Lead Screw Recomendataions

I'm looking at changing out the lead screws on my printer and was wanting to get some recommendations and suggestions for what to get. They need to be 8mm x 500mm. I could cut longer ones down. The ones I have now have a slight bend to them that I have not been able to get out. They are, I believe, 2mm pitch with 4 starts. I remember reading somewhere that single start screws are better.

So where do you get your lead screws from? Suggestions for what to look for?

I got mine off amazon. I have 400mm 8mm 4 start screws that are fairly straightforward from drillpro.

What's better for leadscrews depends on what you want, speed or resolution. An 8mm 4 start moves 8mm in one revolution. 8mm ÷200steps÷16 microstepping = .0025mm per step A 2 start moves 4mm in one revolution so the resolution is twice as fine, but speeds are slower. I don't remember off hand the numbers for speed, but basically the screw can only spin so fast because it starts to vibrate. So, fewer starts will make finer details, but print a lot slower.

One other advantage of a smaller number of starts is the pitch is not as great and when the power to the motors are turned off, a heavy bed tends not to cause the screws to spin and drop the bed.

I'll probably stick with the screws I have now for the time being.

My heavy x axis does not drop with 4 start 8mm leadscrews.

All I can say is, buy good ones. I skimped out on mine and they work great but as I get my quality up I can definately see repeatable banding which my best guess is from the screws. Lesser printers may never see this, but it's something that bothers me.

I currently don't see banding from z wobble, but I can see the vibration from the ball bearings, possibly motors too, which is annoying. I am going to sample out some igus filament and see if I can use it to finish my i3 upgrades. My screws were $12 each and came with a bronze nut. I also have them supported by bearing blocks on top and bottom and driven by one motor using a belt. I was just reading that if they are mounted with 2 bearings on each side spaced at the diameter of the screw it allows for a lot more speed.

1 bearing at each end of the screw can cause more banding if your screw is not true. This is where it is handy to have a screw with no trapped end.

My set up is 2 acme (4 start) screws, driven by a closed loop belt. so that the belt does not force the screws out of alignment, I have 2 bearings on one end, with the pulley in between. I tried capturing the other end of the screw, but the mechanism started to bind and quality decreased. With this set up I get almost completely smooth boxes at 100 microns. I still get some Z banding, but this is me being picky. I would have forked up the extra cash for decent lead screws if I could.

also, Why do you need extra speed out of your Z? It can be as slow as you like. Aim for torque, not speed.

I am building a leadscrew only printer currently. Just have to finish up the enclosure design and get the parts made. I also use z hop during retraction and disable combing so my surface finish is nice and smooth and I don't lose details due to pressure drop while coasting. A faster z lowers print time in that situation. I am still tinkering to see what kind of speeds I can get.

See previous discussion here: [forums.reprap.org]

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