The OB screws ar 8*8 and the RoboyDiggs are 8*20. Faster, same diameter, come with NEMA 17 motor attached. You will have to cut them to length and turn the end 12mm down to 6mm dia, or have them do it and pay more and wait for them. Mine are getting cut this weekend and them I will know how they work. Should be faster than the standard screws for a good price. If you figure that the bed only moves approx 300mm, and is trapped in line with the V-slot rails and wheels, you shouldn't get to the point of shaft whipping.

Robert, if you are watching, how are your screws on yours doing? I think you used 8's didn't you.

 

Here is the trinity labs information for reference:
10 Start 25mm Pitch Lead Screw with Anti-Backlash Nut

The only thing that bothers me about the options identified is they are either slower or have fewer starts. This comes from roton's site:

And here, it discusses the interplay with number of steps by the motor, when looking at steps per inch. Another thing to consider is whether the robotdigg's option is cast, instead of machined, and appears to not have an anti-backlash nut available. It seems like when abruptly stopping, not having this could cause a small shift as the nut is no longer pressed up against the threads that are forcing its movement.

I put in a request on alibaba for quotes with the information from trinity labs. The next best option seemed to be from Roton, the 7/16"x1.0" 8 start, with anti-backlash nuts.

Another thought would be, if the RobotDigg option works, can't we ask if they can add the customized version to the store, even if it is a longer lead item. Just so it is easier to collect the parts for the build.

 

Yes, we could ask, and letting them know it is for a successful build plan might reinforce this. For me, I have no need to go 500mm/sec, or even 280/sec. I am more interested in good prints over fast prints. I see many people bragging about their speeds, and thier prints loo like hammered owl cr@p. I guess if you are happy with that, whatever. Different horses for different courses. If I was (and I am) building a 600x600mm heat bedded printer, I might be more inclined to want the huskier screws, but not something 25% of that size. YMMV (I drive a clunker

 

I agree about the speed vs. quality. The whole reason I'm looking at this build is more about the consistency and precision of screws vs. belts. I think the RobotDigg option would be ideal, but the main thing that would worry me is the quality of the screw, and the lack of the anti-backlash nut.

The picture on RobotDigg's site is horrible. Does anyone have better pictures of the screws?

 

they are the same as the one on OB store, and yes robotdigg have antibacklash nuts

 

They have the antibacklash nuts for the 8x8, but I got an email from them stating:

Also... the OB store has the 8x8, but not the 8x20, unless I'm missing it. That is a much higher lead at a pretty small diameter, so just curious what it looks like.

 

I will take a pic in a bit.

 

RobotDigg motor/screw - 8mm dia. - 20mm lead - 8 start
Y - axis carriage
X/Y axis shim we designed to use these pieces with stock Lautr3k parts

 

That doesn't look bad, and obviously the price is great. I still have the alibaba requests out, and the nema 17 stepper motor plus the 8x8 lead screw are all over. I see a few references to the 8x20, but it doesn't seem like something people commonly keep on hand. The anti-backlash nut could likely come from one of those suppliers. For example, this is the same 8x8 anti backlash nut.

 

I humor myself by being mindful that I am building a 300x300mm printer, not a 4'x8' CNC router. I can buy a ton of replacement nuts when and if they wear enough to get sloppy, for what one of those ABL nuts run.

 

Not sure how distance matters. It could be relativity more important for something small. Here, you will have the shift from one side of the threads to the other no matter the distance. Determining whether it matters or not is just associated with tolerances on the screw and nut. $10 seems like cheap piece of mind to rule it out from the start.

 

Like I said, I humor myself, as I have found no 8*20 10start nuts for them, and RD doesn't sell them for their screws. Distance was referring to the length of a screw and how many possible times it would have over the greater distance to make moves that would allow it to hit both sides of a thread, but i supposed speed versus length migh make that not so important. Wow, that was hard to say, and harder to understand.

 

Where did you find ABL nuts for the RD screws and how many $$?

 

Gotcha. Yeah, the lead screw calculations and specs gets confusing when the multiple starts come into play.

I'm working on finding an Alibaba source that would be more turnkey for us. I'm thinking they could add a listing in AliExpress, which is a straight from China marketplace for small quantities. The $10 was referenced based on the 8*8 ABL nut that RobotDigg stocks. All of the stuff he stocks is just being resold from suppliers that you can access through Alibaba, so I think it would be similar in price.

I think an exact copy of the original lead screw may be difficult straight from China. I can't find any suppliers that have the 12*25 mold on hand. I have located suppliers for the 8*20, which also have a 10*20. The downside on the 10*20 is that it only has 6 starts. I'm not sure which would be the better option of the two.

 

For example, here is the 10*20 lead screw. This is kind of high based on the quotes I've been receiving, but I've been getting them on Alibaba, saying that I'd purchase 10 leadscrew/ABL nut combo's. But, it gives a visual of what it looks like. The timezone difference and language barriers make this take a bit of time.

Thoughts on 6 start 10mm*20mm versus 8 start 8mm*20mm? Still looking for a turnkey package that is closer to the trinity labs solution.

