Simple flared feet. Connection capacity still needs design.
The default top-entry model now has actual housed dovetails at the lower cupola feet, matching cavities and removable wooden pegs. Nominal fit and local withdrawal pass. Strength, fabrication and hurricane resistance remain unqualified. Saved historical variants retain their earlier straight-foot design holds.
The default foot has a 3 × 8 inch neck, a 4 inch wide head, 4 inches of engagement, a 1:8 side flare and a ¾-inch transverse peg. The cupola opening remains 6 feet 4 inches clear. The receiving post has a minimum one-inch cheek, which needs a structural check; geometric fit does not establish adequate strength.
What the references establish
The default foot adapts the documented housed-dovetail family to a bottom-entry cupola-post connection. The reference establishes the joint family, not this orientation, dimensions, capacity or the concealed joints of the original building. A through wedged half-dovetail is another documented horizontal tie-to-post family; it has not been adopted here.
The TFEC design guide requires matching bearing interfaces and adequate mortise cheeks. Its full-depth wedged-head recommendation cannot simply be applied to the historical flush-bottom layout. The new bottom-entry adaptation needs its own neck, cheek, bearing, peg and splitting checks. The guide also leaves shear-bearing shoulder and housing design outside its scope.
A suspended kingpost through a continuous tie is a different arrangement: the vertical post tenon is retained with pegs and a wedge. These cupola uprights receive horizontal radial tie ends and carry the cupola assembly. Their appearance of floating does not establish the direction or magnitude of the joint forces.
The Vermont Timber Works F-6 sheet, detail 7 labels a double tenon, not a double dovetail. Its post extends below the bottom chord. For the upper connection, a housed rafter-to-post tenon provides a traditional family to evaluate. None of these references establishes the concealed joints in the original Bluetime building.
Structural release requires resolving the cupola, ring and tie forces and verifying bearing, remaining timber and withdrawal restraint. Full-scene assembly is assessed separately by the source-bound disassembly sequence; local joint tests alone do not certify the whole building.
The proposed step-lap model and saved baseline model each have a separate passing cavity-fit audit bound to their own geometry. Both checks account for every original timber stock envelope and require the actual mating wood to occupy each recess. The section proportions and traditional-joint discussion below refer to the saved baseline; see the proposed joint comparison for its changed perimeter cuts.
Nominal cavity fit
The independent cavity-fit audit checks the actual removed wood against the mating solids. The false pointed lower-cupola overlays are corrected. Invalid residual meshes have been retired; the reported gap checks use separate occupancy and section methods. All results refer to the exact model and cavity hashes in the report and their stated numerical tolerances.
Gravity and wind must be followed through every joint
Roof covering/deck → short rafters and hips → perimeter bearing and central cupola assembly → ring/tie system and posts → anchors → foundations. The cupola ceiling has a separate path through its spokes and upper frame. Lateral loads need the enclosed walls or a designed bracing/diaphragm system. The central opening must remain clear while the surrounding system transfers both compression and tension.
Main-roof horizontal projected area: 747.65 ft²; cupola-roof area: 61.60 ft². Each uniform 1 psf of vertical load therefore contributes 809.24 lb in total. A symmetric bookkeeping share is 93.46 + 7.70 ft² per radial bay. These are load coefficients, not joint reactions; asymmetric snow and local wind suction require separate cases.
Measured remaining sections
Representative bay-zero members, sampled where the original stock has its full rectangular section. These are geometric cross-sectional areas; their percentages are not strength percentages. Bending, shear, grain, notch stress concentration and bearing must be calculated separately.
Member
Gross in²
Minimum sampled net in²
Area retained
P0
64.00
51.33
80.2%
C0
36.00
24.89
69.1%
R0
80.00
54.43
68.0%
J0-0
32.00
27.93
87.3%
T0
60.00
55.50
92.5%
B0
48.00
41.58
86.6%
CRITICAL · T0–T7 / R0–R7 / C0–C7 / cupola rings
Center connection capacity remains unresolved
The saved baseline and historical perimeter variant retain straight lower-foot tongues without positive withdrawal restraint. The default top-entry variant now has actual flared feet, exact matching bottom-entry cavities and removable wooden pegs. Their nominal geometry passes, but the one-inch minimum receiving-post cheeks are not structurally qualified.
Design response: Resolve neck, cheek, bearing, peg, splitting and block-shear demands from the cupola/ring/tie forces. The default foot is an adaptation of a documented housed-dovetail family, not verified hidden joinery from the reference building. Do not assume the polygon or plywood alone supplies ring action.
HIGH · R0–R7 to C0–C7
Main-rafter tongue exceeds the receiver-based proportion
The generic width rule uses the 8-inch rafter: 8/3 = 2.667 inches. In a 6-inch receiving post, nominal cheeks are only (6 - 2.667)/2 = 1.667 inches before neighboring cuts. TFEC 1-2019 §§3.4.10–11 use the receiving member and require each cheek at least the mortise width for the prescribed tension-joint provisions.
