INCA 259 Saw - Broken Elevation Arm

August 3, 2015
A couple of years after I received the gift INCA 150 table saw, I took the plunge and purchased a secondhand INCA 259 table saw from a fellow here in Portland.  Unlike the gift 150, this one worked and was functionally complete; well, mostly, since it is missing the tenon-cutting guide.  I put a Forrest Woodworker II blade on it and have been using it happily since.

About 10 days ago I was working on some shelves on which to store wine in my basement, and attempted to lift the table (what we think of as lowering the blade, but since the arbor on the saw is stationary we instead change the table height).  I don't know if the lift mechanism was poorly adjusted or I reached the limit of travel, but there was a sharp "plink" noise and the table fell to its lower limit.  The height control knob turned freely but the table didn't move.  I had an unhappy feeling that was confirmed once I took the machine apart to examine the lift mechanism.  I found that the cast-aluminum elevation arm had snapped:

I chatted with a couple of folks (Jesse at Eagle Tool, and Jerry Walker in Ontario) and found some facts:

• This is a common problem, and Jesse sees a couple of requests each year for this part.  The casting cross section is a U, and the missing material and stress concentration at the "neck" seem to cause this part to snap at the same point.
• New parts are not available from INCA
• Jesse services requests for this part by either taking the part from a donor saw, or by having a local machine shop machine a new one from billet aluminum.  The machine shop focuses on other work, and there's frequently a delay for them to get around to making a handful of INCA parts.
• Jerry appears to have similar machining capabilities and has made a number of frequently-broken parts for INCA tools

Because I couldn't find someone with the newly-machined solution, and since I didn't want another used arm off a donor saw (I fear it would break under use just like mine did), I took the approach of casting my own from aluminum I have on  hand.

First I made a model out of wood scraps.  I traced the outline of the metal part on the wood, and gave it a bit extra (say 1/8" in each dimension) since the hot metal will shrink as it cools.  The surface holes in the oak are caused by my cheap Harbor Freight pin nailer misfiring instead of nailing together the two half-inch thick pieces of oak.  Oh, and don't use oak for this, it's too hard to shape; use a softer wood.

Here it is with a bit of shaping, and with voids filled in with some really light & airy spackling compound I had lying around.  It's amazing stuff in that it air dries quite hard, but is water soluble and very easy to work.

I eased the edges, created a slope on the sides (so the model will pull out of the casing sand easily). Some sanding and a coat of spray shellac yielded this.  

Pär on the INCA list asked for for me to trace the original part over 1mm graph paper.  I have posted the original size photos here and here.

I created a sand mold from the pattern, melted up some aluminum, and pored it.  However, I failed in a key area: I estimated the amount of aluminum to melt and I estimated too little.  As a result, my metal didn't fill the mold and the casting is incomplete.  You can see this in the rough surface here, which should actually be nice and flat:

I'll get to do that again tomorrow.

August 12, 2015
I remade the mold and melted more aluminum, and this time I got a full part.

I'm not in love with the graininess of the casting, but I'll machine it a bit and see how it looks.  If all else fails, I'll try again on the casting.  The grain in the finish is caused by my liquid aluminum being too hot.

My sand mold didn't part cleanly when I opened it up to remove the pattern, and that's why I have leakage around the parting line.  That means I have some clean up to do.




























September 13, 2015
There has been a delay in the project while I fix some car items and clean the garage enough to get both cars inside at the same time.  Yesterday I was able to spend a little time thinking of how to extract the steel pin from my old elevation arm and install it in my new part.  I assumed that the pin was a regular cylinder pressed to fit into the hole in the arm, so I set about trying to pull the old part out.  It wouldn't move.  At all.  I used heat to expand the aluminum with no luck, and ended up melting/mashing the old aluminum arm in order to get the steel pin out.  And now I understand why it was hard to remove -- it is fully knurled in a diamond pattern:

I don't see how this could have been pressed into place and I imagine instead that the aluminum was cast around this pin so that the molten aluminum could conform to the knurling.  If that's the case it means I get to redo my aluminum casting.  I'm almost glad about that since I feel like the aluminum in my prior melt got too hot and created a pretty grainy finish on my casting.  But this does mean a bit of a delay so that I can alter my pattern to accept the pin, make a new mold, insert the pin, and cast aluminum again.

April 16, 2016

Much car fixing completed (that's a whole other story, but I have replaced most of the consumable elements of my 1997 Jetta GLX: clutch, timing chains, suspension bushings, coolant overflow tank, radiator, "crack pipe", thermostat housing, water pump, valve cover gasket, oil pan gasket, intake boot, oil and air filters, spark plugs, and sundry other bits).  Now I hope to return to hobbies.

On the saw repair, today I drilled a hole in the wood pattern to accept the pin.  This was made more challenging by the presence of the pin nails I used to join together two layers of wood in the pattern -- one pin was nicely centered under the end-mill I used to make the hole.  I think I'm now ready to make a sand mold and try another casting.

April 21, 2016

I have cast a new part.  This time around my mold had a space for the pin, and I left the steel pin in the mold when I poured the molten aluminum, allowing the aluminum to flow around it and secure it in place.

Here's a shot of it with sand removed, but with sprues attached and other casting errors unfixed.

The new casting with embedded pin is on the left, while my prior attempt is on the right.

April 19, 2017

Time passed and other projects came to the fore.  Through it all I had this project stuck in the back of my head, and I really didn't have a good way to machine the slots I needed in the cast part.  I don't own a mill, and doing this much material removal by hand or in a drill press seemed doomed to failure.  In the end, a fell member of the INCA Tools listserv parted out his old saw, and I bought his elevator arm.  The part arrived around 10AM, and by 2PM the saw was back up and running.  

Did I take the coward's way out, or was I just being smart?  I don't know, but my saw works :-)