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Flatining Table Tops

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Forum topic by Harryn posted 05-06-2016 04:13 PM 563 views 0 times favorited 5 replies Add to Favorites Watch
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Harryn

34 posts in 2054 days


05-06-2016 04:13 PM

Making a coffee table with red oak slabs 3/4” thick. The slabs are about 15” wide and 4’ long. They have a slight curvature from side to side. Thinking about cutting slots end to end on the bottom to flatten them. How many, how deep, how far apart?


5 replies so far

View mahdee's profile

mahdee

3553 posts in 1233 days


#1 posted 05-06-2016 06:09 PM

I wouldn’t. Red oak so porous that you can introduce some humidity to the convex side and flip it over to see if it straighten out. If not, place 1” boards at each end and clamp the center.

-- earthartandfoods.com

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pintodeluxe

4859 posts in 2279 days


#2 posted 05-06-2016 06:31 PM

15” wide oak that is 3/4” thick? Flatsawn lumber that wide will almost always cup or warp to some degree.
For better luck on your next project…
1. Try using quartersawn lumber.
2. Make panels from boards 6-8” wide.
3. Start with 5/4” rough lumber for a 1” thick finished top.

To fix the current problem…
1. Use a jointer to square and straighten the edges.
2. Clamping cauls during panel glueups.
3. Alternate clamps on top and bottom of the panel glueup.
4. Build adequate framing into the coffee table to attach the top to (with figure 8 fasteners for instance).

Good luck with it.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View JBrow's profile

JBrow

818 posts in 385 days


#3 posted 05-09-2016 01:29 AM

Harryn,

I had a red oak coffee table top and a red oak side table top that set outdoors under a patio cover, both which cupped badly. When I re-made the red oak tops I elected to introduce relief cuts on the underside of the table tops, much like what you would like to do. While I cannot say the relief cuts done as I did will flatten your top, I can say that the re-made tops have remained perfectly flat.

My approach was to rout equally spaced grooves with a 3/8” core box bit the full length of the tops parallel with the grain. The depth of cut was ¼”. If the ¼” depth does not allow your top to lie flat under light pressure, increasing the depth could be required, but I would be concerned about weakening the top and would not exceed 3/8” depth. The center to center spacing of the flutes was 1-1/2”. I cut the center of the first flute at the center of the top and worked outward toward each edge to keep the flutes symmetrical.

I considered simple and easy to cut saw kerfs at the table saw, but since the cuts would be visible from the ends of the top, I chose the core box bit leaving flutes on the bottom surface of the top. The bottom-surface flutes do not detract from the appearance of the tops, at least to my eye.

View rwe2156's profile

rwe2156

2198 posts in 946 days


#4 posted 05-09-2016 11:44 AM

This might be useful to you.

-- Everything is a prototype thats why its one of a kind!!

View JBrow's profile

JBrow

818 posts in 385 days


#5 posted 05-09-2016 02:29 PM

Harryn,

rwe2156 provided a link to a YouTube video that is interesting and a pretty cool method for flattening badly misbehaving planks before glue-up. While I was browsing the related videos, I ran across a 2 part video where the author flattens wide and already glue-up cupped panels. rwe2156’s video and the 2 part videos are all well worth a look before putting blade to wood on your table top.

https://www.youtube.com/watch?v=wEy4zJ0cizM

https://www.youtube.com/watch?v=wijLDuPL4LA

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