Gluing up African Mahogany - Woodworking Talk - Woodworkers Forum
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post #1 of 25 Old 02-20-2018, 10:57 AM Thread Starter
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Gluing up African Mahogany

I bought some 8/4 African Mahogany to build a counter top for living room cabinets. I paid the place I bought it from to clean it up for me and make it glue up ready. When I got it home and laid it out, I was a bit disappointed with a few things... looked like it was ripped with a rough cut blade... lots of tiny tear out chunks on surface... visible blade marks and could feel them also... a couple boards had cracks angled toward the surface... a couple have bows in them that will take a lot of vertical pressure to get to line up with neighboring boards... and one board is very twisted to the point that it will be tough to get a good glue joint, and even then, the twist may be hard to sand out of the final counter top (at back edge). I am going to run it through a sheet sander when done and have about 1/4" to work with, so I am not so concerned about the surface imperfections. Luckily my neighbor has a floor standing jointer and we ran them all through which helped a lot... but the twisted piece is my biggest problem... I feel like buying FAS, glue up ready wood should not have these issues. Anyway, I will deal with the lumber yard on that... my main questions are:

1) After jointing the edges of African Mahogany, are they glue up ready or should I sand before glue up? if sand, what grit? And do anything to remove sanding dust?
2) If the wood sits for a few days between jointing and glue up, do the edges need something else done to them? ie do moisture, tannins, etc. cause any glue issue if it sits too long?

Thank you! First glue up!
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post #2 of 25 Old 02-20-2018, 11:03 AM
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Jointing the wood should be enough preparation. Sanding is more likely to make the edge oval. The only thing you might do is research the wood and see if it's oily. Most of those exotic woods have a natural oil like teak. If this is the case then you should wash the edges with acetone to remove as much of this natural oil prior to gluing.

You should not let excess glue sit on anything you build. If you keep a bucket of water and a rag handy when you glue something it's very easy to wash off what oozes out.
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post #3 of 25 Old 02-20-2018, 03:37 PM
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I would really like to know the Moisture Content. Anything above air-dried (12-14%) has the potential to move.
That means some change in shape. One piece stressed against another is like a fault line ready for an earthquake.

Of all the thousands of table top glue ups that get done every day, I have seen the result of one which exploded.
Nobody hurt but the little table had been a magnificent piece of fine furniture, just sitting quietly in a spare bedroom.
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post #4 of 25 Old 02-20-2018, 06:50 PM Thread Starter
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I have a Lignomat SDM... and it shows moisture content from 8.5-9.5% on the various pieces of wood.

Wood database says "easy to work, glue and finish."

How many days can the wood sit between jointing/cutting and glue up without me having to worry about having to sand or clean with solvent?
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post #5 of 25 Old 02-20-2018, 07:21 PM
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I looked up the wood and it doesn't appear you have to clean any natural solvents from the wood.
I did find this old message from 2008 from our moderator Leo G. From that I would say anything you do with the wood you should machine it and then glue as soon as possible.

"I have only bad things to say about African Mahogany. I have ordered two large batches of it and cursed it every inch of the way. The wood looks nice, it is easy to cut, it will glue well. Sometimes you get a fuzzy grained pc. But I have had horrible luck with cutting stability. When you cut the wood it moves, a lot. When you joint the wood it will not stay flat. When you run it through your planer it changes shape. I had a tough time getting trued 3/4" material out of 5/4 stock.

Man, I hope you have better luck with it than me."
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post #6 of 25 Old 02-20-2018, 07:31 PM
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The African Mahogany I have used finishes easily with Nitrocellulose lacquer and glues easily with TB, no oils present. I have heard about the fuzzy nature but haven't experienced it (yet, I still have several boards waiting to be used). One use I had is for an acoustic guitar neck and so far it doesn't seem to have moved. It is laminated with Honduras Mahogany and Maple down the middle, though.

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post #7 of 25 Old 02-20-2018, 07:37 PM
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I have been reading a lot of woodworking books lately. I can't remember which book(s) said it, but they said to glue as soon as you can after jointing. One said something to the effect of, "Don't joint in the evening and do the glue up in the morning."
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post #8 of 25 Old 02-20-2018, 08:02 PM Thread Starter
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Quote:
Originally Posted by Tool Agnostic View Post
I have been reading a lot of woodworking books lately. I can't remember which book(s) said it, but they said to glue as soon as you can after jointing. One said something to the effect of, "Don't joint in the evening and do the glue up in the morning."
I wonder if that is more for movement than oils/glue issues.
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post #9 of 25 Old 02-20-2018, 08:13 PM
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Quote:
Originally Posted by jtech1 View Post
I wonder if that is more for movement than oils/glue issues.
What Leo was saying you could joint the wood in the evening and by morning the wood would no longer be straight so that would affect the joint. Oils with that wood isn't an issue.
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post #10 of 25 Old 02-21-2018, 09:39 AM
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Quote:
Originally Posted by Tool Agnostic View Post
I have been reading a lot of woodworking books lately. I can't remember which book(s) said it, but they said to glue as soon as you can after jointing. One said something to the effect of, "Don't joint in the evening and do the glue up in the morning."
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Originally Posted by jtech1 View Post
I wonder if that is more for movement than oils/glue issues.
I think so. I also remember reading something about the grain can partially raise up during the resting period, making the surfaces less flat for gluing.
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post #11 of 25 Old 02-21-2018, 02:38 PM Thread Starter
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I assume that it can't hurt to give it a few runs with a 150 grit sanding block and wipe with acetone, right? May not be necessary, but will not hurt anything, right?
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post #12 of 25 Old 02-21-2018, 04:09 PM
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The Acetone probably won't make a difference. Sanding won't hurt but just don't round the edges.

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post #13 of 25 Old 02-28-2018, 07:04 PM Thread Starter
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OK. I wound up hitting it with some 150 grit on a sanding block to make sure not to affect the flatness of the joint. Vacuumed off any dust and then wiped with acetone. Did the glue up and the first counter top came out pretty good. I am going to have it run through a drum sander to clean it up. The place I bought it from must have used a rough cut blade to rip it, since there is a lot of tearout... but i have almost 3/8 to work with, so the sander should be able to get it nice and flat and remove all imperfections.

Now for the second counter top... same size. The wood I have left has a couple pieces with bad twists. To the point where when I clamp it up dry, the boards are not flat across the top, and looking at the end, a couple joints are not tight because of the boards that have a twist. I paid decent $ for the wood and to have it prepped for glue up... and I am very disappointed. But going forward, can these twisted boards be made right? or should I be asking for replacement lumber that is flat and square for glue-up? Although I have about 3/8 in thickness to work with to final thickness, in depth I only have about 1/8" inch... I had asked for 24" deep rough and I got 20.5"... then jointing to clean up the rough cut edges cost me 3/8. So, even if I can clean up the twisted boards I may still need a wider piece to get back to at least 20" deep.

Any advice would be greatly appreciated.
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post #14 of 25 Old 02-28-2018, 07:16 PM
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Is the counter tops exposed on the ends or do they go wall to wall. If it goes wall to wall you could spline the bad joints and pull the twist out when you mount it to the cabinet. If the end shows it's going to look bad to use those bad boards. It would be best to replace them and use the bad boards on a smaller project.
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post #15 of 25 Old 02-28-2018, 07:57 PM Thread Starter
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The ends don't show at all... but the gap is top to bottom... ie. because of the twist, the top is tight on one side and the bottom has a gap, and opposite at other end... on 2 of the 6 joints. Even under clamp pressure. My main concerns is whether the glue joint will be strong enough and possibly separate over time because of the gap, where there will not be good wood to wood contact for the glue.

Is there any way for me to send this through my planer to get top and bottom flat again, and then re-joint the edges? ie. any "safe" way to plane out the twist on faces? I have seen a youtube video of an elaborate sled to support the twisted lumber while you get one face flat... and then you can flatten the other face... but i don't have a few days to build it... :) any other method?
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post #16 of 25 Old 02-28-2018, 08:14 PM
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Ok, you will have to find a way to joint the edge so that the joint fits well. You could screw another board to the twisted board and shem it so it is uniform to machine the edge.
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post #17 of 25 Old 02-28-2018, 08:30 PM Thread Starter
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These twisted boards were put through a jointer, but I think I did not realize how twisted they were when that was done, so the twist followed the jointer fence and the jointed edge was just made perpendicular to the face, twist and all... I see what you are saying... shim the board against the jointer fence so that I can get the edge straight. I read another post where they screwed rails to the edges of the board (I don't mind a screw hole or two in the glue joint) and that allowed them to plane one face flat... if I can get one face flat, I can then plane the other face flat and then joint both edges. Sounds right in my head, but since I have never done it, not sure.
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post #18 of 25 Old 03-01-2018, 05:58 PM Thread Starter
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Can anyone help me identify exactly what species the wood is? I was told it was African Mahogany, but I know that term is used by many people as a general term for a few different species of knock off Mahogany... I am guessing it is either Khaya, Sapele or Sipo... is there something about the face or end grain that you can identify? I have tried to compare to pictures on the Internet but it all looks the same to me... :)

Also, once I have this glued up, my plan is to use a drum sander (24") to clean it up. Because of the twisted boards, the top will have some ups and downs. I have about 3/8" of height to work with before I get to my finish height. Is it reasonable to expect the drum sander to get it reasonably flat, and the top and bottom faces in parallel planes? If so, what is the best process? Alternate top and bottom until it looks good? What grit should I start with and finish up with?

Thanks for your help!
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post #19 of 25 Old 03-01-2018, 07:44 PM
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It doesn't look like african mahogany. To me it looks like the pink sande wood I've been working with the last couple weeks. Have you been having trouble with the wood dulling your tools? Is it bad to tear out when jointing or planing? This is some of the problems I've been having with sande. It also doesn't sand very well. If you sand it against the grain with a belt sander it tends to tear out like machinery does.
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post #20 of 25 Old 03-02-2018, 03:38 PM Thread Starter
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May be this is a better image of the face grain.
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