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1953 Valco El Grande Steel Guitar Customer's Work Progress Reports ~ Page 5; Knob Repair ~ |
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The task: With original vintage knobs selling for as much as $15 a piece on-average, it makes as much sense to repair them as it makes sense to allot of people to retain original knobs on their vintage instrument. Here we have a knob with the most common problem; The pot shaft receiving hole is broken, ....probably from someone trying to twist and pull it off without seeing there is a small screw to first loosen. Physical impact upon the knob with it set to high off of the deck of the guitar is also another common cause. Here someone has added some "elephant snot" type non-drying, sticky, sealer putty which must be cleaned out while cleaning / prepping the knob for repair so the epoxy will have absolutely clean (and lightly roughed up) surfaces to grip onto. |
First put an ample size sheet of wax paper on your work area so that any drips or spills can be cleaned up by simply throwing the wax paper away. The piece of wax paper in the picture below is NOT the bigger piece it was when I started the work .....but is a remnant of it I kept on the bench should a need arise to roll or form the epoxy on the toothpick. Epoxy will not stick to wax paper once it starts setting up well, such as it is by the time the picture was taken. I then clean the knob with Simple Green DILUTED 10:1 WITH WATER. Then Q-tips dipped in acetone AND SQUEEZED OUT into a clean rag, are used to wipe down the interior of the knob to remove any oils remaining. Then using a small piece of medium grit sandpaper, I lightly rough up the surfaces that will receive the epoxy for the repair. I use white epoxy for white knobs, black epoxy for black knobs, clear epoxy for clear knobs. Since epoxy thins with Naptha (common cigaretter lighter fluie is pure Naptha and doesn't require buying a darn pint), then we know that small amounts of common enamels such as hobby model enamels can be used to tint epoxy to closely match the color of a knob .....although a repair such as this will not be seen on the guitar, but a matter of doing the best job possible is a very good work ethic habit to acquire if you're gonna work on more than just a few superficial guitars / repairs. Next I turn a Q-tip slowly into the screw hole whose threads will pull the Q-tip into position to seal the hole from epoxy repairs on the inside of the knob. The Q-tip also acts as a convenient handle to handle the knob during work. Next I cut off about 1" of a fat plastic drinking straw and cut it along it's length so I can overlap the cut to make the piece of straw fit a hole exactly, ....and insert that all the way into the pot-shaft hole. Epoxy will not stick to slick plastic such as the straw; And you can wipe a bit of oil from your forehead onto your finger and wipe it onto the outside of the straw before inserting the straw, which will act as a mold-release "wax" at just the right amount. Then I tear off a cigarette filter, roll it between my fingers to compress and reduce it's width, and push it down into the straw to exert internal pressure and fit the pot shaft hole tightly. Next I pull out my trusty old 50 year-old soldering jig to hold the Q-tip / knob at any angle I desire; And many angles will be required as said further below. Next I mix epoxy on the bottom of a CLEAN tuna-fish can turned upside down and wiped off with a rag dampened with acetone, ....mixing twice the amount of epoxy I think I'll need. A taller food can pallet will also work but has a higher center of gravity while the low center of gravity of the tuna can works much better and reduces the chances of knocking a pallet of wet epoxy over. If the epoxy is an overnigt setting epoxy, I keep an extra tube of hardener to add a little bit to accelerate the epoxy setting up within the working time window I desire ...usually about an hour. Then while the epoxy is still runny, I spin a small amount onto the end of a round toothpick and place it into the joints between the straw and the knob, so it will get down into the smallest crevices. All you need is just enough to get down into those crevices; Any more can create a real hassle being too runny. Tilt the knob in the soldering jig so that gravity will pull that epoxy down into the crevices and not run in a direction you don't want it to go. Set the end of the toothpick back into the puddle of epoxy so you can feel the epoxy's consistency at any point in it setting-up further. I then let the epoxy set and monitor for when it starts thickening up into a workable but still slow sagging putty. A light bulb set 6" or-so from the epoxy will heat and accelerate the epoxy starting to set-up; Or a pistol grip hair dryer can be used to accelerate the epoxy setting up (ALWAYS put a finger on the edge of the can to warn you should the heat start to get too much. I check the epoxy's consistency regularly with a round toothpick because that will be my application tool. When the epoxy is close to being the right consistency, it will start to roll-up on the end of the toothpick when you spin the end of the toothpick in the puddle of epoxy. Lift that portion that rolled up onto the toothpick out of the puddle and see how fast it sags off of the toothpick back down into the puddle of epoxy. Staying on the toothpick for about 30 seconds is a good initial working consistency. ---------- In the picture below you can see the toothpick in the soldering jig with epoxy sagging off of it, ....although when this picture was taken, the epoxy was set up enough for it to stay on the toothpick for several minutes. |
