PC 7539 and table sag - - Router Forums
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post #1 of 19 (permalink) Old 04-17-2012, 02:32 PM Thread Starter
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Default PC 7539 and table sag -

Hi everyone, new guy here although not new to woodworking.

I have a PC7539 mounted in my router table which was constructed of 2 sheets of 3/4" MDF laminated together, covered on both sides with laminate, and edged in cherry. The router itself is mounted to a Rockler aluminum insert which does not have a problem with sag. This is the second top I've made, and for the second time, this tabletop has sagged to the point that it's visibly affecting whatever I'm routing. I discovered this whilst routing beading for a bookcase I'm building, and now this problem has caused the bookcase project to come to a complete halt.
I've read through some of the archives so I know some of you are using the same router (I had been considering selling it and buying a lighter-weight machine), but regardless of what I do I need to do something about the sagging top. I suppose my first question is whether or not I can fix the current top or whether it's even worthwhile to attempt a fix, and then the second question would be by what means do I stabilize a new or repaired top so I don't have to worry about the sag. If I make a new top I would consider sandwiching steel bar stock within the MDF, as suggested by Wally Kunkel in his tome on radial arm saws. If I attempt a repair to the current top I was considering just milling some hardwood ribs to attach to the underside of the table, removing the laminate from the underside somehow, and with glue and a heck of a lot of clamping pressure bringing it back to flat, but I don't know if even can get it to flat that way - there's about a 1/16" dip in the center of this thing.


Sorry to be so wordy, but I couldn't explain in enough detail with fewer words.

Thanks in advance for your thoughts

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post #2 of 19 (permalink) Old 04-17-2012, 03:15 PM
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Philip, properly supported a single layer of 3/4" Baltic birch plywood with laminate on the top and bottom will not sag. This is how the Router Workshop table is built. I am testing some 3/4" phenolic impregnated Baltic birch with a 7518 on the oversized Rockler plate. So far so good.
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post #3 of 19 (permalink) Old 04-17-2012, 04:47 PM
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"whether it's even worthwhile to attempt a fix,"
I think you've had it.
Moreover, @>17 lbs, you have the heaviest US router in history.
To minimize deformation & maximize flatness I use a skinny top (5/8" MDF) on top of 6 stout beams.
All in the same plane, supporting a 7518 x >10 years!
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post #4 of 19 (permalink) Old 04-17-2012, 05:24 PM
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Can you turn the top over and use the other side?

Pat hit on the answer. The temporary table I last built is only 1 thickness of 5/8 melamine coated particle board and I cut through most of that to put track into it and still haven't had a problem. Underneath is a ladder frame of 1 x 4 with crosspieces on either side of the opening. I also don't leave my router in the table when I'm not using it.

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #5 of 19 (permalink) Old 04-17-2012, 05:26 PM
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One could take Pat's solution a step further and add a second skin below (torsion box) and configure a dust collection chute within the available channels between skins. Router can "breathe" and a goodly amount of dust that the fence port misses gets collected .
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post #6 of 19 (permalink) Old 04-18-2012, 06:35 AM Thread Starter
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Thank you, gentlemen, for your input. I guess I'll start making a new top today.

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post #7 of 19 (permalink) Old 04-18-2012, 06:50 AM
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MDF = Most Definitely Faulty.

Has to be the WORST material ever developed, carcenogenic dust, reacts to humidity, cannot be resurfaced.

Use Baltic ply with laminate both sides

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post #8 of 19 (permalink) Old 04-18-2012, 10:35 AM
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Yep, proper support underneath. I'm on my 3d or 4th homemade router table. None have sagged, and they all were made with 1/2" plywood tops. And well supported by a web of 2X4 pieces under, glued on edge. The latest version is probably 3-4 years old now. My first one was basically a learning experience and worked, but was too small, and actually kind of crude. So #2 was much better. Now I only make a new table when my needs change, not because the table has problems - in fact the last one was only made because I needed a larger top - the previous table was 5-6 years old at that point.
I'd need to actually look at your present table top to determine if I thought it could be salvaged or not. That said, it it was mine, and I decided to try to salvage it, I would give it a shot, regardless - sometimes just the challenge is the most fun.
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post #9 of 19 (permalink) Old 04-18-2012, 10:40 AM Thread Starter
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Thanks Theo. Just 1/2" ply for the top? do you use an insert or just mount the router to the tabletop? I have some 3/4" birch (not baltic multi-ply but cabinet-grade) that I was going to double up. Under that I would put ribs for support.
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post #10 of 19 (permalink) Old 04-18-2012, 06:47 PM
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Can you straighten the table with angle-iron? The Incra tables have angle-iron screwed to the underside of the table on either side of the router opening, to accommodate a PC7518/19.

Just a thought.
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