[](https://hackmd.io/vnldW8TBSnO_LEm4tbxbGQ)

# `frame-design` Gridbeam-inspired frame
:::info
(c) Holger Kienle
License (if not stated otherwise below):
[CC BY-SA](https://creativecommons.org/licenses/by-sa/4.0/)
:::

*Left: Frame made up of beams. Right: Joint for connecting beams.*

## TLDR Parts
- `beam` (11x):
- :owl: recommended: `s`=17..22mm (`frame-17x17`..`frame22x22`)
---
- `beam`, optional:
- `board`, optional:
- :owl: recommended: To support a bag more securely, have either a board () or an extra beam ().
---
- `fastener-mX`: `nut-mX` `bolt-mX` `washer-mX`
- :owl: recommended: M4 (`fastener-m4`), M5 (`fastener-m5`), M6 (`fastener-m6`)

## Basic structure of the Gridbeam frame

[Gridbeam](@hkienl/diy-gridbeam) is a modular building system that originated in the 1970s, which enables easy assembly with minimal tools.

The frame is assembled from
- `beam`: Gridbeam *beams*
- `fastener-mX`: Metric (DIN/ISO) machine-type fasteners

### Beams (`beam`, `beam-N` `beam-SxS-N`)
*Single beam with full hole pattern, AI generated*

Beams have a hole-pattern. A true Gridbeam beam has all holes drilled (for maximum re-configuration) and only few holes are used for an actual design. The beams in this project have *reduced hole patterns* where all/most holes are used.

The diameter of the holes match the bolts' diameter (`mX`).

#### Beam profile

The profile of a beam is a square with sides of `SxS` (in mm), for example `17x17` for a 17mm square.

       S=17mm
    ←─────────→
    ┌─────────┐  ↑
    │         │  │
    │         │  │
    │         │  │ S=17mm
    │         │  │
    └─────────┘  ↓

The short-form for`SxS` is `s`.

#### A beam is made up of segments

A beam can be thought of as a string of individual segments `N`. Each segment has length `s`. The shortest beam has 1 segment, resulting in a cube (SxSxS).

              _________
             /        /|
            /        / |
           /________/  |
          |        |   |
  S=17mm  |        |   |
          |        |  /  1 segment of 17mm (N=1)
          |________|/
          
           S=17mm

:::warning
:judge: Strictly speaking, this "deteriorated" beam is not an offical Gridbeam beam.
:::

A true Gridbeam beam has 2 or more segments.

   ___________________
  /        /        /|
 /        /        / |
/________/________/  |
|        |        |  |
|        |        | /  2 segment of 17mm each (N=2)
|________|________|/

:::success
:bulb::straight_ruler: The size of a beam can be specified by giving
1. `s` (e.g., `s`=17mm)
2. `N`: number of segments (e.g., 10)

For the example above, the beam has dimensions 17x17x170mm. If the profile is clear from context, this beam can be denotes as `beam-10`.
:::

### Tri-joints
*3 beams connected with a tri-joint,
(c) Gridbeamers [:link:](https://www.cnet.com/tech/tech-industry/after-more-than-30-years-grid-beam-modular-construction-system-comes-to-market/)*

Beams are connected with fasteners via Gridbeam-style *tri-joints* ("3D") and (optionally) with "2D"-joints.

The stability and right-angles of the frame are derived from the 3D/tri-joints.

## Fasteners (`fastener-mX`)

### Spec
- `fastener-mX`
- :exclamation: do not mix `mX`
- `screw-mX` [DIN 912 cylinder head screw](/@hkienle/std-din-912) (:de: Zylinderkopfschraube)
- Length (`screw-mX-height`): >= 2*`s`+2*`washer-mX-height`+`nut-mX-height`
- `nut-mX` [DIN 934 hexagon nut](/@hkienle/std-din-934)
| `nut-mX-flat` [DIN 439 low profile hexagon nut](/@hkienle/std-din-934)
- `washer-mX`
- :monkey: OK, but discouraged: DIN 912 (both form A and B)
- too flimsy, both OD and height
- `washer-mX-dia`
- :owl: recommended: OD of washer as near as possible to `s`(e.g., 16mm)
- :exclamation: OD of washer <= `s`
### Notes for spec
- `L`: It may not be possible to select a screw length `L` that perfectly matches the suggested length.
- Decide whether to got a bit shorter or longer.
- If you go a **bit shorter**, tightening the nut may squish the material and you end up with a perfect length.
- If you go a **bit longer**, it may open up the possibility to have 2 nuts at the end (for secure locking).
- If the screw is **too long** it has an unpleasant esthetics and the user may scratch themselves when handling the frame.
- `washer-mX-dia`: The softer the wood, the more important becomes a washer with larger OD to better distribute the load and to not dent/squish the beams when tightening the nut.