 

Yeah, I still have some requests out on customization. Other options are:

Roton:
Part #59785 Torqspline Lead Screw, 7/16 X 1.000
Part #19670 Torqspline Anti-Backlash Flange Nut, 7/16 X 1.000, RH, Plastic

McMaster Carr:
#99030A300 1/5 * 1.0 Lead Screw, Carbon
#98980A183 1/5 * 1.0 Lead Screw, Stainless (6ft only)
#6350K64 1/5 * 1.0 Anti-Backlash Nut

The main downside to this kind of supplier though is in trying to get a more stable and repeatable solution setup. If I got something setup on AliExpress, it would just be a matter of each person going, selecting 2, and checking out. This could be with the 8*20, with anti backlash nut, motor, bearing?, and all of the length customization already stored in the product listing.

 

Keep in mind the less starts on your Leadscrew means more torque is required to move the nut.
More starts = faster moves from your motors with out stalling

 

Right, just ideally would like to keep the diameter as big as possible. Still, I think the 8*20 is probably the best all around solution. Hoping to get an aliexpress listing setup. I think we might be able to get the entire purchase, x and y axis, and maybe z axis included as a package buy, and have it come out cheaper. There are 2 x NEMA 17 motors, 8*8 lead screws, and nuts for ~$80 shipped. It would just be 5-15 days wait for delivery, which isn't too bad.

 

I got an offer from Igus:

• DST-LS-10X25-R1000ES lead screw: ~47 EUR (incl VAT)
• DST-JFRM-2525DS10X25 nut: ~42 EUR (incl VAT)

for total of 89 EUR

These prices are for the EU.

I am also considering using TBI ball screws bought from alibaba (much cheaper, though the quality may suffer):

• SFE1632-3 (SFE01632-3) lead screw. -3 meaning 2 starts
• SFE1632-6 (SFE01632-6) lead screw. -6 meaning 4 starts

I recieved several quotations for my inquery

3 X SFE1632-3
L = 550mm each
10mm diameter machined ends for supports​

some time ago for the SFE1632-3 and here is one:

• The price of ball screw SFE1632-3 is 40USD/set. This price is includ the nut and the machining cost.

Here is some more information on the ball screws offered by TBI: http://www.tbimotion.com.tw/product/category/14/1/en

 

I saw a lot of ball screws while trying to find lead screw suppliers. I hadn't come across ones that were high lead and reasonable diameter, but these aren't too bad. The things I considered on them was they require more maintenance (probably not too bad), possibly more noisy, and more expensive.

Another thing is that if they have low number of starts, it isn't just torque that is affected, it is also the printer's accuracy. Few starts means fewer steps per inch. So, you'd end up with lower resolution in positioning in the x and y axis.

 

The convention I'm using, but isn't always used, is:

Diameter * Lead

Lead being the distance traveled with one turn. The reason this is used instead of turns per inch, the other convention, is because pitch and you become inconsistent with multiple starts.

Fewer starts, holding lead constant, results in more "stretched out" threads. This is why the increased torque and decreased resolution.

This was the best explanation I found: https://www.buildyourcnc.com/leadscrews.aspx

 

A single tread, turning one complete trip around a given diameter shaft will be the exact same path as 4 or 6 or 8, etc., they will just each start at a different place in the circumference and run parallel to each other.. A 12mm screw that traveled 25mm up the shaft in a single turn would look very odd, with much of the shaft being smooth. Adding more starts does 2 things in a longer lead screw, it reduces torque on each thread needed to turn and takes up a more uniform spacing on the shaft.

 

+1 Justin

 

That's what I get for trying to respond on a phone, I think I was mixing up thoughts from multiple sources, where I thought what they were saying was while keeping the lead constant, but it wasn't.

I agreed on precision, more turns per inch, is obviously giving you better precision. I think the confusion was my misunderstanding that keeping lead constant, and increasing starts, combats the lost precision by going to the larger lead (in other words, 5 start 25mm lead was more precise than 1 start 5mm lead, which isn't directly true). This came from a misread of the last bit of that source I referenced. I wasn't trying to suggest that a large lead, lead screw was more precise than one with a shorter lead.

This previous post of mine correctly references the downsides of fewer starts, while keeping the lead the same. The nut for a 1 start 25mm lead screw would need to be very long to have reasonable surface contact with the screw.

 

I believe you are mixing up starts with the lead of the screw.
You can have single start with aggressive pitch but the one thread does all the work, two threads half the load and so on

 

lead = pitch * starts

He is considering keeping pitch constant and increasing starts, and is using the "Turns per inch" TPI notation, not to be confused with "Threads per inch" TPI. I'm pretty sure that this is universally not the notation being used when looking at specs on alibaba because everything is metric on there. So, when they say 6*32, like in his example, they mean one turn results in 32mm of travel, not 32 turns to move one inch. It is funny looking around at all the forums that have discussed this topic. It is annoying due to all of the overlapping terminology and conventions.

What we were discussing at the time was keeping lead constant and increasing or decreasing starts.

 

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Definition of lead per ANSI/AGMA 1012-G05

Definition of lead angle per ANSI/AGMA 1012-G05

Depiction of the lead angle of a screw thread. dm is the mean diameter of the screw thread.
Lead is the axial advance of a helix or screw during one complete turn (360°)[1] The lead for a screw thread is the axial travel for a single revolution.[2]
Pitch is defined as the axial distance between adjacent threads on a helix or screw. In most screws, called "single start" screws, which have a single helical thread along their length, the lead and pitch are equal. They only differ in "multiple start" screws, which have several intertwined threads. In these screws, the lead is equal to the pitch multiplied by the number of "starts".
Lead angle is the angle between the helix and a plane of rotation. It is the complement of the helix angle, and is used for convenience in worms and hobs. It is understood to be at the standard pitch diameter unless otherwise specified.
The lead angle can be expressed as: