leveling a workbench top

[HowardH]

I built this veritas workbench about a year ago and it was one of my early projects.  The top is hard maple and the center is pauduk.  Each top was leveled at a commercial hardwood supply shop using a wide belt sander.
[attachimg=1]

Something happened during the phase where they were joined together and the result is the table is now crowned as you can see in the pictures. 

[attachimg=2]

The Pauduk was rabbeted into the sides of the bottom of the maple top and then 4 1x2 boards were screwed into the two sides perpenticular to the length of the tops to help support the whole structure which is quite heavy.

I need to level this top and was wonder the best way to do it.  I have a twin screw veritas vise at one end don't want to remove it unless absolutely necessary.  I have at my disposal a RO 150 FEQ and a 4 1/2 smoothing plane.  Is this a job for a jack plane and a winding stick or is there a festool way of doing this?  The bench is about 60" long.  Any advice would be appreciated. 

 

[Woodenfish]

Can you shim it level?

 

[HowardH]

Not really, it's not a shimming issue.  The two tops are also connected together at each end by a board that spans across both sections.  It's really a unified top at this point.  I'll have to look again and see how I attached them.  I believe the end boards are screwed into the tops and not glued.  That would be my saving grace if I have to take them apart to relevel. 

 

[Jim McFarland]

You might try a router bridge as shown in this article.

 

[romlee]

How are the legs attached to the top on your bench?  About 4 years ago I purchased a factory built Veritas bench.  Two years ago I noticed the top had crowned.  The top is attached with large screws to the trestle base through holes bored through the base's upper rails at each end.  There was a gap between the rails and the bottom of the bench top. 

I found that all I needed to do was to lay a straight edge across the top and retighten the bolts.  It's stayed flat since then but if it does go out of level again, I will use shims.

However, if your top is attached mortise and tenon, then this may not work.  Did you install rails between the legs at both ends of the bench?  Have the rails warped in the same direction as the top?  Is there a gap between the rails and the bottom of the bench top?  If there's a gap (and the rails are still flat and level) then you may be able to bore holes through the stretchers and then screw the top flat to the base.  You may still need to shim.

The Veritas twin screw vise is attached through a thick wood block screwed through the end of the bench.  You might have to slightly loosen the screws attaching the end block (not the vise) in order to tighten the screws holding the rails to the top.

Hope this makes sense. 

Rom

 

[Jesse Cloud]

Definitely use a router bridge!

I just connected two pieces of angle with two scraps of wood and some screws.  The two pieces of angle need to be parallel and roughly the size of your router base.  The wood pieces should be attached so that they just clear the width of the bench.  Then clamp a straight board to each side of the bench.  Make sure the boards are level and that the router bridge is level when you place the scraps connecting the angles on the side boards.  The bridge needs to ride just above the bench and not touch.

Put the widest straight bit you have in the router and set the depth to just kiss the lowest part of the bench.  Then just run the router across the width of the bench, move the bridge and repeat until done.

You may need to clean up router marks with a light pass of a sander.

The bridge I made has been dissembled and the parts reused, so no pic of that, but here's the bench....[attachthumb=#1]

 

[tvgordon]

Are each of the maple slabs warped or are they just sagging at the edges?  If each maple piece is crowned, I would either use a hand plane, power plane (reason to buy a new Festool!) or a router bridge.  If the top is dropping at the edges, I would do what the other guys suggested and loosen the fasteners and shim if necessary (and if possible).

Tom.

 

[HowardH]

each slab was milled perfectly flat separately and then joined.  I'm not sure how they can sag as shown in this picture.

[attachimg=1]
You can see the endboard being flush with the top surface of the two slabs.  It was straight when I mounted it but must have bowed in the interim. 

...

However, if your top is attached mortise and tenon, then this may not work.  Rom

The top is held on by essentially a M/T joint, really more of a 1 inch peg into a hole.

[attachimg=2]
I have the end pegged so there is no way to remove the end board.
[attachimg=3]
It seems to be resting flat on the base but isn't flat on top.   ???  Strange

 

[Eli]

Just curious, the underside shot looks like the entire board doesn't have finish on it. Were both sides sealed? That would be a good candidate for culprit right there.

 

[CharlesWilson]

I did the router bridge operation on a benchtop consisting of three glued layers of MDF a couple of years ago. When done it was dead flat, and within a week it started to bow up in the middle. Both top and bottom surfaces were sealed. (We had a long discussion of this on the previous Festool Owners Group.)  We didn't come up with any authoritative conclusions at that time. Maybe there were some built in stresses during the glue-up of those three layers. I'll never know.

I am glad to say, however, that the top of my MFT (only a single layer of MDF) is still dead flat.

