Replacing all the brackets

I thought I was almost done, having reattached the tailpiece and neck to the pot I went to insert the head and found it wouldn't fit. :-o I'd previously fitted it into the pot before reassembling it. It'd been a squeeze but had been doable. Now it was all reassembled it wasn't going in at all. Two of the brackets were 2 or 3mm over the edge of the pot. Levering it into place would've probably damaged the pot and maybe even buckled or broken the tension ring. I was going to have to make eight new slightly smaller brackets for an easier fit. Luckily I still had most of the flat rod I'd used to make the first two brackets from. As before the first thing I needed to do was thin it down.

Clamping it in two tiny vices I started making a cut right along the length to give the rod a width of just over 5mm. The first Dremel cutting disc fell apart not very long after starting, the rest managed a few inches before they were too small to continue.

After cutting the width of the rod I then cut out nine 7-8 cm lengths. They were longer than I needed but as before I planned to cut them down after bending them. I only needed 8 brackets but decided to make a spare just in case I made an error on one.

With the rough blanks cut I then used a grinding cylinder thing to finish getting them the right size and smooth off the cut edges.

That done I bent the brackets in the vices using one of the old brackets to measure the distance between each bend.

That done I trimmed the brackets to size then drilled the holes and countersinks into each bracket. I used the same drill bits as before but using two vices and two brackets in each sped things up compared to when I made the first two brackets. To make the head a better fit into the pot I moved the hole the hex bolts screwed into 1mm towards the outer edge of the bracket.

I tapped new 3/16" threads in the the hole at the bottom of each brackets where the hexbolts will screw in.

The shiny new brackets were cut to size. I used a lot of metal cutting lubrication for the whole process.

The brackets were attached to the hexbolts and the head tested for fit in the pot. It was spot on, although the edges of the bracket heads protruded beyond the edge of the pot in some places.

I marked the protruding edges in blue ink then removed the head again. To remove the head I threaded a string below two of the brackets and pulled it up.

I filled the bracket tabs down to size with the Dremel. The new brackets were very shiny. Not the kind of lustre you'd expect on an instrument of it's age so I decided to force a patina on the new brackets.

 I left them for a few hours with some vinegar soaked tissues paper on the metal then gave them a rinse and dried them before lightly sanding them with 2000 grit paper. In the picture below the thee brackets on the left are my new ones, the shiny one is the spare one I made and the one on the right is the original bracket.

The patina only mattered in the top visible part of the brackets, the lower part would be hidden by the metal hoops and vellum. Having got the patina I wanted I gave the brackets a spray with clear acrylic sealer to protect it and stop it ageing further. I used the same satin finish I'd used for the pot. I gave the a couple of coats then set them aside to dry.

Threading the new brackets

Having cut and bet some steel to make new brackets fo the head I neeed to cut screw holes and tap a thread. Apart from not knowing how to tap a thread my initial problem was identifying what thread I actually needed to cut. There's a load of complex maths and confusing measurements involved in working out a screw thread, more so if it's imperial or you can just do it the easy way using a thread guage.

Each of the guage leaves matches a screw thread. You just hold the screw thread to the stencil till you find the one that fits. It's that simple. This one had fiftytwo imperial and metric threads.

The hex bolts seem to have a Whitworth 55 degree thread with 24 threads to the inch and a size of 3/16" which according to Wikipedia gives them a core diameter of 0.1341". I guess when Whitworth developed his threads in the 1840's people really hated round numbers, but they must've liked Whitworth's threads as they eventually became a standard.

I'd ordered a job lot of thread taps and dies from eBay and there was a 3/16" 24 thread tap amongst the rest. According to the chart on Wikipedia I needed a 3.7mm drill to make the hole for this sized screw, just to keep in confusing a 3.7m drill is apparently called Number Drill 26. As luck would have it nowhere I tried sold 3.7mm drill bits. I opted for a 3.5mm bit and figured the thread tap could probably cut out the extra diameter.

