Saturday, March 27, 2010

A Garden Fork Repair

Needless to say, the little marriage breakup pictured needs mending. This project will make an excellent illustration of the usefulness of CA adhesive and epoxy. But let me begin with a bit of fork terminology that I gleaned from the Lee Valley catalogue.

It seems that there are digging forks (bigger) and border forks (smaller). Lee Valley's digging forks have an 11" x 7" business end. Their border forks have an 8 1/2" x 5 1/2" business end. My fork measures 9 3/4" x 6 1/2" -- betwixt and between. So I've called it a garden fork and I'll leave it at that.

The Problem

Originally, the fork's tang was force-fitted into what I take to be hardwood inside the steel ferrule. There were no rivets securing it, which was fine so long as the hardwood remained sound. But water incursion and retention caused the hardwood to rot and the fork to come loose. What I have left in the ferrule is a loose bit of the original hardwood tang-surround sufficient to hold the tang in position, but hopelessly inadequate to secure it. Above that up to the bottom end of the handle is a cylindrical void roughly 1" long x 1 1/4" diameter.

Two things need to happen here. The loose tang-surround must be secured in the ferrule; and the void, fissures in the tang-surround and the tang/tang-surround interface must be filled with an unyielding material.

Securing the Tang-Surround

This is where CA adhesive really shines; it's very runny, and wicks into cracks and pores and interfaces by capillary action. With the dust blown out of the ferrule's cavity with compressed air, and the loose tang-surround in position, I only need to present drops of CA adhesive to its edges and the adhesive will make its way in to bond the piece in place to the ferrule, and to fortify what's left of the hardwood that's still halfway sound.

Filling the Void and Securing the Tang

This is where epoxy comes in. I've never found epoxy to be all that great for outright adhesion, but it has characteristics that can be exploited to achieve remarkable results. It hardens, without shrinking or swelling, to become quite a hard, very tough material. Since it starts out as a fluid, albeit a very viscous one, it will take the shape of whatever it's enclosed in; and therein we have the key to permanently retaining the fork's tang in its ferrule. Here's the wire-brushed tang ready for installation with epoxy.

Note the sequence of shallow grooves that were cut with a 1 1/4" diameter reinforced Dremel cut-off wheel. All four sides of the tang got that treatment. Consider what will happen when I shove that tang into the ferrule's opening after I've filled it with epoxy. The fluid epoxy will fill and conform to every cranny, fissure and groove in the tang-surround and the tang, and then harden there. The void and the tang/tang-surround interface will contain a contiguous, hard, tough incompressible filler. As a retention medium for the tang, one can't do any better.

The Epoxy

I usually use the five-minute type, but I bought the slow-curing variety for this job; this will take more epoxy than I'm accustomed to working with at one go.

A Little Math Digression

I wanted to calculate the volume of the cylindrical void in the ferrule, just to be certain that I had enough epoxy on hand, and it dawned on me how fuzzy I am on the fundamentals of metric volume units. (I really shouldn't have dropped out of high school. I'd know all that stuff if I had a diploma.)

Pop quiz: What's the definition of a litre?

(I'd love to know how many Canadian citizens, particularly the ones who are always spouting off about education and the 'knowledge economy', know that right off the top of their head.)

It's a cubic decimetre; i.e. the volume of a cube ten centimetres on each side. 10cm x 10cm x 10cm = 1,000 cubic centimetres = 1 litre. So, a millilitre is the same thing as a cubic centimetre (cc). That fact makes for an exceptionally easy way to find volumes in millilitres.

Normally, when using metric linear measure one is well advised to express everything in millimetres only, no matter how huge a thing may be. That practice is good insurance against decimal point placement errors, which are all too easy to make with centimetres. But for finding millilitre volumes, calculations based on centimetres work out directly as millilitres.

Pop quiz: What's the formula for finding the volume of a cylinder?

It's 3.1416r2h or 0.7854d2h.

Where r = radius, h = height and d = diameter.

Truthfully now, did you know that right off?

Anyway, plug in centimetre values and the answer will be in millilitres.

Using a rough conversion from my inch measurements for the void in the ferrule, we have:

0.7854 x 2.5cm diameter2 x 3.2cm height = 15.708ml. Call it 16ml.

That's well within 37ml, the volume of the epoxy tube I bought. (Actually, I knew I had enough epoxy just by looking at the size of the tube compared to the size of the ferrule, but this little math exercise was fun. And I know what you're thinking, "This guy doesn't get out enough".)

By the way, epoxy is a two-part adhesive -- resin and hardener. From what I've observed, if you mix up, say, 10ml of epoxy resin and 10ml of hardener, you'll end up with just a little more than 10ml of epoxy. The two components intermingle without increasing one another's volume by very much at all.

Mixing the Epoxy

As I said, I'm unaccustomed to working with so much epoxy at one time; most of my epoxy requirements are for quite small amounts, easily mixed on a business card with a small screwdriver.

I simply scaled up that method for this job, and it proved to be a clumsy way to go about it.
Were I doing it over again, I'd contrive a way to measure the needed amount of resin and hardener into a disposable cup and mix it there all at once. As it was I had to mix three consecutive batches to fill the ferrule.

Nonetheless, the outcome looks good. There was a tiny bit of subsidence at the rear of the tang. I back filled that with some five minute epoxy, and touched up all around to produce a nice fillet.

Here's the fork back in its natural habitat.

This fork wasn't always the dowdy looking thing you see in the photo. In its youth, it had a glossy yellow fibreglass-clad handle. Beware of fibreglass-clad handles on yard tools.

What they are is a hardwood core in a fibreglass sleeve. If the sleeve acquires a slight fissure, and the tool gets left out in the rain, water will wick into the fissure and be unable to evaporate out at any appreciable rate. The hardwood core will rot and you'll end up with this:

So much for the glossy yellow handle. It looked good in the store.

Anyway, I expect this repair to be a complete, durable success. This was a great example of the sort of application that epoxy excels at.

Something I Didn't Foresee -- SUNDAY, DECEMBER 9, 2012

The fork got left out in the rain, the wooden handle took on moisture, swelled up and split the ferrule of the all-plastic handle. A couple of hose clamps are in order, like so.

That'll work fine.

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