Parts sliding along each other - design questions
 
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Tango
(@tango)
Estimable Member
Parts sliding along each other - design questions

Short version: I'm working on a design that will have one part pulled back and forth and will be sliding along on top of another part. I'm wondering if one filament type will work better than another and if just having the one top part slide along the other will work okay or if I need to find a way to include some kind of wheel to reduce the wear and tear I'll get from two parts continually rubbing against each other. Imagine the bottom part as a rail, like for trains, and the top part more like the train, but it'll be pulled back and forth along the rail. Will just one part sliding along the other work, or do I have to include some kind of wheels for it?

More in depth about what I'm doing: I've gone through Printables and some other sites looking for a good camera mount for my Prusa. I found I hated stationary mounts, since they made timelapses that made me disoriented to watch, since the printed objects were going back and forth. So I modified parts of some mounts and ended up with this:

When I designed it, I made sure the rail that holds the camera mount (and a Pi Zero) was high enough up that it didn't hit the end of the frame under the print bed and also missed the top of the case for the LCD screen. It's worked fine for a year or so, but today I did my first print with PETG and ran into issues. While this isn't attached directly to the bed, the parts of the bed support frame heat up along with the bed and apparently that extra heat for PETG instead of PLA was enough that the extensions started to sag so the crosspiece now hits the end of the frame and the LCD case.

As I mentioned, I prefer a camera that moves with the bed. I'm thinking I can make a support or rail that will attach to the channeled aluminum frame under the bed and a camera mount that'll ride along on that. I'll attach part of it to the bed so it moves with the bed, back and forth, along the rail I make. That means the part attached to the bed will ride back and forth on the rail. I'm wondering if I need to include some kind of wheels or rollers so the two parts aren't just sliding against each other and if the type of filament I use will make a difference.

Is this something I even need to be concerned about? Will PETG (for example) handle the friction better than, say, PLA? Or should I do a design where the weight of the mount slides along on ball bearings or on some kind of roller that rolls along on the rails? And if I find I can easily make a metal part for the rails, and still use a printed part for the mount that slides back and forth on the rail, do I still have to consider those issues?

Posted : 05/03/2024 7:53 am
_KaszpiR_
(@_kaszpir_)
Reputable Member
RE: Parts sliding along each other - design questions

I've done this. In short plastic parts can slide over metal parts like rods but need lubrication, otherwise they will start to melt. The same for plastic vs plastic. The best option would be to have a metal clamps on the plastic so the metal is on the metal, for example brass.

Yet the heat will cause plastic to eventually warp. Replacing some parts or all parts close to heat with metal frame is an option but you need to make it stiff in all axes and this becomes a problem in certain points. You probably end with putting some flat metal beams between the frame and the screws that hold the heat bed.

This leads to increased weight of the bed so notice this will increase wear to the printer.

Even with those metal parts I still had some camera wobble, so I switched to static camera outside of the printer with custom gcode after layer change to trigger button press to take a picture. This makes beautiful time lapse videos. You can also do this with add-ons to the printer software such as octoprint.

 

See my GitHub and printables.com for some 3d stuff that you may like.

Posted : 05/03/2024 9:01 am
fuchsr
(@fuchsr)
Famed Member
RE: Parts sliding along each other - design questions

For occasional use I think plastic on plastic is fine but for this application, I don't think you'll have a lot of joy for long. It'll make the design more complicated but I'd try to get some bearings in here. 

Posted : 05/03/2024 1:59 pm
Tango
(@tango)
Estimable Member
Topic starter answered:
RE: Parts sliding along each other - design questions

I've done this. In short plastic parts can slide over metal parts like rods but need lubrication, otherwise they will start to melt. The same for plastic vs plastic. The best option would be to have a metal clamps on the plastic so the metal is on the metal, for example brass.

Okay, I suspected something like this, so I'm glad to have confirmation.

You probably end with putting some flat metal beams between the frame and the screws that hold the heat bed.

Actually, in my head, I have an idea for putting the rail (or rails) on the outside of the bottom frame, so they can easily extend out on the front, past the LCD case. I've really liked having the cam in the center front. I'm thinking it'd be easier to do one rail and have the cam on one side, but then I lose the center view. So I'm not sure if I'll do one rail or two at this point.

This leads to increased weight of the bed so notice this will increase wear to the printer.

The idea I was thinking of would have the weight resting on the rails. There'd be a small trolley on the rails and the only thing connected to the bed would be an arm from the trolley that moves the trolley, so there'd be VERY little weight on the bed.

Even with those metal parts I still had some camera wobble, so I switched to static camera outside of the printer with custom gcode after layer change to trigger button press to take a picture.

I think there's a setting or plugin for OctoPrint that I read about somewhere that makes it easy to trigger the webcam at layer changes. That would be nice, but I've also had issues where the shots between the layer change showed me what the issue was. Recently I had a problem with layer shift that went back to the X axis belt. It had been nagging me for a few weeks and it was the timelapse that showed the printhead not moving all the way back where it should on the X axis that finally showed me what was going on.

