Overcoming common challenges with Holographic Fabrication

Careful and precise alignment of holograms with bench mounted tools

In order to successfully follow holographic guides using analogue tools (like pipe or bar benders) you need to ensure that the hologram describing the part geometry is as precisely aligned with your tool as possible. Even a few mm of misalignment with the center of a bending radius will mean that no matter how carefully you try to follow the hologram describing a bend, the part after bending will not align with the hologram as it should (it will be a few mm too long or too short, and these will accumulate with each bend making the situation worse). It is worth spending some time getting your fabrication setup properly calibrated:

  • Ensure workbench doesn’t move (weigh down or brace tables if required)
  • Fixing tools in place (screw fix to a base board then clamp to table)
  • Fixing QR codes near tool (fix to base board)
  • Making very fine adjustments to hologram placement using either:
    • Moving a reference point in Rhino while wearing the HoloLens
    • Moving a reference point by hand in mixed reality
    • Changing slider values for x/y/z coordinates of reference point
  • Model a few simple two-bend parts and use these to verify that you can maintain alignment with the hologram after multiple bends. Most likely you will need to make several adjustments to your hologram (to the reference point as well as potential to the bend radius in your parametric model) before you can achieve a good result.

Maintaining alignment of holographic parts during fabrication

It is impossible to work from a holographic guide during fabrication if you are unable to maintain alignment between a physical piece of material and the hologram describing the shape you are attempting to form it into. If this forming process takes place through multiple steps (e.g. multiple bends in a piece of steel rod), it is critical that performing the act of bending does not move the part such that previous bends no longer match the hologram. You can follow these tips to try to maintain alignment:

If free forming parts in space

  • If forming simple parts, you can use a holographic guide just as a ‘check’ after manually forming a part. The fabrication process becomes an interative one where you form a part by memory, check it with a guide, and then repeat.

  • For more complex parts, start with your stock material or existing assembly firmly clamped to a work surface

  • Before starting any bend, double check the part or existing assembly has not moved and correct any misalignment

  • During bending, ensure the formed section of a part or existing assembly does not move. You may have to use additional clamps or bracing to minimize this.

  • Avoid the need to go back and correct parts - this will be much more difficult than a single bend. This means learning to anticipate elastic springback and other material / tool behaviours.

  • Avoid working with long parts that will sag under self weight during fabrication.

If using a bench mounted bender / roller

  • Ensure a snug fit with your stock material in the bender die
  • Ensure the stock material is firmly held in place during bending. Any slippages will make it extremely difficult to match the holographic guide
  • Learn roughly how much overbend is required for each part due to springback, but be very careful not to actually overbend parts as this is difficult to neatly undo.

During assembly

  • Fix your parts to a sturdy work surface (e.g. sheet of ply)
  • Ensure your placement QR code is also attached to this work surface so if you need to move the prototype you can replace the hologram in the exact same spot relative to the assembly.
  • Avoid assembling parts that hang or dangle from the existing structure as these will not match the hologram. This generally requires careful consideration of joint types and locations during design, or teams of multiple fabricators.

Leaving and returning to workspaces

After leaving a workspace with the HoloLens, or restarting the device, the headset will attempt to identify your space in order to reposition holograms where you had previously placed them. This can occasionally introduce drift (especially if some objects in the space have been moved) and if this is the case you should clear the spatial mapping on the headset and re-scan the environment. You can do this by:

  • Close any Fologram apps that are running
  • Go to the HoloLens settings, then System -> Holograms -> Remove All Holograms.
  • Spend 5 minutes or so walking around your space to rebuild the spatial mapping.
  • Start Fologram and place your model on your QR code.

Hologram representation

Judging depth (distance from your eyes) of holograms is difficult because of the fixed focal plane of the HoloLens (about 1.5m) together with the inability for small objects (e.g. your physical parts) to correctly obscure holograms when the physical objects are in front of them. As a result you may have found that it is challenging to locate the position or orientation of parts in 3D space. You may also have found that curves in Fologram are approximated to polylines, making it slightly difficult to fabricate some geometries. Here are a few tips for improving hologram representation for fabrication:

  • Often want to show edges / outlines of parts rather than surfaces (even transparent surfaces). It is slightly easier to judge depth using wireframes than it is when holograms are rendered as opaque surfaces simply because you will still be able to see (and focus on) the physical object you are working with.
  • If needing to work with very smooth curves, you can force rendering of smoother holographic curves by converting them to polylines in grasshopper first with the desired segment resolution (e.g. divide by length > polyline through points)
  • Use colour to differentiate between parts
  • Use text to describe part information (e.g. part number, bend number, curve radius etc)
  • Minimize the amount of holographic information displayed at any one time

Representing bends

Depending on the tool you are working with you may need to explore several different approaches to representing bend geometry. This may include:

  • Interpolating between the before and after bend geometries to show the bend sweep. This can be useful as a guide to overcome any undesirable part movement (e.g. twisting or slipping) during the bend.
  • Incremental bend angles could be used with rolling processes to help guide fabricators during forming.
  • Animating part movement. This can be very useful when working with a section roller where you want to be able to quickly visualize the shape of a formed curve as it moves through the rolling wheels.
  • Part flipping. It is often really useful to fabricate a curve ‘backwards’ rather than the arbitrary order that it was drawn in Rhino. This can help avoid collisions with the work environment.