I have read through 3 or 4 books on timber framing, and generally understand the use of wedges in wedged dovetails etc, and in tightening other joints.

There is lots of information on Pegs.. BUT I have not found any design guidelines for the size and wedge angle to be used in different wedging situations. And all the references are to "hardwood" with no specifics. I'm sure I'm missing this somewhere. Can someone point me to information on wedges?

I have a specific case in mind (but I'm sure I'll have others). Right now I am building a utility barn using a combination of traditional framing techniques and some metal fasteners in some cases. I am now placing 4x6 inch joists for the main floor into 8x8 inch beams that are supported on 8 foot centers. The engineering numbers for hemlock work out well for a vehicle up to 6000 pounds on this frame with 2 inch floor boards. My Question:
I am setting the 4x6 joists (reduced to 4x5) into 4x5x2 simple pocket mortises in the 8x8's. (Note: the square layout means the 8x8's have joists let in on only one side, in a 'checkerboard' sequence). Still, I want
to wedge the 2 inch sides of the tenons to help compensate for drying over time, and to reduce the effect of the 4x5 by 2 deep mortises in the 8x8 beams. I see quite a few examples of this kind of wedging in the books, but nothing specific on the size and shape of the wedge.

1. Should the wedge be the full 2 inches wide, or is it better to avoid the opening edge area?

2. What would an appropriate wedge angle be?

3. Would maple be an OK 'hardwood' for wedges?

4. Frosting on the Cake: Does anyone have a favorite layout for cutting a number of wedges out of hardwood stock??

I've learned a lot from the TFG "Joinery and Design Workbook" and other books like Steve Chappell's, and these forums.

I would appreciate any pointers, comments or critiques!

More more quick question re Wedges:

Should I design the initial joint tolerance to be "tight", and expect the wedges to be doing some compression and taking up later shrinkage?
Or should I design in some spacing that the wedge will start in?

Thanks!!

BUMP: Any pointers to wedge design, anywhere??

i haven't seen wedges in basic pockets before, that being said:
i would design in a bit of space if you are planning on wedges(1/4?)
i would use the full 2" and fill the space or you will see a gap(take a second and round the back bottom corner of the wedge)
i would use a very small amount of taper and design the leading edge of your wedge slightly smaller than your gap, so that the wedge will be tight all the way down (3/32-3/8?)
you want to compress the fiber without destroying the fiber so it can still bounce back
i would use wood that resists rot, like oak.
i think a table saw would be hard to beat for cutting wedges...
-Mark.

What Mark said. I have never wedged a housed joint because it will not work like you hope it will. What will happen is the joist will shrink and the wedge will fall out. If it is important that the joint appear tight I will step the housing in so you cannot see the gap when the frame shrinks. ( I also lag or oly screw the joist so it does not fall out of the housing )
Wedge material should be matched to the job it is doing. If it is used to assemble a joint it might be better for it to be softer than the wood being assembled so you do not split your work. I cut a hammerhead splice and ruined it when the wedge sheared off the head and dang near split the morticed piece because the wedge face was not parrallel to the grain.
Bake

Thanks to The Usual Suspects AKA Mark and BAKE!

OK, this makes sense, now. Originally I was concerned about the decrease in beam strength due to the pockets for the joists/summers. I have 4x6 joists in 4x5 by 2" deep pockets in 8x8 beams in this 'barn' floor because I needed to engineer it to handle up to 6000 lb vehicles. I was concerned about the strength reduction of two aligned 2" deep pockets in an 8" beam. I wanted to use the wedges as I had read about, to take out the space so the beam strength was largely retained.

Now I have a somewhat different situation. I realized that with uniform 8 foot spacing of the 8x8 beams and their concrete/steel supports there was no need to orient all the joists the same way and have aligned opposite pockets. So I changed that so the joists run alternating directions, and the flooring is in an 8 foot checkerboard pattern. Looks cool. I think. So the most any 8by8 8 foot beam section has is one side row of 3 pockets 2" deep by 4" wide by 5" high (the 4x6 joists have a 1" curve-in on the bottom)..

SO.. the wedging is less important, but I'd still like to understand how it can be used effectively. I will monitor the shrinkage the next 2 or 3 years to see if I get open there. It's not a cosmetic issue, and the joists should bear weight well, especially as the safety factor I used in Hemlock goes from 5:1 wet to 8:1 after it is dry.

I'm terminology-poor here. Whaza "Oly Screw" and where do they come from? I've heard of them used in Log construction, maybe? I'm thinking that I might put a lag screw into the end of the center joist in each section. Although I somehow don't think a well-joined 8x8 that's 8 feet long is likely to 'spread' much. I'll have a different feeling about the second-floor joints, I think.

Thanks for responding; I keep on learning stuff from other peoples experiences, which is good!

Terry;

An 8 by 8 Girder / Summer / Tie Beam, with 4 Inch Wide, 5 Inch Deep and 2 Inch Long Pockets?

Designed to carry 2 Inch Decking and a 6,000 Pound Rolling Load? That's a Pretty Intense Point Load, By The Way.

and, when you say;
Do you mean that only One Bay will have Joist Pockets or merely that your Joists do not line up?

