Adjustable Inside Form - Ukulele

April 27, 2020

Adjustable Inside Form - Ukulele

As the luthiers building experience grows, they will want to add additional luthier tools to their shop, which will give more versatility and focused attention to certain tasks, and at the same time giving better accuracy and repeatability to the build. The adjustable inside form is one of those tools. The adjustable inside form is a variation of our standard fixed inside forms that we offer with every ukulele drawing we have listed on our site GenOne Luthier Supply. This tool does many tasks and does them well, with minimal time and maintains a high degree of accuracy in the instrument building process.

The adjustable inside form gives you the freedom to use this tool with any size ukulele that we offer and therefore you don't need a different form for each ukulele size. The process that makes this form adjustable is the use of a series of (6) adjustable retainers at the upper bout, the lower bout, and at the waist of each instrument.

The Three Elements That Make up This Tool:

The Form Base: The base is the 19mm piece of cabinet grade plywood where all the other adjustable elements are anchored. It consists of several curved channels which allow for complex adjustment angles of the side retainers. Also you can optionally install an option to this base so the form can easily be clamped into a woodworkers vice. This give the form incredible rigidity so major operations such as crown sanding can be completed without the concern of the form sliding around on the workbench.

The Inside Form Shape Insert: This is an additional insert made from 19mm plywood fits onto the top surface of the base. By installing  smooth-shanked pocket screws around the perimeter of each of these inserts, you can glue down top and back plates with surprising speed. We include ample pocket screws to easily go around the edges of the insert for either rubber band attachment or elastic banding.

Side Retainer Clamps: The 6 retainers are key to the working of this form. Each retainers is attached to the base with a carriage bolt/free-spinning knob assembly, giving the luthier easy adjustability for any size instrument. The retainers can easily retracted to release the  the instrument body, and again easily tightened to secure the instrument back in the form. The form is shipped with the front surface of the retainers that contact the instrument body curved to easily fit the subtle curves of the body. The retainer bases are slotted giving a lot a adjustability for different instrument body types.



If it is your intent you use this tool for attaching strapping or rubber bands to clamp

the plates of the instrument, you will need to install the included pocket screws into the Form Insert. Here is the procedure to accurately accomplish this task:

  1. Install the shape insert on the form base. Next install the (6) retainer clamps onto the base and adjust to the proper setting to the inside shape insert. Mark the location of each side of each retainer clamp on the side of the insert so you know these areas cannot have the pocket screws installed that these locations.
  2. Remove the shape insert and clamp in a vice. You will want to mark the locations of each pocket screw around the perimeter of the form with a pencil. I usually stay away from the line of each retainer clamp about 12mm (1/2") for the first hole. Then I take a flexible tape (like a seamstress tape) and measure between retainers and divide by about 1" (25mm). Then mark each screw location using this method completely around the shape.
  3. Drill the pilot holes for each pocket screw. Use a pilot hole will allow the screw to grip, but not crack the plywood. Use a depth stop on the drill so you can drill a hole about 2/3 of the screw length. Try to drill these holes as closely to perpendicular to the edge of the form as possible. Upon completion of the side drilling, screw all the pocket screws into place so about 1/2" (12mm) of the shank is exposed.
  4. Upon the installation of the instrument sides into the form, with the inside form shape insert in place, the tops of the retainer clamps may need to be trimmed for clearance needed for sanding edges of the instrument. You may want to make additional retainers if you use a wide range of instrument depths - although this really is not necessary. The retainers clamps at the lower bout of the instrument will naturally be higher than the clamps at the waist and upper bout.


This tool can be used for the following tasks:
  • Installation of kerfed linings to the sides
  • Finish sanding the sides to prepare for mounting the top and back plates
  • Holding sides in place for fitting plates and cutting brace channels into the lining
  • Holding sides during gluing of separate blocks for floating top installation
  • Holding body during binding and purfling channel routing
  • Holding body during purfling and binding installation
  • Holding body for scraping, rough sanding and final sanding
Differences Between The Guitar & Ukulele Inside Form:

These forms basically operate and are setup identically. Of course the Guitar Form has a much larger footprint and the Retainer Clamps are large for more stability. The biggest difference is the Guitar Form has optional head and tail block retainers available as an additional option. Again this is for more stability for certain tasks. These instructions apply equally to both the guitar and ukulele versions of this tool.

Leave a comment

Comments will be approved before showing up.

Also in GenOne Blog

Neck Assembly Jig Setup Instructions
Setting Up The Neck Assembly Jig to Cut Scarf Joints

March 26, 2023

Here is a short description of how I setup my neck assembly jig to cut scarf joints for a typical 14 fret to the body, acoustic guitar with a 25.4” scale. 

Continue Reading

Neck Construction for Stringed Instruments
Neck Construction for Stringed Instruments

February 26, 2023

One of the most difficult pieces of the acoustic, classical guitar and ukulele construction puzzle is precise construction and adjustment of the instrument neck. The neck has several important duties to perform

Continue Reading

Wood Bindings add to the beauty of a hand crafted instrument
Bending Wood Binding Strips

November 08, 2020

Wood purfling used on a premium instrument is one of the crowning touches you can use to bring your build to the next level. This tutorial gives detailed instruction on how to make these beautiful ornimentations.

Continue Reading