Linear Rail X Gantry Support (MGN12)
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Hi Guys,
When using 2 flange bearings to double as an idler (SF605ZZ in my case), would you put a shim between them?
Also my X gantry is looking like it'll be 530mm. would a 2020 profile this length be strong enough to carry 800g?
Dizzwold.
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@Dizzwold said in Linear Rail X Gantry Support (MGN12):
Hi Guys,
When using 2 flange bearings to double as an idler (SF605ZZ in my case), would you put a shim between them?
Yes, I would - definitely. You need to ensure that each bearing is free to rotate in isolation. All open builds wheels and idlers use two bearings and there is always a shim between them.
Also my X gantry is looking like it'll be 530mm. would a 2020 profile this length be strong enough to carry 800g?
I did the calcs (which are a bit tedious) for my machine. Here is a link to a resource that'll help https://openbuilds.com/threads/how-to-calculate-v-slot
-deflection.4881/For my machine, the X gantry rail is 600mm between supports. I can't off hand remember the exact mass but it is similar to your 800g. For that length with that mass, the deflection using 2020 was unacceptable. Again, I can't remember the exact numbers but I would consider anything greater than 0.15mm deflection as unacceptable, 0.1 to 0.15 borderline, and below 0.1mm OK. 4020 was OK and that's what I used (the 40 being the vertical dimension so 20mm wide, 40mm tall).
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Cheers Professor Ian,
I wasn't to sure on the shims, and with watching your new build and image above it made me wonder about the length of my proposed X Gantry (530mm and roughly 800g extruder parts), and the use of 2020 profile for this purpose.
I'll have a read of the linked thread above.Thank you for your input and advice.
The link above to different profile types and deflection is a very good find. It's a shame they don't go any further with beam types such as aluminium angle etc. But non the less very informative.
Dizzwold.
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I may have given you bum information.
But first, if you follow the link I posted it'll take you down a rabbit hole and you need to have an account and sign in. If you get through that process, it'll take you a page where you can download a spread sheet. To save you the trouble, I've downloaded it and then re-uploaded it to my Google Drive. Here is a shareable link to that spread sheet.
It seems that you need to put an "x" in the box next to the profile, then enter the "beam" length and mass. You want to look at "Simply supported bean with concentrated load". I put in length of 0.6 (metres) and mass of 0.8 (Kgs). I haven't checked the calcs but assuming the formulas are correct, then the maximum deflection is only 0.07mm for 2020 extrusion so you'll probably be OK with that.
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A piece of same-size (3/4") square aluminum tubing would likely be lighter and stiffer than a piece of 2020. T-slot is nice stuff to use when you don't know what you might want to attach to it in the future, but is about as rigid as a wet noodle. You know what you're attaching, and where, so you don't really need to trade t-slot convenience for rigidity.
The trick with tubing is to figure out how to bolt your linear guide to it without having to drill a lot of big tool access holes. Fortunately you have a 3D printer so it isn't a problem. What you do is print a plastic piece that will hold a bunch of nuts (M3?) to match the screw spacing for mounting the linear guide, and will fit inside the tube. Then drill holes one side of the tube that will just clear the screws. Now slide the plastic piece into the tube and align the nuts with the holes and mount the linear guide, then slide the plastic tool back out of the tube.
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@mrehorstdmd Ivan Miranda @Ivan-Miranda does a great job of making things out of square tube! eg https://www.youtube.com/watch?v=qnOci3cJapQ
He tends to drill and tap the tube, but I guess that's because he's using thicker walled tube.Ian
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Hi Ian,
Just to revisit this before I consider getting some items machined;
What, if any gap should I add to the hole for the extrusion to fit. I'll be using something along the lines of your solution of adding a T nut perpendicular to the extrusion, but should the hole be machined exactly to the dimensions of the extrusion?Hi Mark,
The paper you mentioned on the Gates Timing belts, was it the following I've found;
https://drive.google.com/file/d/1POritr7FPCOrrN1QoxM0UfkxK0Y2iGMk/view?pli=1 -
@Dizzwold said in Linear Rail X Gantry Support (MGN12):
Hi Ian,
Just to revisit this before I consider getting some items machined;
What, if any gap should I add to the hole for the extrusion to fit. I'll be using something along the lines of your solution of adding a T nut perpendicular to the extrusion, but should the hole be machined exactly to the dimensions of the extrusion?If you are going to clamp it in place, then a small amount of clearance will make assembly easier. I'd give your machinist a tollerance of -0, +0.5 mm. I.e the hole must be no smaller than than the extrusion but can be up to 0.5mm larger. It's important that the distance from the bottom of the block to the bottom of the hole must be the same for both blocks otherwise the rail will be higher one end than the other.
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@Dizzwold Thanks! Page 63, bottom right - smooth idlers should have diameter equivalent of the pitch diameter of a 40 tooth pulley. Page 18 shows the pitch diameter of a 40 tooth pulley (for 2mm pitch belt) is 25.46 mm. So the 608 bearings are a little small at 22 mm, but I haven't seen any issues with them.
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Hi Ian,
Thank you for your advice. I'm most grateful.
Hi Mark,
Glad to help and actually contribute for a change.
Are either of you moderators, or can put the Gates Timing Belt info in a file somewhere, where everyone can access it easily from the forum main page or something?
I think most users of the forum use Gates belts (or similar), so could be very handy for others.Thanks again,
Dizzwold.
