Drawers without supports: 45-degree slots.

157

97%

11d

I'm sure I wasn't the first to think of this, but I did have this idea and it's worked very well for me so thought I'd pass it along to others.

I'm making some simple drawers to fit in a specific area. There's a basic box that servers as the holder and then 4 drawers that stack up and slide into the box on "rails." I wanted to be able to print the drawers flat so that I could included any sort of dividers that I wanted, but this presented a problem if I went with just a straight lip on the edge to have them slip into the box. If I printing laying flat then this horizontal piece would either need supports or it wouldn't print smoothly and likely wouldn't slide in an out of the box smoothly.

So I came up with this plan. The box sticks out 2mm (half the thickness of the wall) but at a 45 degree angle. Then it retreats 2mm, again at a 45 degree angle from horizontal, then returns to normal. The wall of the drawer does the opposite. It retreats 2mm at a 45 degree angle, then extends 2mm, then returns to normal. This provides a relatively large "rail" for the drawer to ride on, but requires no supports to print smoothly when printing "flat."

Now I can do any sort of printed dividers without those needing supports either.

Edit to add: I want to point out u/VestEmpty raised a very valid concern for this plan. This shape of "rails" with create a force that tries to push the box sides horizontally. In my particular situations this is a low concern me as my boxes will be confined horizontally and I will not be putting heavy objects in them. BUT, if you use this design with the intent of putting heavy things in the drawers it very well could be an issue for you. Plan accordingly.

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(Edit to clean up my grammar... I really need to proofread before I post!)

boermac

11d

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Final note and then I'll shut up... this is probably the easiest way to add this into a design. Put in short construction lines and then dimension them all the same (or make them all equal and dimension one of them). Then channel your inner 3-year-old and play connect the dots with regular lines.

boermac

11d

Also, in case anyone is curious, the little "protrusion" on the front of the drawers is for a combo handle/label. The protrusion is of course 45 degrees as well so that it doesn't need supports. The handle just slots in and can be swapped out if I change what's in the box.

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VestEmpty

11d

Think about forces. What are they doing? Creating a wedge that will tighten the more weight is put on it? You are squeezing the drawer and expanding the frame. It will jam. Constantly and more when weight is put on it.

Flat surfaces will have only one direction of force: down. Friction increases naturally, you don't get the "friction fit" problem that you will get with 45 degree slots. Nothing will expand of contract, your force direction is against the most structurally solid direction.

Print walls and roofs separately. That way you get nice smooth surfaces for sliding things.

edit: lol, downvoted.. Oh well... I just happen to be right: the direction where the weight is pulling the drawer will try to expand the walls, will squeeze the drawer and it WILL jam. There is a reason why this was not chosen as the way we do things as it would be quite beneficial to just saw two 45 cuts rather than making it the hard way, 90 degrees. We would save material and time. Why is it not used by furniture makers for the past 3000 years?

SignedJannis

11d

Material and weights are a factor as well

E.g.if these are 4“ plastic drawers to hold electronic components, with a little lube on the slideing edges and printed in PLA, I would be very surprised if there is any jamming.

A bigger box full of wrenches? Sure, jam.

"In theory, practice and theory are the same, in practice they are different"

boermac

11d

You are 100% correct... and I don't care! :)

Seriously though, you are very right that this method will cause there to be pressure pushing the "boxes" to expend horizontally. But this won't be a real issue for me for two reasons:

First, I'm putting these in a snug, confined space where all the boxes will be lined up next to each other with hard walls on top, bottom and the outside edges. This won't completely stop any expanding, but it will prevent expanding from happening significantly.

Second, I don't plan to put very much in the way of heavy items in these drawers. These are mostly going to be just odds and ends... parts for my printers, storage for this or that... nothing dramatically heavy.

So yeah, for certain situations this is a VERY BAD plan. But for my situation it will work very well. (At least, I strongly suspect it will... who knows... maybe 3-6 months from now I'll be back here eating crow saying how it failed me.)

Researcher-Used

11d

Agreed, hard tongue n groove for a reason. My kids plastic bin drawer set from ikea is proof.

