How much is enough ? ? ?
Dave,
DOT expects any load to be restrained .8g in the forward direction and .5g in all others. If you round the .8g up to 1g, this means the restraint in the forward direction needs to be the weight of the mill = 10,000# (or whatever it really is -- you need to find this out).
A grade 70 (gold) 3/8" chain has a rated working load limit (WLL), so at least two chains would be required in the forward direction. A grade 30 3/8" chain is the lowest rating -- it has only a 2,650# WLL and four chains would be required in the forward direction. If your chain is not gold-color plated or otherwise marked, DOT will assume it is only grade 30. (As discussed below, the number of "chains" above is the number of "falls" -- if a piece of chain is long enough, it can often provide two "falls" by going around and returning to the same or another anchor point.)
DOT regs do not focus on the fact that a load might be top-heavy, but reality and any inspecting officer will expect you to have some common-sense attention paid to restraining the load from tipping over. One common way to approach this is to provide at least the minimum amount of restraint for both the bottom and the top of the load independently. If you provide the full level of restraint for the top and bottom independently, then you will also give yourself a bit of safety margin. (By the way, do not take a chain or strap over the knee or table. The jack screw's bronze nut is not up to taking this kind of load and could fail. One way to overcome this is to put some wooden blocking between the knee and the base, with the knee run down on it to take the load. I would avoid this myself.)
Geometry comes into the picture, causing you to need 1.5 times more restraint if a chain is at a 45-degree angle to the direction being restrained, but if you have chains going to all four corners each pair works together so you pick up a bit of safety margin if you skip the trigonometry and think in terms of the chains being run fore & aft (or side to side) even though they are going to the corners.
Under the base you can put in a rubber pad to help the weight of the machine get a grip on the deck -- DOT allows this, but does not tell anyone how much of the required restraint to be allowed, so I recommend doing it in addition to meeting the minimum restraints. On a wooden deck, you can have a nest of 2x lumber securely lagged to the deck -- I even have lagged the four holes in the machine base, but on a 4CH these will be some rather large lag bolts. If you have a non-wooden deck, you can still provide blocking against a solid bulkhead or side panel, but it will probably be best to use horizontal chains running around the bottom of the column, above the base. I can send you some old fire hose to pad the chain -- just tell me how much you want, I have plenty. (Alternately, check with your local Fire Department -- they throw away old hoses as the reach their age limit.)
Once you have the base restrained, you still have a serious amount of weight up high. Many folks use chains down low where their weight is not a problem to deal with and then straps up high. If you buy straps, make certain that they are marked with their WLL or at least keep the package for reference. The laws (both of men and of physics) want the sum of all the staps to add up to the restraint required. This may mean a number of straps, but if you wrap the strap around and take it back to the same anchor point, it counts as two straps -- each portion (or "fall") will be carrying its own share of the load. In most cases this is probably better than taking the same strap to a different anchor point, although it can be argued either way.
You may see some "real" truckers using only top restraint, but they are counting on all the downward force generating serious friction to restrain the bottom. This works only if the rig is VERY stiff -- your truck bed might be in this category if it is very heavy, but I would still recommend some sort of restraint of the base, at least in the forward direction. Most rigs will flex during a big bump and relieve some of the tension at the worst possible time allowing the load to shift.
The above is only the beginning, but I hope it is a good start. Ask questions and I hope others will also contribute.
Archie
P.S: Your chain binders will also need to be rated. Strangely, the anchor points do not have to be rated, but will still need to pass the common sense test. Describe what you have to work with and I can help you decide how to use them. I also recommend a plan on what you are going to say when they ask to see your log book -- see my blog on
"Proving you are not engaging in commerce".