It's sort of a balance. The more footage, the more helpful it is for debugging, but then that makes the timelapse long and boring to watch, but less footage and something like what you're talking about is nicer to watch.

For occasional use I think plastic on plastic is fine but for this application, I don't think you'll have a lot of joy for long. It'll make the design more complicated but I'd try to get some bearings in here. 

Okay, definitely bearings. I did think of metal riding on metal. Not sure if I want to do that, since I'm sure that at some point the noise will be maddening.

Posted : 05/03/2024 3:54 pm
Tango
(@tango)
Estimable Member
Topic starter answered:
RE: Parts sliding along each other - design questions

I hit the wrong key (didn't know I could submit a reply from the keyboard) while thinking over my post. There's one issue I could use help on:

I know I can go into parts stores or a place like, maybe, Lowe's, and get ball bearings, but I'm not sure where to go or even what kind of search terms to use to look for ball bearings in some kind of package that I can attach to something I print. Any suggestions on how to find something like that?

Also, if I have ball bearings rolling on metal, will they role or just slide? I'm wondering if I'd need something like a rubber surface for the bearings to roll on - and, even then, the rubber would wear down.

Posted : 05/03/2024 3:57 pm
JP Guitars
(@jp-guitars)
Estimable Member
RE: Parts sliding along each other - design questions

Regarding the bearings just search for bearings on ebay, you can fix it using either a bolt or model a tolerance fit cylinder to go in the middle and print that. Try to get sealed for life bearings as that will mean you will not need to degrease. You shouldn't need to make a tyre for them.

But don't discount metal on metal, if you put a thin layer of lithium or copper grease between the two it will slide virtually silent; the cylinders in your car engine work by metal to metal with lubricant between. You will need to reapply occasionally but that shouldn't be hard.

What I would probably do is greased metal bar rails, with petg running on top. You could model the carriage to have replaceable runners but if you keep the grease up you will probably never need them

Posted : 05/03/2024 4:49 pm
salazar
(@salazar)
Active Member
RE: Parts sliding along each other - design questions

 

Posted by: @tango

Short version: I'm working on a design that will have one part pulled back and forth and will be sliding along on top of another part.

I had a question on design advise. 

I have a 3d model of a sheath that's closed and solid. I also have a 2nd 3d model of a sword. 

I I wanted to ask if you had advise on how to how hollow out the sheath and make an opening so it can fit the sword.

Posted : 05/03/2024 7:53 pm
fuchsr
(@fuchsr)
Famed Member
RE: Parts sliding along each other - design questions

Unless you have the CAD files I think one of the easiest ways to do that is to load both into Tinkercad, scale the sword a bit to create so the hole is going to be a bit larger then the sword, then turn the sword into a hole, align it with the sheath, and combine. Of course then print the sword at its original size. How to deal with the unsupported curvature inside the sheath is of course a different issue...

Posted : 05/03/2024 8:39 pm
Tango
(@tango)
Estimable Member
Topic starter answered:
RE: Parts sliding along each other - design questions

I tried posting last night, but the forum wouldn't let me upload an image and ate my post!

I'm thinking that I can do it all in PLA and a few screws. The camera stand trolley will have wheels that will run in tracks on a rail or base that is near the print bed. Something like this:

I'll use a screw for the axle for each wheels and the wheels will roll along in a track. I may make the wheels a bit more wedge shaped so they fit in the track better and I'm considering adding teeth to the wheel and track, so it fits like a gear, which will ensure the wheels turn instead of sliding - but that could also cause a problem if something goes wrong and the wheels might jam. My thought with this design is that screws have rough edges and I'm wondering about the friction of the wheel against the screws/axles.

Posted : 08/03/2024 6:02 pm
Neophyl
(@neophyl)
Illustrious Member
RE: Parts sliding along each other - design questions

If you are concerned about the wheel on the screw thread then just use a screw with a shoulder.  

For the ultimate you could just use a suitable bearing as your wheel

Posted : 08/03/2024 6:06 pm
Tango
(@tango)
Estimable Member
Topic starter answered:
RE: Parts sliding along each other - design questions

If you are concerned about the wheel on the screw thread then just use a screw with a shoulder.  

Good point - had thought of that. Still early in the design process and have other things that are taking priority, so I'm just thinking about this when I have time here and there.

For the ultimate you could just use a suitable bearing as your wheel

One concern I have is the possibility of the wheels (or bearings) sliding sideways. If I use metal bearings, any suggestions or thoughts on an easy way to get a metal track? I'm thinking maybe some kind of angled aluminum for that.

Posted : 08/03/2024 6:11 pm
JP Guitars
(@jp-guitars)
Estimable Member
RE: Parts sliding along each other - design questions

If you use a bearing there should be no issue with sliding providing you don't pinch the outer race. Easiest way to make sure is to put a washer on each side about the same size as the inner race.

You don't need a metal track, there should be no wear if it is rolling, and trying to buy or make a rail of the right size in metal is going to to be a pain. If you are worried about wear then make sacrificial tracks and when they wear out (they won't) you can reprint just those.

