Making a truss plate press

[FordTruckWench]

I have decided to use/make trusses for the roof of a shed. Therefore, I need to build a press to install truss plates. This is essentially an arbor press, but using a bottle jack for the pressing force. See the attached picture for a mockup.

If there's interest, I'll add replies showing the engineering math for each portion.

 

[FordTruckWench]

The design specifications:

Apply force on a 6" x 6" square, 2" from the back of the press's throat. This means the jacking load is centered 5" from the throat.

Jaw height of 10". This is ~7" for a stubby bottle jack, 1.5" for 2x wood, and the rest for a truss plate.

Jacking force of 20 tons.

Maximum steel stress of 36000 psi. This is not a lifting nor life safety device. This design is already over specified. Thus, no safety factor is necessary.

 

[FordTruckWench]

Cut-offs and scrap available at the steel yard:

W4 steel beam:
b (width) = 4.06
h (height) = 4.16
flange = 0.345
web = 0.28
I (moment of inertia) = 11.3
S (section modulus) = 5.5
area = 3.8
weight per foot = 13

W6 steel beam:
b = 5.99
h = 5.99
flange = 0.26
web = 0.23
I = 29.1
S = 9.7
area = 4.4
weight per foot = 15

S6 steel beam:
b = 3.332
h = 6.0
web = 0.232
I = 22.1
S = 7.37
area = 3.67
weight per foot = 12.5

And just for grins, specs for a solid steel bar:
b = 8.0
h = 2.0
I = h^3*b/12 = 5.33
S = I/(h/2) = 5.33
area = 16.0

 

[FordTruckWench]

The tentative design:

Base of two 14" W4 beams side by side. This base extends under the upright. (See above picture.) The usable base is 8" wide and 8" deep.

An upright of two S6 beams side by side.

A bridge of two side by side S6 beams.

I have two ~24.75" long S6 beams. This is long enough for the 10" jaw height, an 8" bridge (to match the base), and 6" for the corner.

How should the upright and bridge beams be joined? The upright could run long, with the bridge welded to a side. (See above mockup.) Or the bridge could run long similar to the base. Or the beams could be cut on a 45 thus mitering the top corner. I've tentatively decided to miter this corner. The 24.75" lengths mean I can lose 1/4" to the 45 degree cut, and then have a 10.5" jaw height.

 

[jack stand]

Looks like a sound design, I'd suggest a air over hydraulic jack for a little added speed and lots of sawhorses!
I'd also be generous with the opening, throat height. I'd imagine that allowing another 1 1/2" for the 2 truss plates so a minimum of about 4" plus the jack.
You might put a shallow "capture" for the top of the jack to nest in. A simple 1" long pipe would do. As for welding, I'd put 3-4 tacks on the bottom of the 2 "feet" and fully weld the top seam, grinding flush. Then fully weld the vertical to the base (feet) and the "top" to the vertical. A couple of minutes chamfering these 2 wouldn't hurt.
Keep us "in the loop" with at least your results.

 

[mike93lx]

Don't forget something of matching height to support the rest of the truss while pressing on the plate

 

[36truck]

I agree to add more to the height to give you more breathing room. Also make some way to hold the top of the jack so it lifts up when you release the pressure. Otherwise I like the set up.

 

[FordTruckWench]

I'd suggest a air over hydraulic jack for a little added speed

Already considering this! Unfortunately, this means a no-name Amazon jack versus an off the shelf jack from Lowes or Tractor Supply.

You might put a shallow "capture" for the top of the jack to nest in. A simple 1" long pipe would do.

I've thought of putting a "channel" on the underside of the bridge. This would constrain the jack in one direction, while allowing it to be slid in place via the other direction.

[QUOTE
As for welding, I'd put 3-4 tacks on the bottom of the 2 "feet" and fully weld the top seam, grinding flush. Then fully weld the vertical to the base (feet) and the "top" to the vertical. A couple of minutes chamfering these 2 wouldn't hurt.
Keep us "in the loop" with at least your results.
[/QUOTE]

As every piece will be doubled, my thought is to tack the pairs together. Then do the base to vertical and vertical to top welds. Then grind the tacks away, thus cleaving the assembly in two. Then weld the inner/back side of the welds that will need to carry the tension load. Finally put the two halves together, welding the seams.

Don't forget something of matching height to support the rest of the truss while pressing on the plate

This is one reason for going with W4's as the base: Short 4x4 pieces and scrap 1/2" plywood will keep everything lined up.

Also make some way to hold the top of the jack so it lifts up when you release the pressure.

The air over hydraulic jacks seem to have retraction springs. Just need a way to link them to the frame...

 

[FordTruckWench]

Cantilever calculations:

For a cantilevered beam with a point load:
Maximum stress (tension) = Load * Distance / S
Maximum deflection = (Distance ^ 3 * Load) / (3 * Y * I)

Y = Young's modulus = 29,000,000 (for steel)

This applies to the bridge (top beam). It is also applicable to the base as an approximation.

For a single W4 beam:
stress = 40000 * 5 / 5.5 = 36400
deflection = (5 ^ 3 * 40000) / (3 * Y * 11.3) = 0.0051

Two W4 side by side:
stress = 18200
deflection = 0.0025

Single W6:
stress = 20600
deflection = 0.0020

Single S6:
stress = 27100
deflection = 0.0026

The 2" x 8" flat bar:
stress = 37500
deflection = 0.011

So, a single W4 just fails. Of course it (and the S6) are not wide enough for the base. Both the W6 and S6 are strong enough, though there is a problem with the W6 (see below). Interestingly, the massive flat bar also fails!

For a cantilevered beam with a distributed load:
Maximum deflection = (Distance ^ 4 * Load) / (8 * Y * I)

For the flange of the W6 with a distributed load:
deflection = (2.88 ^ 4 * 6678) / (8 * 29000000 * 0.008788) = 0.23

This means that the flange of the W6 would bend down nearly 1/4"! Shocking, until you realize the flange is essentially just a 1/4" plate. Twenty tons on such a plate will distort it.

 

[FordTruckWench]

Column calculations:

Column parallel load = Load / area
Column bending moment = Load * (cantilever distance + neutral point)
Column bending tension = Bending moment * neutral point / I
Column bending compression = Bending moment * (h - neutral point) / I
Column max tension = bending tension + parallel load
Column max compression = bending compression - parallel load


Single S6:
parallel load = 40000 / 3.67 = 10900
bending moment = 40000 * (5 + 6/2) = 320000
bending tension = 320000 * (6/2) / 22.1 = 43400
bending compression = 320000 * (6 - 6/2) / 22.1 = 43400
max tension = 43400 + 10900 = 54300
max compression = 43400 - 10900 = 32500

Single W6:
max tension = 42000

Single W4:
max tension = 62700

Double S6:
max tension = 27200

Double W4:
max tension = 31300

This is why I've chosen to go with the doubled S6's for the column. As an aside, I did the math to add a 1/4" plate to the tension flange. This dramatically reduces the stress - enough so that a single S6 would be enough for the column. This explains why arbor press forgings often have a fat flange on the inner edge of the column portion and no flange on the outer edge.

 

[FordTruckWench]

I agree to add more to the height to give you more breathing room.

With the material I have, I could slightly trade off height for projection of the top beam. The top certainly does not need to be the same length as the base. Hmm...