Sunday, May 1, 2011

DTI Mag-Base repairs

a while ago I discussed a broken mag-base I salvaged from being tossed out. That article discussed the dis-assembly of the mag base.

In an effort to get the "To Do List" a little smaller I finished off the repairs to the indicator base.
I used the spindle from a discarded tap to make up an actuating system for rotating the mag-core. I simply filed the required square shape into the section which used to hold the jump valve.
The threads which actuate the original tap were turned away, and replaced with a parallel section.

Figure 1 - Tap spindle filed to square

A plastic bush was turned to locate the mag-core inside the void in the mag-base, and to provide support to the spindle. The plastic was from a sheet of 25mm (1") thick plastic (nylon I suspect) that I rescued from a bin. A suitable square was cut from one corner, and a 10mm hole drilled through it. A 10mm bolt and nut were inserted, tightened up, and used as an arbor for the turning. Whatever the plastic was, it certainly was "stringy" in the swarf.

Figure 2 - Commencing turning the plastic bushing

A brass indicator/ handle was made from an old brass fitting, and some sheet brass, and soldered together.

Figure 3 - Actuating knob and pointer prior to soldering

The spindle was designed to pass through the front plate which was made from some brass strip. The front plate is shown on the RHS of the exploded view below (Figure 4)

Figure 4 - exploded view of mag-base

In the above exploded view, everything to the right of the magnetic core, and everything above the magnetic base were made from salvaged materials.

The magnetic core was filled back to remove the old damaged paint, and engraving markings. A few minor dings were cleaned up, and then the base was primed with cold-gal paint (Zinc-it) then followed up with a couple of light coats of Silver Hammer finish paint.

Upon assembly it was deemed too difficult to re-drill the existing holes to their proper spots, so new holes were drilled for securing the face plate.

Figure 5 - the magnetic core in the base with the spindle and bushing in place.

Figure 6 - The mag-base assembled

One of the salvaged lengths of steel from a gas strut was used to make the mast on this base - although a brass socket and washer was turned from an old extinguisher part (CO2 nozzle) to stiffen the joint instead of simply using the M8 thread.

Figure 7 - The  mast on the mag-base made from gas strut

An offcut of the gas strut remains, being about 125mm (5") long which will most likely be used for making one of the connecting rods.

Figure 8 - The completed mag-base next to the Taig lathe.

I've possibly made the mast too tall, but standing next to the Taig lathe, it has sufficient height to ensure access to anything I put in the lathe, or the vertical slide. I've yet to make the other smaller poles, joiners, and DTI connectors, but that should be fairly easy to do over the next few weeks.

That said, guess who's added more projects to the list... You'd think I'd have learnt by now, or maybe it's my curse (or is it blessing) to always have more jobs than hours to complete them...

I did up a quick explanation of how a mag-base works for someone, and decided to include it here in case anyone else needs to know how they work. I've since cleaned it up and converted it to a JPG.

Figure 9 - Theory of operation - magnetic stand

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