Okay this will hopefully be my last post before I post the mechanical design.

3D Printing
, , ,
1

Okay this will hopefully be my last post before I post the mechanical design. I’m trying to source all the parts as I design and I just need a supplier for the motors, heated bed, build plate (although I think I may go with GeckoTek for a magnetic removable plate), and lead screws. I like the 1.25 mm pitch (mm/revolution) of the M8 lead screws but I want something a bit thicker. I can’t find a 2.5 mm pitch scew, should I just go with 2 mm or 3 mm and use pulleys for gearing?

2

I haven’t followed the design goals very much - what is the purpose of “pulleys for gearing”? 2mm pitch lead screws are very common and effective on direct drive Z-axis.

3

@Alan_Thomason my bad, I put the value into the calculator wrong. 2mm pitch works perfectly. So I’ll get the lead screws from Misumi with most of my other parts.

4

This is for a CoreXY, right? Personally I’d go with longer lead than 2mm if you’re belt-syncing Z screws or 2mm with separate motors. (Locking pitch vs non-locking.)

5

@Ryan_Carlyle IDEX, but that shouldn’t change anything with the Z axis. What pitch would you recommend?

6

@Adam_Steinmark right, I knew that, sorry. When you have multiple non-synchronized screws, you want a self-locking lead/pitch, for which the most popular option is Tr8x2. That keeps the bed from falling out of alignment during power down. Likewise for Z nozzles where you don’t want the nozzle to fall onto the bed.

With one screw or multiple synchronized screws on a build plate, I recommend a back-drivable pitch like Tr8x8. (Although note that your ideal layer height multiples with 8mm lead are .12mm not 0.1mm.) It will let you move the Z stage way faster and manually reposition it during maintenance.

7

5mm and 10mm lead are good options too; don’t know offhand what Misumi has.

8

@Ryan_Carlyle Looking for layer heights in multiples of 50 microns so the 8 mm wouldn’t work too well. Is the Tr8x2 just a generic 8 mm diameter lead screw with 2 mm pitch? As far as I understand what makes it self locking is just friction angle.

9

@Adam_Steinmark Yep. TrYxZ is a metric trapezoidal thread (slightly different from Acme) of nominal diameter Y and travel per rev (lead) of Z.

Rule of thumb for back-driving with a lubricated brass nut on steel lead screw is that the cutoff for back-driving is lead>diameter/2. To have some safety factor, pick lead>=diameter if you want to back-drive, or lead<=diameter/4 if you want to lock.

Pretty much any ball screw will back-drive.

10

@Ryan_Carlyle thanks man you’ve been more help with this than I could imagine. Any recommendations for a good supplier for motors, power supply, and heated PCB? Last few items I need to source.

11

Eh. I usually order motors from Kysan in batches. They have a $100 minimum order IIRC. Lots of other options though. Do you know what you’re looking for in terms of motor specs? Easiest thing to do is pick a popular motor like a Kysan 1124090. But you can optimize on weight or torque/RPM curve or go to 0.9 degree steppers if you want. Plug the motor specs into the torque curve predictor here https://github.com/rcarlyle/StepperSim to check if a particular motor will keep high torque at the max speed you want.

PSUs, Amazon.

Heatbed depends on size I guess. Haven’t shopped for one in a while.

12

Okay Amazon was the last place I got a PSU. As for the heated bed, I’m looking for a 300 mm square PCB heater but I’m a bit flexible on size.

13

I still have a few 200mm PCB heaters but I’ve mostly switched to silicone heaters RTV’d to an aluminum heat spreader. Way more sizes available, differential thermal expansion of the build plate stack is somewhat less of an issue, they tend to come with thermistors built in, and you don’t have to worry about getting a warped PCB.

Not sure offhand who’s selling 300mm square PCB heaters. That’s on the big side.

14

I could check out silicone heaters, haven’t had much experience with them. RTV’d? I’m not familiar with the term.

I found a few PCB heaters in that size on AliExpress but they’re all cheap Chinese parts.

15

RTV = “room temperature vulcanization.” Shorthand term for rubber adhesives that cure on exposure to air/moisture. Silicone is very low-adhesion stuff so you basically have to use another silicone to bond it to the heat spreader. https://www.google.com/search?q=silicone+RTV

Dow Corning 736 is a really good choice. 90mL tube is plenty for one heatbed. Amazon has it.

16

Thanks man. I guess I’ll try a silicon heater for this project, any recommendations on a supplier?