September 2008 – bolis.com

Flat panel TV swing-arm mount

Flat panel TV mount Jessica bought a flat panel TV, and wanted to attach it to the wall with some sort of swing-arm mount. The prices at the store were outrageous. Armed with my moderately-trustworthy arc welder and couple of discarded bed frames, we set out to construct one ourselves.

Mock-up

We started by building a cardboard mock-up model. We needed to determine the proper size and shape to fit the TV and wall. First we made a rough model by just bending the cardboard where we thought the joints should go. Then we made a second cardboard model which accurately fit the exact shape and size. We used bamboo skewers for the hinge pins. Once we had everything right, we were ready to build the real thing.

Cardboard TV First rough cardboard arm Second refined cardboard arm Second cardboard arm

Construction

Construction mostly consisted of copying the cardboard pattern onto the angle iron. Most of the arm was fairly simple. The hinges were a challenge. I could not find nylon bushings at the hardware store to match the size of the bolts, so I used polyethylene sockets for caster wheels and trimmed them to fit.

The TV was made to stand on a large foot; it did not include anything for a wall-mount bracket type of configuration. However, it was made with an aluminum frame around the perimeter. We removed the foot and made an X-shaped metal bracket, which we screwed to the frame at the outer edges.

After the sections were welded and filed down smooth, we painted it black with semi-gloss spray paint. We bolted it to the wall with concrete anchors (since this wall is a solid concrete wall behind the panelling) and it works great.

Arm pieces First hinge
Hinge bushings

Wall bracket
TV pivot
TV frame bracket Bracket on TV
Arm on wall

Finished

Submitted by amillar on Sun, 2008-09-21 22:43

Baldor Grinder Restoration

I received a Baldor metal grinder with 10-inch wheels, on its own pedestal floor stand, discarded from a school metal shop program. Several owners before me did not know what to do with it, mainly because the motor is wired for three-phase industrial power which is not found in U.S. residential homes. My job was to fix it up and get it working.

There were two major tasks to the restoration: cleaning/repainting, and making the three-phase motor work.

Cleaning and Painting

I started the cleaning process by removing all attachments that I could, including the wheel shroud side covers, the wheels themselves, and all electrical boxes and covers. I remove all of the old flaking paint and minor rust spots using a wire wheel brush on the electric drill. Some of the paint was still good, but much of it was stripped down to the bare metal. I could not remove the riveted-on motor label and didn’t want to paint the wheel axles, so I covered them with masking tape.

I spray painted the entire grinder and all the separate parts with primer for a good base coat. I followed it with a few coats of grey paint.

I cleaned up the hardware to make it look a little nicer. I filed and sanded the heads of the screws and bolts while spinning them in the drill press. I buffed all of them with a cloth wheel, which made them nice and shiny. I finished it with some clear spray varnish.

I reassembled all the pieces, back in the order they came off.

Electrical

Originally this grinder was hard-wired to the wall using “BX”-style flex conduit. There was a power relay and circuit breaker box, which engaged and disconnected all three phases in sync, using start and stop push buttons.

For the 3-phase power, I built a
static phase converter using capacitors.

I rewired the relay box to supply single phase power to the phase converter. I attached it to the pedestal stand of the grinder. I drilled holes in the pedestal and tapped screw threads into them, and screwed the relay box in place. Instead of flex conduit for the power line, I added a standard power cord. Since it uses 240 volts, double the US standard, I used a different plug and outlet.

The phase converter needs an extra momentary push button to start the motor, so I added that to the front of the grinder next to the main on-off switch.

3-phase motor static phase converter

Start buttons I received a Baldor metal grinder with 10-inch wheels, with a motor wired for three-phase industrial power. Three-phase power is not provided in U.S. residential homes, so I needed to power it from normal single-phase power. My solution was to build a balanced static phase converter, requiring only a few relatively inexpensive capacitors. (Much less expensive than the nuclear reactor I was considering.)

