Maker & Restorer of Violins, Violas, Cellos & Double Basses.

 

      I have illustrated the following instructions with a series of photos taken during the fitting of a 4 string set of these machine heads to a Jay Haide double bass. As the instrument was new no repairs, filling or bushing of existing holes was required thus simplifying the job considerably.

    

    

     Start with marking the centre line on the sides (cheeks) of the peg box. I use a Chinagraph pencil as this does not spoil the finish and can be cleaned off easily.   The most suitable position for the ‘E’ cog and shaft ('B' cog for 5 string bass) is determined and similarly the position of the ‘D’ cog ('A' cog for 5 string bass). The line is then divided into 3 (4 for 5 string bass). Equally well  a pattern in thin wood or cardboard could be made of the side of the peg box and string spacing determined on it. Drill pilot holes and then open out large enough to be able to use a 1:25 tapered reamer (standard cello peg reamer) and ream holes out sufficiently for the cog’s shaft to enter full depth and without binding. The photo right indicates  how large the holes are required to be reamed which is a little less than the maximum a standard cello peg reamer is capable of achieving.  

        Insert shaft in hole and scribe the amount to be cut off it's length and also mark position for the string hole with a centre punch. Cut shaft to length, drill string hole and countersink its edges, ensure that the remaining thread is deep enough for the retaining screw to enter easily, tap deeper if necessary with a M6 tap, photo right. Note-it is good practice to run a tap into all threads after any cut off operation has been performed, in addition note the use of 'soft jaws' in the vice to prevent marking the work.
       Insert cog shaft into hole and screw on retaining washer with machine screw, adjust length of shaft if necessary. I recommend that a screw driver suitably modified to be a good fit in the retaining screw is used as this will prevent damaging it's head.

    Carefully determine the position of worm gears and their bearings  ensuring it provides for a good mesh  and that the corners of the bearings do not foul the cog, drill appropriate pilot holes (somewhere around 1.8 mm diameter) for the mounting screws, I suggest initially using just one screw per bearing until the set up has been proved, this approach provides for a little adjustment if necessary. In the photo right the thumb screws have been temporarily mounted on the worms.

     To determine the respective lengths of each worm gear, mark with some masking tape where you wish the thumb screw to be on the shaft. Unscrew worm assembly from instrument With a M6 die that has carefully been adjusted to match the original thread (this only applies for split dies) extend the thread just up to the masking tape and then reduce the length of  threaded portion of worm gear back to 20 mm. Photo right.

    Note there are two slightly different approaches to determining the worm length, one is to have the overhang the same for all worms and the other is to graduate slightly the over hang so it is more in proportion to the width of the cheek at that point, this often gives the most visually pleasing result. 

    Ensuring that the 2 components are clean, place a few drops of bearing retaining fluid ( I use Loctite 603)  along the thread on the worm gear and screw the pieces fully together, be careful not to get any fluid on the bearing surfaces. Note the photo shows the continuing use of masking tape originally applied to mark the thumb screw's position. Leaving the tape  protects the bearing and indicates when the thumb screw is fully home. Clean off any excess fluid and re mount the worm gear assembly. Please note the use of 'soft jaws' again.

 A few notes:

In some respects the size of the pilot holes for the wood screws is dependant on how hard the wood is therefore the size quoted can only be a guide.

All bearing mounting screws that pass through a brass plate will require a clearance hole in the plate; attention brass screws can easily be broken!

 Special Tools required over and above measuring, marking, twist drills, machine countersink, files, hack saw and screw drivers ect:-

A standard cello peg reamer 1:25 taper.

M6 tap and die with their respective wrench and holder.

Customising Options

For those customers so wishing I offer various customising options on these machines.

Customers can specify what lengths of worm gears they require and I will supply sets so assembled. String holes can be drilled and counter sunk, please specify distance from back of cog to centre of hole. Machines can be highly polished and lacquered. Brass plates can be made to order. Perhaps there is something else you require? Please contact me.