# How to prevent router table sag?



## prhen (May 20, 2013)

I've been reading a lot about the evils of table sag in home-built tables, and am considering using 3/4" square steel tubing under my table saw extension to avoid it. My question is this: if I put laminate on both top and bottom of the table, can I screw through the laminate into the MDF if I predrill? Will the laminate chip? Has anyone done this?
Thanks all.
Paul


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## MikeMa (Jul 27, 2006)

What I did with my table was I had rails running across the stand to support the table with the weight of the router. I built the table in 2005, haven't had any sag.


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## Willway (Aug 16, 2012)

Hi Paul, it seems to me that a simple longitudinal double H angle iron frame would stop all possibility of sagging of the top. It would probably work better with your fence rails. Most of the sagging I have seen is in the long fence rails, these need some kind of legs with levelers for added support. If you are going to build a cabinet it can be designed to fully support the top and prevent sagging. If you are in a very high humidity area you can silicone under the screw heads. There is no chipping problem drilling pilot holes in laminate.


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## WurliTzerwilly (Jun 9, 2013)

You can screw through the laminate, but better to pre-drill first. There may be a small amount of tearout, but it usually gets covered by the bolt/screw heads.

I just attached a Wixey gauge to the underside of an Incra laminate covered table, with large self-tapping hex screws - no problem.


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## rwbaker (Feb 25, 2010)

I've never read or seen in this column anything to do with sag. I contact cemented 2 pieces of shellaced (humidity proofed) 3/4 MDF with a final coat of laminate on the top. This unit is supported solely on the 3 edges on 1 1/2 inch of slotted angle. Every 90 days I check it and other equipment for square, sag and any other issues and since 2008 no sag has shown on my Starrett gauges. I could see sag if a single piece of 1/2" MDF was used, but your suggestion seems to be massive overkill.

Best Luck - Baker


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## senebraskaee (Apr 29, 2012)

If you drill a pilot hole for the screw threads, it will still be too small for clearance through the laminate and it may chip. When I do this, I follow up the thread size pilot hole with a countersink (some folks call this a chamfer bit) which gives clearance to the screw through just the laminate.


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## OPG3 (Jan 9, 2011)

I am going to make a completely different suggestion:
If you're speaking of the thin "laminates" such as formica - only adhere it. Don't drill through it - chips will occur (almost guaranteed). I personally do not ever terminate the sharp tip of a wood screw into MDF - it will make "anthills". Your better option is to drill through your MDF and use washers, lock washers and nylon insert nuts. Counterbore your "entry wounds" and over-drill into a sacrificial piece of wood - this should give you a clean hole. Use a good non-shrinking wood filler atop the bolt heads and use a spacing that is uniform (think of lug nuts). Use a J-roller or rolling pin to ensure adhesive is evenly applied.


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## prhen (May 20, 2013)

Thanks everyone! As usual, there's more than one way to solve a problem. Richard, do you use shellac to moisture-proof the MDF everywhere, eg in miter track, along the edges that the insert rests on, etc? I've also heard that CA works well.
Cheers,
Paul


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## JOAT (Apr 9, 2010)

Overkill is always good. I've often mentioned that my router table top is 1/2" plywood. It's something around 10 years old, probably older, with no sag. However, underneath it is supported by a spiderweb of 2X4 pieces, on edge, not flat. I don't think there is any section, except for where the router and router plate goes, that is open for more than about 2" X 4", usually less - I had a lot of small pieces of 2X4, and used 'em. I would say that if you support your top sufficiently, you should have no problem.


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## rwbaker (Feb 25, 2010)

*reply to coatings of MDF*



prhen said:


> Thanks everyone! As usual, there's more than one way to sovle a problem. Richard, do you use shellac to moisture-proof the MDF everywhere, eg in miter track, along the edges that the insert rests on, etc? I've also heard that CA works well.
> Cheers,
> Paul


Yes, any pressed wood product is highly hydroscopic and needs to have all areas covered with a moisture resistant coating. When I order MDF (usually 8 sheets) I spray them with shellac (3lb cut) and brush the edges. I will probably switch to polyurethane as the cost of decent shellac is killing me. Contrary to common belief over-kill is just as bad as under-kill as it increases the complexity of the project, the number of items and the probability of failure. This was immortalized with the differences between the Apple 2 and Apple 2+ computers - more parts, more problems. The mounting plate is held in with dead weight from the router (no screws) and leveling of the plate was accomplished with epoxy putty on the edge of the plate route out, place plastic wrap over the plate insert in hole and turn the whole mess upside-down on a flat surface. This eliminates the leveling issue for life. Again, the simpler the better. The epoxy putty also works on zero clearance inserts for table saws, only use bricks to cover the inserts and a piece of lawnmower pull spring steel makes great short back captive springs. No leveling and only 1 screw. Screwing into MDF - use a paper or wooden match stick - depending on size.

Thanks for asking - Baker


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## Mike (Nov 22, 2004)

Or you can just build a table top out of 3/4" Baltic birch plywood with laminate on both sides. When properly supported with a 1/2" Baltic birch plywood cabinet it will not sag.


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## prhen (May 20, 2013)

Thanks, Richard, for the tip on polyurethane...I don`t have much experience with shellac, but poly is easy
Mike, thanks for mentioning the Baltic birch. I`ve been planning to use MDF for a table saw extension, but I need 28`x 27`and can`t find anything other than 2 x 4 (too small) or 4 x 8 (too big) sheets in MDF. Would a double thickness of ply work as well? Most contributors seem to favour the MDF. Is there a reason for that? 
Cheers,
Paul


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## Mike (Nov 22, 2004)

Price is a big factor Paul. Something to consider: floors are not made from MDF... get my point?


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## paduke (Mar 28, 2010)

How to prevent router table sag? Keyword Support How Much? Depends IMHO MDF tries to curl when you dado a mitre track into it. I dislike 2 X 4 on edge cause they seldom are straight enough. I ripped 3 1/2" strips from 3/4 ply and built a box frame by doubling them on edge. I thru bolted from top. Its never moved but if it does I can loosen bolts and shim


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