Fox Bender

Here I show the production of the so-called "Foxbenders", a device for bending massive Gitarrenzargen.

Anyone who has ever built an acoustic guitar knows that it is not one of the simplest operations to bend frames. Normally, the luthier bends over a bending iron the frame free hand. The approximately 2.5 mm thick, is inserted to about 5 minutes in water and bent on the hot bending iron. In order to produce the outer contour exactly the frame is held again on a template. Advantage of this approach is the low cost to you need to start: a bending iron and a mask made of pressboard.

But disadvantage is the low accuracy and the required large Cleverly with the handling on the bending iron. Any unevenness in the wood structure as eg in a maple every few millimeters occurs, a potential breaking point is when the bending pressure, velocity or -Temperature is wrong. The bending of the frames can easily take per frame times 60minutes. Of course, there is also a satisfying job, when you look at the finished frames - but the thrill if firewood or not!

In a simple way you can help with a device here. Originally from the US luthier and repairman Charles Fox has set its "Universal Wood-Bending Machine" a standard which is used both in small series in the workshop as well as companies such as Martin Guitars in special series. The principle is simple: A half of the guitar body is made as a hollow form. One type press takes up this mold. In the interior of the hollow mold bring three bulbs a '200Watt enough heat on to deform plastically the Zargenholz as on a bending iron hand. The wood of the frame is placed to protect against breakage between two 0.5mm thick stainless steel sheets. The plates distribute the one hand, the heat, on the other hand the power of the press. Press I call the device because a, exactly in the waist fitting shoe, applying a trapezoidal screw force on the stainless steel sheet / Zargenholz Sandwich and so presses on the mold. The sandwich can be secured at both ends to the press.

About a timer starting the bending operation (actually baking) with the lights and after a good 15 minute baking time is a frame so far. One waits until the device has cooled completely and finish the frame.

An exact description of the prices (in English catalog) of the bending machine and the following items are found in Luthiers Mercantile International:

designation description Price in US $
PL13 Plan of the Universal Fox Benders 13,00
SPBU Complete kit for the preparation, incl. Lamp socket, screws, springs, etc. 425.00
SPBUM Kit for self without wooden parts and timer 195.00
SPBUP Kit for self only wooden parts 145.00
SPBUCUT Additional for bending Cutaways 418.00

So I bought the plan and in the following I will show the production in few steps. The entire construction process can be divided into the following steps:

Material List

Making Right and left side of the press

Making the feet Benders

Assembling the exterior parts and wiring the electrical system

The production of the hollow mold

The acme screw

Preparation of the block bottom (shoe)

Inserting the block bottom (shoe)

The finished Foxbender


Before you get started, of course, all the material must be provided. For me the material list looked like this:

Material List:

designation Quantity Dimensions material
Side panel Press 2x 600x400x19 plywood
Feet Press 2x 250x230x19 plywood
Klotz above (parent) 1x 155x75x60 Hardwood
Klotz bottom (shoe) 1x 155x60x60 Hardwood
Shoe moldings 7-10 Pieces 155x50x8 plywood
Shoe (performs "Klotz bottom" in the guide slot) 1x 190x80x8 plywood
Clamping shoes (sandwich presses to mold) 2x Ø60x158 Hardwood
"Ears" for clamping shoes (lateral guidance to mold) a '2x = 4 pieces 70x60x8 plywood
Handle large 2x approx 80x20 Baumarkt
Handle small (fixing of the sandwich to press) 2x approx 80x20 Baumarkt
Side panels mold 2x ca. 500x200x12 plywood
Cross connector mold about 10-12 pieces 155xØ12x1 Metal (zBAlu) pipe
Support plate 2x 850x152x0,5 (0.6) Stainless steel (no aluminum wg. Coloring!)
Mount supporting plates a '2x = 4 pieces 152x60x1,5 stainless steel
Backstop (holding sandwich with spring force from inside against the clamping shoe) 1x 250x40x6 aluminum
Acme screw 1x TR16x350 steel
Flange for acme screw 1x TR16 Gray cast iron
Handwheel 1x > Ø120 Alu, Kunstsoff
Carriage bolts 2x M8x120 Galvanized steel incl. Large washers and nuts
Main springs 2x about 140xØ20xØ2 Spring steel
Spring clamping shoe on the "belly" 2x about 120xØ20xØ2 Spring steel
Spring clamping shoe at the "waist" 2x about 80xØ20xØ2 Spring steel
Mounting brackets for springs 10x eg screw hooks  
Tension belts for end attachment of the sandwich 2x 25-30 wide, 350 long DIY articles and then cut
Timer 1x 0-45 min shortest step min. 5 minutes
Schuko plug 1x 220V  
Lampholders 3x E27 incl. flange for screwing M10x1
light bulbs 3x E27 / 200W eg OSRAM "Classic"
cable 1,5m 3x1,5mm² Flexible rubber pipe
Terminal box 1x - Norka eg damp locations
Alufoil - - solid kitchen quality
Incidentals - - Screws, Pattex, box terminals,

Making Right and left side of the press

From the plan I have transferred the external dimensions on a sheet of plywood 19mm. In still rectangular state of the disk of the guide slot to be milled via the router. It should be noted that the slots are of uniform width and that they are placed at right angles to the bottom side. If you have both slots, the outer contour can be seeded and ground.

