Requirements
These are the requirements the design must keep. A change to the model that breaks one is a design change, not a tweak, and this page changes with it. The structural assertions and collision checks screen many of them; none of them replaces testing printed parts.
Load rating
- The platform is rated for 49 kg (about 481 N). The Crimpdeq itself is rated to 1500 N (about 150 kg); the printed lugs set the lower limit.
- The printed structure is sized with a 2.0 structural design factor, but the platform is never loaded above its 49 kg rating.
Printing
- Every part is 3D-printed. There are no bolts, pins, inserts or other purchased hardware.
- Every part prints without supports.
- Each base half fits within the 240 mm printable length of a 256 mm bed (Bambu Lab A1). The halves join with vertical dovetails whose joint faces are in compression under load.
Case and load path
- The platform holds the crimpdeq-case
v2.0.0enclosure and every earlier release. - The case lies flat, lid up, and floats at least 1 mm above the deck and clear of every printed part. Its shell, lid and screws never carry load.
- Hand force passes through printed round lugs in the Ø15 mm ring bores of both load-cell eyes: the anchor block’s lug and the grip’s lug. Each stands on a tongue rising through the case’s eye U-slot, at least 1 mm from the case and its lid battery walls.
- The lugs are solid. The anchor block and grip print upright, so the lug and tongue roots are screened across the layers.
- Two snap-on eye clips hold the load cell down under the lug heads. Each fits by dropping into its U-slot and sliding onto the lug neck, with finger room beside the grip-side fin.
- The clips carry the grip’s tilt but not the pull; the clip ring and lug neck are screened for that tilt.
- The switch and USB port stay reachable from the open +Y side of the base.
Finger pocket and stoppers
- The four-finger hangboard pocket is exactly 25 mm deep, with an opening at least 80 mm wide, a 6 mm back wall and an 8 mm loading lip. Its +Z opening stays clear.
- The mid-depth of every edge is within 5 mm of the load-cell plane. The current model is at most 4 mm off, on the 10 mm edge.
- Two stackable drop-in stoppers, 5 and 10 mm thick, give 20, 15 and 10 mm edges. The closed pocket walls locate them.
- Their pull tabs run in slots in the pocket end walls and stand proud of the grip top, leaving the whole top of each stopper free for the fingers.
- The stoppers are stored in a well in the deck beside the case.
- Grip-guide ledges run under the grip’s side walls with a 0.8–1.2 mm Z gap and free X travel, so they catch tilt without carrying measured load.
Palm rest
- The solid heel deck is level with the pocket mouth. The palm bolster rises 10–14 mm above it and at least 2 mm above the key heads.
- The rest has seven positively locked positions, for hand openings of 25 to 85 mm.
- The rest is captured on a dovetail rail and locked by two printed index keys in deck slots outside the palm area. Adjustment needs no tools.
- Either index key alone is screened for the entire design force, and both travel extremes are checked after every geometry change.
Phone stand
- A tilted phone slot runs across a two-cheek stand at the far (−X) end of the base. A narrow phone rests on both cheeks.
- The slot floor is at Z = 15 mm, so the case hides the phone only from viewpoints less than 20° above the table.
- The stand leaves finger room by the stopper well, is outside the load path, and is clear of the hand at every rest position.
Clearances
- The base, anchor block, grip, clips, rest, keys, phone and case are collision-free except at explicitly modelled contact surfaces.
Structural screening
dynamometer_dimensions.scad fails with an assertion when a parameter change
takes any of these checks past its limit. Values are at the 961 N design
target: the 481 N rating times the 2.0 design factor.
| Check | Stress | Limit |
|---|---|---|
| Eye bearing on each lug (14.3 mm × 4 mm) | 16.8 MPa | 20 MPa, lug bearing |
| Lug root bending across the layers, eye force at the load-cell mid-plane | 6.7 MPa | 12 MPa |
| Lug root shear across the layers | 5.98 MPa | 6 MPa |
| Tongue root at the deck, bending across the layers | 3.1 MPa | 12 MPa |
| Anchor block bearing on its pocket | 1.1 MPa | 12 MPa, bearing |
| Clip on the flat ring under the lug head, largest finger-pull tilt | 11.1 MPa | 12 MPa, bearing |
| Lug neck pulled by the clip, across the layers | 4.4 MPa | 12 MPa |
| Finger lip bending over the full 25 mm edge | 18.0 MPa | 30 MPa, bending |
| Grip side and back walls in tension | 1.2 MPa | 12 MPa |
| Either index key alone, in shear | 10.0 MPa | 12 MPa |
| Key bearing in the rest wing / base slot | 5.5 / 4.3 MPa | 12 MPa, bearing |
| Base slot ligament between positions, in shear | 9.3 MPa | 12 MPa |
| Palm bolster root, across the layers | 0.9 MPa | 12 MPa |
| Rail flanks holding the rest down at its shortest engagement | 3.6 MPa | 6 MPa |
The clip check takes the 10 mm edge’s 4 mm offset, reacted between the clip and the tongue seat 10 mm from the eye centre. The base joint is in compression and is not screened; the stoppers, grip guides, stopper well and phone stand are outside the load path.
The printed-material limits (allowable_printed_* and
allowable_lug_bearing_mpa) are assumptions that need coupon tests. The
calculations leave out the 3D stress field, notches, one-finger loading,
print defects, creep, fatigue and temperature, and they are not FEA or proof
tests. The design factor is not a demonstrated safety factor and never
permits loading the platform above 49 kg.