Let’s Design a Box John Cobb www.treenshop.com www.treenshop.com/downloads/ john@treenshop.com 466-3973

MAIN TOPICS Making a working drawing An easier way Variations Design choices & arithmetic An easier way Variations Rule of Thirds

‘Design’ Meaning In this context Design means determining all of the box’s measurements One can then make a dimensioned block diagram

Grain Orientation Boxes can be either End grain Side or face grain This discussion assumes end-grain or spindle grain

Suppose we have a very large blank 10 inches square 36 inches long A chunk of burl, for example That is, plenty large enough to make a box any reasonable size. How do we proceed?

a box with an over-fitting lid Select a Lid Type Over-fitting Spigot is on the body Easier to turn and get right In-fitting Spigot is on the lid Let’s agree on a box with an over-fitting lid

Box With Over-Fitting Lid

Box With In-Fitting Lids

Box With In-Fitting Lids Show African Mahogany cigar box with in-fitting lid.

Face-Grain Box

Diameter or Length? We can specify either (or both) Let’s specify diameter first.

Select the Diameter BUT Boxes with a diameter over 4 inches Uneasy to hold Difficult to take the lid off if there is a friction fit. BUT Boxes smaller than 2 inches diameter Have small tolerances Fitting the lid is error-prone

Let’s agree on about 3 inches in diameter or 75 millimeters 15

A TIP I always design using metric measurements as they are MUCH easier to work with. i.e. rounding to the nearest millimeter is easier than rounding to the nearest 64th or 32nd of an inch. There are 25.4mm in 1 inch 16

So, Cut a Square 3 ¼ inches square and 36 inches long from our large block We now need to find the blank length.

How Long Must the Blank Be? Can specify it Or derive it – let’s derive it Decide on the relationship Diameter to height

Diameter vs Height There are many options Height = Diameter (square box) Body Height = Diameter (tall box) Body Height = 2/3 The Diameter Body Height = 3/4 The Diameter Body Height = 0.618 The Diameter And many more …

Select an option Let’s agree on body height = diameter This will be a tall box So body height = 75mm. Show 3 inch tall box in huon pine by Richard Raffan

Select a Proportioning Scheme There are several options: Golden mean or 0.618 the height Lid 1/3 and body 2/3 the height Lid 4/9 and body 5/9 the height Something else entirely Avoid body and lid both ½ the height Show Richard Raffan’s 3 inch mosque box in shee oak. Explain why it looks OK. Show my mosque box – it does not look like 1 to 1 but it is

Select an option Let’s agree on using the golden mean Body height = 0.618 the total box height So, total box height = 1.618 the body height Note that

Some More Selections Specify the chucking waste at each end Specify the waste for the parting cut Specify the length of the spigot

Our Specifications Let’s agree on the following Waste at each end is 3mm (1/8”) Waste at parting cut is 4mm (Narrow parting tool) Spigot length is 10 mm (3/8”)

Now Calculate! Body height is 0.618 total height Body height is 75mm Total height = 75 / 0.618 = 121.36 mm Round Total height to 121mm

What We Know So Far Diameter = 75mm Body height = 75mm (bottom part) Total height = 121mm

Find the Lid Height Lid height = total height – body height Lid height = 121 – 75 = 46mm

Find the Blank Length Blank length is the sum of: Total box height Total waste Spigot length Note that the total waste is: waste at each end + parting waste 3 + 3 + 4 = 10mm

Find the Blank Length The blank length is: 121 + 10 + 10 = 141mm

Check the findings Body height goal = 0.618 total height Body height ratio actual 75/121 = 0.62 waste at body end = 3 + body height = 75 + spigot length = 10 + parting waste = 4 + lid height = 46 + waste at lid end = 3 Total blank length = 141 3 + 75 + 10 + 4 + 46 +3 = 141

The Remaining Dimensions Spigot inside and outside diameters Body inside diameter Body inside depth Lid inside diameter Lid inside depth

Wall Thicknesses 1 ½ to 2mm are the minimums 2mm is about right for a spigot wall 2mm is a bit less than 3/32 inch Body and lid wall thickness must accommodate any decorations such as beads

Select Wall Thicknesses Let’s agree on the following: Spigot wall thickness = 2mm Body and lid wall thicknesses – 4mm Allowing for a bead at the join