Research and Testing

Electric Motors in the Home Workshop
cover

Amazon | Powells
IndieBound

I knew I had some homework to do, to figure out how to make this work. I had ignored much information on 3-phase motors in the past, thinking that I would likely never need it. When would I ever come across any 3-phase equipment that would fit my miserly budget? Well, now, it seems.

The first resource I turned to was Electric Motors in the Home Workshop by Jim Cox, my favorite book on the subject. This book is written specifically to address reusing various industrial and appliance motors for home-built tools and uses, which fits my crazy schemes. It covered the basics of 3-phase motors, but did not go into great details. It did describe a very common method of generating 3-phase power from single phase, which is called a rotary phase converter. In this method, you use a single-phase motor to mechanically drive a 3-phase “idler motor” which generates the other 2 phases. This is a robust and flexible method which can handle multiple varying 3-phase loads. It also takes up some room, and requires two large electric motors dedicated to it. If you had a variety of 3-phase motors to run, it is a good solution. But it seemed like overkill for just my one grinder.

Phase converter schematic I did some more Internet searching, and came across another idea: the static phase converter. This is a very simple converter which uses capacitors matched to the amperage draw of the motor to generate the extra two phases. As long as your amperage draw does not vary much (meaning you can only really use it for one motor), this is a simple and inexpensive solution to the problem.

I found the best explanation and description in Rick Christopherson’s page on
building a balanced static phase converter. I used his guidelines to determine the likely capacitor values I would need for my converter.

There are two run capacitors for the extra two phases. The two capacitors create pulses 120 and 240 degrees out of phase with the primary, so the second capacitor is twice the size of the first. Based on his tables, I guessed that my motor would require about 6 uF and 12 uF for the two phases.

I went to a local surplus store, and was able to find smaller capacitors of 2.2 uF. My electricity textbook said that capacitors can be combined in parallel to add them up, so I just combined 3 for one phase and 6 for the other, providing 6.6 uF and 13.2 uF.

Just putting the run capacitors in the circuit would get it to run, but it would not start from a stand-still. With my dad helping me, we were able to spin the motor axle with a rope to get it started, and then turn on the power to make it continue running. It worked! I checked the power draw of all 3 phases with an inductive ammeter, and they were all nearly identical within 0.2 amps of each other.

Final start capacitor To bring the motor up to speed under power, it needs a large starting capacitor, connected in with a momentary push button. They are readily available, sold simply as A/C start capacitors. I had a capacitor from an old washing machine motor, which worked to start it as a test. I ordered another one of 86 uF from an Internet mail-order surplus place. Holding the start button for about 3 or 4 seconds is all that is needed to bring the motor up to full speed. Run capacitors Test start capacitor

Construction

Figuring out the capacitor schematic and values was the hard part. The rest of the construction was relatively simple. The grinder already came with a large magnetic relay contact switch and circuit breaker, previously wall-mounted separately. I attached it to the back side of the pedestal stand, and put the push-button on/off switch on the front. I added two new electrical boxes: one on the front for the momentary start push button, and one on the back to hold the capacitors.

Since the voltage is double at 240v, I needed a different plug and outlet. But the amperage is low at 5 amps, so did not need a large super-heavy-duty power cord and plug like one might use with an electric clothes dryer or kitchen stove. I found a plug and outlet the same size as a standard US power plug, but with both prongs rotated at 90 degrees from standard, so neither side could be accidentally interchanged with a normal plug. Since the total amperage draw is only 5 amps, a 14-gauge power cord was adequate.

Tapping holes Switch boxes Converter and relay boxes Relay Wiring switches Power to relay
Converter in box

Result

Start buttons Converter closed and labelled I created some labels using Inkscape, printed them on photo paper, and attached them to the various boxes.

The end result was very satisfying. The motor only takes about 4 seconds to spin up to speed, and the grinder works great.

Submitted by amillar on Tue, 2008-09-16 12:08