Threaded rod VS leadscrews I use threaded rod mainly because leadscews are insanely expensive, but it seems that it may be the only way my printers get the the next level of accuracy. can anyone tell me if they have a threaded rod setup they are happy with. I run M5 or M6 threaded rod and am thinking if I go to a M8 if it would be better.
@Tech2C his end result with threaded rod is pretty good.
I’d really recommend getting leadscrews still–they can get you really accurate layers and are actually designed for linear motion; I really liked this eBay store:
http://stores.ebay.com/All-for-CNC-Slo?_trksid=p2047675.l2568;
he was able to give me a custom length, and he’s actually really cheap for the screws
Here’s some really beefy 10mm leadscrews for a MendelMax: http://www.ebay.com/itm/2pcs-Trapezoidal-Screw-Tr10x2-310mm-MendelMax-1-5-2-0-2x-nut-15x30-/321773979908?hash=item4aeb394904
I’m using TR8x1.5 trapezoidal lead screws for my first 3d printer and am about to build my second one with TR10x2 leadscrews (in both cases for the Z axis). The major advantage is the accuracy you get. The leadscrews are not bent (thus no wobble) and you have effectively zero backlash.
Also, mine were not really that expensive: about 7€ per meter. The most expensive things are the nuts. I use high-quality igus threaded nuts for both printers. They cost about 9€ per piece but are well worth the price. Plus they sometimes give you some for free.
I like the motors with integrated TR88 leadscrews (which allow your Z axis to move a LOT faster, but still have more than enough resolution and precision for FDM) from robotdigg. For a small printer (or an SLA, which is what I’m planning to use mine for), you can also get a Nema14 with a TR52 screw.
Openbuilds also sells TR8*8 leadscrews, but I believe they only have 1 meter lengths.
@Whosa_whatsis , they have 300mm lengths too now
Most of the low cost TR88 screws come from the same part of the world where Robotdigg is located. The speed and precision is a factor of the thread configuration so you can couple a properly calculated screw to any good quality motor and get the same results as an all in one package. You can find pairs of TR88 over there for under US$20-30 a pair with nuts. From Igus or Misumi that same size could be $80-100 though they’re quite a bit better particularly the nuts.
@dstevens_lv Except that most couplers for attaching a leadscrew to a motor suck, and will negatively affect print quality in one way or another. Even if they didn’t suck, they would be an added expense, which is an argument in favor of the integrated screws.
I’ve seen too many problems with two or four start lead screws. They’re at risk of back driving. I know one person that has a couple M2s that have the problem where the bed will drop if the motor is turned off. Unfortunately most integrated lead screws are four start. I’ve had to go in on a small batch of single start lead screw motors.
@Mark_Rehorst multi-start leadscrews have a longer lead, which changes their mechanical advantage. As the lead gets closer to the diameter (or even larger than the diameter, in some extreme cases) it gets easier to turn the screw by pushing the nut along it.
All of my machines with TR8*8 screws (1:1 ratio of lead/diameter) have very tight bearings on the Z axis that will almost prevent the axis from falling even with no screw present. I find that this is better for print quality anyway, so falling when the motors are deactivated is not a concern.
@Mark_Rehorst
Some setups turn off all the motors after the machine has been idle for a set amount of time. Dropping has also been a problem for some MendelMax 3 owners. When you shut off the machine, one side drops more than the other.
Motors wired in parallel is also better than using separate stepper drivers unless you have code to drive the motors independently to actively sync them up. It’s not as good as a belt in that respect, but when one motor turns it will induce a current that will try to turn the other motor to keep it in sync.
@Mark_Rehorst I don’t have to worry about backlash on the X axis because it’s always hitting the layer from the same direction. If Z lift is off, the motor only moves one direction while printing, and if Z lift is on, it always moves down to start printing in a layer. With “auto-leveling” (platform compensation), this would not be true, and it’s just one of the many reasons not to use it. Machines using that would always, at the very least, be equipped with anti-backlash nuts (which also create more friction, and would thus help with the getting-out-of-sync problem).