even if they were solid steel bars, there would be enough movement over several

feet that you would be able to pull the sled out an inch or so.

get a good heavy rope or chain, attach it between two cars that are on a hill

(the uphill car in park, the downhill car out of gear)

then pull on the center of the rope/chain and see how far you can move it before

you move the downhill car noticably (and note that you *will* be able to move it

noticably if you have a good long rope)

this is a similar problem to chain sag, you cannot pull a chain tight enough to

eliminate sag. some back-of-the-envelope numbers

if you have a 20 pound sled, with 5’ of line on each side (10’ total), a 1

degree sag would move the sled about 1", would put 280 pounds of tension on

the lines, and would strech the lines (or move the mounts) only about 0.02" Even

if we had a welded steel frame and brackets, you aren’t going to prevent the

mounts a few inches out from the main support behind the workpiece from flexing

that much.

you just cannot pull tight enough to eliminate sag, the multiplier as you get

closer and closer to zero sag just keeps going up. even solid steel bars will

strech

this isn’t exactly right, but do a chain sag calculation with tension of 4500N

(~1000 pounds), over 3.3m, with a total chain weight of 3Kg/M (~10Kg) and the

chain will sag ~9mm

https://www.spaceagecontrol.com/calccabm.htm?F=4500&a=3.3&q=3&g=9.81&Submit+Button=Calculate

in reality the sag will be a bit more as it would be a point load, not a heavy

chain as this calculates, but I couldn’t quickly find a proper calculator.

realistically, we are not going to get much above 100 pounds of tension, because

the wood will start flexing at that point (we already see it a little bit on the

current machines)