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I cannot fault you for that. When the holidays are over, perhaps a mechanical engineer may see this segment and help out. Meanwhile, Cheers!I can't argue because I don't have any data either
I cannot fault you for that. When the holidays are over, perhaps a mechanical engineer may see this segment and help out. Meanwhile, Cheers!I can't argue because I don't have any data either
I'll do the maths later... &c.
I would like to consider self build... maybe later in 2024Those who have been with this thread since its inception will understand why I feel a bit vindicated.If anybody is contemplating self build this may be of interest: SFU1605 BallScrew with Motor Mount Bracket +BK/BF12 End Support +Ballnut Housing | eBay
That was the issue for me: I can look up the formula for calculating inertia of the various parts of a system, but it doesn't mean I'd understand the true impact of the values, or whether I've considered everything relevant to a gantry style CNC machine. There are people on the CNCZone forum who I've seen put some of these sorts of values into posts, so I suspect there are people "in the know" there.I'll do the maths later but I did the maths 40 years ago when I was asked to design a piston ring turning machine (in open profile not closed) since piston rings are (or were) mainly cast iron and very very precise this machine was pretty big and I needed to drive a very stiff little carriage holding the cutter blade. The rotary inertia was the critical calculation and made up far more than the simple weight inertia. Back then (big stepping motors were a thing of the future) so you needed large control motors with optical feedback so there was a danger that every thing just got bigger and bigger, but we found a compromise. I suspect that is why the Chinese version of the Open Source has stuck with 10mm ballscrews rather than 16mm ballscrews rather than their nonsense explanation which frankly left me bemused.
Anyway, thanks for this additional discussion. Today is going to be a fine weather day so I'll be out, but the storms come back tomorrow so I can have a serious read.
Rotary inertia is to the radius to the fourth from memory (you'll find google tells you to the square but remember that mass is also to the square and square x square is to the fourth)
Just one word about steel. Youngs Modulus for steel is 210, it varies a bit with alloy variation but unless you are buying some amazing very expensive stuff it is 210. Youngs Modulus is the number that physics uses to tell you how stiff a piece of steel is. Hardness is something else. A harder piece of steel is not any stiffer than a softer piece of steel (excluding alloy alternatives as above), hardness nearly always comes from treatments again nearly always heat based and or chemical based (see also alloys).
I see. Thank you. I can see that I made a fundamental error in wanting to determine the inertia of a belt on its own. I thought an inertial moment could be determined from the mass of the belt relating to its mass and its inherent resistance to movement based purely upon its mass. I misundertsood the term inertia. Inertia will derive from the stepper motor being used to move the belt. Thank you for your explanation. I may not be much wiser but I now think I have a better grasp of the subject.from memory and after Christmas cake I think it works like this...
Trouble is there are so many options. So definitive is a bit tricky.Lot of discussion on self build here... has anyone got a YouTube link or forum link to a definitive build guide for the recommended options - heavy frame, linear rails, water cooled spindle with VFD as I understand it?
It is likely a function of matching the screw nicely to the torque and speed of the stepper or servo. So could be chosen in either order. If you find a good deal on screws of a certain type then get motors that match or vise versa.I've been playing with ideas during the day and calculating why some suppliers use 1604 ballscrews and other 1210.
Then I found these guys LEAD 1515, HGH15, SFU1604 Ball Screw
it is a bit more complicated than that, it is a negotiation between cost, critical ballscrew rotational speed, top acceleration required, X and Z mass being driven, axis motor characteristics, quality of ballscrew set up. This is born out when you read home-builder's blogs as they keep running into these variables. For a private individual remaking is just another cost. For a Maker Space that would be club money I was spending.It is likely a function of matching the screw nicely to the torque and speed of the stepper or servo. So could be chosen in either order. If you find a good deal on screws of a certain type then get motors that match or vise versa.
I agree with worn thumbs about the overthinking.it is a bit more complicated than that, it is a negotiation between cost, critical ballscrew rotational speed, top acceleration required, X and Z mass being driven, axis motor characteristics, quality of ballscrew set up. This is born out when you read home-builder's blogs as they keep running into these variables. For a private individual remaking is just another cost. For a Maker Space that would be club money I was spending.
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