Using biscuits - table tops


In a dicussion at one of our woodworker group meetings, the issue of using biscuits for tabletops came up. I know this has been discussed in many ways, but not sure if this particular hint ever came up:
The suggestion was to use biscuits as a LOCATING aid, vs as a glueup aid. Meaining don't put glue in/on the biscuits and the slots, leave them dry. Put glue along the edge and use that as the glue joint. The point being is that glue never seems to dry completely in the slots and that at some point (don't remember exactly what was said) the biscuit will shrink leaving a small dimple in the top. I know Norm has said he doesn't use biscuits anymore in tabletops because they telegraph through.
Curious as to other experiences you might have had with biscuits and tabletops.
I have some projects in the wind and will need to glue up some panels and want to use biscuits, but now I'm not sure. I've glued up panels with just a clean rip cut and dowels but thought biscuits were the way to go.
Comments?
MJ Wallace
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snipped-for-privacy@onebox.com wrote:

Don't see any reason they couldn't be used that way---that's they're primary function for most edge-line gluing anyway.
I've heard the stories of biscuits "showing through" too, but never seen it even here in a very dry area where stuff dries out more than in most other areas for anything 3/4" or more in thickness.
IMO, that it is a problem is the woodshop equivalent of the urban legend. I could see it for a very thin piece or a biscuit inserted near the surface of a thicker piece (such as two rows of biscuits) but just don't see it as a problem.
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Makes no sense to not glue the biscuits, IMHO, unless they are such a tight fit in the groove that, on swelling after getting wet, they distort the piece enough to be seen.
This might happen in balsa, or where you glue it, finish it, and ship it. Without any scraping, sanding, planing, whatever. Unlikely enough to be irrelevant.
Every bit of joint strength is valuable.
Norm still abuses brads.
J
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snipped-for-privacy@sme-online.com wrote:

The usual "showthrough" that is complained of is after finishing the area over the biscuit is claimed to be slightly sunken, not raised, owing to the subsequent loss of the residual glue moisture from the biscuit.

I agree it seems far fetched except as I noted in another response that the thickness above the biscuit to the finished surface is quite thin. I can also only presume it would happen if the piece were finished in such a short time frame after glue up that the residual glue moisture hadn't reached equilibrium. In a production shop environment I suppose that's realistic--in a hobby/rec environment I don't believe so...

A typical 3/4" well fitting glue line joint is stronger than the wood, anyway...

:)
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Some people say you should wait a day before sanding it give the wood a chance to get back to normal after gluing; but that is true even without biscuits. Otherwise you can show a slight slot at the glue line. I probably have never sanded immediately just because of time requirements.
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I too have given up using glue on the biscuits in panel or tabletop assembly. I've had 3 occasions where they showed in the finished work. These panels were 3/4 pine and I had surface sanded them within 2 days of the glue-up. Since the dimple isn't ever visible until sometime after the project is completed, this has been a very disturbing situation for me because it wasn't possible for me to go back and replace the defective panels. I now glue only the board edges when I'm assembling panels and use the biscuits dry, for alignment purposes only. If I build something that requires a biscuit for strength I'll glue it, but I'm much more careful about when and where I use the glue.
--
Charley

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On 15 Nov 2005 10:36:15 -0800, snipped-for-privacy@onebox.com wrote:

I use biscuits for panel glueups, and I apply glue to both the biscuit and the slot. I've never had one telegraph.
this doesn't mean that it won't happen in your shop though. I live in arizona. the glue in the slot definitely dries completely- and quickly, too.
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In my shop I have spec'ed biscuits in tops for 23 years now and we don't have complaints or problems. The first table I built 23 years ago with biscuits sits in my office and as close as I look I can't see any problem with the joint or the biscuit showing.
R

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OK Rumpty, now try it with a pine top and see what happens. I have the trouble with PINE tops, do a lot of colonial pine stuff here.
--
Charley


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How thick is your board and where are you putting the biscuit? Also do you glue the slot AND the biscuit or just the slot?
Regards,
Rumpty

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On 15 Nov 2005 10:36:15 -0800, snipped-for-privacy@onebox.com wrote:

I never heard of that. So I just did an inspection of all the furniture I have in the house that I made with glued up biscuit panels. Some cherry, some walnut, some oak. I couldn't find any dimples and while no tables, some of the panels were large glue ups.
I did, however, find a couple of splits in side panels from ignoring the cross grain gluing law. Oh well, gives them that antique look. and they'll close back up next spring.
Frank
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They work fine. The telegraphing happened to me once, pine top and way to much glue on the biscuit. I've more tops but now I brush a thin coat of glue in the slot and on the biscuits. No problems.
Dave
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Biscuits is all I use, a couple dozen panels now, and nary a biscuit showing.
That might be because in this very newsgroup someone asked how come he had little depressions everywhere in the tabletop that had a biscuit, and someone said it was probably because he sanded a few hours after he glued up. Everyone else in that thread allowed how they'd always waited at least a day before they sanded their panels, and never had a problem. I've kept to that habit.
The theory is, the biscuits do swell when you glue 'em, and then after ten or twelve hours, they shrink back to normal. If you flatten the top when they're swelled up, there'll be a depression everywhere there's a biscuit.
Norm says he doesn't do biscuits any more because they leave depressions. I'd tell him it was probably because he doesn't let it sit long enough, but I know he's on a tight schedule.
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If you're using a composite core I think the original statement here might hold some wieght.. meaning a veneered flake panel or MDF... but in most solids, I would say a glued biscuit in the edge center, properly set, will probably never show in our lifetime or in your great grandchildrens for that matter...
health n laughter
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