Nice work to do it with a spreadsheet! I wrote mine in Python. It does render a scale drawing (more for sanity checking) and mitre templates. You save the bike design (in an .ini file) and then it produces output like the below, which I print out, along with the mitre templates, and take to the garage. That's everything I need. It's basically all 2D but does a bit of 3D on the rear-triangle to check the fit of the tyre and chainrings.

On the first frame there was a lot of careful double and triple checking of everything before I cut any tubes but I now just trust it.

BikeCAD looks good but there comes a point where there's just too much detail and it's easier just to match up the fiddly physical parts like dropouts and bridge tubes and things in the real world-- put them where you want them and make sharpie marks etc instead of trying to encode them into the computer as well. And although I can write a bit of code I never get on well with those complicated GUIs that CAD programs have.

Mitres
======
Rendered to tt_ht.png
Top Tube to Head Tube Mitres at (10.00, 23.35, 36.71) from tube top
Rendered to tt_st.png
Top Tube to Seat Tube Mitres at (39.28, 52.56, 65.84) from tube top
Rendered to dt_st.png
Down Tube to Seat Tube Mitres at (577.73, 594.41, 611.09) from tube top
Rendered to dt_ht.png
Down Tube to Head Tube Mitres at (94.68, 111.19, 127.70) from tube top
Rendered to st_bb.png
Rendered to dt_bb.png
Rendered to cs_bb.png
Rendered to lss_st.png
Rendered to rss_st.png
Rendered diagram to side_view.png

Front Triangle
==============

Tube Cuts
---------
Head Tube cut square 140.70
Top tube length between outside mitres: 522.14
Top tube length between inside mitres: 522.63
Seat Tube length from top to BB mitre (at side of frame): 583.00
Down Tube length from inside ST mitre to inside HT mitre: 584.88
Down Tube length from inside BB mitre to inside HT mitre: 596.17
Offset between DT/BB mitre and DT/ST mitre on DT inside centreline: 11.29
Down Tube length from outside BB mitre to outside HT mitre: 579.66
Down Tube length centre to centre: 620.60

Other Metrics
-------------
Stack: 557.97
Reach: 383.89
Trail: 62.18
Front Centre: 593.90
Rear Centre: 420.15
Wheelbase: 998.54
Wheel flop: 18.27mm axle drop over 90 degrees
BB height (ground to centre of BB): 267.00
Pedal clearance: 82.00
Min steerer length threaded: 157.70
Min steerer length threadless: 192.70
Angle between ST and DT: 59.01deg
Angle between DT and HT: 119.99deg
Angle between ST and TT: 73.00deg
Angle between TT and HT: 108.00deg
Chainring radii: 97.02
Approx total mass excluding dropouts: 1.95kg
Flexural Rigidity of Down Tube: 1034.94Nm^2
Approx deflection of Down Tube under 100kg load in centre: 4.72mm
Flexural Rigidity of Seat Tube: 1351.06Nm^2
Approx deflection of Seat Tube under 100kg load in centre: 3.31mm
Flexural Rigidity of Top Tube: 719.20Nm^2
Approx deflection of Top Tube under 100kg load in centre: 4.85mm

Rear Triangle
=============

Tube Cuts
---------
Chain Stay length from inside mitre to dropout: 365.33
Chain Stay length from outside mitre to dropout: 362.50
Seat Stay length centre-centre: 501.91
Seat Stay length from inside mitre to dropout: 474.21
Seat Stay length from outside mitre to dropout: 487.91
Angle between CS and BB: 97.25deg
Angle between CS and dropout: 172.75deg
Angle between SS and ST: 45.61deg
Angle between CS and ST: 63.52deg
Angle between CS centre-line and horizontal: 9.71deg
Rendered chainstays to chainstays.png