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Flattening Slabs

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Forum topic by jmurf posted 05-20-2022 01:34 AM 544 views 0 times favorited 5 replies Add to Favorites Watch
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jmurf

24 posts in 1076 days


05-20-2022 01:34 AM

Topic tags/keywords: slab bowed planner maple kiln dried

Hello, We had a maple tree taken down 18 months ago. I had the trunk cut into 8 qtr slabs. They are roughly 60” long and 12”12 wide. They were kiln dried. They have been standing up in the garage for over a year, off the concrete. I have a planner but not a jointer. I created a sled from 1” MDF, wedged the slab, and flattened one side. It looked great. I came out the next day and it has a bow along the length. When I place the two ends on the bench the gap in the center is about 3/16. I am down to 6 qtr thick so I hate to take much more off. Any advice? If I placed weight on it in the center to push it down on the bench will it stay? Thank you.


5 replies so far

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Aj2

4492 posts in 3292 days


#1 posted 05-20-2022 02:21 AM

There’s no secret voodoo that will take the bow out of big wood. Without further milling
The best but not 100% guaranteed procedure to milling wood is to take off each side evenly.
Another way that I’ve found good success is to sneak up to your final thickness. Take a little oof each side over a longer period of time usually weeks sometimes a month or two.
If you have the time to sneak up and you pay attention the slab will tell you what side needs more or less taken.
So you don’t upset the balance of stress
Good Luck

-- Aj

View Lazyman's profile

Lazyman

9779 posts in 2881 days


#2 posted 05-20-2022 02:38 AM

If you had the freshly milled piece so that air could not get to both side (laying on a bench for example), that will often cause a warp like that, especially right after milling. Sometimes just flipping it over for a couple of hours will allow it to equalize. Another thing you can try is laying the board on your lawn in the sun concave side down. The sun will dry out the convex side and the lawn will give off some moisture to the concave side. It can flatten out pretty quickly so keep an eye on it or it could go warp the other way and make sure that you store it so air can circulate around it. This works best on cupping but can work on bowed boards too.

Note that if you plan to cut the boards to shorter lengths later, it will be easier to mill that warp out of them if you cut them to rough length first.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View Andybb's profile

Andybb

3501 posts in 2097 days


#3 posted 05-21-2022 02:43 AM

I’m having a hard time visualizing what you are trying to do.

You can’t cut them and leave them overnight. Don’t mill them until you intend on using them or they will turn into thick potato chips overnight. At the very least they need to be stacked and stickered.

When you say “gap” not sure which gap you are talking about. I use a track saw instead of a jointer on slabs.

Here are a few shots from a couple of tables.
First off I always use c channel on the underside to make sure it doesn’t move over the years. I had a slab that had been dry for a couple of years albeit with a cup in it. That 2.25” slab would have ended up being 3/4” thick if I just sent ot to the mill so I ripped it into 13” planks and ran them through my 13” planer. Then instead of using a joiner I laid them adjacent to each other and used my track saw to cut them both at the same time giving me a joint better than I seem to be able to get with my jointer. It still ended up being 1 7/8” thick.

This joint was done with a tracksaw.

I’d use cauls to make sure they are dead even.

-- Andy - Seattle USA

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EdDantes

90 posts in 1404 days


#4 posted 05-21-2022 05:28 PM

Unfortunately not all that uncommon. They may not have been uniformly dry throughout (even after kiln drying and letting them sit), so you exposed relatively more wet areas that then cupped as they started to dry. But it may also be that planing released internal stress, and those flat sawn slabs will have a tendency to cup with the growth rings.

Honestly 3/16 isn’t that much. You could probably find a way to restrain it as you attach it to the base. I had a 36” wide hickory slab that cupped. I pulled it flat as it attached to the base and haven’t had any problems over 6 years in a cabin that isn’t climate controlled.

In situations where you would try to mill it again, you can rip it in half, mill the halves separately, and then glue them back up. You’ll minimize the amount of material you have to take off, at the expense of a seam (which is usually not that noticeable).

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Andybb

3501 posts in 2097 days


#5 posted 05-21-2022 07:24 PM

In situations where you would try to mill it again, you can rip it in half, mill the halves separately, and then glue them back up. You ll minimize the amount of material you have to take off, at the expense of a seam (which is usually not that noticeable).

- EdDantes

+1 That’s what I was suggesting in the previous post except I milled it in 3rds so it would fit through my planer.

-- Andy - Seattle USA

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