Cast Iron Bed Tolerance

[aborza]

I know that no cast iron table saw is perfectly flat. They all have a tolerance (+- something) from flat. But high quality saws are flatter than cheap ones. And I have a cheap HF saw. My question is, "What is the worst acceptable center table sag for a cheap saw?"

For example, my brand new cheap HF saw has a sag of .006" (measured) across its central width (not including its wings). The sag is a smooth curve down resulting in a depression of .006" in the center of the table when measured from side to side without the wings on. It seems almost perfectly flat front to back.

Obviously, this is not what it ideally should be. But is it really that bad? Should I consider taking it back when I only paid a hair more than $200 for the saw new? What is a reasonable tolerance for that measurement if my goal is making speaker boxes, book shelves, cabinets, etc.?

I know you should shoot for mirror flatness but what I am asking here is how bad it can be and still give good performance.

Thanks

ab

[tpratt]

It sounds like < 1/64". You might be able to shim in the center (front and back?) to bring the table flat again.

[aborza]

Actually .006" is less than 1/165".

Have you ever done this? Where would I shim from? I doubt the sheet metal base would be a good place. It is not as strong as the cast iron top.

Thanks

ab

[Jim Boyd]

Quoted from the rec.
"Duginske
(in his book Mastering Woodworking Machines) says the table should be flat
to within 1/32"."

[aborza]

Well, I edited and corrected my prior posts to show my table is actually flat to .006" which is less than 1/165".

So I guess this means that I have nothing to worry about. Right?

Thanks

ab

[LCHIEN]

I could have sworn that I saw that your saw had .060" of sag
but now that it has dried out and reached equilibrium with your shop and the sag reduced to only .006"
it would appear to be OK.

[monte]

I wouldn't worry about the minimal amount of sag in your table.

[aborza]

Thanks All

ab

[Knottscott]

I wouldn't give that amount a thought...

[aborza]

The reason I was concerned is that when you put a straightedge across the table and look at the space between the table and straightedge the gap looks huge. When backlit, the amount of light that comes through is remarkable. In fact, when I measured the gap with guages I was surprised it was only .006"

I don't have a high quality table to compare it with. But I would expect a high quality table to show essentially no visible gap at all.

So if I understand correctly, this small an irregularity is insignificant when making finished speaker boxes, cabinets and household furniture even though I will not be using a jointer. Right?

Thanks

ab

[Knottscott]

quote:Originally posted by aborza

The reason I was concerned is that when you put a straightedge across the table and look at the space between the table and straightedge the gap looks huge. When backlit, the amount of light that comes through is remarkable. In fact, when I measured the gap with guages I was surprised it was only .006"

I don't have a high quality table to compare it with. But I would expect a high quality table to show essentially no visible gap at all.

So if I understand correctly, this small an irregularity is insignificant when making finished speaker boxes, cabinets and household furniture even though I will not be using a jointer. Right?

Thanks

ab

Backlighting the gap tends to exaggerate it.

[Tom Slick]

.006 is fine. general machining tolerances for most parts made in the USA are +/- .005. something ground to spec should be less but for a table .006 doesn't sound bad to me.

[Flyingscooter]

I would not worry about it at all. .006 is about the thinkness of 2-3 human hairs.
I worked in a machine shop for a few years as a grinder on steel, alum, and urathane work rolls for the mills (ltv, usx. etc) If you were within .005 across 90" of urathane, you were great. Can't imagine much of a differance on wood.