Tuesday, November 20, 2012

Dining Table: Trestle Structure

The support trestle is all made out of old Douglas Fir framing lumber that came out of our house, which was built in 1911.  Roof rafters were 2 x 4 and will live on as the stringers and legs, a 6 x 6 porch post will become the feet, and a 2 x 6 joist from the bathroom floor will become the horizontal brace.

The stringers (aka battens) were made and attached several weeks ago, as I flattened the top.

Mmmm.  Lead-based paint.
The big post that became the feet was coated in nasty old paint, had a ton of nails in it, and has been sitting out in the weather for a couple of years.  Even in that condition, I couldn't throw out a big chunk of clear lumber like that.  First I pulled all the nails (one I couldn't remove got driven in deeply with a nail set) and used a thrasher ebay jack plane to clean off the paint and flatten the surface.  The wood was wet from a few rainy days, so it kept the lead dust down.  I cut off a couple of 26" lengths with one of my grandfather's old hand saws, and then ran those through the power planer to clean them up.  After deciding how to orient the parts to hide most of the defects, I used the band saw to rip down the foot blanks to 3-1/4" x 4-1/4" x 26".

Ah, the irony.  I'm not a masochist.  That stock is too long to crosscut on the table saw.

To make the curved shape of the feet, I spent some time designing patterns on hardboard, then used that to draw and cut a couple of test pieces on 2x6 lumber to show my wife and refine the shape.  Once I got to something we were happy with, I used the template to draw the shape on both sides of the foot, and then cut off most of the waste on the band saw.  I used a hand saw and chisels to make the sharp arrises where the flat top transitions to the curve.  A paring chisel took off most of the remaining waste, and then a little quality time with the oscillating belt sander smoothed things out.

Shaped Foot
The legs are glued up from two 26" pieces of 2x4, with a 1/4" strip of walnut between them as an accent.  Final blank size is 25-1/2" x 1-5/8" x 7".

Roughing out mortises at the drill press
I put a 1/2" x 1-1/2" x 6" mortise in the stringers.  I made one with a brace and bit followed by chisel work, but roughed out the second one at the drill press with a forstner bit.  The quality is the same, but the drill press is quicker.  The foot got a larger mortise, 3/4" wide by 1-3/4" deep, because there's a lot more to work with on that part.  Matching tenons were made in the leg blanks, cut close with the table saw and fine-tuned by hand.  I have a Lie-Nielsen rabbet block plane that is my go-to tenon tuner.  It can even be flipped over and used to clean up the shoulders if the wood is nice.

Cleaning up a bottom leg tenon with a L-N rabbet block plane.  Haven't cut the narrow shoulders yet.
The cross brace is just a 2 x 6, planed down to smoothness.  Big 4" x 4-5/8" long tenons were shaped on either end, fitting into 1-1/2" x 4" through mortises in the legs.  Those were carefully chopped from both sides, since the edges would be visible in the finished piece.  After fitting the legs to the cross brace, a tapered 1/2" x 1" (to 3/4") through mortise was made vertically through those for tapered walnut tusks to hold the assembly together.
Drilling for the mortise that will hold the tusk tenon (in background)
that secures the leg to the horizontal brace.
A few more details:  the ends of the horizontal brace's exposed tenons were rounded off at a 5" radius, and 1/4" was removed from the bottom of the feet to leave square pads on the ends.  Most edges were eased or slightly chamfered with a block plane, to prevent splintering and keep the incidence of damaged shins to a minimum.  The stringers and feet were glued onto the legs and that's all the permanent joinery on the base.  Bam.  Done.  Now these parts can get out of the way while I finish the top.

The big question now is, will I finish in time to use this table for Thanksgiving dinner?  My family's not coming up until Saturday, so I've got a couple extra days.

Thursday, November 8, 2012

Choosing a water heater

Like everything else in the world, picking a new water heater requires an unreasonable amount of research and nail biting.  Here's a taste, based on a friend of mine's situation.  It should be pretty easy to plug in your own numbers for usage and utility rates to do this for yourself.

Some terms:
Sorry for the units, all you socialist users of the metric system!
BTU: the amount of energy it takes to heat one pound of water 1˚F (aka British Thermal Unit)
1 kWh = 3412.3 BTU  (common unit for selling electricity)
1 therm = 100k BTU  (common unit for selling natural gas)
1 gallon of water weighs 8.35 lbs.
EF: efficiency rating - tells you how much incoming energy makes it into the hot water.  Manufacturers like to bs around with this.  For example, I believe they ignore any electrical consumption made by a gas appliance.

First, estimate your usage.  For my friend, I figure one shower a day (10 min @ 2.5 gpm @ 105˚F) uses about 20 gal of hot water (the rest of the 25 gallons used is cold water mixed in the shower valve).  1 load of laundry average per day = 4 gal in her high efficiency front loader. Dishes, hand washing, etc. takes another 10 gal.  So, 30 gallons a day.

How much energy is that?  The average incoming cold water is about 50˚F here.  If the tank is set to 120˚F, that's an increase of 70˚F, and that 30 gallons weighs 250.5 lbs.  70 x 250.5 = 17535 BTU per day.

The most basic electric water heater has an efficiency rating of about 0.90, and putting a thicker layer (3") of foam insulation gets them up to 0.95 pretty quick and cheaply.  Note that the EPA no longer gives Energy Star certifications to any electric tank models except for the heat pump hybrids.  The bottom line is it's too easy to get right close to the theoretical maximum EF of 1.0, so they don't feel like they need to reward anyone for that.  Given how many people and programs base their buying on the Energy Star label, I think that's a mistake, but anyway...  So, I'm looking at a 40 gallon model with a 12 yr warranty at Lowe's for $450.  Nothing fancy.  At EF 0.95, this model will consume 1974 kWh per year.  (17535 BTU / 0.95 = 18458 BTU input needed per day...  18458 / 3412.3 = 5.41 kWh / day...  5.41 x 365 = 1974 kWh / yr).  Our electricity is 0.11 per kWh, so operating cost is estimated at $217 a year.

Natural Gas
A very basic gas water heater is only about EF 0.59, but it's easy to find them up around 0.64.  Energy Star models have to exceed 0.67, and the highest efficiency models get up to 0.70.  I'm looking at a 0.67 Energy Star, 12 yr warranty model at Lowe's for $570.  This model will consume 95.5 therms of natural gas per year.  (17535 / 0.67 = 26172 BTU input per day...  26172 x 365 = 9,552,649 BTU / yr...  divided by 100k = 95.5 therms / yr)  Our natural gas is $1.08 per therm, so operating cost is estimated at $103 a year.

So even though the gas unit costs more, it should pay for itself pretty quickly, and the savings is more if you use more than the fairly minimal amounts in the examples above.  But of course there are other things to think about.  All-new installation of a gas unit can be very expensive.  It needs an exhaust vent (chimney), or for some models they can vent via a plastic pipe out through the wall.  Gas units are dependent on both the electricity (fans, controls, igniter) and gas utilities to operate.  Electric just needs electricity.  Electric units have no moving parts, and are much less complicated.  They also are very cheap to repair (replace an element or thermostat) and the little bit of energy that they do lose ends up in your house.  We live in a coolish climate, so the extra heat is a good thing for eight months of the year.  Gas units dump all their excess energy out the vent, and they also poke another hole in your house's building envelope, requiring installation of a motorized vent damper if you don't want air flowing through the stack when the unit isn't operating.  Electric heaters are much less likely to cause explosions if you happen to spill something flammable near them, and the carbon monoxide hazard is zero.