Tarkin bed re-leveled

The bed got out of level due to one of the lifter’s sprocket screws being loose.

It’s back to precision and I replaced the grub screw so it can lock down significantly tighter now and shouldn’t be able to loosen up again.


@dannym Unfortunately, the main drive screw sprocket in the back right came loose again tonight. It completely stopped lifting the bed after I raised it just high enough to focus on a bit of cardstock. After that, the bed would no longer move.

Since it happened literally a few minutes before they wanted to start the Tarkin class, @JoeN and I did some troubleshooting and discovered that the sprocket that is supposed to drive the chain had slipped super low and the set screw wasn’t holding it to the main axle. We were able to lift the sprocket back into place and tighten the set screw.

STATUS: The machine is now basically functional, but we ran out of time to precisely level the bed. The back-right corner of the bed is a few millimeters lower than the rest. It was close enough for the class to continue, but it seems like a situation that could cause cone collisions if someone focusses really close to the material on the back-right quarter of the bed.

Darn it, I changed from grub screws to cap socket set screws, it should have been plenty tight. I will be by tomorrow to look.

Re-leveling is the same as with other lasers, at least this is what I’ve learned to do- start with one as the reference, jog the carriage near it. The focus stick is a good way to measure, but it just needs a thing to measure. The other screws are matched by loosening the set screw and using a paper towel to grab the leadscrew and turn it to lift or lower the corner without turning the sprocket with it.

There is a new lift kit with 4 ballscrews, motors, and brackets as a long term upgrade, but it will need some modification to match up with the frame. The belts with it aren’t long enough, I’m getting longer ones and waiting on those.

I think we can precision level it tomorrow and get it tight enough though, I just underestimated how tight it needed to be.

The cap socket cap screws are a little too long and rub the timing chain. I’m going to order some bicycle chain wax to lubricate the chain. The wax doesn’t leave the surface too greasy and is persistent. I think the lifting screws also need some grease. I think the timing chain system is seeing too much resistance.

It is a bit odd the the lifting screws don’t have a ring for a c clip to prevent the timing sprocket from dropping too far

Yep I saw the cap screws were rubbing slightly, but I don’t think it’s a problem.

The timing chain system IS seeing too much resistance. It was frozen up at first, and can still stall the Z motor when moving the Z to really low points. The screws are lubricated, I don’t think that’s the prob. Maybe not parallel enough.
Thus the new ballscrew lift kit (it’s a cardboard box on top of the cabinet). This will also fix the prob where the table shifts in the XY when moving the Z. I know we talked about putting in a bracket to stabilize that, but I think we just need to focus on fitting that new ballscrew kit that is on hand.

That kit just uses a separate motor for the left and right sides since it’s less practical to run a continuous belt across a frame that big. The original design was a sprocket and chain because you can make a chain of any length and locking the end links together. I do think timing belts are better- but you can’t start with a roll of timing belt stock, cut to length and bind the ends together to make a continuous loop.

But, the lift screws on a single side are pretty far apart on a machine this large, the timing belts that came with the kit are HTD1569-3M and too short to actually loop around even the two pullies on the ballscrew ends on one side, and they actually need to loop around those pullies AND the motor’s timing pulley.

So, need longer belt, but we need to figure where the motor goes to get the correct HTD-xxx-3M size first. There are several sizes larger than this, but they have to be ordered in quantity 5x and a little pricey to shotgun by getting every size and seeing what works when you go to install.

Let’s level out and tighen up what’s there for now, and take a look and make a plan for the ballscrews and get the size we decide on.

I will see if I have shorter socket head cap screws to install. I’m going to wax the chain. It will have less resistance. We shall see what happens after.

I don’t think there’s any problem with the socket head cap screws. I don’t see enough rubbing to be of concern for now- if it does make contact, it moves in sync with the link as it turns so it’s not much of a rub. There is a kit with all the standard metric cap screw lengths there, this is the shortest length that fits- also, IIRC there didn’t seem to be a length where the cap would not extend over the chain link area.

I would say don’t worry about this one, since we have a new lift kit that will fix several things (including that shifting upon z-movement). I did the math on the needed HTD 3M belt lengths and ordered them. It needs some work to match up the brackets with the mounting points on the frame.

I re-leveled the bed last night. It was pretty significantly off, it slipped on the far right sprocket where the motor drive is.

I pulled out the replacement lift kit and measured for awhile to determine the necessary belt length. They’re ordered and will be here in a week or so.

I could use some help on those mounts. Difficulty is avoiding downtime. Once we open up the existing chain, I don’t have a way to reassemble that, so we need to be ready with the complete solution that can drop in for sure that day.

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@dannym, what sort of help do you need? Design/fabrication, or just extra hands for install?

I’m willing to help if I can. Not sure about design/fab part, assuming that might involve metalworking? Regardless, I will have some days off between now and December 30th.

I will be in to lubricate the chain tomorrow.