Blade Switch Modification - Part 2

My last post laid out how I planned to modify a high current DPDT blade switch, making it easier to connect eye terminals from a solar charger, starter motor, and battery.  The goal is to add threaded posts to the terminals by soldering some screws through them.    This post is just an update of my efforts.

I started by drilling a hole in the end of each terminal plate and tapping an M5 thread in it.  It may seem strange to tap a thread for something I'm going to solder in place, but I thought it would be an easy way to hold everything together while I soldered the screw to the plate.  I originally intended to use 20mm long brass M5 hex bolts, but they were over a dollar each, while M5 cheese head screws the same length were 20 cents.  The head didn't really matter so I went with those.

To solder the parts together I used a 2% silver solder and a MAPP torch.  The image below shows the results from soldering the brass screws to the plates.  Those of you with a keen eye may notice the first four look like crap.  After I did the first two, I took some time to reassess things and thought my surface preparation could be improved.  So I spent some more time thoroughly filing all the surfaces to be mated.  You can see from parts three and four, things didn't get much better.

It was at this point I realised I'd been using the wrong flux.  I'd been applying the stuff for just basic plumbing work using lead free tin solder.  I needed something a little bit more powerful for silver solder brazing rod.  Luckily I had some flux that contained boric and phosphoric acid.  The poison warning on the bottle was bigger than the brand name so it had to be good, right?  Indeed it was. My last two joints were a lot better.  Joint five is almost perfect, but I think joint six got too hot.  It was going well and then the solder started spitting (always wear goggles).  I was tempted to rework the first four parts, but even though they were they ugly, they were electrically and mechanically connected.  I didn't have spare parts, so if I made a mistake it would be a month before new parts arrive from China.  I played it safe and left them alone.  If I had to do 100 of these I think I'd know what I was doing after a few more attempts.

Brass strips with screws soldered in place

It was almost easy sailing from then on.  Joint 6 caused me some problems.  The solder wicked its way through the thread and about 5 mm down the bolt.  This was easily fixed by running an M5 die down the thread to re-cut it.  The flux was then removed and the entire switch was reassembled.

Screw Terminal

All I need to do now is make a mounting bracket and finish the wiring.

Reassembled Blade Switch

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DIY Relay Brackets

I finally got back to a long term project I've been working on.  I'm building a small control box containing relays that needs to be waterproof.  The layout and how to mount everything is sorted except for the relays.  I'm using automotive relays that have a metal tab coming out the back with a single hole.  This makes them easy to mount but if any force is put on the cabling the relays could rotate and work loose.  I'm using nylock nuts so they wont come loose and the spade terminals on the relays will have insulated boots so things can't short out.  Having said that though I want this to be reliable, work for as long as possible, and require little maintenance.  So adding some support for the realys seems like a good idea.

Relay Brackets

My solution was to pop rivet two small aluminium pieces to either side of the relays to hold them in place so the can't rotate.  I put my OCD tendencies to the side on this one and used some of the holes that were already in the plate, so unfortunately everything isn't symmetrical, but it'll still work.

Relay Brackets

I'll keep you posted with the progress of the project but at the rate I'm going I might get it done by Christmas.  I've been having trouble finding time to do anything lately.

Removing Dynabolt Sleeve Anchors

While putting up the frame for my sister's chicken coop I made a slight mistake.  My attention wandered and I managed to fit a Dynabolt, or sleeve anchor as they're sometimes called, in the wrong place.  The bolt was being used to anchor a 35 mm thick pine frame to a concrete slab and once in place they're notoriously difficult to remove, so I thought I'd document how to go about doing it.  I'll refer to the bolts as Dynabolts from here on.  Although it's a brand name, it tends to be what all bolts like this are called in Australia.

First remove the nut from the bolt and tap it into the hole with a hammer until it bottoms out.  The key to removing a bolt like this is being able to get to the sleeve that surrounds the bolt.  To do this I had to remove the nuts from the surrounding anchors and lift the frame slightly.

Top Sleeve in the Frame

Dynabolt and Lower Sleeve

To understand how to remove Dynabolts it helps to understand how they work.  In the image below you can see the 4 parts of the bolt I was using.  The nut, bolt, upper and lower sleeves.  Before installation the bolt needs to be assembled by placing the lower and upper sleeves onto it and doing up the nut loosely with your fingers.  A hole is then drilled into the wood and concrete you want to join and the whole assembly is tapped into place by hammer.  The nut is then tightened with a spanner until the required torque is reached.  As the nut is tightened it draws the bolt with the flared end up into the lower sleeve and spreads it against the walls of the hole wedging it into place.

Dynabolt Parts

Trying to remove the bolt at this point is futile, the nut needs to be removed and the bolt tapped into the hole to release the pressure forcing the sleeve against the wall of the hole.  The sleeve will stay in place due to its own springiness, but it's now moveable.  I was lucky as I could still get at it.  If you can't somehow get to the sleeve you might as well cut the bolt off with a grinder.

In most cases your hole won't be deep enough for the bolt to be pushed under the level of the sleeve, this means you can't just grab the sleeve and pull it out, and pulling the bolt will just wedge the sleeve against the walls again.  The trick is to pull them both out at the same time by using a pair of vice grips to lock the sleeve onto the bolt.  This can then be pried out with a wrecking bar or similar tool.  You may need to reposition the vice grips a couple of times, but you'll get there in the end.

Prying out the Dynabolt with Vicegrips

Prying out the Dynabolt with Vicegrips

Once removed you should be able to reuse the hole.  In my case the hole was in the wrong place and the easiest option was to fill it and put the bolt in a different place.  You could probably reuse the bolt if you wanted to, but I had plenty of spare ones and didn't want to run into any problems.

The main advantage of a Dynabolt is also its biggest problem.  They are really hard to remove.  So if you make a mistake be prepared to spend a bit of time to get it out.  Take a couple of minutes to asses the situation and figure out the best course of action.  Not every application is the same, and different situations may require a slightly different method to remove the bolt.

Damaged Anchor