carrier assembly where the mounting surface is a section of a circle of 3 ? ? in diameter.  A section cut from the 3? end of the reducing coupling above duplicates the required radius to match up to the blade and carrier assembly.  Make the width of this section equal to the width of the carrier assembly. It is mounted to the carrier assembly in the same way as the original palm grip and with the original screws.  Holes must be drilled in the curved section of the plumbing pipe to accept these self tapping screws.

Orient one of the 1? Tees  so that the straight-through section of the Tee is aligned to the direction of travel of the carrier assembly.  Using a band saw, cut a radius into this Tee such that it matches the outer radius of the section cut from the reducing coupling.  After checking and adjusting the fit, use plastic pipe joint cement to bond the Tee to the curved base that was cut from the reducing coupling.  Clamp while drying.  

Cut a short section of 1? plastic pipe so that when inserted between the base sections of the two Tees the Tees come together without any of the joining pipe showing.  With the Tee that forms the new operator handle oriented perpendicular to the direction of motion of the cutter assembly, bond the two Tees and the short section of pipe together.  Use plastic pipe cleaner prior to applying the bonding material.  When this bond has dried, cut out a rectangular section about 1? wide and 1 ?? high that will allow the linear cam to pass through the stem of the operator handle (see picture).  Finally, mount the cam roller between the sides of the handle such that the top of the roller is  about ?? above the bottom of the rectangular cutout.

The roller used was a plastic roller, 5/8? wide and 5/8? diameter obtained from a cupboard door latch.  It accepts a 1?8? diameter axle.   Drill holes through the sides of the operator handle to hold this axle.  Shim on either side of the roller so it runs in the center of the cutout section.

Approximately ? ? above the roller axle, drill and tap a hole on both sides of the operator handle to accept a ??X20 nylon bolt.  These bolts ride on the sides of the cam to stabilize the lateral motion of the operator handle and prevent tilting of the handle when the cutter wheel is under pressure.

Mount this operator handle on the cutter wheel carrier as described above.  Please note that the center of the radius of the mounting surface is offset from the center of the carrier and position the mounting holes such that the operator handle is vertical after mounting.  This means that the center of the operator handle is offset from the center of the carrier by the same amount that the radius of the mounting surface is offset from the center of the carrier.

The cutting wheel is in contact with the work over about a 9 ?? length before the cam releases pressure on either end.  Mount guides for 8 ?? paper on the cutter platen such that the paper is included within this 9 ?? operating area.

Assemble the unit, adjust the nylon bolts to center the operator handle about the cam and adjust spring tension at each end of the cam for satisfactory cutting and acceptable operator effort.

RCRV designer is Russell Schuchmann, and was requested by Hills and Dales, James Klossner, Vocational Cordinator. The project was begun Dec 16, 2003 and completed Dec 17, 2003.

              


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