I think they mean breaking strength. This is how hard you have to pull to actually break the material under laboratory conditions. Working strength has a safety factor to allow for real world conditions. Even the working strength may be overly optimistic. And when they say breaking strength, the mean it - it breaks. Brand new under optimum conditions. No knots, no corners, no dynamic loads.
300lb working strength straps are wimps.
If you naively apply webbing straps, there is a very good chance they will come loose and the mill will tip over. Nylon has stretch which is both a blessing and a curse. That stretch means it absorbs shock loads very well and nylon is preferred for that reason. However, the stretch means it has some give. The machine will rock back and forth a bid. In the case of tie down straps, what will happen is one side stretches and the hooks come lose on the other side. Do not trust hooks. Double the webbing back through the eyehole in the straps where possible or run the webbing in a loop with the hooks secured through each others eye hole and the combination secured with lots of duct tape. Note that one end of a ratchet tie down strap is non-removable which makes it very impossible to double back through the eyehole unless you can loop it around something after it is doubled back.
If you tie a piece of webbing around the slats of the pallet 5 times and through the eyehole of a webbing strap, then tie a water knot and back it up with two overhand back ups, and keep enough slack in the webbing to make a 45 degree angle (you want to avoid force amplification which occurs without slack), and tension the knots to secure them that is very secure (but can slide on the slat). If you add a few turns around the slat only, that is more resistant to sliding, though you don't want to rely on anything not sliding for unattended shipping. The slat itself may break or the nails may pull out (if applicable).
Nylon can stretch when it gets wet.
Bear in mind that the forces will not be evenly divided amongst your straps in most configurations so you can't add the strength of your straps. For example, if you run straps to the four corners of the pallet, at any given time only one or two of the straps are taking the load. The more straps you can arrange to share the load in any direction, the better.
Suppose you are strapping around the machine down to the pallet. With 1G sideways acceleration, assume a 500lb sideways force. The machine is probably top heavy and the center of mass higher than the width of the base. So, this may be multiplied to 750lbs upward force.. With 1000lb straps wrapped in X and Y directions on each side of the machine (secured so they can't slip off), you have 2 straps on one side holding down with maybe a little help from one strap on the side. So, maybe 375lb on each strap. Unfortunately, the straps go around sharp corners with the result being that their strength is reduced by more than 2/3. Just bending weakens it (this is why knots weaken). Some knots can weaken rope by
2/3 and a sharp corner is worse. So, the strap is already broken and we haven't considered the preload tension on the strap. Corner protectors can help reduce abrasion and increase the bend radius some but it is still a serious bend.
It is hard to find data on what forces your packaging needs to withstand.
If it was a box, you could drop it on all 6 sides plus each corner from 42".
I have seen shipping impact indicators with 25G, 50G, and 75G thresholds.
Side forces in shipping can be more than the weight of the item.
If a truck breaks hard enough to leave skid marks, with a tire friction coefficient of 0.7 (dry), that is probably about 0.7G. Then the pallet hits the pallet in front and the forces are much higher.
From the air force:
"Containers shall be secured to the pallet tie down rings or aircraft floor as necessary to achieve a minimum of 3 G forward & aft, 2 G up, and 1.5 G laterally .... potential 4.5 G download "
http://www.tpub.com/content/shopequipment/TM-10-5411-236-13-P/TM-10-5411-236-13-P0030.htm
That is for air, of course. But pallets skidding sideways into other pallets could generate some serious G forces - limited primarily by the give of the wood and the straps. And your mill is probably top heavy. The army measured 10G impact force on one truck shipment out of 14 (probably during forklift handling).
http://www.hss.doe.gov/csa/csp/hepa/Nureg_26th/016a.pdf
1" tubular webbing is stronger than your typical steel strap and has better shock resistance. But you have to secure it.
You can use up part of the strength by pretensioning. You lose strength at tight angle bends. Knots can lose 2/3 of a ropes strength. Figure 8 knots have one of the lowest impact on rope strength of simple knot. The strongest method of securing is to wrap the rope abound a beam (watch out for square corners) about 5 times before tying off with a good knot (the wrap takes the tension off the knot) and then tie a backup knot.
Water knots hold very well in webbing (although they are extremely difficult to untie). In critical applications, knots are backed up with other knots. But it is difficult to pretension with knots (except for sliding knots which may then live up to their name). Dynamic loads can exert far more force than static loads. Abrasion can lower strength. Fork lift tines can affect your webbing.
If you put side loads on a straight piece of webbing or rope, you can produce extremely high tension in the rope/webbing with a small load. If you tie a rope between two trees (one end high, one low), and pull sideways, you can topple one of the trees. Done it.
Redundancy is a good idea.
Polyester is an inferior substitute for nylon and you will find it in many straps. Some folks like to sew nylon webbing with polyester thread (nylon thread binds in the machine without lubrication) which is bad news. The sewing is often weaker than the webbing, though I have personally sewn stuff that retains the strength. Unfortunately, what you are likely to find in stores is polyester.
Sam's club sells Goodyear Racing straps with a 3000lb/1000lb limit. for $15/4. They are polyester so you have to consider their poorer shock resistance. They also sell 10000lb/3333lb truck tie downs for $15 each.
These are a little more serious than your wimpy straps.
Be aware that with ratcheting straps, and other strapping methods as well, you can exert considerable force on the machine and stand - and the pallet. Hooks used on the machine end may move around and damage the machine.
The machine may get "rope burn" from strapping in various forms.
This is probably about what you were expecting.
http://www.globalindustrial.com/gcs/group/290/productsPerPicGroups.web#gridAnchor
This is plastic strapping is probably about what you were expecting, cost/kit wise. Unspecified material and strength. It is likely to have neither the tensile strength of steel or the shock absorbing of nylon rope/webbing.
This gives the strength as only 300lbs.
http://www.nstatepackaging.com/Strapping-Supplies/Kits/12-3000-Poly-Strapping-p6469050.html
Maybe if you used the whole box.
Aircraft cable and fasteners from the hardware store might be an option. Maybe. Watch out for the bolts on the quick fasteners working lose. And the thin material can be hard on the machine.
To get to its destination, your pallet may ride on forklifts, trucks, rail, and
ship and be picked up and dropped by a crane while inside an intermodal container.
Threaded rods (with jam nuts or nylock nuts) might be an alternative to straps.
Use bolts or screws instead of nails to hold pallet/crate together. Also, how are you going to screw your crate together if you can't use dimensional lumber for the corner braces? Plywood doesn't like to be end screwed. You can use inserts inserted in a hole drilled orthogonally.
Your 500lb machine may encounter 36G average when handled by a forklift.
http://www3.interscience.wiley.com/journal/112664596/abstract?CRETRY=1&SRETRY=0
Pallets on one model lathe routinely broke:
http://www.cnczone.com/forums/showpost.php?p=270370&postcount=12
Random links:
http://handle.dtic.mil/100.2/ADA310976
http://www.certex.com/products/saftey/Nylon_Sling_Warning_English1.pdf
http://www.astm.org/SNEWS/OCTOBER_2004/mckinlay_oct04.html
http://www.hp.com/packaging/made/beta/testplan/MADE-05.html
