Instructables
Picture of 3D Printed Money Clip
Tired of your bills getting lost or just ending up as a crumpled mess in your pocket? Or maybe you just want to keep your money more accessible than tucked away inside your wallet. Either way, a money clip does keep it all together. And of course if we can customize it to make it more special, all the better.

OK then, let's get started.

This Instructable is a part of the 3D Project Challenge: Money Clip. Create your own 3d file for a money clip or modify the template to enter.

 
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Step 1: Design issues

Picture of Design issues
I came across a few designs for money clips, but many had the same problem: they didn't grip so well. Also, many were thicker than I wanted and would be too bulky in a pocket.

Tinkercad.com is great ant their tutorial for a money clip is great for learning, but the results weren't so hot once I printed them. Too big and bills easily fell out when I printed it on a MakerBot Replicator 2.

So that leads to two things to fix. The size (no problem) and the grip (a bigger problem).

Step 2: The grip

Picture of The grip
moneyclip-6.jpg
With regular money clips made out of metal you can get a slight spring action by folding the metal over. Having the metal flush is no problem here. But that is a problem for 3D printing since you always need some gap. Otherwise the print would fuse together and be useless.

To solve this I created a dip in the body of the money clip. Then the arm of the clip could extend past the original surface of the body. With this done, the money would have a lot more friction since it would have to go around the arm. This also gives us some tension since the default position for the arm is past the body.

The result? Money stays in nice and tight. Even with one bill folded over it held strong, keeping the bill in place while it was being moved or shaken around.
clazman11 months ago
I've ran an FEA on your clip and a "modified" clip to show the improvement in gripping force. With this iteration, given the same loading the "new" cross section has reduced the grip deflection by 75%. From 0.0471 inches to 0.016 inches

The loading I used was just an example, but it was 1 PSI in the grip area.

I am having trouble in adding these images to my library.
clazman clazman11 months ago
The first pic is a good clone of your money clip. The second is my revision of yours.

I hope the scale can be read
Money Clip NEW metric-static-Displacemen.jpgMoney Clip REV B metric-static-Displacement-.jpg
clazman clazman11 months ago
I added a little round over at the tip to help prevent snagging.

I'll add the associated mass for each part, later.
clazman clazman11 months ago
My bad. The revised one weighs 0.0448 lb.. The original weighs only 0.0228 lb.

Havr to trim that weight and still give comparable results!

Anuy way, you got the idea.
karlpinturr11 months ago
I'm confused...

Are your dimensions really supposed to be in cm (instead, perhaps, of mm)? I ask because that would mean your cylinder (and, therefore, width) is a foot long (and, therefore, wide). I assume tinkercad allows you to print at 1/10th of your design size, but wouldn't it be  easier to work with actual size in this case..?

I'm also assuming that the "whole" at the end of the 2nd step above is a typo and should read "hole"?

Personally, I use Sketchup (I'm sure there are ways to output the appropriate file format), so am going to have a tinker/fiddle-about with that.

Just one more question, what's the gap-size necessary for the short arm's cylinder not to 'weld' itself to the long arm?
fungus amungus (author)  karlpinturr11 months ago
D'oh! Fixed.

Need to check the gap size. It can vary between the x and y axis on some printers. With this print it just barely touched and I had to slightly break it apart after printing.
clazman1 year ago
This comment is not be construed as a negative comment. The following comment is to help those without an engineering background, an insight to improve their designs.

Time and again I see designs here that are far from good designs.

Take this one for example. Using some basic stress calculations one would see that these parts are terribly inefficient in material usage.

The bending moment is greatest in the "throat" and goes to zero at the ends. The section modulus appears to be constant throughout. Therefore, material stress is greatest in the throat and zero at the opening.

To make this clip more efficient from a material stress point of view the section modulus needs to be greatest in the throat.

A classic example of this concept is the c-clamp, especially the deep throat c-clamps..