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Making the feet Benders

From the large plywood boards 250x230x19 feet are made. With the router per one stage be incorporated for inserting the inner Lichtabweiser.

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Assembling the exterior parts and wiring the electrical system

Are the feet and the side parts so far produced by the screwing together a box. Inside are three bulbs E27 200W each with "heating" space. All electrical equipment must be carried out heat-resistant. On the bottom I have scheduled a junction box and connect the cables from the three versions of each other. Now a built-in timer would be good. I bought one for intermediate mounting to the feed line. The important thing is that you can adjust the minute. The plug I have adhered to the clock, so do not irgenjemand gets the idea, the thing running without leaving the automatic shutdown (fire hazard!).

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The production of the hollow mold

The mold determines the shape of the body. The desired guitar shape must be recorded to Zargenstärke smaller. This mold is the centerpiece of the Benders and one makes no effort for each model its own form. There is also a structure that allows you then can form a cutaway.

It consists of two side parts, which are held to each other with pipes. To protect against the heat, the side parts (each = lie down the insides of mirror!) Covered with aluminum foil. I have made an attempt on one side, whether it is better to protect them with aluminum sheet, with the result after repeated use, it keeps the same with aluminum foil and make up quickly. When connecting I bought Ø12x1mm aluminum tubes and 12 rods cut to the length of 150mm, with a 12mm Forstner bit to fit the pipes then tightly into it. The holes for the poles must be placed very precisely, which is to be bent rails on the side panels and up on the pipes. Not affect these tubes and are clear, for example, that goes directly into the quality of the guitar. Simply, it is then when. The parts to be drilled and drilled simultaneously successive Moors

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The acme screw

The spindle presses at the waist of the body From a shoe on the half-mold. Inexpensive and relatively easy can run this as a trapezoid thread spindle. You can buy them by the meter. The end processing is carried out on the lathe. At one end of a handwheel toward needs (I sat making a M12 thread and then countered with a nut) to the other one stands a groove into which a screw used in the form of shoe is attached. A Chump receives the spindle nut. Best to buy a flange, depending on the version you have to drill the holes yourself yet. So edit mother, adapt Chump at mother and fasten into the box.

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Preparation of the block bottom (shoe)

The block below refers to the moldings and the trapezoidal spindle. I have made it from maple. The spindle has on its underside a recess for a screw. This screw I used a setting nut from the side into the wood. The advantage of this method is, the metric thread of the screw allows precision adjustment. On the underside of the pad has a groove to be incorporated into the then attaching wood for moldings used (I've done well with Setzmuttern). Once you do that, the lower corners to be chamfered generously, one gives the molded parts more space and can see better what is happening. With the band saw and filing the outer contour is then prepared and protected with paint.

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Inserting the block bottom (shoe)

The moldings (8-12Stück) are mounted with carriage bolts M8x120 to Klotz. For the final fixing of the moldings of the shoe is made to the press and placed on the mold, let rest on the mold, the moldings and then tightened the carriage bolts. The attachment timber is 8mm strong with me, the groove in which it runs 6mm. To insert I cut two flattenings and the wood then screwed.

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The finished Foxbender

At the flea market I bought an old-fashioned muscle expanders as spring supplier. You need to pair 3x2. The abrasive used on the Dremel I abgelengt these things and then reworked the eyelets by pliers. Are hung on hooks, the springs. I have very good experiences using threaded hooks, with a few large washers and two nuts holding the super.

The backstop I have worked with the jigsaw. At the ends he needs only a few slots on which you can mount springs.

According to Plan It takes two clamping shoes, man can in difficult forms but also need three. With bells I have moored the springs not unhinged mind. A simple handle is enough to move.

The frames to be bent are placed between two support plates. At the ends you need holes pass therethrough to a belt. On the feet, I have attached two small handles. Through the handles and holes, a strap is placed which holds the sheet stack during bending. The Pauplan proposes leather straps and tight hooks, with this construction, but I am also very satisfied.

By turning the pears in and attached the bender on the Werkbankt you go.

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  • For bending distilled water hernehmen
  • Baking paper around the sides put, there is a risk that the wood is discolored
  • After bending mooring the frames into a mold and let dry out there
  • The interior is round the lamps with aluminum foil refer, otherwise charred
  • It is worst fire hazard! Urgent note !!
  • I use now Silikonheizmatten. Because I get the heat directly on the wood. Especially with cutaways that has many advantages.