(Grain would still be severed, however)

This seems like an extraordinary section loss, to me, personally the floor seems Very Spongy from what little information you've given, and I don't see how wedging the joint could make up for your piercing the Compression Band in such an extreme manner.

Joinery is a compromise, and is a large element in design (Sizing Timbers as an example). In This case,

Not knowing How many Joists, what centers, whether only One side (One Bay of Joists) or Multiple Bays of Joists merely "Stagered" ("CheckerBoard Style")

And designing to carry significant Loads I would probably go with deeper Beams, say an 8 by 10 minimum, and go with a soffit tenon with stepped housings, rather than a drop in pocket, in an effort to reduce as little of my Carrying stick as possible, placing my section loss as close to the neutral axis as possible, while still endevoring to house as much of the Joist as possible.

I couldn't tell you how I would design for a One and a Half Ton Vehicle, as, I have never had to design for this type of Load before, and simply don't have that knowledge at the top of my head.

But, if you are counting on Wedges to stiffen this 8 By 8, and to compensate for your Drop-Ins, I think you should reconsider.

I would also ask what made you look at this particular Joint, and this particular Dimension (8 x 8).

Tim Berube

Terry, I would suggest not trying to make the pocketed joists work as fillers in your 8x8 girder. The compressive strength perpendicular to the grain is half of the strength parallel to the grain, the modulus of elasticity is lower perpendicular to the grain and it is going to shrink no matter how tight you wedge them now. Calculate the section properties of your girder at the joist pocket. I have repaired timbers with notches in the top using same- species blocks with the grain aligned with that of the timber. In this case only I count it as a full strength repair. (tight blocks with epoxy)
Better use T&G decking to distribute those wheel loads. Also I try to align framing/ sleepers under the wheel paths.
Good Luck, Chris Hoppe

Thanks to Tim and Chris for your suggestions and concerns. I'd appreciate anyone who wants to check thru this stuff to question it! I have used both tables from the books and stress equations as a double-check. I didn't explain the configuration very well. There are 8x8 beams supported on 8 foot centers. The maximum distributed load on a beam is 7040 pounds with a 6000 pound truck right over a beam. I picked the 8x8 from Tables and also by doing the stress (Modulus of Rupture) equations to see the safety factor for a load and beam sizing.

The pockets for the joists are 4" wide, 5" high and only 2" DEEP into the beams. So, taking a worst-case approach where the remaining beam is only 6" wide and 8" high, the numbers come out like this:

Experimental section : Calculation : (Evenly distributed load)
Load lbs 7040.00
Length (in) 92.00
Width Beam (in) 6.00
Depth Beam (in) 8.00
Calculated MOR (psi) [less than 1600] 1265.00

(The 1600 PSI is with a 4 to 1 safety factor (Will be 6 to 1 safety factor when dry). So it's only at 1265 PSI even with a 6x8 beam, and that looks fine. I agree that my original idea of compensating for the loss of material by wedging, although mentioned in a couple of books, is not very controllable, and I won't rely on it.

The 'checkerboard' configuration does mean that there is only ONE set of pockets in one side of any beam. Take a look at some photos at:
http://terryking.us/public/barn/floorframe.htm
to see how this works (click on photos to enlarge).

The joists fit VERY tightly into the pockets (See jig photo) although as Chris points out the compressive strength perpendicular to the grain is only about 1/3 that along the grain. And they'll shrink more in that direction.

OK, the joist sizing is similar: on 2 foot centers the maximum load (1 wheel right on a joist) is about 1500 pounds. The 2" flooring will distribute the load significantly. The stress with 1760 pounds on a 4W by 6H joist is 880PSI, way under the 1600 PSI max I'd want to go.

The next part is the flooring (NOT tongue-groove) and the smallest plank is 8" x 2" (I have 10" wide in the obvious wheel track areas, for even more safety factor). Because of the wide beams and joists, the unsupported space is only about 18". I checked 18" and 19" like this:
1st Floor Floorboard calculation: center load. 1 wheel!
Load lbs 1500.00 1500.00
Length (in) 18.00 19.00
Width Beam (in) 8.00 8.00
Depth Beam (in) 2.00 2.00
Calculated: 1265.63 1335.94 MOR (psi)(Should be 1600 or less)

In the photos you can see one bay that has a removed "pit" area for vehicle repair. I've parked the truck there, and seen no movement of anything and no creaks, etc. at all. Rain stops and I'll have it out on the main deck so I can use my crane for the last 4 beams, and finally get to building UP a barn...

Anyway I've learned a lot from this whole discussion, and gone back over the numbers on every beam and post and joint in the rest of the design. And I checked the PSI in each joint, for both side compression where ends sit on posts, and lengthwise loading.

If anyone's Math Happy, I can put the Lotus 123 spreadsheet I have with all the calculations up on the web. Also, someone asked about the jigs... oh, that was over in a different router discussion; I'll go there for that.

I'll put up a photo of the truck ON the deck, hopefully on the TOP, in a couple days...

Read My Lips: No More Wedges...

OK, the truck's out on the barn floor, with the crane attached, putting a 350 pound beam in place!

Take a look at:
http://terryking.us/public/barn/truckframe.htm
for a couple of pix. I could not see ANY deflection, which surprised me, as I expected just a little...

Thanks for the suggestions and info!