51herringsinabar

11d

I was experimenting with similar concept, ill link that when I get home

abertheham

10d

You alright? Long drive? It’s been 13 hours…

51herringsinabar

10d

Shit, fell asleep right after work, sorry

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So, currently it looks like this, the idea is to print separatly tops bottoms and sides of the cabinets,

51herringsinabar

10d

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The drawers (+ tops and bottoms of cabinets) fit together and can be stacked and even hung on eachother

51herringsinabar

10d

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And they support each other so you dont need walls betwen each drawer, the idea was that you can mix and match drawer sizes. Heres a link to Onshape file if you want to print it or check the dimensions

tzedek

11d

Solid idea. It can be easy to design around support, yet very few people do so. Btw you're going to want an air gap in between if you haven't added it. The image looks like 0 clearance.

boermac

11d

0.75mm gab on both sides. It's kinda hard to see in the picture because it's small, but it is there. I've already printed two drawers and two boxes so far and the drawers slide in and out smoothly.

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miguelake

11d

I think that the tolerance (0.75) is too large relative to the horizontal depth of the rail (2mm(?)).

Such tolerance overall sums 1.5mm offset between the two parts horizontally, which could make that little deviations of the drawer (which will happen as there is no geometry to prevent this). These deviations could (and likely will) lead to the case of the whole support of the drawer to be on only 0.5mm on one of the sides.

This will likely make the remaining contact tip (the 0.5mm on either side after it deviates) to wear out fast, making the whole drawer to dislocate rather easily just as the time passes. This is even further aggravated by the pointy end, which will concentrate the forces on the smallest point (the tip) making it deform very fast. I would recommend to increase the difference between the offset and the rail depth and add fillets, achieving eventually an “S” shape 👌

boermac

11d

Total horizontal depth is actually 4mm. It's 2mm out, then back to center, then 2 mm in. That little snippet doesn't show the 2 mm inset but if you look at my original picture it has it. I probably could have gone smaller, but I wanted enough room for all the angles to allow a good fit.

Fillets wouldn't be ideal here as the point of this is to allow a very smooth, even print without using supports. Rounding fillets would pass the 45-degree angle and mean either a less than perfect, smooth print or needing supports (which could also lead to less than smooth prints).

miguelake

10d

I see. I still think that your depth is 2mm and not 4. If you draw an horizontal line where the rail “goes back to center”, the zigzag shape is symmetrical, hence the “positive and negative depths” cancel each other instead of accumulating.

I see your argument on support, and I agree. However, thinking on the printing and not only on the design itself, I will find that this container is VERY likely to be printed on its back, with the opening for the drawer looking up (otherwise you will need support for the “roof”). This will make the side rails to be printed vertical (not horizontal as you see them when you design them) , thus the filleting not only will not need support but also will indeed increase the print smoothness as there will be less sudden direction changes, hence less flow changes (better wall finish), and also less de/accelerations (less ringing and other mechanical-based artifacts).

Good luck and have fun 👌👍

boermac

I disagree, but I think it's because my illustrations aren't showing the design very well. Let's see if this illustrates it better.

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Now this is a super narrow, short "drawer" but the "rails" and as well as the walls of both the drawer (Blue) and shell (Black) are dimensionally accurate. The drawer would have to clear 2.5 mm for the tip of the drawer to pass the tip of the shell (4mm - .75 -.75). It would require a lot of moving, tipping, and wearing out of the plastic before that happened. Is it possible? Sure... but highly unlikely given the relatively small size and relatively low weight of what's going in these drawers.

You are correct that the shell/box is printed laying on it's back, so fillets there wouldn't be a print quality/support issue, but the drawer are printed flat on their bottom, so fillets on there would be an issue.

In the end your point that I should have gone with less than 0.75mm gap is probably accurate. I was worried that with the crazy geometry that only 1mm total gap would be too narrow but I think I probably would have been okay with doing that now that I have some printed. But I think I'll be okay with the .75 gap per side.

miguelake

I see. Some tests will probably show the way to go. Nice images and comments 👍

KoalaMeth

11d

Are the drawers modular/stackable? Any pics of them in action?

boermac

11d

Yes and not really, and not yet. I designed these for a very specific spot in my home office so they're "4 units" tall, which is exactly the open space I'm putting them in... there's a top and a bottom "shelf" they are going between. Given that my outer box is exactly the height needed, I didn't do anything to make them stackable... I'll never be putting one box on top of another. But the drawers themselves are semi-modular in that I could make them single, double, or even triple or quadruple high as needed. Right now I'm only planning on few double height drawers.