When the epoxy is set-up to a manageable but still sagging "putty", it's time to start putting it onto the repair spot. Lift small amounts about half the size of a green pea, onto the toothpick by slowly spinning the end of the toothpick in the puddle of epoxy. Then carefully place it onto the repair area, ....spinning the toothpick as you pull it away from the work so the curl string that WILL pull away with it will fall upon the straw and not on the work or work-area and have to be cleaned up later; Repeating this process to build up a new wall on the knob that is being rebuilt by the epoxy putty. The epoxy WILL and SHOULD sag from gravity, ....but slowly enough that it is manageable. You will have to reposition the Q-tip / knob angle so that gravity will work in your favor, making the work sag in the direction you desire. If the epoxy is not set-up well enough, you will have to move the knob around to control the sagging, via the Q-tip in your hand until it sets up better. Moving it around about 6" from a light bulb will accelerate the epoxy setting up. ------- Once the epoxy has set up and is sagging / deforming very slowly, then you can dip a NEW / CLEAN toothpick in Naptha and start teasing any forming you need to make upon the putty repair. You can also dip the small-end tip of one half of a wood clothespin into Naptha and tap down the flat surface around the knob's pot shaft hole, ...which will save allot of time otherwise sanding it down if you wait until the epoxy hardens. ------- When the sagging deformities slow down to about 3 or 4 minutes, then you can place the Q-tip / knob in the soldering jig and only have to move it for gravity's sake every 3 or 4 minutes rather than having to hold it in your hand for that long; And this working set-up time can take about an hour if you got the epoxy / hardener mixture right .....longer or shorter if not .....hopefully not longer ....although it's MUCH better to be longer than too short, until you get the hang of working with epoxy as a putty. In the picture below is the knob in the soldering jig, set at angle for gravity to pull the epoxy's slow sag into the shape I desire. The epoxy on the end of the toothpick in the jig has set up to the point that it would take 10 minutes or more to sag off of the toothpick. I put it there so I can monitor the epoxy's set-up consistency by just watching how fast the epoxy on the toothpick is sagging. There will come a time in the epoxy's set up that it will be quite stiff but still moveable. This is when you want to use a fresh toothpick dipped in naptha to put final very light forming touches on your work, and flattening the work around the knob's post shaft hole with the small-end tip of the half of a clothespin. |
When you feel you have the shape of the repair you want, then put a light bulb about 6" from the work to heat it while it cures and you monitor that initial curing. When the work no longer sags over a 3 hour period of checking it, then it's set up well enough to let it set overnight before proceeding. ------- oOo ------- Next day's work: Simply wiggle the straw around and it will come right out. If it is reluctant, remove the masking tape, pull the cigarette filter (or other packing used in the straw), and with long-nose pliers, spiral the straw inward to get it to release from the epoxy. Now all that 's left to do is to sand off any areas that might need it. If the knob' pot shaft hole is too tight, then roll up a piece of medium grit sandpaper and spin it slowly in the hole until it's the right size. |
Now insert the set-screw into it's hole and run it up until it meets resistance from any epoxy residue edge that's probably going to exist. Turn the screw in 1/4 turn and back it off 1/4 turn, repeating 1/4 turn inward against the epoxy residue resistance and backing off, until the screw thus cuts and sets threads into the epoxy. Run the screw in and out of the resistance area a few times to set the threads well. Now remove the screw, oil it and wipe the oil off by pressing the screw in a rag. Put the screw back into the knob; The oil will prevent the epoxy from sticking to the screw during the epoxy's several day fulling-curing time. Run the screw in and out a couple times so the oiled surface will again reface the threads well. |
I made a thicker wall than the original just to be on the safe side. Bits of epoxy residue or unevenness on the inside of the knob can be gently taken down with a rat tail file or small fingernail sanding file (gently so it will look smoothe rather than rough). You can see some of the epoxy residue on the screw that was darkened by the oil residue on the screw during it's final thread setting, and then removed here for the picture to show the epoxy residue that was further cleaned and smoothed off of the epoxy's new threads. Any further finishing / smoothing of the epoxy repair can be easily done as said above; But is too time consuming for me in efficiency of the remainder of the work on the Steel to be done. |
This is the wood block that replaces one of the two magnets in some models of Valco / Supro Steels. |
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