## Matching beams with fasteners

The diameter/strength of the machine screws must match the sturdiness of the beams (parameter `s`).

:::success
:straight_ruler::+1: As a rule of thumb, at the very least, the "meat" around a hole should be the diameter of hole. If the fastener is M4 (hole diamter: 4mm) then
`s` >= 4(meat)+4(hole)+4(meat)=12mm
:::

For example, for `s`=17mm, both M4 (`fastener-m4`) or M5 (`fastener-m5`) is an appropriate choice.

For the structural stability of a trolley (with a load of max. 20kg) **M6 is sufficient.** (For course, larger is also fine if you have larger screws at hand or prefer the bulky esthetics of larger screws.)

## Trolley frame

The design of the frame is primarily determined by the
beam profile (`s`), the length of the individual beams (`N`), and how they are connected to each other.

Since `s` is the starting point for dimensioning and procurement, a particular frame instantiation is denoted as `frame-SxS` (e.g., `frame-17x17`).

:::success
:bulb: The way the beams are connected to each other to form the frame is independent of `s`.
:::

:::success
:straight_ruler::+1: For sufficient strength that balances weight and asthetics, `s` is between 13mm and 25mm. The lower end pushes the sturdiness/strength of the design and you should consider to counter this with better material properties (e.g., harder wood instead of cheap softwood, see [frame-material](/@hkienle/frame-material/)).
:::

### Frame design in [interactive viewer](/dN2oN1qmT-ytX0R6rDyE1Q#Browser-based-construction-Gridbeam-CAD) ("Gridbeam CAD")

Note that each beam has the maximum hole patterns (as required by [Gridbeam proper](https://mammouth.ai/shared/cd22ff1b-0ad2-42a8-a92d-8094b98fab4a)). Counting holes helps grokking the design.

<iframe width="100%" height="500" src="https://play.gridbeam.xyz/#1bc8xDoAgDIXhZ4NCGofK1MEQNldHTmG8_2kkiAzC-uVPX8rewS8OEpQVEScS82teoGsxSht_XVRTzKSjGg86kV1RO9vMdAahbpeGu-h2p2z3r7P5j6vem1tHzfLtBw" frameborder="0"></iframe>

*The above frame is interactive! (Please do not destroy the design, you have all the power :muscle::grin:)*

Source: https://play.gridbeam.xyz/#1bc8xDoAgDIXhZ4NCGofK1MEQNldHTmG8_2kkiAzC-uVPX8rewS8OEpQVEScS82teoGsxSht_XVRTzKSjGg86kV1RO9vMdAahbpeGu-h2p2z3r7P5j6vem1tHzfLtBw

#### Screenshots from interactive viewer

##### Complete frame
- Without optional beam
,
which sits below the handle and provides attachment for the bag.


##### Detail of frame's base
- Without optional beam
.


### Beam hole patterns

True Gridbeam beams have a full hole pattern for maximum flexibility and repurposing of beams. This means that many holes are not used for a particular assembly. Potential drawsbacks are less beam strength, dirt getting into holes, and a more technical-looking aesthetics.

In contrast, this design only mandates holes that are occupied by screws and hence for each beam a hole pattern must be specified.

Since the hole patterns for all beams are not identical depending on the frame profile, the hole pattern is given in the instantiated designs, for example [frame-17x17](/@hkienle/frame-17x17#Beam-hole-patterns).
(Actually, for the current designs only **one** beam type has a different pattern depending on the frame profile: .)

### Prototype
See [frame-proto](@hkienle/frame-proto/).