Head Counterweight for the Industrial Hobbies Mill

The IH Mill's head is extremely heavy--I know, it took 3 of us to lift it up onto the mill when I was assembling the darned thing. I also have an exaggerated bicep from cranking the head up and down. There's really no need to work so hard--a counterweight system can be constructed that will balance the head so it can be easily moved up and down. I intend to use gas springs for this task as they will be far less bulky than actual lead weights. In addition, I will use roller chain to connect the head over a couple of sprockets to the gas springs, which will be mounted on the rear of the mill column. This is similar to the arrangement used to counterbalance this Hurco mill:

Twin roller chains connect the head of this Hurco VM-1 to its counterweight system...

Four sprockets mounted on bearings will be attacked to the top of the head to give the roller chain smooth passage to the correct locations directly over the air springs and the head. I am tempted to cantilever the forward sprockets out to allow the chain to engage slightly outboard of the center of gravity of the head in an effort to reduce any cantilevering effects that may cause the head to cock forward on the ways.

Here is an example that is cantilevered:

A problem with cantilevering the gas springs is that the force they generate will change as the head goes up and down because the angle the spring is acting on changes. One could also envision mounting one or more springs off cantilever brackets directly, without recourse to cables.

Here is Thomas Powell's gas spring counterweight design for the IH Mill, which is closer to my thought, though using cables rather than roller chain:

I could see taking the cable approach too, I suppose. Thomas says he has full travel on the mill by using a 12" stroke gas spring. McMaster-Carr lists a 16" stroke 150 lb gas spring for about $28. Such a spring seems ideal for this application.

I'll need to be sure to leave enough room to clear the servo motor mount that goes atop the column:

Note how high the mill head can travel in that picture. Not a lot of room to clear the IH Z-Axis kit! It's an interesting question whether to go over or under the Z-Axis assembly.