How flat is flat enough for table top? - Router Forums
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post #1 of 12 (permalink) Old 01-30-2014, 09:38 PM Thread Starter
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Default How flat is flat enough for table top?

Hi everyone-

I recently picked up a router table top, and there is a .022" inch dip in the table top (measured with straight edge and feeler gauge across longer width portion of table).

If I flip the table over, the bottom side has a corresponding crown in the same spots.

Is this flat enough, or should I be concerned about accuracy, etc? I do plan to cut joinery on the table, so want it to be as accurate as I can. It seems borderline to me.

Also - this dip is before I mounted the plate and router.

I plan to call the manufacturer tomorrow to see what they think, but wanted some '3rd party' perspective on this.

many thanks
chris
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post #2 of 12 (permalink) Old 01-30-2014, 10:34 PM
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You have a foogazey, get rid of it.
Absolutely no good for joinery
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post #3 of 12 (permalink) Old 01-31-2014, 03:02 AM
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I don't wish to contradict our illustrious member Pat. Warner, publisher of many books on routing BUT, my own experience is that so long as the top of the table is flat or convex, the distance from the top of the table to the bit remains constant as does the cut.

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post #4 of 12 (permalink) Old 01-31-2014, 12:04 PM Thread Starter
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Originally Posted by harrysin View Post
I don't wish to contradict our illustrious member Pat. Warner, publisher of many books on routing BUT, my own experience is that so long as the top of the table is flat or convex, the distance from the top of the table to the bit remains constant as does the cut.
Thanks, guys-

My issue is a dip, so it is concave, not convex... sounds like this one needs to go back.
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post #5 of 12 (permalink) Old 01-31-2014, 07:08 PM Thread Starter
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So a new table top is being sent out to me, but wondering in general what "flat enough" is for a router table top?

I am thinking a 1/64th low/high spot or less across the table, there should not be any issues at all, but would be interested to hear any opinions on this, as this is a pretty uneducated guess on my part!
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post #6 of 12 (permalink) Old 01-31-2014, 08:51 PM
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I commonly route pieces that are larger than the width of my table. Because of this, a table with concave or convex variation will result in imprecise results.

Two hundredths is a bit much. One hundredth is pushing it. Five thousands or less is what I would prefer.

I made by table by gluing together hardwood floor and flattening it using router skiis. I put a couple coats of spar urethane on it and I don't use an inset. I put my 4' rule against it (good to a ten-thousandth) with no light showing underneath.

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post #7 of 12 (permalink) Old 01-31-2014, 09:15 PM
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Quote:
Originally Posted by cjtboy View Post
So a new table top is being sent out to me, but wondering in general what "flat enough" is for a router table top?

I am thinking a 1/64th low/high spot or less across the table, there should not be any issues at all, but would be interested to hear any opinions on this, as this is a pretty uneducated guess on my part!
You do realize that 1/64th is 0.015625? Yours was only 1.5+- times that. I would hope you plan an supporting it really well if you expect to maintain less than 22 thousandths. As Harry said, slightly convex would be better than concave.

For 99% of what you will use it for I don't think the 22 thou will bother you. If I expected better than that, think I would go cast iron.. even that can warp.

IIRC, the factory spec on phenolic tops was about +-.035", but I could be wrong.

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post #8 of 12 (permalink) Old 02-01-2014, 02:59 AM Thread Starter
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You do realize that 1/64th is 0.015625? Yours was only 1.5+- times that. I would hope you plan an supporting it really well if you expect to maintain less than 22 thousandths. As Harry said, slightly convex would be better than concave.

For 99% of what you will use it for I don't think the 22 thou will bother you. If I expected better than that, think I would go cast iron.. even that can warp.

IIRC, the factory spec on phenolic tops was about +-.035", but I could be wrong.
Yes, not trying to sound funny, but I realize what 1/64th is (in fractions and decimals)... the question I was asking is what is seen as flat enough (e.g. +/- 1/64" or less). Clearly seems there is some conflicting info on what is flat enough. I'll figure it out eventually!
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post #9 of 12 (permalink) Old 02-01-2014, 05:09 AM
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Quote:
Originally Posted by cjtboy View Post
Yes, not trying to sound funny, but I realize what 1/64th is (in fractions and decimals)... the question I was asking is what is seen as flat enough (e.g. +/- 1/64" or less). Clearly seems there is some conflicting info on what is flat enough. I'll figure it out eventually!
The first shot shows the spirit level sat on the minimum clearance disc and with a 0.010" feeler gauge under each end. You can just see in the second shot the clearance between the level and table top. I purposely raise the centre as can be seen in the last shot. This ensures that my cuts are accurate. How much higher you ask, well, taking into account the way that wood moves in tune with the weather, I've never considered this to be critical, so long as the centre is higher. If the question was "how flat should the table of a surface grinder for metal be then the answer is spot on.
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post #10 of 12 (permalink) Old 02-02-2014, 07:17 PM Thread Starter
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The first shot shows the spirit level sat on the minimum clearance disc and with a 0.010" feeler gauge under each end. You can just see in the second shot the clearance between the level and table top. I purposely raise the centre as can be seen in the last shot. This ensures that my cuts are accurate. How much higher you ask, well, taking into account the way that wood moves in tune with the weather, I've never considered this to be critical, so long as the centre is higher. If the question was "how flat should the table of a surface grinder for metal be then the answer is spot on.
Thanks, Harry - your input and pics are most helpful!
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