Problem fitting a gas spring to X3

[daedalus]

Hi,

I purchased a gas spring from www.cncfusion.com a long while back, and have only just started fitting it (work keeps getting in the way of my hobbies).

The problem im having is that in order to fit the gas spring in its expanded state, i would have to take the head about 1 inch higher then my maximum height, as i have double ballnuts on my column ballscrew, which takes about an inch off the travel.

it takes a lot of force to compress the spring, so i cant just fix one end, and pull the other into place.

The only approach i could think of is to leave the ball joints on each end of the spring, then build some kind of jig to allow me to compress one end of the spring with a screw to get it to the right length before attaching the ball joints. This is going to be a right pain, so wondered if anyone had any better ideas how to do this?

[daedalus]

here is what i was thinking jig wise, just a length of aluminium angle, with a moving plate at one end driven by some screws. The circular holes are where the ball joint bits at either end of the spring rest in.

The spring is rated for 76lbs (340N) of force, and i would need around 70mm compression, and to be able to manuver the spring over its mounting studs whilst compressed. The bottom plate will probably have to be 4mm thick so i can get close enough to the bottom stud.

[Rodm1954]

Can't see why your idea will not work. Only suggestion I would do is tie a wire arond the cylinder and your jig to stop it slipping out while fitting.

[project5k]

can you attach a good close up pic of both ends of the gas strut for me, i've got an easy idea brew'n

[daedalus]

sorry, cant seem to find the cable for my camera. both ends are threaded, and onto the thread ball joints are screwed. I need to compress the spring with the outer ball joint section attached, then push it onto two studs with the inner balls on them.

I have just been sat next to the machine trying to do this by hand, and all i have for my troubles is a few more bits of damaged paintwork. Im thinking the best approach would be to have the bottom ball joint attached, then form some kind of handle to pull the top end down enough to push it into place.

[daedalus]

Success!!! after getting through almost all of the tools i could think of, i finally managed to use a big toe clamp to get the top ball joint into place. The top ball fitted in the slot, and it was narrow enough to get the two halfs of the ball joint together.

So no messing around building jigs, just an evenings prying and cursing. Oh and there's no chance im taking that thing off in the future.

[cjdavis618]

How well does it work though. I am looking at the same thing for my cnc'ed SX3. i am running the Nema 23 425oz xylotex kit on the Z right now. It work but it is slow.

I'm know that the upward pressure is going to decrease, but I don't want the Z to have problems pulling down on the head. As well as how any rapid movements would be affected by the strut. Most are springy when opening and I don't want that to affect my accuracy. I know the idea is to counter balance, but I have to wonder exactly how heavy the head is vs how strong the spring is.

Are there any numbers or anything on the strut? Maybe to indicate the weight load or something? I would like to take the same idea but split the load across 2 struts. One on each side.

[daedalus]

I havent taken the head off my X3, so dont know its weight, but the spring produces 340N. I can literally feel the difference, as before fitting my z axis ballscrew (with two nuts fitted) felt gritty and i could feel balls sticking as i moved it, now it is smooth as anything. Also whilst before i would have to very carefully crank the head up, then lock the axis without letting go due to the mass of the head, now its almost identical force to move up and down, so i would say its pretty much a perfect balance. Also from playing with it the spring seems to produce an almost constant force over its entire range.

The problem with counterweights is they effectively double the inertia of the axis, and this will limit your max acceleration. The only reason i can see for one strut over two would be that its another thing to hit if you have clamps etc overhanging the edge of your table.

The only markings of relevance on the strut are the force output that i posted earlier.

[cjdavis618]

Thanks for the info. That is exactly what I wanted to hear. Have you tested your tram to see if the side forces are causing any anomalies in your cuts?

Also, I read some where that the strut reduced the overall travel of the mill, is that the case with yours?

[daedalus]

I need to re-tram my machine soon, but i have a few outstanding issues to get sorted first though, mainly changes to my mills wiring. As i have double ballnuts on Z axis I have reduced travel already, as i can only get to 1 inch off the top of the axis, however the spring is too long for me, so you shouldnt loose that top inch.

With mounting in a similar way to that the cncfusion site shows, i have run into a slight snag. The angle of the cylinder means that it will clip the side of the base casting. This means that im limited to only bringing the spindle within 110mm of table height, however the spring still has 50-55mm travel, i just need to make a plate so the top ball joint is further away from the head, and in line with the bottom one. When i get round to doing this i will probably move the ball up about an inch so i can fit the spring unloaded, and gain another inch of travel, at that point i should be able to bring the spindle face to within an inch of the table.

[daedalus]

I have just finished fitting the adaptor plate i made, now i can bring the spindle face to within 35mm of the table surface without any loss of travel.