Margin for recessed, tempered glass table top

[NewWoodWorkerVA]

I have made an end table out of walnut. The pieces are 1 1/2” square and the interior space is 15 inches by 15”. I have cut a 1/4 by 1/4” Rabat to hold a recessed tempered glass top (1/4 inch thick glass). Right now I’ve cut a blank with plywood that fits perfectly snug. Should I have glass made for this exact same size, or go a bit smaller to allow for wood expansion? How much smaller should the glass be?

Thank you

 

[tjbnwi]

Add 1/16 to the rabbit, this will give you 1/32nd per edge. The 1-1/2” pieces will not move much.

Tom

 

[Steve1]

I have made an end table out of walnut. The pieces are 1 1/2” square and the interior space is 15 inches by 15”. I have cut a 1/4 by 1/4” Rabat to hold a recessed tempered glass top (1/4 inch thick glass). Right now I’ve cut a blank with plywood that fits perfectly snug. Should I have glass made for this exact same size, or go a bit smaller to allow for wood expansion? How much smaller should the glass be?

Thank you

Without an explanation of which way the grain is running, I can't make an intelligent comment.

Except that you are likely overestimating the precision of the glass company cutting. For a close fit, you really can't cut the rabbet without having the glass in-hand.

 

[Packard]

Without an explanation of which way the grain is running, I can't make an intelligent comment.

Except that you are likely overestimating the precision of the glass company cutting. For a close fit, you really can't cut the rabbet without having the glass in-hand.

I agree.

Except cutting the rabbet may not have been the best approach.

Putting four 3M Bump-ons, one in each corner will prevent the glass from creeping and there will be no accumulation of dirt in the rabbet around the glass.

You might just want to rip it down flush and get the bump-ons. They are inexpensive, about 1/2” in diameter and about 0.100” thick with a very good adhesive. The adhesive will bond with the wood. The glass naturally has a high level of friction with the resin they use in the Bump-ons. If you enlarge the image below, the package lists the actual dimensions (metric).

In my opinion, the glass should overhand the table base by at least 1/4”. It is way easier to clean glass, than to re-finish the base.

When I get home, I will measure the thickness of the glass table top I have and also the glass coffee table top I have. I will post the dimensions when I have them.

Addendum: I measured the thickness of the glass table tops I have. The store-bought table has the glass sitting on a wooden base in a cross pattern. Thickness: 0.378”. Table size: 42” round. Overhand (at 4 points): 4-1/2”.

Coffee table, shop made: 0.380” thick, 1” overhang. Resting on four 3M Bump-ons, one in each corner.

Two points worth noting: It is possible that both glass tops are the same thickness. The deviation of 0.002” thickness might be a result of poor measuring technique.

The second point, possibly of greater importance is the fact that the glass top on the coffee table has appeared to have bonded to the bumpons. That is not how they are supposed to work. I have not removed the top from the base since I built the coffee table (about 27 years ago), and I assume that the soft resin in the bumpons has bonded. The resin appears to be similar to what is used on suction cups. I will have a go at them with a razor blade when the mood overtakes me.

But the dining table top does lift off and that is only about 15 years old. Apparently I should clean both side of the glass from time to time.

My introduction to Bumpons was from my picture framing days. Two were added to the bottom corners to keep the frame from shifting against the wall and from marking the wall at the contact points.

 

[MacBoy]

Add 1/16 to the rabbit, this will give you 1/32nd per edge. The 1-1/2” pieces will not move much.

Tom

I just now examined our late 80’s golden oak smoked glass coffee table and end tables.

Tom’s advice matches up to our living room furniture.

 

[smorgasbord]

I inherited a couple end tables with marble tops inlaid like the OP describes, except the marble was thick enough that they stuck up about ¼" beyond the frame, but fit the frame pretty closely - less than 1/32" gaps. The wood tables were ugly, so I just kept the marble but have yet to build something around them.

I have glass tops on a Louis Vitton trunk that we use as coffee table. Due to all the wood webbing, I have thick clear bumpers at the corners, but the glass top was sized to match the outside of the trunk, so no real overhangs nor recesses (but yes, it's not exact, which doesn't matter given the space between them). That top is ½" thick.

I also have ⅜" thick glass tops on two drawer units in our bathroom whose tops are just a bit bigger than the OP's, and they look/function fine.

 

[rst]

Tom's advice is absolutely correct. glazing tolerances industry wide are plus/minus 1/16", the extra 1/16" allows for deviation on the rabbit or opening. this practice is similar to setting doors and windows with the tolerances being larger as the deviations grow the longer the side. On commercial glazing framing must be absolutely square as there is no room for deviation on a 10' x 8' glass as the units are only 3/4" over the opening size.

 

[Packard]

Whatever tolerance you settle on, I suggest you get one of those hand-held vacuums to clean crumbs from the gap in the rabbet.

 

[Steve1]

I have an old coffee table with glass insert into rabbets. Relegated to the basement now. The rabbet is about .060" to .080" bigger (overall) than the glass.

The glass sits directly on the wood, no bumpers. But it's old now and there is a certain amount of rocking of the glass.

Yes, crumbs have fallen into the gaps, but has never really been a problem. Every once in a while I would vacuum the edges.

 

[Crazyraceguy]

I've only done a few tables, with inset glass tops, but a whole lot of doors and windows, similarly trapped. Generally, those don't have movement issues, because the grain runs around the glass. It's really only a concern when you set it into solid wood. The shrinkage only happens across the grain, not along it.
@NewWoodWorkerVA I assume, from the original post that this is a constructed frame, so you really shouldn't have a problem there. The biggest issue for you is fitment in general. This will depend on a couple of factors, mostly your glass supplier. The ones who cut with traditional scoring techniques are not likely to give you a very precise tolerance, for either size or squareness. Once you get into tempered, things change some, but again, it depends. You would have to be dealing with a pretty big place, for them to do their own tempering. Otherwise, you are running into middlemen and the accompanying finger pointing, if something goes wrong.
Having the edges polished adds to accuracy, but it also adds to the cost. You would still have to inquire about accuracy.
All in all, the best thing to do is have the glass "in hand" and build your frame around it. Even better yet, if you can buy standard sizes, that someone may maintain as "stock," it can reduce both cost and eliminate delays.
Windows are easier, since gaps are covered.

 

[Packard]

There are places online that will produce table tops to your exact specs. They list their manufacturing tolerances, so no mysteries.

I bought glass shelves on line, but not table tops.

I reverse designed the coffee table, first buying the glass from Pier One Imports. Their glass was less than 1/2 the price of any other source I could find. But I think they are out of business now.

No recommendation, but they list their tolerances. If you go to a local glass shop and ask what their tolerances are, they will probably make up a number on the spot. I know that my local shop did. And then did not keep to that spec.

Also, small, local shops may not have the right equipment to properly edge a piece of glass. Ask to see a sample.