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Project Estimating and Decision Making- My Solutions by Bill Kuhl |
Example Calculations
Balsa Sheets
Step #1 Calculate how many strips are in a sheet 3" wide
1/16" sheet thickness
3" wide sheet / 1/8" strips = 24 strips 10% waste = 24 x .1 = 2.4 Round up to 3.
24 - 3 = 21 good strips in a sheet.
1/8" sheet thickness
(3" wide sheet / 3/8" width of motor stick) x (36" length of sheet / 12" length
of motor stick) 8 x 3 = 24 motor sticks 10% waste = 24 x .1 = 2.4 Round up to 3.
24 - 3 = 21 good strips.
Wing hold downs are made from allowance for waste of motor sticks.
Step #2 Calculate how many sheets needed for 80 airplanes.
1/8" x 1/16" x 36" Strips
160 strips needed 160 total strips / 21 strips in a
sheet = 7. 6 round up to 8.
8 1/16" x 3" x 36" sheets needed.
3/8" x 1/8" x 36" Strips
80 strips needed 80 total strips / 21 motor sticks in a sheet = 3.8 Round up to 4 Sheets.
8 sheets 1/16" x 3" x 36" 4 sheets 1/8" x 3" x 36"
Balsa Sticks
As the sticks are pre-cut, do not need to allow for waste in the cutting process, two extra strips were allowed for handling breakage. Requirements are:
162 sticks 1/16" x 1/8" x 36"
Motor sticks 80 / 3 = 26.7 Round up to 27 sticks + 2 extra = 29 sticks
Calculate Cost based on Requirements:
Balsa Sheet Mail Order Prices
| Quantity |
Sheet Description |
Price | Calculation |
Totals |
| 8 | 1/16" x 3" x 36" | .46 | 8 x .46 | $3.68 |
| 4 | 1/8" x 3" x 36" | .66 | 4 x .66 | $2.64 |
| Subtotal | $6.32 | |||
| Balsa Stripper | $7.00 | |||
| Total | $13.32 | |||
| 2 | CA Glue | 3.00 | 2 x 3.00 | $6.00 |
| 1 | CA Accelerator | 3.15 | $3.15 | |
| Subtotal | $22.47 | |||
| Shipping | $8.00 | |||
| Grand Total | $30.47 |
Balsa Sheet Hobby Shop Prices
| Quantity |
Sheet Description |
Price | Calculation |
Totals |
| 8 | 1/16" x 3" x 36" | 1.50 | 8 x 1.50 | $12.00 |
| 4 | 1/8" x 3" x 36" | 2.10 | 4 x 2.10 | $8.40 |
| Subtotal | $20.40 | |||
| 1 | Balsa Stripper | $8.00 | ||
| Total | $28.40 | |||
| Sales Tax | $1.70 | |||
| Grand Total | $30.10 |
Balsa Sticks Mail Order Prices
| Quantity |
Stick Description |
Price | Calculation |
Totals |
| 162 | 1/16" x 1/8" x 3" x 36" | .10 | 162 x .10 | $16.20 |
| 29 | 1/8" x 3/8" x 36" | .18 | 29 x .18 | $5.22 |
| 10 | 1/8" x 1/8" x 36" | .11 | 10 x .11 | $1.10 |
| Subtotal | $22.52 | |||
| Shipping | $8.00 | |||
| Grand Total | $30.52 |
Balsa Sticks Hobby Shop Prices
| Quantity |
Stick Description |
Price | Calculation |
Totals |
| 162 | 1/16" x 1/8" x 3" x 36" | .35 | 162 x .35 | $56.70 |
| 29 | 1/8" x 3/8" x 36" | .70 | 29 x .70 | $20.30 |
| 10 | 1/8" x 1/8" x 36" | .45 | 10 x .45 | $4.50 |
| Subtotal | $81.50 | |||
| Sales Tax | $4.89 | |||
| Grand Total | $86.39 |
Propellers
80 total planes / 35 props in a package = 2 packages plus 80 – (35 x 2) = 10 more props needed 35 props per package x 3 packages = 105 props 105 – 80 props needed = 25 spares
Cost $10.56 per package of 35 Shipping $6.50
$10.56 x 3 = $31.68 + $6.50 shipping = $38.18 total cost
Rubber
Convert grams to ounces .0596 (weight in grams per inch) / 28.35 (grams
in ounce)
= .002102 ounce per inch of rubber
One pound = 16 ounces, 16 / .002102 = 7611 inches of rubber
Convert to feet: 7611 / 12 = 634 feet
Number of motors: 634 / 2 feet in each motor = 317 motors
If each student receives three motors: 317 / 3 = 105 Motors for Students, Three Motors per Student
Advantages / Disadvantages for Balsa Wood Purchase Options