More on Aluminium Tube Masts

A couple of extra points:

Suppliers

Finding suppliers for tubes that will definitely fit is proving harder than I expected. In particular I’d like a 70mm diameter by 3mm wall thickness tube for the main tube, as this should fit a 2 1/2″ inner tube with everything at its nominal size. However 70mm is very close to 2 3/4″ so 70mm is hard to find.

I’m also struggling to find suppliers who will measure what they have in stock.

Adjusting the size

I found a discussion on using Car Exhaust Tailpipe Expanders to adjust the size of an aluminium tube. Neat idea but rather scary – I’m not sure what that would do to an aluminium extrusion with a T6 temper.

However:

  • It might be possible to make the internal diameter 0.1mm larger, should that be necessary;
  • I could always wrap abrasive paper around the tool and use it to make the internal diameter larger using an electric drill on low speed.

Free-standing mast: Aluminium Tubes

Aluminium tubes are easily available in the UK and fairly cheap. Aluminium is strong, light and has very predictable properties.One issue is that aluminium is only available in lengths of 5m, so we can’t make the mast out of a single tube – we’ll need to extend it somehow.

Another issue is that cutting and welding aluminium destroys the properties – you are likely to end up with a very soft material. So we can’t cut and weld the tube to create a tapered tube – we’ll have to stick with the tubes as delivered.

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Wanderer centreboard pivot bush

Making the bushings for the centreboard. This has an iroko bush fitted to the centreboard, pivoting on an acetal bush around the bolt. The acetal bush serves two purposes:

  • It acts as a spacer in the centreboard case, ensuring that the centreboard bolt cannot clamp the centreboard too tightly. This makes stopping the centreboard bolt leaking simpler.
  • It provides a nice surface for the iroko to move on.

Note that the hole in the acetal bush is countersunk – hopefully this will make it easier to get everything aligned when it is fitted.

Kitchen tap replacement – making an adapter

Replaced a tap in the kitchen this week. The old tap leaked and it wasn’t possible to fix it. It should be a straightforward job but as usual there were issues…

The main issue was that the hole in the worktop is too big for the new tap – the edge of the tap would only overlap the hole by about 1mm. Not enough. So I made an adapter from acetal/Delrin.

Starting the job in the lathe

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Metal-cutting bandsaw blade adjustment

I’ve got an Axminster 4″ MCB100A metal cutting bandsaw, and a wonderful bit of kit it is too! However the blade started coming off and it wasn’t obvious how to adjust it.

I took both of the wheels off – they just unbolt. The driven wheel isn’t adjustable, so it is important to ensure the back of the spigot is really clean so the wheel is correctly aligned.

The idler wheel is adjustable, but I didn’t realise this until I took it off. This is what it looks like:

The two grub screws sit on the marks on the aluminium casting between the springs. You can adjust them without removing the wheel through the two holes in the wheel, although you will need to slacken the centre fixing bolt first.

In my case I wanted the blade to sit slightly further back on the wheels, so I tightened both screws by about 1/4 turn. The blade now runs perfectly with no more jumping off.

Focusser

Time to start on the last major component – the focuser! This will be a Crayford Focuser using some 3x3x8 ball bearings, some aluminium tubes and bits and pieces lying around.

The first part to be constructed is the base-plate that will attach the focuser body to the telescope. This is threaded to take the bottom of the focuser tube; this will then be secured with locktite.

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