Bench Leg Attachment Question

[Isaac]

3 hours ago, Chestnut said:

Do the hardwood dowels count for little in terms of moment reduction? I didn't really see the screws as resisting the moment but more so as stopping the joint from separating. If the corner of the leg acts as the fulcrum and the dowel resists the moment the screw is left to take the tension forces trying to separate the joint?

Sorry this is slightly off topic but the only structures stuff i know is what i remember from school and that was concrete and steel design i never took timber design. REALLY wish i had though.

The dowels help, but have the same problem as the screws.

Imagine flipping this bench upside down, with the legs sticking up. If you push on the broad, flat face of one of the legs, It will want to lean and a fulcrum will develop at the corner where the leg meets the bench surface, on the opposite side that you pushed. If the leg is 16" long, then it is 16" between the point of your force application and the fulcrum. Now the resistance to movement comes from the dowels and screws, which are located about 1/2" to 1" from the fulcrum.

So we have a teeter totter that is 16x longer on one side than the other. so you need a 160lb man on the short end to lift a 10 lb baby on the end of the long leg. This is why we want a bracket, to widen the connection base and reduce that 16x to something more reasonable, which the screw(s) will be sufficient to resist. 

1 hour ago, zole2112 said:

The dowels are tight in the legs and fit tight into the bench top. they are glued into the legs currently.  When I originally searched for a piece of wood for a stretcher I searched only for pecan, any suggestions on a wood that would compliment the pecan that would be appropriate for the stretcher? Also what is the best way to attach the stretcher?

So my plan now is:

1) check to see if I can flatten and clamp it, the initial check i did looked like I couldn't

2) wait a couple of weeks for it to acclimate to my climate

3) Use a router sled to flatten the bottom if necessary - this looks interesting to me

4) attach the legs with glue, the dowels, the pocket screws and a stretcher board for strength against my grandsons

Thank you guys for all of your comments, it's been really helpful!

Sounds like a plan. Try Hickory, which is related to pecan. 

Rather than go to all the trouble of a router sled, which will leave a rough surface that you'll have to sand, you could take that board with you to the lumber mill and have  them plane it. Where I go, Kettle Moraine Hardwoods in Southeast, WI, I pay $.15 a board foot for this service, so your bench top would probably be around $1 and you'd be done in about 10 seconds. 

I would put the stretcher right under the table top (see below) and you can fasten it along  its length with some figure 8 fasteners. 

[zole2112]

1 hour ago, Isaac said:

The dowels help, but have the same problem as the screws.

Imagine flipping this bench upside down, with the legs sticking up. If you push on the broad, flat face of one of the legs, It will want to lean and a fulcrum will develop at the corner where the leg meets the bench surface, on the opposite side that you pushed. If the leg is 16" long, then it is 16" between the point of your force application and the fulcrum. Now the resistance to movement comes from the dowels and screws, which are located about 1/2" to 1" from the fulcrum.

So we have a teeter totter that is 16x longer on one side than the other. so you need a 160lb man on the short end to lift a 10 lb baby on the end of the long leg. This is why we want a bracket, to widen the connection base and reduce that 16x to something more reasonable, which the screw(s) will be sufficient to resist. 

Sounds like a plan. Try Hickory, which is related to pecan. 

Rather than go to all the trouble of a router sled, which will leave a rough surface that you'll have to sand, you could take that board with you to the lumber mill and have  them plane it. Where I go, Kettle Moraine Hardwoods in Southeast, WI, I pay $.15 a board foot for this service, so your bench top would probably be around $1 and you'd be done in about 10 seconds. 

I would put the stretcher right under the table top (see below) and you can fasten it along  its length with some figure 8 fasteners. 

sounds good to me. One last question, the top is finished (as you surely know) will I have to refinish the top after planing or will they be able to plane the bottom without damaging the top?

[drzaius]

I would be more inclined to just joint the bottom face & leave the top untouched. You need a properly flat side to get good results running the through the planer & the top will not be flat. And trying to do it with a planer will probably mess up the finish on the top.

[Ronn W]

LIf you check the end grain in the pics - the grain is a pretty tight circular pattern and the cupping is consistent with normal drying.  The wood was not dried enough before if was milled.  I would guess that that that board, so close to the center of the tree, would have cupped a little anyway.

[Mark J]

I would also apply some kind of surface coating to any bare wood after attaching the legs and stretcher (I still have to read the Flexner article, but it won't hurt).

19 hours ago, zole2112 said:

any suggestions on a wood that would compliment the pecan 

If you can't find any pecan then I might try something completely different, like ebonized maple.  

[Mark J]

@Isaac great article.  It does pit my finishing guru, Flexner, against my wood guru, Hoadley, though.  

[zole2112]

5 hours ago, Mark J said:

I would also apply some kind of surface coating to any bare wood after attaching the legs and stretcher (I still have to read the Flexner article, but it won't hurt).

If you can't find any pecan then I might try something completely different, like ebonized maple.  

Yes, I will apply a polyurethane coating to the back as well when it's done.

[zole2112]

thank you all for your help with my project, it turned out great and my wife loves it!

I am a novice at this but it turned out really good. I used my buddy's mill to mill a flat spot for each leg and a flat channel between the legs as there was a bow in the long direction as well. I then used Figure 8 desktop fasteners on the ends of the stretcher, glued the legs and the stretcher and it worked beautifully. I did end up ordering a hickory live edge board from ebay and used that for the stretcher.

 

[Mark J]

Looks good.  Now it's time to set yourself down a spell.

[Brendon_t]

I'm a little confused with how the stretcher is attached with figure 8's. If that's all that is connecting the stretcher to leg, your boys Will destroy that in a hurry. 

[zole2112]

I have 2 figure 8s on each end and i glued the stretcher to the bench top. I figured i could always remove it in the future if i had to and replace it.

[Brendon_t]

Good on ya gluing in the stretcher to the top, but the joint that is giving you racking strength is the stretcher height, attached to the legs to triangulate it. 

Figure 8s are good for that they are for. Replacing a mortice or traditional hardware isn't its best idea. I've got two boys, 13 and 10. I would worry for the piece.

[zole2112]

I will keep an eye on it for sure, thank you for the help on this. My wife is planning to use it more for looking at, different plan than i had which was using it by the table but she loves it so she doesn't want it to be used much lol go figure.