A brief look at a WikiHow post told me how to tap a thread. It also left me wondering why I never learnt this sort of basic stuff in metal work at school, I've never felt the need to make a crappy pen holder from a bent piece acrylic but how to cut a thread seems a really useful (and easy) thing to know.

Working in daylight, unlike when I initially cut them, I secured a bracket in my cheap but adequate unbranded chinese made vice and gave it a squirt with Metal Cutting Lubricant. A week ago I didn't know Metal Cutting Lubricant existed, thanks WikiHow. I then drilled a hole using the 3.5mm drill bit. That done I sprayed the bracket with more lube and put the thread cutting tap into a handle. Never used one before but it's basically a handle with a little vice type arrangement in the middle, one of the handle is threaded counter clockwise which is a bit confusing but means you don't loosen a handle whilstcutting the thread.

The tap is tapered at the start so had no trouble getting it into the 3.5mm hole. Basically you just press and twist the tap clockwise with an occassional counter clockwise twist to break off the shavings. The challenge is keeping it vertical at the start. It's surprisingly easy to be honest. at one point I gave it a little more lube but once the tap was a quarter of the way  into the bracket the thread was cut so cleanly that with a flick of the handle it was able to rotate freely.

I then tested it with a bolt. Perfect. At the other end of the bracket I cut a hole for the smaller screw to attach the bracket to the pot and using a larger drill bit countersunk the hole. These didn't need a thread as they were for wood screws which were going straight into the pot. I did the same with the other bracket.

Shaping new Brackets

Normally banjo's have a skin stretched over a wooden pot, but the zither banjo has a skin suspended on metal brackets within the wooden pot which acts as a resonator. The 'zither' part of the name comes from sounding similar to a zither apparently -the stringed instrument not the African wooden thing of the same name you rubbed with a stick at primary school.

On this instrument two of the metal brackets appear to have been replaced with brackets from another instrument which didn't really fit and seem to have contributed to warping the pot. When I removed the head I could see some of the brackets were slightly bent and the replacement two were thicker than the rest. The two replacement brackets were going to need replacing.

It looks like Zither Banjos like this haven't been made for about 70 years, having fallen out of favour as with a budget instruments like this one the strings can pull up the lower edge of the pot ruining the instrument. To get a couple of replacement brackets my choice was to either find another instrument with the same size brackets to cannibalise or make them myself. The chances of locating an identical 120ish year old instrument are a bit slim, and unless it was wrecked I wouldn't want to ruin it by taking parts from it anyway so I decided to make some brackets from scratch.

I popped to B&Q and picket up a metre of 10x2mm steel rod and a Dremmel. Measuring the brackets roughly they're length was about 55mm but have two bends in so I cut some 70mm lengths from the rod as I wasn't sure how they right angles would affect the length. Thanks to the early sunset I was working by torchlight, made things a bit awkward but the Dremmel sparks looked impressive :)

The brackets are 7mm across so I needed to trim the width too. I measured it all by sight instead of marking measurements as my pen wouldn't mark the metal and the Dremmel made quite a wide cut anyway. Each bracket used up one cutting disc completely, I also used a cylinder shaped sanding bit to finish the cut edges

With the pieces more or less cut to size I clamped the metal in a vice and bent it to as near to a right angle as I could manage before giving it a wallop with a little 3lb sledgehammer. Seemed to do the trick. The important thing was the distance between the two bends which I measured by holding an existing bracket to the one I was making when figuring out where to bend it. Once bent I trimmed the ends to the right length, again gauging the length by holding an existing bracket to the new one.

I got the brackets pretty close to the size of the originals. The thickness wasn't spot on but I'm learning as I go. The picture below shows my two new brackets needing to be drilled and one of the original brackets which is a little buckled.

The top hole is just a hole straight though for a countersunk screw but the lower one is threaded for the bolt. I'll need to find out how to cut a thread and identify the thread of the bolts at some point too.