Monday, June 24, 2019

hot wire foam cutter

I built a simple hot wire foam cutter to make parts for a couple of projects.

I wanted to slit a full sheet of 1.5 inch insulating foam into strips for a mooney wall. Another project, a water heater insulator, required large foam discs.

What started as quick and dirty ended up a very useful tool.

Using scrap wood, I began by adding a slot and a "fence" to a partial sheet of particleboard to make the table. The board was what I had, about 3 foot by six foot supported on two saw horses. I added a strip of wood lengthwise opposite the fence to support the front edge. The table is hung on the wall when not in use. [click any pic to enlarge]

Using particle board was problematic. When fed across the table, large pieces of foam would catch on the tiny sharp fibers sticking out of the particleboard. I later sanded and painted the top surface with several coats of latex paint which helped. It would have been better to use a smoother surfaced board.

The cutter arm is U shaped to support the cutter wire and slides in a groove under the table to adjust. It is then fixed in place for the cut.

I thought to make a variation with the hot wire slide-able to make cross cuts but haven't done that yet.

The slotted hole in the table is for the hot wire. I didn't want to cut through the fence on the back of the table. There is a minimum width that the wire can be set to, about 6 inches and a maximum of about 18 inches. The width of the slots for the mooney wall are 14.5 inches so this is a good amount of adjustment. Varying the dimensions could give other capacities.

The hot wire on the bench with power supply testing cutting action!

It turns out that the wire does not need to be red hot as shown, but just slightly less, sort of a dull red. I have an adjustable DC supply giving the wire about 4 amps at 8 volts. The voltage and current will depend on the wire type, gauge, length and the desired temperature so the adjustable lab supply is a good fit for a hot wire cutter. Normally the supply sits under the table and is connected to the two ends of the hot wire with test leads.

The wire I am using is heater wire (nichrome), typically used in toaster ovens. The first samples of wire I used were harvested from an old appliance. Later I found that I could easily buy small amounts of nichrome wire on Ebay from China so ordered 0.3, 0.4 and 0.5 mm coils.

I found that 0.4mm nichrome gave good cutting life and resistance to breaking. Getting the right temperature and the feed rate requires a bit of experimentation.

Nichrome wire expands when heated, as much as 5%, so there is a spring in the mount to put the wire under tension. When at the operating temperature, there should still be a bit of tension from the spring to get a straight cut.

The wire is simply looped through the eye bolt and wound around itself a few turns. The nuts on the eye bolts are adjusted to put the wire under tension. Normally I form, adjust and test the wire on the bench out in the open, then remove it from the arm, mount the arm on the table and then remount the wire through the slot in the table. It's easier.

Shows the smooth cut on blue type styrofoam. The edge obtained is very smooth.

Cutting foam discs with a pin through the center into the table as a pivot.

Using a thin template to guide the wire to produce a cutout in one of the discs.

Again using a template to make cutouts in one of the discs which has been already cut in half with the wire.

One of the many eight foot by 14.5 inch slabs for the mooney wall that was cut with the wire cutter.

Thanks for your interest.

George Plhak
Lions Head, Ontario, Canada

Detail under the table showing the mount for the arm made from scrap wood. The arm (with the wire removed) is inserted in a slot from the back and fixed in place with the screws that protrude to the right. Crude but adequate.

Thursday, June 20, 2019

water heater update

INDEX to the series

This graph [click to enlarge] shows the big reduction in standby energy use between my old (blue) and new (red) water heaters at different basement temperatures. The new uses much less electricity, about 25% less. Same capacity, same size heat elements. 25 year age difference.

What's changed?

The new heater has better insulation, a DIY insulated mounting base and is time of use controlled so it does not use peak priced electricity.

I will show the key physical differences between the new and old. The old was produced in 1994.

My old water heater had been quietly making hot water in the basement here for 25 years. It was not leaking and did not require replacement. It had no maintenance during the last five years with me. It worked well but could have been more efficient.

I pay tribute to this fine Canadian product by Giant Factories Inc. It owed me nothing.

To become more efficient, I purchased a competitor's product from GSW (division of A.O.Smith). Although Fergus is on the nameplate, the GSW factory in Fergus hasn't made anything in years.

I might have made a better comparison by getting a replacement Giant. Local stock product was competitive in price.

In any case, I will compare old product to new product. Both are standard electric domestic hot water heaters, now called "Automatic Storage Water Heater". Both are the same size (give or take a cm or so, I lost my actual measurements). About C$350 cost now. The technology of even the most simple commodity hot water heater has improved dramatically. Much of the improvement is federally mandated to improve efficiency. My old and new have the same capacity and the same elements but are 25 years apart in manufacture.

In other words, GSW's Fergus product of 1994 is probably much like the Giant of 1994.

So if you haven't thought about improving your trusty old hot water heater, you might save significant electricity if you do. Here is what I found:

The top of the old with the cover removed. I can see the steel tank where there is no insulation.

I am holding the anode which does not help efficiency but adds life expectancy. This anode rod (aluminum or magnesium usually about the size of my little finger) is completely corroded. An anode rod is replaceable but who ever does that?

