Fixing it back

We came across this wooden swiveling chair and thought it would go well with our computer table.

It did not have castor wheels (like the modern computer chairs) but the swiveling facility was there. In fact it was one of those antic chairs which was reconditioned and restored. So we bought it and asked the shopkeeper to deliver it home.

It was packed well and shipped to our residence.

While unpacking we found that the base of the chair was not fixed properly and was almost falling off.

Getting it back to the shopkeeper was one option but the shop was 800 kms away. When I spoke to the shopkeeper he said “see if you can get a local carpenter to fix it and I will foot the bill”

After having a closer look at the design of the assembly of the chair I realized that they were joined together with three taper screws (suitable for wood)

I always gave credit to our forefathers and their design ability, but this was one design that perplexed me. How did they assume that these three screws would hold the base to the chair. (the base is of solid wood and it weighs about 8 kgs) And it is obvious that if one has to move the chair from place to place, it would have to be picked up by the hand rests and not from the base.   

I did notice that there was a bigger hole too (20mm diameter) on both the halves. Was this used for locking while swiveling? Or was this used for fastening both the top and the bottom?  In all probability it was for the latter, which means the actual locking fastener was missing and was not put in place by the reconditioning/restoring agency.

I did not want to get any carpenter and get it done as he will try to open the base where the roller bearings existed for the swiveling arrangement. Disturbing that was not something that I wanted as it was assembled with the old type of metal and wood wedge arrangement.

I took it upon myself to set this straight.

I decided to reassemble it using a stud with nuts at both the ends for positive locking. So fixing it back using the same screws was ruled out.

Problem number 1

The existing holes were suitable for M4 studs and M4 studs come in short length.

So I got some M4 screws of the required length and cut off the head to convert them to studs.

Problem number 2

The big hole of  20 diameter could accommodate a screw of M16 but how do I insert the head of the screw which has a dimension of 26 mm across corners of the hexagonal head? I also had to insert some sort of washer to hold the bottom (base) while tightening. After a lot of brain wracking, I came up with the idea of  using a smaller size screw, something like M8. 

 For inserting a washer, I took a big plain washer and modified it to have an across flat of 19 mm.

To keep the screw centrally located, I got a nylon bush made with a hole of 9 mm dia.

(two views of the bush assembly)

Sequence of assembly:

For the three M4 Studs:

1)   Place the M4 nuts exactly under the three small holes.

2)   Insert the studs through the holes and slowly screw in the studs so that the nuts get engaged from below. This had to be done just by the feel of the hand as there is no spanner to hold the nut below. 

For the bigger screw of M8:

1)   Assemble the washer in the screw and slowly slide it in through the 20 dia. hole so that the head of the screw and the washer are inside.

2)   Slide in the nylon bush. (care had to be taken that length of the bush was lesser than the total  thickness of base plus upper part)

This is how it looked before assembling the top half of the chair to the base. (the screw and the studs are looking white as I added some tuflon tape for snug fitting of the nuts)

Place the chair on the base (taking care that all the four holes match) and tighten the nuts from the top.

 I realized that, even though everything was clear in my head it is always advisable to put it down on paper. Even a rough sketch will do, and while making the sketch its better to draw it to scale.

Here is a cross sectional view of the assembly.

Mission accomplished  -  now I hope that the top and the bottom will never get separated.

And yes, I did take a suitable payment from the shopkeeper, which he was ready to pay the “carpenter”