8' workbench top - screws in the middle?

[kirkroy]

I'm making an 8' workbench for a motorcycle mechanic's shop. The top is going to take a lot of abuse and doesn't need to be pretty or particularly flat (per the mechanic) so I'm just using pocket screws to attach 'raw' 2"x10"x8' construction lumber. I've never built something so wide. Should I attach the top to the center support or just the ends? I don't know if this sort of thing is likely to crack when the weather changes if I screw down the middle...

Here it is without the top:

[chopnhack]

I don't think you have to worry much on that, despite it being kiln dried construction lumber is relatively still green and has some give to it. You can screw down the 2x10 flat across the top. I personally would go ahead and do it from the top down if there is any concern of warping and movement as they dry. Another concern would be weight, if the mechanic decided to use one end for something heavy or mounted a vise and was prying on something, you wouldnt want the pocket screws to just suddenly give and the top to rip out or move!

[cabinetman]

If you didn't want the screws to show from the top, just install some corner gussets on the top corners of the frame, and screw the lumber from underneath. Those could be ¾" plywood.

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[vaking]

I would:
Used bisquits to connect 2x10 together and keep them flat and alligned.
Attached top to frame in center. In corners I would use gussets like C-man suggested and made alongated holes in those, so the top can contract or expand as needed. All screws from underneath.

[LCHIEN]

I don't like screws in the top of a table. could scratch the work, could take a hit if he's drilling something. Last of all you'd use flat head screws more than likely and have no give.

With an 8' span I think it would be good to ties down the middle.

What you should do to fasten the middle is take a small 3/4x 3/4 blocks the width of the opening and attach it to the side of the cross members and flush with the top.

When you mount the top you can put a screw through the bottom of the block into the bottom of the top to hold the top down. Oversize holes in the block, round head screws and washers would allow for some material movement. This would also work for the ends. However, since you are using contructional lumber throughout, there shouldn't be too much mismatch of movement/expansion.

Another option: take a block of wood, and rabbet one edge. Put the lip left by the rabbet down, it will be below the top, make a small channel in the aprons of your frame, to fit the lip. Slide the lip into the channels and screw the block to the underside of the top. The channel should be low enough so that the block can pull the top to the apron.

[cwsmith]

You didn't mention what the top was... sheet goods like plywood or are you going to use solid boards similar to the base structure?

If you are concerned with expansion and contraction, I would use "gussets". In the past, I've used wooden gussets (ply or solid), drill a half-inch hole in the middle, and use a screw with a fender washer up through the center of the hole and into the bottom of the top. Don't tighten the screws too tight... you want the top to creep a bit as it expands and contracts.

While that keeps the top from going anywhere, it will also allow for "movement" due to humidity and temperature changes.

CWS

[cabinetman]

You didn't mention what the top was... sheet goods like plywood or are you going to use solid boards similar to the base structure?
CWS

In the OP he stated...'raw' 2"x10"x8' construction lumber


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[kirkroy]

Thanks for the ideas! Mulling them over now...

[tropicalarcadian]

If you're doing it for someone else, you want it to be purdy, so that means no screws in top. It might be for a workshop, but it will look more professionally made. You also dont want to glue it in case the top ever needs replaced. i would take 3 3/4" t-25 screws and go from the bottom up into the top and sink the heads 1" into the wood. You must use star drive's though so the heads don't strip out driving through that much wood.

[chopnhack]

kirkroy, it seems you have already used some lag bolts. That is yet another option to consider. They are quite strong!

[jAngiel]

Simpson strong tie L brackets, the ones with two holes on each side.
Two on each side of each support, only on inside of end supports and stagger on each support so the screws do not hit each other. Use inch and a quarter screws. Thats eight screws at each support and four on the ends holding the top down and no screws from the top. Strong and replaceable if needed.

I guesss that would be for a one piece top, for boards use two for each board on each side of support except the end. Only on inside of ends.

[cwsmith]

Thanks... I misinterpreted the use for the 2 x 10 construction lumber, thinking it was meant for the structure.

So, if you are using it for the top and if it is indeed "raw"... it's pretty likely to shrink as it ages and over time may expand and contract.

I don't think you want to fasten it down to a point where it can't move without effecting the base. So once again, fasten it from the bottom using corner gussets or whatever; but, do it in a manner where it can slightly move. It will most likely shrink more in the width of the stock, then it will over the length. But you should allow for shrinkage/movement in along all three axis.

CWS