In other words, simply designing with CAD and utilizing 3D printing are only a small part of the design. Engineering concepts are a large part of the design.

For the layman, observing the deflection of the clip as it is opened will show the designer where the section modulus needs to be increased.

Making these design changes will most definitely result in a higher griping force.
tovey clazman1 year ago
It's a money clip. A money clip for your information, not a clamp that you use to hold two pieces of something together while the glue dries.

A money clip is a device that one uses to hold their paper money while it is stored within ones pocket. This design, which you are so critical of, is shown to be sufficient enough to hold onto a single dollar bill. Something that store bought money clips are not so likely to do. I bought one years ago from a store and it would not hold onto the money even when there were several bills and fairly thick. And it was made out of metal!
clazman tovey1 year ago
I am sorry that all of this discussion I have set forth has met with such resistance.

It doesn't matter that it is a lowly money clip. The fact that is only a money clip does not mean that we can throw physics out the proverbial door. I see this time and again, where consideration of operating stresses were not understood or, as you stated, were ignored as it was a lowly “whatever”.

I'm sorry that you cannot understand the analogy of the c-clamp. I was ONLY using it as example to help explain a concept. The analogy was only to illustrate how the cross section varies in the c-clamp to increase the holding capability. In this case, increase the gripping force of the money clip.

The reason for this is that material strain in this constant section money clip (as with your metal clip example) greatest in the throat. This occurs even when only one single-folded bill, as you keep alluding to, is inserted. Increasing the cross section in the throat (which is difficult to do with your steel example), will increase the holding force. For example, increasing the section thickness in the throat area by only 50% will result in little over a 300% increase in the force on the single-folded bill. I grant you that this increase may not be observed at the pinch area because of material strain increases in other areas of the clip. To compensate for that increase in material one could remove material in areas of less strain (stress). Your use of voids in the less strained areas is an excellent example.
Try, if you may, consider replacing the material in the throat area with a torsion spring. Can you not see that the gripping force can be increased by increasing the strength of this spring? But, as I stated previously, increase in the gripping force will not be proportional to the not increase of the torsion spring torque.

Your thought on “preload” was rather astute. I appreciate your attempt to compensate for that in your design. My attempt was to show that the strength of you money clip can be increased by simply increasing the thickness in and around the throat area. Yes, preload can be obtained in the steel clip. How much preload can be obtained may still not be insufficient to hold that single-folded bill.

If my comments here are not understood then please do not reply. I will understand that my input has been fruitless.
tovey clazman1 year ago
>>>
If my comments here are not understood then please do not reply. I will understand that my input has been fruitless.
>>>

If your comments are not understood, it may be that you are not explaining your point efficiently enough. Images illustrating what you mean would have been quite helpful as I kept dyslexing the thickness with the width of the clip.

(Dyslexing: 1. The present or recent activity that is occurring within ones brain which is the symptom of dyslexia such as the switching of characters or words, or any other word blindness symptom.
2. The involuntary activity within ones brain that causes one to become confused due to the symptoms that accompany dyslexia.)

Since the word Dyslexing is not in the dictionary, I figured I should provide the definition to insure that people understand what I mean by dyslexing.
clazman tovey11 months ago
Sorry, I was only trying, in my feeble way, to utilize my mechanical engineering studies in conveying possible suggestions to the clips design to improve its function.

I'm not sure if dyslexia is the culprit. Width and thickness are generally defined as I have used them here. However, I can see, and have witnessed this, where some have reversed the definitions resulting in confusion.

Varying the width also has an affect, although only linear, on the clip force and, consequently, not as pronounced as the thickness, which has an exponential affect.
tovey clazman1 year ago
Questions regarding the 300% increase in strength:

I am assuming that this will increase the life of the clip as well, is this a correct assumption?

Would this not potentially, make the money clip unusable to those who have week hands? (Not everyone can squeeze an aluminum can like the six million dollar man.)

Would you increase the thickness of the round area of the clip or the entire clip?