Charles

 

[HowardH]

Eli, you are correct.  The underside was never sealed.  Never gave it a passing thought at the time.  If I end up flattening the top again in some form, it will require re-finishing so that would be a good time to do both sides.  Thanks for the tip.

 

[Woodenfish]

The top may be resting flat on the base but I think the laminated base is not flat itself. Have you checked it?

 

[HowardH]

not yet.  the top is pretty heavy so I'll have to recruit the neighbor to help me lift it off the base.  I'll check and report back.

 

[Dave Ronyak]

Eli, you are correct.  The underside was never sealed.  Never gave it a passing thought at the time.  If I end up flattening the top again in some form, it will require re-finishing so that would be a good time to do both sides.  Thanks for the tip.

Howard,

I live in NE Ohio; the humidity level where I live is generally high, but swings fairly widely between its low in winter and highs during the other seasons.  I strongly agree with Eli's recommendation that you should apply equal layers of sealant to all surfaces, but even then the bench top may not be stable and remain flat when subjected to humidity swings.  I note that you live in an area of Texas which I presume has fairly low humidity at this time of the year (January - Winter).  Was your bench top flat when you first assembled it?  Does it become more or less crowned with seasonal changes in humidity?  From your photos, it appears your underlying cross supports are made of laminated 2X4 stock.  Normally, such construction grade lumber is not dried to as low a humidity level as are hardwoods used in furniture (and workbench) construction.  Thus, I would also be suspicious of the flatness of those laminated cross supports, and recommend that you confirm they have remained flat and straight.

Here's another tip/trick you might try - letting nature work for you to straighten out your top, although I have never tried this on such a thick workpiece.  When I have needed to straighten (bring back to flat) a glued up panel that warped after glueup (due to sapwood and different shrinkage rates), a trick I have found very effective is to lay the concave side of the panel down directly in contact with the grass of my lawn on a sunny, dry day.  This creates a moisture differential between the underside facing the ground and the topside facing the sun.  Using this technique, a 3/4 inch thick glued up panel of black walnut with a 1/2" crown straightened itself out in about 1 - 2 hours, and I assembled it into the rest of the case box quickly before it warped again.  (I still have that stereo cabinet and that end panel is still flat and did not crack!)  A thicker workpiece would be expected to take longer, but it, too, should expand more on the side that is facing the soil, and thus cause the workbench top to become flatter.  But then you would have to reattach it to sturdy and flat support membes before it tries to rewarp, shimming it as needed when fastening it to your cross-members to bring it flat.  And seal it - all surfaces.  Note that shellac is an excellent sealer and surprisingly has lower permeability to moisture than most polyurethane varnishes, despite the fact that shellac is attacked by moisture.  I seal first with shellac, then overcoat with varnish or lacquer.  I have a 30 year old workbench (that I purchased complete) whose ~3 inch thick top is formed of glued up strips of hard maple, with 3 embedded steel reinforcing rods.  Despite all surfaces being sealed, and the ends further sealed with parafin, it has become crowned about 1/8 inch with the center being high, and the amount of crown changes with the seasonal humidity change.  I just live with it, and much appreciate my Festool MFT top that is relatively very flat.  I use the MFT top for assembly to keep drawers flat during glue-up.  I just finished making 5 drawers that are 24" deep by 33" wide and they appear to be dead flat.  I use the maple workbench for heavy duty work, for planing and pounding, including automotive repair work.  Good luck!!

Dave R.

 

[HowardH]

thanks for the help, Dave.  It is indeed quite dry this time of year, today notwithstanding with a record high and very high humidity.  I used what the local Woodcraft store called the bomb proof method of finishing.  Started with 3 flooded coats of raw linseed oil, then 3 more of boiled LO, rubbing out between each coat.  The first three coats were pretty easy, the next 3 or 4 got progressively more difficult to rub out because the maple became saturated.  After 6 coats, I finally had enough.  Final coat was paste wax.  No actual sealer was used.  After I re-level, should I apply something like Zinsser Seal Coat as a pre-finish sealant or did the BLO accomplish the same thing?  It would seem to me that once the surface is sealed, I should use some sort of film finish as the wood won't be able to absorb anything else, correct?  BTW, the frame is indeed a BORG supplied material.  The top alone was about $500 in 8/4 hard maple so I economized on the base, a mistake maybe? I also use my MFT for glue ups and recently found a huge roll of butcher paper at Sam's to help keep the top clean.   I get a lot of compliments on the big bench so it will be relegated to holding down stock to plane, etc. 

 

[Dave Ronyak]

I've used a finishing system similar to what you describe for some laminated maple tops, the key differences being that I used Watco (Danish type) oil on ALL surfaces to seal them before I top-coated with solvent based polyurethane.  Of course, I let the oil finish dry a considerable length of time (weeks) before applying the polyurethane.  I'd try to seal all surfaces, and recheck your base supports.

Dave R.