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Understanding tolerances for Markforged 3D Printed parts

Tolerances are one of the common questions we receive when people are looking into printing parts that fit together. Within this blog post we shall explore some different models that help to explain tolerances. The repeatability of printing with a …

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Tom Watkins

October 21, 2020

Tolerances are one of the common questions we receive when people are looking into printing parts that fit together. Within this blog post we shall explore some different models that help to explain tolerances.

The repeatability of printing with a Markforged 3D Printer allows us to use the correct tolerances for our applications with ease. However, there are some areas we need to be aware of.

Orientation

The orientation of the part will play a role in how well our parts will fit together. This is simply due to the process of FDM (fused deposition modelling) printers. Lets use the image below to help explain this. From left to right we can see different variations on a similar print.

On the left we have a part with a continuous curvature. As each layer is laid on top of the previous it slowly steps out, producing the curve. This will create “steps” when looked at closely.

In the middle we have the same part without the continuous curve. The part will be very accurate when printing vertically. However as it tries to span/bridge the distance over to the right, we will start to see issues. The filament will fall, causing either a print failure at worst, or at best the incorrect geometry.

This now leads into the last option on the right, the use of support material. Although Markforged support material is easy to remove, there is still a chance that it will leave blemishes on the surface. Without post processing these potential blemishes will hinder the tolerance between the components. This could cause parts to not fit, or reduced movement.

Fabrication limitations of FDM 3D printing. Below a certain threshold, horizontal layers can cantilever freely (left); Beyond this threshold, gravity would cause deformations and artefacts (middle); this can be resolved by introducing auxiliary support structures (in red, right). These support structures are mechanically removed or chemically dissolved at the end of the process Source: DBT, ETH Zürich, 2017
https://i1.wp.com/www.researchgate.net/profile/Timothy_Wangler/publication/335676750/figure/fig5/AS:800402626859009@1567842265186/Fabrication-limitations-of-FDM-3D-printing-Below-a-certain-threshold-horizontal-layers.png?w=640&ssl=1

Lets continue these theories further, by looking at two more examples as below. Using an angle greater than 45 degrees from the horizontal will ensure that supports are not required. Furthermore it will give the printer ample layers to produce the geometry. This means that layers “stepping” will be visibly reduced.

https://i1.wp.com/static.markforged.com/wf-assets/wf-i9asbk2v-50.png?w=640&ssl=1

Layer Height

Due to the class leading layer adhesion you can experience with a Markforged 3D Print, it allows us to create complex components with high precision. This is because the aforementioned”stepping” is a factor of bad layer adhesion, and a smooth print allows for consistent tolerances across faces.

3D Printed Lifting Tool Close Up

How to print a tolerance tester!

Therefore, the following part has been designed to not just explain how tolerances work, but also to further our explanation of how important orientation is.

On the front side of the tolerance tester, there are five slots. A slider is printed separately, and is used to give tactile feedback on the five different slots.

tolerance tester cad
tolerance tester slider

The slots are sized from no different to the slider, to a 0.15mm increase. The increase was applied to both side faces, as shown in the image below.

explaining the move face command

The exact same slots are also printed on the back of the tolerance tester, however these are now printed in the z axis.

As we saw in the explanation above, printing in the z axis means that support material will be required, and therefore the accuracy that can be printed can potentially decrease. As mentioned, this is due to the removal of support and the “stepping” of the layers.

By having the mixture of both it gives a direct comparison that can be used. We can then establish the exact tolerance fit that you require for your parts.

reverse side of tolerance tester

Before you print you should to make sure that everything looks correct in Eiger’s interal view.

Printed Parts and Testing

The Front Slots

Here is the 3D printed tolerance checker. We will run through the different tolerances and why you would want to use them. Also we will talk about the differences between the tolerance holes on the XY plane and the Z plane.

(Starting from the left)

0mm Tolerance: Use this if you want to create a strong friction grip between two parts in your assembly/product. Once the part is in there it will be locked in.

+0.05mm Tolerance: This tolerance is what you would want if you need a frim friction grip. But using this tolerance also allows you to disconnect the two parts when you need to.

+0.08mm Tolerance: Use a tolerance of 0.8mm if you want your part to be secure without any external forces applied to it. However be able to remove it with relative ease.

+0.125mm Tolerance: A tolerance like this means that the part will hold its position with no external forces, however will not be secure. It will be very easy to remove by hand however.

+0.15mm Tolerance: Apply a tolerance such as this to your part will result in the part moving around with no external forces applied. Use this if you want a part that can free move in the assembly.

Extra Tip:

Bear in mind that the Nylon White material will overtime find its setting point, meaning that at first, depending on your tolerance it will be very difficult to put in. However overtime will become easier to manipulate to the desired fit.

The Back Slots

The slot on the back behave in the same way as those on the front with the same tolerances. However as they print with support material, the edges are rougher. As a result they grip the part much more and make it more difficult to move.

Bear this in mind if you are printing tolerances on the Z-plane as you may need to make the tolerance slighlty larger than if it were on the XY-plane.

The Pillars

The tolerances on the pillars work slightly differently to those on the slots. As a result you need to think carefully about what you desire when it comes to your part.

+0.05mm Tolerance: Using this tolerance when desiging pillars will ensure a stong friction grip between the parts. Therefore the parts won’t move and will remain static when put in place.

+0.08mm Tolerance: This will provide a very stong grip between the parts that will only move if an excessive amount of force is applied. If you want your parts to stay secure but also want to be able to remove it when necassary you should use this.

+0.125mm Tolerance: If you want your part to still be secure yet be relatively easy to remove, then you should use this tolerance. It still has a strong grip, but cand be moved quite easily depeding on the parts design.

+0.15mm Tolerance: This tolerance lets the part hold it’s position, however it will move then subjected to force. If you want your part to be easily removable/move under force then use a tolerance like this.

Conclusion

In conclusion, make sure that you take into account how you want your parts to fit together, and what tolerance would be the best to enable that. Consequently by doing this you make sure that your part works in the desired way with no extra hassle.

Struggling with tolerances? Solid Print3D is here to help you with the right decisions when it comes to 3D printing. For more information, please call Solid Print3D at 01926 333 777 or email at info@solidprint3d.co.uk

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