[rlrhett]

I'm having trouble keeping the trucks tight on the rails. The worst culprit are the two trucks on the gantry.

I have a few modifications, but my gantry and z axis are straight out of your plans. I have a 4" steel rail attached to 8020 extrusion. I have two short trucks, one top and one below. They are mounted to another extrusion that is the main structure of the z axis using carriage bolts in the slots of the extrusion. As I said right out of the plans.

The problem is that there is quite a bit of torque on the z axis as it cuts. The trucks begin to slightly open. Soon the z axis begins to have a lot of play.

I have squeezed the trucks tight to the rail with clamps and tightened the carriage bolts, but the torquing of the z axis eventually forces them open again.

How do I keep the trucks tight to the rail?
Attachment 229764



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[rbjem]

Tighten them back up then take lighter passes. Don't take heavier cuts than the machine can handle.

I prefer reliability (and not having to tighten down/realign the machine) versus a shorter cycle time.

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[Dylwad]

I think the main problem is the length of your Z hanging below the carriage http://www.cnczone.com/forums/fineli...ight-rail.html too much leverage for the trucks to handle on the 4" rail.

Could go to the newer Z design and a 6" rail (which would make a whole lot more sense if your trying to get maximum Z clearance) or shorten the whole machine back closer to the original design specs.

[ger21]

That's really a poor design. Raise the bed up 6-8" and it'll be a lot stronger. If your gantry beam or rail was twice as tall, that would also help distribute the loads better.

With such a long lever, you're applying more force than the bearings can handle.

[rlrhett]

That sounds like a good suggestion. It's amazing how a design morphs as you build. This is obviously a fusion between the Momus design and the fla design. Somehow the gantry ended up father above the bed than I would ever need.

I'll raise the bed up 6". I was thinking of adding a vacuum hold down like mr donek has on his website. This will be the perfect excuse for more fiddling!

I'll report back on results.

Thanks again!


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[FineLineAuto]

That sounds like a good suggestion. It's amazing how a design morphs as you build. This is obviously a fusion between the Momus design and the fla design. Somehow the gantry ended up father above the bed than I would ever need.

I'll raise the bed up 6". I was thinking of adding a vacuum hold down like mr donek has on his website. This will be the perfect excuse for more fiddling!

I'll report back on results.

Thanks again!


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Solid suggestions to raise the bed up. I definitely think you'll see a benefit there. If it's still a problem, you may also want to try the z-axis interface plate instead of the front mount plate. The Y and Z carriages in that configuration are mounted to a plate instead of the extrusion, which makes them less susceptible to slipping out of position. Also, you may try switching to extended carriages as they offer 4 hold down points over the 2 on the regular carriages.


Nate
Fine Line Automation
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