How flat is flat? - Router Forums
 
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post #1 of 9 (permalink) Old 02-14-2011, 02:07 PM Thread Starter
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Default How flat is flat?

Just discovered that my cast aluminum saw table extension is not perfectly flat. I placed a very dependable straight steel edge across it and can see a crack of light under it on the infeed side of center... not large enough to slide a business card under, but a very thin piece of paper does slide in. Sorry that I don't have any means to give you an exact hundredths or thousandths. It's about a 7" wide bow (dip). Would this still be considered flat enough for a router table? Or will it compromise my work?

If after expending all the effort and time involved to convert this extension, I found that it did not deliver the quality of workmanship I expect from my work, I'd be very distraught. If I purchased a Rockler or Kreg table, would they be PERFECTLY flat?

What are acceptable flatness tolerances?

Thanks,

Joel
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post #2 of 9 (permalink) Old 02-14-2011, 04:20 PM
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That sounds like a fairly minor variation, Joel. If you put a piece of stock on it, does the stock wobble? If not, you're probably OK.

- Ralph
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post #3 of 9 (permalink) Old 02-14-2011, 09:32 PM
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Those other tables you mentioned are probably flatter. Unless you are doing something that requires great precision, like rails and stiles for cabinet doors, I doubt if it will be a problem. It may not make a difference in precision work either. Two pieces that don't line up by the thickness of a piece of paper is not very much.
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post #4 of 9 (permalink) Old 02-15-2011, 07:29 AM
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If your stock wobbles as in Ralph's reply, you can torch-er board the surface with wet and dry to true it. I done this to a lot of worn machines and the results are extremely satisfying
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post #5 of 9 (permalink) Old 02-15-2011, 09:42 AM Thread Starter
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Thanks for the info.

I can't detect a wobble unless I simulate an end cut on a 3" wide board. When I move it through this slight dip, I can feel it drop in ever so slightly. Hardly detectable. However, by the time it's at the router bit's position in the table, it's on the flat again.

The cast aluminum top is anodized and has a dark gray surface. I really don't want to ruin the coating by sanding it. It is 30 years old and has survived so well, I just don't want to invite new problems like bare alumininum "marking" the wood.

My first router table project will, in fact, be stiles and rails. That's why I'm concerned about the accuracy.

Thanks again. Joel
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post #6 of 9 (permalink) Old 02-15-2011, 10:23 AM
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Hi Joel

Not a big deal, you can always stick down a sub base(top)with tape, to your router setup, if you think it may not be flat, a simple 1/4" thick MDF board will take that little error out..so you get a true pass by the bit for the R & P parts..("stiles and rails parts")

OR screwed to the bottom side of the fence

See below


===========



Quote:
Originally Posted by joel74 View Post
Thanks for the info.

I can't detect a wobble unless I simulate an end cut on a 3" wide board. When I move it through this slight dip, I can feel it drop in ever so slightly. Hardly detectable. However, by the time it's at the router bit's position in the table, it's on the flat again.

The cast aluminum top is anodized and has a dark gray surface. I really don't want to ruin the coating by sanding it. It is 30 years old and has survived so well, I just don't want to invite new problems like bare alumininum "marking" the wood.

My first router table project will, in fact, be stiles and rails. That's why I'm concerned about the accuracy.

Thanks again. Joel


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post #7 of 9 (permalink) Old 02-15-2011, 12:02 PM
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Quote:
Originally Posted by joel74 View Post
Thanks for the info.

I can't detect a wobble unless I simulate an end cut on a 3" wide board. When I move it through this slight dip, I can feel it drop in ever so slightly. Hardly detectable. However, by the time it's at the router bit's position in the table, it's on the flat again.

The cast aluminum top is anodized and has a dark gray surface. I really don't want to ruin the coating by sanding it. It is 30 years old and has survived so well, I just don't want to invite new problems like bare alumininum "marking" the wood.

My first router table project will, in fact, be stiles and rails. That's why I'm concerned about the accuracy.

Thanks again. Joel
If you can feel the dip, it may be more than you'd want. If you have a dial indicator, try attaching it to the end of a board to see how much movement the dip translates to at the end of the board where the router bit will be. If you'll be using a sled for end cuts, the sled might bridge the dip, however, and provide accurate cuts. Hard to say without testing it.

- Ralph
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post #8 of 9 (permalink) Old 02-15-2011, 12:24 PM
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My recommendation would be to make a few test cuts. If your parts are coming out square and true, then you will probably be fine.

I do feel your pain as I had a similar problem on my last table saw, which is much newer than yours (less than 10 years old) where it developed a hump in the table over the years. (the saw was stored on its side, as intended by the design) and I believe this came as a result of the weight of the motor pushing on the top. It got to the point that no matter how I adjustment, something was out of alignment.
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post #9 of 9 (permalink) Old 02-15-2011, 06:45 PM Thread Starter
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Default Can't test yet

I agree that running a few bords as a test would be the way to go. However, I have not cut the hole in the top yet and don't want to until I'm sure that the table saw extension conversion is the option I'll choose. I know... the old chicken and egg dilemma...

Thanks bobj3 for your "attaching a thin sub-top" idea and photos. That would be a great fall-back solution for me if I go the conversion route and wind up unsatisfied with the result.

BTW, I took my trusty straight edge to a Rockler showroom today and checked out the flatness of the their 24"x32" table top. Guess what... it had a dip in the center which was a little deeper than mine. So, what might that look like after a few years in my humid barn?

I appreciate your "talking me through this".... Joel
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