Design response: Redesign this joint from the receiving post and load demand. A broader head is not a remedy for thin cheeks. A dovetail is a different connection requiring its own neck, bearing and splitting/block-shear checks.
HIGH · Unchanged generic two-inch shoulder tenons in the saved baseline
Two-inch insertion is not a ready-made pegged tension joint
No peg location or end distance is modeled. For illustration, the TFEC full geometry factor calls for 4D loaded-end distance in a softwood tension member: a 3/4-inch peg alone needs 3 inches from peg center to the loaded end. The current two-inch tongue cannot provide that distance.
Design response: Resolve species, peg diameter, receiving-face edge distances and joint arrangement together; do not simply drill the existing tongues. This comparison does not assign a capacity or prohibit every alternative tested detail.
HIGH · R/P heels and J/B seats
Outer seats carry gravity but do not lock against uplift
R0 bears across the 8 × 8 post head (64 in² nominal horizontal footprint). Each short rafter has approximately 12 in² of horizontal bearing on its ring beam. These are real support surfaces, not merely the colored cavity edge seen in the screenshot. No rated uplift or sliding restraint is modeled.
Design response: Keep broad gravity bearing; check heel/block shear, remaining rafter section and the signed force direction. Retain or adjust the seat only after those checks. Add a designed restraint for force reversal; a deeper notch alone is not a solution.
HIGH · K/B/P families and foundations
Braces, eave-ring joints and post bases need a complete lateral system
All 24 main braces now use full 2 by 6 inch stock, matching one-inch face housings and 48 physical half-inch wooden pegs. Local withdrawal and fit checks pass; their bearing, peg and reduced-section capacities remain unverified. Eave-ring joints share post heads with other cuts. Foundation hardware is a geometric proposal, and enclosed-wall sheathing and attachments are not designed.
Design response: Trace wall/roof shear through collectors, braces or shear panels, post joints and foundations. Check both wind directions, load reversal, combined notches and erection stability.
HIGH · CC/CR/PLY families and upper rings
Cupola ceiling and roof require attachments
The horizontal half-inch plywood and eight exposed horizontal ceiling spokes now follow the user-confirmed arrangement. Ceiling spoke 4 × 6 sizes and roof-rafter 2 × 6 depths are assumptions. Center miters touch but do not themselves resist separation. Finish boards are not assigned an invented thickness.
Design response: Design center and perimeter connections plus plywood grade, panel joints, edge blocking and fastening. Do not credit the plywood as a diaphragm until its complete boundary load path is specified.
REVIEW · Historical keyed version
Earlier prototype is not verified stronger
The earlier model used algorithmic keys and larger-looking interlocks. Its own engineering review recorded severely reduced webs and unresolved raising/tool access. Those shapes were not a verified traditional joinery schedule.
Design response: Retain useful viewing features and compare real housings/shoulders, but do not restore arbitrary keys as a structural fix.
REVIEW · All modeled recesses and mating timber solids
Nominal cavity fit passes independent checks
The actual removed-stock cavities pass independent occupancy and section checks at the recorded numerical tolerances. All timber pair overlaps, registered contacts and connected-solid checks also pass. The former residual meshes were numerical artifacts and are no longer exported or displayed.
Design response: Read the hash-bound cavity-fit audit for methods and tolerances. Geometry agreement does not establish connection strength, shrinkage allowance, tool access or a complete raising sequence.
Inputs still needed
The building is confirmed enclosed. Actual location, species/grade/moisture, assembly weights, openings and foundation details remain unresolved. A timber-frame structural engineer needs those inputs to size the final joints and verify gravity, uplift, lateral and erection cases.
Vermont Timber Works F-6 joint sheet, detail 7 — The kingpost/bottom-chord detail labels a double tenon, with pegs; it does not show a double dovetail. The post continues below the chord. This is a different structure, not an approved replacement schedule.
TFEC Bulletin 2018-13: Wedged Dovetail Tenon Joints — Pages 2–5 and 9: through wedged half-dovetail family, full matching bearing, cheek proportions and full-depth head recommendation. Required shear housings are outside its scope. Its 8×10 beam/10×10 post example does not qualify this 6×6 cupola post.
Timber Frame HQ: kingpost-to-tie wedged tenon — Documented Windham Congregational Church example: vertical through half-dovetail, two pegs and top-inserted hardwood wedge. Different orientation and member arrangement from a radial tie ending at a cupola post.
Timber Frame HQ: upper kingpost joinery — Rafter-to-kingpost precedent uses a diminished housing and tenon. It supports evaluating housed bearing and retention instead of requiring a flare at every connection; its oak dimensions are not adopted.