Posted : 08/03/2024 7:12 pm
Tango
(@tango)
Estimable Member
Topic starter answered:
RE: Parts sliding along each other - design questions

I've been thinking about this off and on. I'm redesigning my print station and may need room for more printers, so even though I want to do this, it might be wasted effort if adding more printers makes things more cramped. So it's on the back burner for now.

But here's why I'm thinking about printing wheels instead of using bearings: I've had times in the past, not in printing, but in other projects, where I design something around parts I can buy somewhere and then the parts change and I have to redo my design. (I first ran into this in the 70s as a teen when Radio Shack changed cabinets they sold and some other parts they removed from their shelves.) If I use only something like M4 or another standard screw, that will always be available. If I use a type of bearing, then it's quite possible the model with the casing I find works becomes unavailable before the next time I want to make one of these.

I'm not ruling out bearings, as I said, I'm thinking it over slowly and considering all options.

Posted : 14/03/2024 5:10 am
Neophyl
(@neophyl)
Illustrious Member
RE: Parts sliding along each other - design questions

My only comment is that common bearings are pretty much a standard part, just like M4 screws.

Posted : 14/03/2024 7:33 am
JP Guitars
(@jp-guitars)
Estimable Member
RE: Parts sliding along each other - design questions

Beat me to it. I was going to say exactly the same. 

Posted : 14/03/2024 7:37 am
Tango
(@tango)
Estimable Member
Topic starter answered:
RE: Parts sliding along each other - design questions
Posted by: @neophyl

My only comment is that common bearings are pretty much a standard part, just like M4 screws.

What about mountable casings? Same with that?

Posted : 14/03/2024 6:22 pm
Neophyl
(@neophyl)
Illustrious Member
RE: Parts sliding along each other - design questions

I don’t know what you mean by ‘mountable casings’. 

Posted : 15/03/2024 6:06 am
Tango
(@tango)
Estimable Member
Topic starter answered:
RE:
Posted by: @neophyl

I don’t know what you mean by ‘mountable casings’. 

If you can't tell, I've never used bearings in any projects, so I could be using the wrong terms.

I'm assuming that the bearings don't fit directly into a hole in what I'm printing since it seems that if they did, they'd easily fall out whenever that part is picked up and they'd be rubbing directly against the printed material. I would think it'd be possible to get bearings that are already in a casing I can just attach to the parts I print.

But I could also completely misunderstand the situation.

I was thinking of something like this (on Amazon) - bearings that are in a casing that could be mounted to something else.

This post was modified 1 month ago by Tango
Posted : 15/03/2024 7:31 am
Neophyl
(@neophyl)
Illustrious Member
RE: Parts sliding along each other - design questions

Bearings come in all shapes and sizes.  For your use case where you mention 'wheels' then something along the lines of a good old 608 https://www.amazon.com/SHKI/dp/B09PKD8QZZ/ref=sr_1_3?crid=X94PXF1CTCDW&dib=eyJ2IjoiMSJ9.aW_G4E-6IMbYW6jX9o6XeS44jHTaEH4awtWGXDMY1p7OUZHyqUOfGq5MVNMzxMKtaCx0385E85nEoclVbW3G3FAmk-FaqqM7WHdJmdzqPHUdFbqqJoRudphYzbL9rqOgDA1XEXm4BFuU6rRHfjPWokMUzuVd-R3A8JQ-CzwPB99iLHUjdnV3AWA7PnRlyqSFzX1AwWKZQmUHFJOcFmGROOtNDKXckd-tjw2iOY_LNH0.6Butu5oibg9UyFWe9lRbi9iorKeQaJruz7uParfOsTM&dib_tag=se&keywords=602%2Bbearing&qid=1710509463&sprefix=602%2Bbearing%2Caps%2C208&sr=8-3&th=1   would work.  The outer would be your metal contact point with your rail and the inner just needs a part printing sized for your axle, in your suggested case a M4 screw ort similar.  Nothing to fall out and sideways movement along the axle taken care of by your 3d printed parts of the carriage.

The ones you linked to have mounting holes and so would also be easy to mount as you would normally just screw them to the bottom of something.

Posted : 15/03/2024 1:35 pm
JP Guitars
(@jp-guitars)
Estimable Member
RE: Parts sliding along each other - design questions

To expand on what I said earlier

Posted by: @jp-guitars

If you use a bearing there should be no issue with sliding providing you don't pinch the outer race. Easiest way to make sure is to put a washer on each side about the same size as the inner race.

From the image in the link neophyte posted, the inner race is the inner silver ring, the outer race is the outer silver ring. What you need to do is make sure the mounts don't restrict them turning, a common problem people unfamiliar with bearings is they put a suitable size bolt through the middle but don't give any space to allow rotation of the outer. The easy fix is a washer about the size of the inner race between the bearing and what it is mounted on, that gives you a clearance of the thickness of the washer for the outer race. If you are 3d printing rather than using a washer you can just design in a spacer.

I also mentioned getting sealed bearings, the ones neophyte posted are sealed, that's the black bit between the races, it's basically a cover over the ball bearings that keep the grease in and dirt out

Posted : 15/03/2024 2:41 pm
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