Crowned Cast Iron Extension Wing

No it isn't "unreasonable" that it will (might) give but I'd be ready to ask for a swap if it didn't.

UA100

He actually said that?! Cast iron's main virtue is that it is really stiff. If you could find a clamp big enough, it would shatter rather than bend.

it'll flex some. I've done it....

I agree that it might flex enough, but I have a problem with that. According to my straightedge, my saw table is flat, but the extension wing isn't. If I follow the advice of the dealer, I might be able to get the edges to line up, but the amount of force needed to bend the extension wing up, will also act to bend the table down. Since the materials are the same, I expect that half of the movement will be from the extension wing, and half of the movement will be from the already flat table. This will result in the seams matching up but the surface not being perfectly flat. If I'm right that the crown is about 1/32", that the table would be off by about 1/64" where the seam is. I know this isn't very much, but this is a new and expensive (at least for me) saw. Is this type of flaw par for the course, or is it something that I should make a bigger deal out of with the dealer? I'm new to furniture making, and so I don't know what the common expectations are.

-Peter De Smidt

Peter,

I tend to agree with your assessment that you might introduce a bend to the table using the suggested clamp method. Another approach is worth considering: Cast iron is malleable... It is possible that you could straighten the wing first, and relieve the stress that caused the post machining crown at the same time. Do this by putting spacers under each end of the concave up wing and carefully bending the center down with slow and steady clamp pressure. I've done this with a 22" jointer plane with good results. I've also read an account of jointer fence castings being tweaked back into shape by bending at the Powermatic factory. If bending cast iron back into shape is OK for Powermatic it should be OK for General!

John

I'd tell him to replace it or he'd get the whole damn saw back.

but that's just me

KY

Hello Peter,

I disagree, 1/32" over ~27", do as the dealer said, it will flex that much. Greg

You got out of there with only one tool? Still have a Powermatic 3520 on the floor? Almost pulled plastic on that one last time I was down there, but I had a plane to catch....

If a properly annealed casting, should be no problem. If one of those quick-cooled large-grained Grizzly castings we hate so much, might crack. You got name and number of advisor? If it cracks, it's replaced.

Peter, I had the same problem with a Powermatic 64A contractors saw. You will be surprised at how very easily you can bend the cast wing by 1/32" and more. I did it by clamping a 2x4 across the width of the saw (side to side) and putting a small block of wood under the 2x4 at the point of the wing where I wanted to push down. The wing will flex with no effort at all. I tightened up the bolts and I could not measure any induced deflection in the main table. YMMV, in which case get a replacement from general. I would try to bend it first. Ken

If it's a new saw, take it back and have 'em make it right. The wing obviously warped after it was ground flat or else it was improperly fixtured on the grinder. Castings for quality machine tools are seasoned for many years before being machined. I have taken two new saws back for having non-flat tables/wings. One was a Craftsman! They sent the whole table with wings attached out to be Blanchard ground. Man that thing was Flat.

dean s

I would like to thank everyone who gave me advice. I matched the seam on the front and middle, tightened the corresponding bolts, and then gently tapped up on the extension wing with a piece of 4x4. This brought that part of the extension wing up even with the table. So far, so good! I don't have a long precision straight edge yet. When it comes, I should be able to find out how flat the whole surface really is.

Thanks again, Peter

I once had a (Jet) jointer whose fence had a bow in it. The company's advice was to prop up both ends (bow up) and put my weight on the middle of the bow till I felt it give. It worked. The same technique should work on your saw extension.

Grizzly's instructions specifically tell you to snug the bolts, and use a hammer to get all the seams right, then tighten the bolts a little more, hammer a little more, etc.

Another trick I figured out: If the wings aren't coplanar with the table (i.e. angled up or down), do this:

• Remove one wing, "fold" it over so that it is laying face down on the table with the "seam" edges together.

• Line up the "seam" edges as best you can and clamp the wing down tight.

• Use a file along the "seam" edges, keeping the file across both the table edge and the wing edge, to make those edges coplanar. In my case, I mostly needed to remove paint (yes, they painted the nicely ground seam edges. Sigh).

• Replace the wing. Repeat for the other wing.

Even if the filing didn't give you a true 90 degree angle, it *will* make the two angles you do get add up to 180 degrees - i.e, the wing will now be coplanar with the table.

Note: this is the same trick as used on a jointer! Even if your jointer fence isn't exactly 90 degrees, as long as the two edges are jointed in the same direction (before flipping one piece over), the errors will cancel out (if you do it wrong, the errors add together and make it worse). Try and see - set your fence a little tilted, joint to boards, and put them together.