It has been some time since I did some machining, so what better time than in the past few days. We have a sofa set, which comprises of a 3-seater and two single recliners. They are about 8 years old, and previously – the back of one recliner had sort of come loose. We rectified it by taking it apart and replacing a broken screw. Then recently the other one had the same problem, another broken screw. The back of the recliner has a bracket that clips onto a mechanism that allows the back to recline. On the back (inside) there is a thing that is screwed onto the sides with two 8-gauge screws, these are the ones that keep breaking.
After some consideration, obviously we could keep replacing the screws, but maybe the screws are too small for the job. Anyway, after some consideration – I came up with a solution that should work. Replace the screws with 10 gauge screws, which are thicker and stronger. The wooden panel where the top screw position goes was worn, so thicker screws won’t work, so I chose to use a couple of pieces of flat bar steel, with a circular groove milled into it so that the bracket would fit in more securely, tapped to fit a metric 6mm bolt – then a couple of hole drilled for the new screws to fasten it to the wooden panel. The left bracket is shown assembled, with the other end of the bolt – sawn off flush.
That sounds easy – doesn’t it? Milling the circular groove, needed a rotary table on my milling machine. I hadn’t used this rotary table before, but had bought it in readiness of a job like this. After unpacking the rotary table, I found that I cannot clamp it to my milling table. My milling table has Tee-nuts with a M10 screw thread however the rotary table mounting holes will only fit a M8 screw. Not a big problem, since I must have known this when I bought the rotary table, but just conveniently forgot. Ok, so I need to make Tee-nuts that have a metric 8mm thread to suit my milling table.
I just happened to have an off-cut of steel that I had put aside for this purpose over a year ago. I put this into my drill vice, then used a 12mm endmill to mill the sides to the appropriate dimensions.
After this was done, I wasn’t happy with the surface finish – which should be flat, but wasn’t – after some head scratching, I worked out that the moving clamp of my drill vice was lifting a little when tightened, but during the milling, the force pushed down on the work which gave the uneven finish.
It was time to bring out the big guns, a K-type machine vice was mounted on the milling table, then I went and re-milled the top and bottom surfaces. Once I was happen with it, I drilled three 6.5mm holes because this piece of steel could become three Tee-nuts. When the holes were drilled, I then removed it from the machine vice and then put it in my drill vice, which was now clamped to the table, and proceeded to tap them with a M8 thread.
Here is the my piece of steel with all holes tapped sitting on my machine vice – note the size of the vice, it also weighs 11Kg.
Now compare it with the original Tee-nut.
And finally, cut into pieces.
I then slid them into the slots on my milling table – yes, they do fit. I put one of the original Tee-nuts in for comparison.
Then I mounted the rotary table.
From this point, all I had to do was to mount my piece of steel and use a 6mm end-mill to mill out the circular groove – and work out how deep to go. It was easy, once the end-mill is cutting into the my steel plate, just keep rotating the black knob until I had a donut shape. Well, it was sort of easy – I had to adjust the offset from the centre of the rotary table once, to get the right fit. The rest was easy, drill 5mm holes in the centre of the donut, and for mounting, cut them apart, since I needed two of them.
Here is the end result – this should now handle a lot more stress, since there are now three thicker screws holding this bracket on, instead of two.
In terms of material costs, the pieces of steel that I used for strengthening the brackets, for the new Tee-nuts, six 10G timer screws and two hex-head M6 bolts – would be only $2 or so.
Now, I hear you all thinking about the cost of the gear that was used for doing this job? Much of my tools and equipment was accumulated over a period of time, like that past 6-7 years or so. I happen to have recorded how much it cost when I bought it, so here goes – what I used for this job.
HM-10 Mini-mill $759
CK-10A Clamp Kit 12mm $129
End mill set $95
100mm K-type Milling Vice $145
Work Bench $319
Tap & Die Set $49
Eco-Tap Threading Fluid $23
BS-4A Band Saw $297
M5-M20 Tap Wrench $18
3MT 6mm collet $31
3MT 12mm collet $31
100mm Rotary Table $163
All up, if my calculator is correct – $2,222 Australian dollars. Some of the more expensive equipment was purchased during the periodic sales that come up, so if it was bought retail, it would have cost maybe 20% more.
[P.S. That is why custom made parts can be expensive, not so much because of material costs, but due to the equipment needed to do the job. To cut the Tee-nuts apart was done on a band-saw – about 5 minutes, plus a few extra minutes working out to hold these small pieces in the vice so that it could cut them apart. If I had to use a hacksaw, I would have a spent maybe an hour doing this. Overall, in terms of time, I probably spent around 8 hours total, six on making the Tee-nuts, and 2 hours making the strengthening plate and installing them back into the recliner. Now, if I had to make more Tee-nuts, I would be able to make them in much less time, especially if I made them out of aluminium. My Mini-mill is really too under-powered to work on steel but I don’t have enough space in my garage to fit a larger mill.]