Regardless of exactly where you would increase the thickness of the clip, does not removing material in other areas make those areas prone to quicker wear?

Regardless, the design as is may be sufficient for most 3D printer enthusiasts and users. One nice option would be to remove material in the throat in the shape of characters. This would provide a personalized money clip and would likely necessitate the thickening of the clip as you have suggested.
clazman tovey11 months ago
I will attempt to answer some of these concerns.

As to life that is another discussion. Life is a function of stress and cycling. However, if my suggestion is taken too far life might be reduced. The problem was to increase the gripping force. The best way to accomplish this is to increase the thickness in the throat. The bending moment increases in a linear fashion as we move from the gripping area to the throat. Suffice it to say, increasing the thickness from the grip to near the throat takes advantage of this increase in bending moment by counteracting it, the "moment". This results in reducing the stress in the material as we move towards the throat. while making the stress more uniform as we progress to the throat. Now, in the throat area we should gradually increase the thickness to a maximum thickness NEAR the midpoint of the throat. As I said before, look at the typical C-clamp to understand what I am trying to convey. This also helps make the stress more uniform as well as increasing the gripping force.

To say that this will make the clip unusable, except to Hercules, is taking my suggestion to extremes. We only want to improve the gripping force of the present design by taking advantage of the material properties. We definitely do not go so far as to make the clip unusable.

As to wear, which is also another measurement of life is yet another point of discussion. However, wear is normally a condition of material loss. Wear in this case is where the clip makes contact with the currency. Yes, increasing the gripping force would be slightly detrimental to wear.

Finally, as to designs in the throat that would remove material would definitely require the thickness of the throat to increase. But again, stress distribution would get very complex due to this. Therefore, thickness distribution would also get quite complicated. The only way to get a precise "handle" on the stress distribution and the required thickness distribution to eliminate stress risers can only be studied with a very complex mathematical routine called finite element analysis. That is again another area of discussion.

Whew! What questions will this discussion elicit?

I only wanted to suggest a little bit of change to the money clip.
fungus amungus (author)  clazman1 year ago
This is one of the most interesting comments I've received in a long time. Interesting as in good.

I'm not an engineer and don't claim to be one either and am welcome to any insight. From what I gather you want to increase the thickness in the bend in order to make the design stiffer and stronger. A strength that will only appear as more items are inserted.
bfk12 months ago
I think a positive comment from an engineer would be nice here: You've done a great job problem solving using the scientific method and coming up with (creative and correct) solutions to some of the issues that properties of printed plastics have.

Kudos to you, fungus amungus.
clazman bfk11 months ago
My comments are an engineers comments.

Yes, from what I have gathered, 3D printing adds yet another capability to material stress utilization. That is, material density distribution. This adds yet another dimension to the stress/deflection study. Whew! and does it ever!
fungus amungus (author)  bfk12 months ago
Thank you very much, bfk
clazman12 months ago
Sorry for not replying sooner but other more personal situations here had come to the forefront. Discussions such as this had to be put aside.

Yes, Increasing the thickness any where will increase the stiffness. Any deflection, no matter how small, will increase the force exerted.

It is that the bending moment, being the highest in the throat. Thus, increasing the thickness here would have the greatest impact.Just study my c-clamp example. You will note that the cross section is greatest in the throat.

I know that others also adept in mechanical design may have a issues with my statements. I know from where these comments come. They are attempting to say that there is more to the description I have presented. Yes, there is, I just didn't want to go there. I only want to stay with the basics.

When you increase the thickness "blend this increase back to the existing thickness as you exit the throat. This so not to develop any "stress risers".

I have to go now for I am needed here.
Jakob28031 year ago
Why would this be featured, except for the fact that it was 3D-printed?
Awww.
When I saw the title I thought you were offering a recipe for
3D printed MONEY-- nickles, dimes, quarters, halves, and
dollar coins.
Which gives me an idea . . .
great job fungus amungus! those are really cool!
Lindie1 year ago
Nice!
I love it!