The anode protects the inside of the steel tank by being sacrificially dissolved itself as a dissimilar metal, like a zinc anode on the hull of a sailboat. When it is gone, the tank starts to corrode so this one is well past its best before date. 25 years old! Probably never been changed.

Note the iron pipe fittings out the top for inlet, outlet and pressure relief. Copper lines were attached to these fittings with no thermal break (insulated coupling).

These UN-INSULATED metal pipes had been heat radiators into my cold basement. The pipe from the hot water outlet (the one on the left with the pressure relief valve) was always HOT to the touch. Lost heat.

Note also that the insulation inside is a glass fiber wrap with lots of empty space/air! Particularly over the very top center. Perhaps I pulled some of it off with the top? It could not have been this bad could it?

I didn't determine how the steel tank was supported inside the steel can but there must be some metal support structure from the tank to the outside which would probably cause some heat loss.

The new heater has about 2.5in / 6-7cm of foamed in place insulation at the top near the center. I am measuring to the steel tank through the anode access.

In fact I had to dig out some insulation to get access. I wanted to look at the installed anode. The top of the anode rod bolt will be my measuring point for water tank temperature once I insert a sensor and cover/insulate the opening I have made in the insulation.

The anode access has a cute cover plug but once removed, you need to dig out the foam down to the hex head on the anode bolt.

Note the insulated fittings for hot and cold on the top of the tank. The pipes that lead to these fittings are no longer warm to the touch.

Likely the foamed in place insulation completely supports the tank mechanically (unlike glass fiber) so no need for a bridge structure hence lower heat loss.

The fitting to the drain valve at the bottom of the tank was an iron pipe to a metal valve. Both good conductors of heat to the basement.

The old tank used to sit right on the cold concrete basement floor.

"Verified for Energy Performance" in 1994!

The drain is now a recessed plastic valve, a much better insulator.

I've raised the tank off the floor on an insulated base, making it easier to do the annual residue draining and reducing the heat lost to the cold concrete floor.

The wooden base (about 8 inches high) is topped with a 1.5 inch foam disk.

The diameter of the base is larger than the water heater by about the thickness of a batt of rock wool insulation. It could have been a square platform to be simpler to make.

I will wrap the entire new water heater with an insulating blanket after installing seismic straps. Not required by the code here but a good idea anyway for a 100 year event. Earthquakes do occur in Canada.

Time of use inhibit I wrote about here.

I plan to install direct energy metering for the water heater as it is one of my top energy consumers. NRCan on water heaters. Note that there are no storage tank electric water heaters that are Energy Star rated. I think mine will qualify when finished!

Thank you for your interest,

George Plhak
Lions Head, Ontario, Canada.

INDEX to the series

Nameplate for the old Giant.

The date code means the tenth month of 1994.

Nameplate for the new GSW lists Fergus, ON CANADA for address of manufacture?

Monday, June 03, 2019

reader project 6

Project description from Matt Janssen:
[click any pic to enlarge]


Here is a 3/16" laser-cut steel-framed parabolic trough array based on your design.

There are a lot of things I really like about your design and there is no way I could have learned so much about parabolic trough technology that would have not taken more time and more money than building your design and experimenting with it. I believe your geometry with the fixed absorber tube is key for small trough construction. I have fought rotary joints on steam projects before and they are just too finicky and expensive.

One improvement I made after my first trough using your CAD files is to add a countersunk angle iron under the sheet at the longitudinal rim edge of the trough which assists with clamping the edge and avoiding corrugation caused by bending stress around fasteners.

We re-drew the ribs and added this countersunk notch as well as an offset for the reflector sheet thickness. The troughs have 68" T316 24 gauge Super 8 SS sheets which have about a 63% reflectivity. I am using one of the bottom holes for a 1/4" through stay rod. The troughs are powdercoated.

I started out with (9) 3/8" black pipe return bend elements slid in the borosilicate vacuum tubes running forced-flow in series and at no flow could make 200F. The geometric concentration ratio of this setup is about 22. While the array could make significant hot water with flow, I did not test it further as the max temperature was too low. I then installed 1/4" sch 40 pipe bare absorber tubes and reconfigured the pipes to parallel flow. In 40F with high insolation I could make 265F steam with no flow. This is about the limit of concentration ratio that a thin sheet reflector compressed to a rib frame will support - about 35.

I think even more performance could be achieved with these troughs by using silvered mirror film and encasing the tubes in glass. I have decided to start over and this array is now available.

I have about $15K in parts in it and a reasonable offer with timely removal takes it. There is one spare trough like these, my first trough, an aluminum trough, the other absorber elements, a bunch of borosilicate tubes, and a welding fixture.

The array was stored inside all winter and was just hauled-out 05/30/2019.


Matt Janssen
Sandpoint, ID

If you like, you can email Matt directly.

Thank you for your interest

George Plhak
Lions Head, Ontario, Canada

reader projects
reader project 0
reader project 1
reader project 2
reader project 3
reader project 4
reader project 5
reader project 6 this article
reader project 7