I’m going to be starting a dinning table made of Cherry. The table will be 60″ long x 42″ wide.
With other projects I have sometimes had a problem with a small crack in joints that is barly visable and does not open up but you can feel the seam with your finger. I want to avoid that happining with this table.
Someone told me that the movement will be less if I use narrow boards instead of wide boards. Is that true?
I plan for the boards to run the long way on table so there will be less joints. I saw in the March issue of American Woodworker where they ran the boards across a table so that anchors would help prevent cupping. Is that advisable?
Finanally, do biscuits help maintain joints? I’ve heard biscuits help with allighnment only.
Will appriciate any info or tips. Thanks.
Replies
The best thing that you can do is make sure that your jointer blades are sharp, or your plane-blade, and that the edges are straight and square. If you use a yellow aliphatic, or even white, the glue-line and the cells that the glue permeates and fortifies will be stronger than the wood on each side of the glue-line, so gluing the plates really isn't necessary.
<Someone told me that the movement will be less if I use narrow boards instead of wide boards. Is that true? > If the top is free to move, narrower boards will only likely give you more joints to show up later. If you sand too soon after gluing, the edges of the boards are slightly swollen because of the extra moisture that is in the glue, and will be slightly raised. If you sand too soon after glue-up, then later when that moisture is dispersed into the surrounding wood, you will end up with a depressed glue-line by the amount of the raised/swollen amount that you sanded off earlier.
It can in fact cause problems. If you fill them with glue, as you apply the clamp pressure, you can apply quite a bit of hydraulic pressure which can force the glue in the pockets to bulge the sides of the pocket, and over saturate the wood causing it to swell, leaving a bump, that if sanded too soon, will end up a depression later, and or somewhat of a shadow from the glue saturation / stain blocker.
Another thing that can cause glue-lines to show up later, especially on thicker glue-ups, is to have a Quarter-sawn face glued to a Plain-sawn face on the other side of the joint. With any change in MC, the QS will change in thickness at twice the rate of the other. It may only be a couple of thousandths, but you can see that much, and you can defiantly feel that amount.
These kind of problems can most easily be seen with a good polarized light source held down to a low reflective angle, and getting in close with magnification. I like to wear a jewelers visor.
Thanks Keith,BG and Midlebury. I printed all replys and will try to follow all directions. I do have a 22" performax. Never sanded anything wider than 22" but its supposed to do the job by turning the piece around. we'll see. Thanks very much .
WAIT !! If you've never flipped edges of a board on your Performax. First try it on a scrap piece of flat Ply, You'll probably have to tweek the drum ever so slightly to keep from putting an unwanted ridge in the middle. Been there / Done that. Thought mine was adjusted right. Things do go out of wack.Work Safe, Count to 10 when your done for the day !!
Bruce S.
you're right, I remember am supposed to have the outside edge slightly higher than the side next to the motor. don't know for sure if mine set exactly correct. Will closely check before proceding.
My worry is that I won't be able to handle a piece that big, hold it flat, etc. ,while getting it started. If not able will take it out for sanding. Maybe if can glue top up good enough will be able to finish with random orbitor.
First challenge is to get glued up properly. Concernrd of wheather to use a bread board. Will decide after glue up.
Thanks much.
42" X 60" I believe your right to worry about starting and finishing that size. Three people for sure. I can appreciate your thoughts on the orbital sander, I'de probably do it that way myself after hitting it with a good sharp cabinet scraper. No point in testing fate after a big glue up. Slow and sure isn't a bad thing.Work Safe, Count to 10 when your done for the day !!
Bruce S.
woodshoplast,
Keith provided some great advice, but getting that perfect finish....its just so frustrating. I planed, scraped and sanded to 220 and then washed down with mineral spirits. The top had a beautiful glow and smooth as a baby bottom.(maple) Just touched it a bit with the scraper to remove a thumb print or two. With the finish on, everyplace I touched that top with the scraper has a hash mark showing.
With the size and cost of your project maybe I'd make sure there is a wide belt sander available to help with that perfect finish.
good advice from all......... If I could add one more tip, it would be to make sure all of your wood is well acclimated to shop conditions. Wood will shrink in thickness and if each piece is not of similar moisture content then the glue lines will surely show later on.
good luck
WSL,
I just finished making a 78 inch long, 42 inch wide table top in pitch pine, the planks of which were cut from a very rough 8 inch X 8 inch beam out of an old mill building. There was a lot of board-straightening and flattening to be done to get a flat, well-joined table top.
