Z Axis Design - Researching Prior to Build

[dameronw]

Alright, I sort of get it - sure would like to have one in hand to play with and see what mounts where, and in what orientation.

I'll play around and see if I can come up with a way to make it 'ideal' - after all if I go through all this work to build a nice CNC I'd hate to have one small aspect of it not work as well as the rest of the machine (hopefully) will. But, if I can't fit it with my low profile design, then maybe shaft collars it will be.

[louieatienza]

Just use FK8 then you only have to have one side machined; on the free end just make up your own bearing block and use a bearing with 1/2" ID. On the drive end you'll have a bearing journal at 8mm and the drive journal at 1/4". Mount the flange bearing block to your top plate. Really, you don't even need a bearing at the free end since the z axis is so short.

I believe Gerry and a few others "machined" their ACME screw ends by putting a cutoff wheel in the table saw and making a jig to roll the screw with the blade raised at different increments. Another way would be to make or buy a reducer coupling. 1/2" on one side and 8mm on the other; then get some 8mm drill rod, cut a length that's long enough to go through the bearing block and still have room to attach your motor coupling. I've done it this way on a few builds and it works just fine. Mill or file flats if you use set screws.

[ger21]

I believe Gerry and a few others "machined" their ACME screw ends by putting a cutoff wheel in the table saw and making a jig to roll the screw with the blade raised at different increments

I have a faster way now. I have a jig with two 1/2" ID bearings in it. I slide the screw through, and chuck one end in a 1/2" drill. I lock the drill trigger, and clamp the drill to the table, then use an angle grinder to "turn" the screw down, carefully checking the diameter. When it gets close, I switch to a file. I can get it remarkably close this way.

And I don't plan on using bottom e bearings on my new machine. Just the two angular contact bearings at the top, and the nut to support the rest of the screw.

[dameronw]

You guys are making my day - I really don't need to constrain the bottom end of the leadscrew? That is great news - makes things a bit easier to work in there, and I was thinking I would have to mill out a recess on the back side of the Z plate to let everything clear itself - not the end of the world, but I'd rather not if I don't have to, and eliminating that bottom block is one less thing to try to get perfectly lined up.

Also, Ger21, above when I asked if anyone could identify the nut used in that Kerk leadscrew setup, I realize now that I totally put in the wrong link (hence why I mentioned I was looking at the Hiwin site). Here is the thing I was actually trying to identify, although it's a moot point at this point, because I believe I've identified the 'Z-nut' that will work well for my application. Anyway, what I was wondering about was this. Any idea what the 'nut' thing in this link is called, or where you can get those or similar, just for curiosities sake? Like I said, I searched the Hiwin site, but I definitely might have missed it.

[ger21]

That looks like a hybrid linear bearing with an integrated nut.