Best way to manage vertical forces on lead screw
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@claustro There's no need to use 4 guides for the bed. Two is sufficient to constrain lateral motion. Adding more does not increase stability and can cause problems. It can be difficult to get two guide rails parallel to each other. Aligning 3 or 4 guide rails is a much bigger problem.
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@claustro said in Best way to manage vertical forces on lead screw:
@deckingman your and mrehorstdmd printer are really monster printers
If I understand correctly looking you blog and your tube video at least on the older setup you was using a no cantilevered bed guided by 4 V-slot carriage with with 3 wheels each and 3 thread.
Your Z rod thrust and ball bearings seems quite clever and simple but can I ask you how the threaded road retained in place?No that's not correct. I use 3 screws to lift the bed but only two V slot linear guides. Each guide carriage actually has 4 wheels, 2 per side but they could have been made using 3 wheels (2 wheels on 1 side and 1 wheel on the opposite side).
The (trapezoidal) threaded rods just sit in the bearing blocks with the ends resting on the thrust bearings. Gravity keeps it them place - the weight of the bed means that it can't rise up. The flanged bearings fitted above the thrust bearings prevent any side to side movement. The lead screw nuts have a compressible O ring where they fix to the bed mount and a ball type rod end is used to connect to the linear guide carriages. This allows some degree of flexibility for the initial bed levelling. The 3 screws are driven by a single motor via a continuous belt. Bed levelling is accomplished by slackening the grub screws on the pulleys and rotating the lead screws by hand. I don't use any other form of levelling or flatness compensation and I only need to level the bed if the machine is taken apart and transported to another location.
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@deckingman said in Best way to manage vertical forces on lead screw:
No that's not correct. I use 3 screws to lift the bed but only two V slot linear guides. Each guide carriage actually has 4 wheels, 2 per side but they could have been made using 3 wheels (2 wheels on 1 side and 1 wheel on the opposite side).
The (trapezoidal) threaded rods just sit in the bearing blocks with the ends resting on the thrust bearings. Gravity keeps it them place - the weight of the bed means that it can't rise up. The flanged bearings fitted above the thrust bearings prevent any side to side movement. The lead screw nuts have a compressible O ring where they fix to the bed mount and a ball type rod end is used to connect to the linear guide carriages. This allows some degree of flexibility for the initial bed levelling. The 3 screws are driven by a single motor via a continuous belt.
I can't fully understand your setup it isn't cantilevered right? , I am studying your video but maybe I am not to smart enough to understand ..
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@claustro Those two VSlot sections are linear guides which prevent the bed from moving in the X or Y directions. They have nothing to do with supporting the bed. There are 3 lead screws that support and lift the bed. One is located in the front left corner, the second is located in the front right corner, and the third is in the centre at the rear. Those 3 screws therefore form an triangle and as 3 points define a plane, then turning the 3 screws simultaneously lifts the bed evenly.
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@claustro I have posted details and photos at "My Hypercube Evolution CoreXY variant" in the category "My Duet controlled machine."
https://forum.duet3d.com/topic/10270/my-hypercube-evolution-corexy-variant
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@deckingman excuse me but maybe my poor language propriety prevent me to express clear concepts.
I clearly understand that you have 3 screw in a triangle disposition
From your video and from what I believe to understand your printer has only 2 guides positioned in diagonal respect of the bed and If correct this is the first time I see such disposition.
Your printer is AWESOME, my congratulation for the results achieved.
@garis thank you for posting images, very beautifull printer , it seems sturdy with many aluminium component have you noticed improved shifting the z roads in the middle? at what speed is able to print with good quality?
Andrea
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@claustro Originally the two linear guides were both at the front of the bed. But I discovered that if I gripped the bed with 2 hands, I could rotate it in the XY plane. The reason was that the guides were 2020, fixed to the frame with a single bolt top and bottom. This arrangement meant that the guides could "flex" around that single fixing. So I could have either replaced the 2020 with 2040 and used 2 bolts side by side, or move one of the guides to the rear. The quickest, cheapest and easiest option was the latter. In reality, it might never have been a problem because there wouldn't normally have been any rotational twisting force applied to the bed. But it was a potential problem and easily fixed so that's why the guides are placed as they are. Hope this translates well into your native language.
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@deckingman thank you for taking time of answering me, very cleaver solution
I am afraid of solution with only 2 guides on one side , it seems impossible to me totally eliminate the tendency to bend for the gravity. Have you ever had this problem in the previous configuration? Your solution seems to solve both problems: XY rotation and Z flexI was thinking about the thrust and ball bearing setup.
I can't understand how the thrust bearing work in your setup.I never had a thrust bearing in hand so excuse me if I am wrong.
If a thrust bearing behave like a regular 608zz bearing an 8mm lead screw can easily pass trough it.
This lead at two phenomena- The lead screw can can make friction to underlying plastic support.
- There isn't vertical force to dissipate 'cos nothing rest over the thrust bearing
My statement above decade if the lead screw fit perfectly in the trust bearing without passing trough it.
I usually saw trust bearing and lead screw mounted with collars or other type of vertical stop .
I am confused
@Dougal1957 If you are planning to use a flexible coupler , that seems reasonable , are you planning to use a shaft for letting the coupler to flex?
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@claustro The outside diameter of the thrust bearing is the same as the outside diameter of the screw. The hole in the centre of the bearing is very much smaller. So the screw sits on top of the bearing - it cannot pass through the smaller hole in the bearing.
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@deckingman ok now I understand thank you very much for you patience
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@garis said in Best way to manage vertical forces on lead screw:
@claustro I have taken some photos, will edit them and post tomorrow (Australian time).
Rods and screws at 3 and 9 o'clock and T brackets keep the bed frame (2020 tubing) horizontal. The bed itself is 4mm glass suspend on 3 levelling points (12 4 and 8 o'clock) on the bed frame. 3 is a good number - even the X carriage runs on 3 short linear bearings, 2 on the lower X rod and 1 on the top rod in self aligning slots. The idea is all the mechanicals provide the accuracy. The rods and bearings arranged so no binding on the rods, and with no need for XYZ corrections or bed levelling or Z probes but the bed is only 250 x 250.Can't see your photos. Will you upload them?