The advice given so far is all very good stuff. Can I therefore just add a couple of things or so:
Try to orient the grain of your planks so that the pattern showing on the top merges across the planks, as far as you can manage. My table top has one slightly anomolous plank and now it has all been sanded and finished, that plank is rather obvious.
When joining the long edges I always plane or sand a small dip in those edges over their length. The gap shows as a crack of light in the middle (but not the ends) when you butt the plank long edges together.
This gapping eases clamping, as 2 or three clamps in the middle close the gap there but also tend to transmit clamping force to the plank ends as well. You can use less clamps. Also, if the plank ends are not breadboarded, any further drying out and shrinkage of the end grain at the plank ends will be less likely to open up small gaps between them - the plank ends are somewhat compressed together by the gapping technique.
On my 78 incher tabletop, I made the gaps 1mm (just over 1/32 inch) as the longer the plank, the bigger the gap that can be closed.
I always use biscuits to align planks glued on edge. It eases alignment during the clamping operation a great deal, especially with long, unwieldy planks. Also, biscuits add a bit more grab to the middle region, where I have created that 1mm gap....Also, biscuits become internal clamps, after about 3 hours glue-drying, so you can remove the external clamps rather earlier than you otherwise might (normally 24 hours).
Consider breadboard ends on wide table tops, especially if you have used through and through-cut boards (those with curved grain on their ends). If there is any tendency for the top to cup, the breadboards will restrain it. On very long tops (like the 78 incher) I put at least one cross piece between the middle of the two long aprons of the table frame and button down the top to those (as well as to all the aprons) to stop any potential upward bulge in the middle region of the top from manifesting.
These cross pieces also help stabilise the table frame against racking forces.
Lataxe
Consider breadboard ends on wide table tops
I will tell you that this is a must to do. It will only help keep the table flat so read up on it and pratice on some scrap until you feel comfortable doing it. I remember the first time I did breadboard ends and I had to re do them. What a diaster. But I learned and thats what is important. Good luck to you.
Thanks very much.
Did you put breadboard ends on your big table? I did this years ago on a small table and have never had any problem with it.
Have read some postings and can't decide if should use bread board. Many believe won't make that much difference. Probably just wait until top glued up then make a decision.
Thanks for your help.
Edited 5/14/2006 4:18 pm ET by woodshoplast
W,
Yes, I put 4 inch breadboards on the big table top, especially since all but that anomolous board are through and through cut - that is, the curve shape of the growth rings shows on the ends. This kind of cut is more likely to cup than quarter sawn boards, which I would have liked to have used but the growth ring pattern and dismemberment-plan of the original 8X8 beam didn't allow it.
In addition, The table is a basic 4 thick, tapered legs on the corner style, which aways seem to look best with a breadboard-ended top.
We have an inherited oak trestle table in our house which is 6.5 feet long and 3 foot wide, made of four large English oak planks. The maker didn't breadboard this top and (the table having lived in a hot conservatory for a while) there is manifestation of both cupping and plank-separation on the plank ends. If the maker had breadboarded and used that gapping technique, I believe both these manifestations might have been avoided.
Lataxe
I'm still undecided re" the breadboards. Im building that table in the March issue of American Woodworker. They put all the planks sideways. I guess because was designed for extra leafs to be added. Also assume that leaves the entire lenght of their table subject to cupping and warping?
Finished size of my table will be 40" wide and 60" long. 42" looked really wide. Ran all planks lenghtwise. Am not building for extra leafs as my sister doesn't have room for anything bigger. Installed just sharpened knives in my jointer and got smooth, square joints. Amazing the difference sharp blades make! It was only on my last plank to glue up that I noticed a very small gap on ends. Needed very little pressure to pull planks togather. Couldn't figure out how to get the gap in middle but did do the stack and look for light procedure.
All my planks were flat sawn and just by luck the best looking side left all planks with the inside out, or in this case, inside up. Someone told me that's the way planks should be assembled if possible. Going to take the top out to cabinet maker who has a wide sander. Too big for me to handle in the performax.
Just don't know about the breadboards, don't really want to do those.
Thanks again for all the help.
The question of breadboards depends on what is under the top. They are useful when the ends are unsupported for a significant distance as on a trestle table. But if the top is secured to rails on a table with 4 legs, they aren't necessary. A top can be secured to rails to curtail cupping, while still allowing width-wise movement with the seasons.
That's good! This is the first large table I've built. There will be aprons under table top. Aprons will be 2" from sides and 2" or 3" from ends. I was really worried that not building breadboards was a miatake. Now I'm relieved. Thanks much.
Lots of good advice so far, though I would quibble here or there. As too your specific questions:
"Movement will be less with narrow boards" No, that is not true. Cupping might differ a bit, but with properly dried and aclimatized boards there won't be a problem. Width variation over the seasons is likely to be less with wide boards than with narrow (basically because wide boards tend to have more quartersawn or rift sawn portions while narrow boards are more often all face grain.)
Running "the boards across the table so anchors prevent cupping" I don't understand this one. If this is a typical table with legs at the four corners connected by rails, the anchors will prevent cupping just the same in either direction.
"Bisquits are for alignment only" This is sort of true. Bisquits aren't needed for strength, but you have to be really good with technique and have a very good bisquit cutter for them to actually help with alignment.
"I have sometimes had a problem with a small crack in joints that is barely visible..." This is a question of meticulous preparation, whether you use a jointer or a hand plane to prepare the joints. All your equipment should be well tuned so you start with flat boards that are jointed at precisely right angles to the face. Check with your square along the entire length. The technique of jointing two facing boards together so that when are laid out any error of angle offsets on the two boards works, but makes keeping track a bit harder.
I would recommend against using the "sprung" joint with a gap in the center, not because it is wrong or a bad idea, but because it is so hard to execute really well. (I do think 1/32nd is too large a gap.) Without the gap you have an easy test to see if your joint fits properly. Clamp one board on edge on the bench, and then set its adjoining board on top. With only gentle hand pressure you should not be able to see any light between the boards, even in a dim room with a bright light behind. Usually you will see several points where the boards touch and light in other places. Mark those touching places. Often you will see the problem--a rough spot or a grain "feature". To eliminate the "touch spots" go back to the jointer and set it for a light cut. Then, taking care as to safety, lower the board on to the blade to take a short pass just around the problem area. Then, make a full length pass. This prevents the grain, etc. that caused the initial "bump" from causing the problem to reoccur. Then test again, until you reach the goal of seeing no light. With a sprung joint it's too easy to say to yourself--its OK, the clamps will close it up.
Make sure you have plenty of clamps. Titebond recommends 150-200 lbs. per square inch of clamping pressure on hardwoods like cherry. If you do the math, that makes it almost impossible to "over clamp". (On 1" thick boards that calls for a Bessy clamp every 5" or 6" with each at its maximum 1000 lbs. pressure.)
Thanks very much.
Steve,
You're right about the 1/32nd really. You could/should use a gap half that or less, especially with tough hardwoods. However, on long boards (over 6 feet) I never have had a problem using a relatively large gap. Remember, the gap is only "large" in the middle and tapers to nothing at or near the ends, so most of the gap is very small. As to needing good technique to make such a gap evenly, I must just be lucky as "Cackhand" is my middle name. :-)
You surprised me a bit with the clamping force recommendation from Titebond. At those sort of pressures, the clamps are surely going to crush the wood quite badly, where the jaws sit on the outer plank edges. Another advantage of the gap technique is that you have an additional sign of when the clamps are tight enough, as the glue squeeze-out is the same along the whole length of the join(s) and the gap is well gone.
Also, I have often managed to glue up 6 foot-plus long edges (using the aforementioned gap technique) with three or at most five T-bar or Plano press clamps, all of which are across the middle 2 - 4 feet of the planks being joined. That gap, as it closes, spreads clamping pressure along the planks from the middle to the ends.
All this, by the way, was initially learnt as theory from FWW and Co but has been borne out well by a lot of succesful tabletops (circa a dozen largish ones to date). None of them have opened up in the slightest - yet (fingers rapidly crossed and grabs quickly to touch some wood).
Lataxe
In practise, I first get the light tight fit, and then take a few tapering passes with a Bedrock #7, cheating by using a fence mounted on the plane to maintain squareness. I consider this an application where the blade gets sharpened right up to the translucent hard Arkansas stone. The original poster was having problems with "small gaps" in the final joint, so I recommend using the meticulous technique to be sure of getting a very smooth surface on both sides of the joint.
I learned clamping using heavy I-bar clamps which were sure to crush wood if not protected, so protective sticks are the norm with me. The Besseys can't apply nearly as much force, but I still use the padding.
I was surprised by the amount of force recommended when I first saw it. Hoadley also reports similar numbers, presumably coming from the wood science literature or his own experiments. In the scheme of things clamps and cauls are cheap so I don't see a need to hold off on clamps on the ends.
Could you describe the "cracks" in greater detail, especially where they occur and how long they are? That you can feel them with your finger suggests a few possible conditions that aren't cracking but are caused by differential wood movement.
John White, Shop Manager, Fine Woodworking Magazine
This forum post is now archived. Commenting has been disabled