As for pictures... I don't have any yet. I'm still working on printing everything... I just started this a day or so ago so only a few pieces done.

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Nightxp

11d

Love it, great idea and made super well. I’m always trying to find a way around supports. Thanks for the idea and I look forward to using it! I’ll try and get a photo of my next part using this and credit you

Researcher-Used

11d

The only issue I can think of is gravity. The case will bow while your drawers will slide down as your rails are mini ramps not like tongue/groove. I’ve experienced this w my kids plastic toy chest. Great empty, but shifts with objects inside.

boermac

11d

Yes and no... I mean yes the drawers will sit a touch low as there is a small air gap on both sides, but I accounting for that with a slight air gab between the drawer and the bottom of the box. Also they can only slide so low as the ramps are in opposing directions on each side.

As someone else pointed out these ramps will also try to push the box sides outward if you have too heavy of stuff in the drawers, but as I'm only putting light stuff in them this shouldn't be an issue for me.

Researcher-Used

11d

“The word you’re looking for is “tolerance” not “Air gap” and yes, there needs to be a tolerance between the two surfaces. But two angled faces against each other will constantly fight each other bc of gravity. The weight of the drawer itself will pull it down - indefinitely.

Researcher-Used

11d

Unless you add additional supports and materials and cuts. Then it becomes cost-prohibitive.

boermac

11d

What I'm trying to say is that the drawers will only drop so far because of the small distance between the drawer and box wall.

Yes, gravity will still be trying to pull it further down, but it can't move further down unless the drawer or the box are pushed out of shape. This shouldn't be an issue for me because I don't intend to put very much in the way of heavy stuff in these drawers. Beyond that there will be horizontal walls on the outside of these lined up boxes which will prevent (to an extent) the walls from being able to bulge.

In general this is probably a terrible idea for large and/or heavy drawers/objects. But for small, light storage this should work just fine.

Researcher-Used

11d

You’re right, i have no idea what your putting in there nor the scale of this. It could be a 8”x8” desktop trinket box. Best of luck. Keep pushing the boundaries.

boermac

11d

Life is weird sometimes. I try my best to communicate well with stuff like this... part of my job is tech support and I'm so aware of people giving minimal information for me to try to help solve their problem so I usually end up adding more details when I try to talk about something to others.

Obviously I have in my head a very clear picture of how big these are so my gut reaction is just: "Yeah, but these are small, so it's not a problem." I'm just assuming you can see in my head and know the scale, which you can't... at least I hope you can't. (Quick, what number am I thinking of?)

The box shells are 137mm wide by 240mm tall (5.4 by 9.4 inches), so pretty small scale here. Mostly for small pieces and parts.

Researcher-Used

11d

No I get it completely. My initial response was much different I assure you lol. Then took a step back and heard what you said “it’s not that big”.

You got this.

jschall2

11d

You already have a slide-on part on the front, why not make the whole front of the drawer slide on so you can print in an orientation that lets you make a proper rail? Added benefit of being able to fit more on a print bed.

Or make the rails slide or snap on.

boermac

11d

A slide on front would only sorta help as many of my drawers also have internal dividers so they would have to be slide on too... which is doable, but I prefer printed in place dividers when possible as these will be much more solid.

Slide on rails? Hmmm... I'd have to think about how I would make something like that work. It's an interesting idea.

Honestly, the best solution that I only thought of while talking with others in this post would be to just put the rails at the bottom of the drawer.

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DerMeister7

11d

This is probably the best solution, but you can improve on it a bit more by slanting the top of the rail slot upwards by 45 degrees to allow the cabinets to be printed upright and thus reduce friction by having the layer lines run in parallel between the drawer and cabinet.

It won't matter if the top of the slot is slanted since the force is all on the bottom of the slot.

SickAndBeautiful

11d

Kinda like this? Not my model, just reminded me..

boermac

11d

Oops, I didn't notice that "this" is a link. A little different, but certainly similar.