Calculate Again! Body inside diameter = Spigot outside diameter = Body outside diameter – 2 x (2mm + 4mm) = 75 – 12 = 63mm Spigot outside diameter = Body inside diameter + 2 x 2mm = 63mm + 4 = 67mm Lid inside diameter = spigot diameter 67mm

Specify End Thicknesses Let the body bottom thickness be 5mm Let the lid top thickness be 8mm Allow for some decoration

More Calculation The depth of the body cavity is: body height + spigot length – end thickness 75 + 10 – 5 = 80mm The depth of the lid cavity is: Lid height - end thickness 46 – 8 = 38mm (Must be greater than the spigot length)

Mark for Parting From body chucking spigot: From lid chucking spigot: Body height + spigot length + + half parting waste 75 + 10 + 2 = 87mm From lid chucking spigot: Lid height + half parting waste 46 + 2 = 48mm These marks should coincide!

Point out the two critical measurements for turning: Parting distance from either end Spigot length

We’re Done There is now available all information to make a dimensioned drawing (What a pain in the …) Use a spreadsheet! One is provided at www.treenshop.com/downloads “Lets_Design_a_Box.xls”

Variations Here are some variations on the straight box. Notice how close the dimensions in all of them are. They show several ways to get to the same result. The 'Straight Box With Body Height 3/4 the diameter' is the only one that is noticeably different.

This gives a square box if the proportioning scheme is also 0.618

The ¾ box is the only one that is significantly different. Observations The square box, the 2/3 box and the 0.618 box are nearly the same The ¾ box is the only one that is significantly different.

Another Design Method Specify the total height Or blank length Specify the diameter Specify a proportion scheme ( Ex: We have a 2” square 24” long.) This is a more normal case. One usually has a turning square and so the diameter is mostly determined. So specify it and then specify the height and the proportion.

Body height is 96% the diameter Proportions are 0.613

1/3 the total length between spigots Thirds Rule of Thumb Measure from lid chucking spigot 1/3 the total length between spigots Mark for parting off For most lengths we use, it works well and the proportions will be near 0.618 Totally accurate for exactly one length http://www.treenshop.com/Treenshop/ArticlesPages/RulesOfThumb_Article/RulesOfThumb.htm Is on my website in the Articles pages: “Rules of Thumb” Keep the spigot length about 3/8” or 10mm and use a narrow parting tool.

Not the same measurements as the example I showed which was 100mm between the chucking spigots

Avoiding Errors The preceding methods are error-prone and tiresome I have found it best to make a spreadsheet Worth the effort if making a lot of boxes http://www.treenshop.com/downloads/ Lets_Design_A_Box.xls

How To Save Some Money Suppose I hold my box blank between centers for roughing out. 4-prong center at the headstock Revolving center with a point at the tailstock

Saving Some Money There will be about 10mm waste at the headstock and 5 to 6mm at the tailstock. That is 16mm waste If I part off with a 3/16” parting tool then there is an additional 6 to 8mm wasted. That’s a total of 24mm waste!

Saving Some Money By holding the blank in a chuck for roughing and using a spigot chuck to turn it, there will be 3mm waste at each end. By parting with a thin parting tool, there will be about 4mm parting waste. That’s a total of 10mm waste. We save 14mm of wood! Show with a square blank in a chuck with shark jaws. Show revolving center with leather washer for support

Saving Some Money Suppose we make 100 boxes using kingwood. Further suppose that kingwood is $40/bdft We save 100 x 14 = 1400mm (55 inches) by conserving waste

Saving Some Money 55 inches of 3x3 is 3.44 board feet Each board foot is $40 Our savings are $137!

Saving Some Money Its even better than that! Since the chucking spigots are not damaged on the end grain, we need not waste them. So our total waste can be as little as 4mm – where we part off

The Lesson Careful design to minimize waste can result in serious savings! When designing, do not rough out expensive blanks between centers; include the chucking spigots in the design where possible Show the 70mm buckeye burl box as an example.

Small Differences Small changes can make a major difference in appearance and visual appeal Check the form vigorously For a new design, consider making a prototype Show the thuya burl dome box. Body = 47; lid = 30; height = 77; 0.618 proportions The dome looks too small for the form. Maybe 4 to 5 would be more attractive. The color is a contributor to this. Show the maple dome box. Body = 45; lid = 45; height = 90; 1 to 2 proportions The size of the dome looks better to me but could be a bit shorter. 4 to 5 proportions would give: body = 50; lid = 40; height = 90

Not Covered Boxes with in-fitting lids Stacked, multi-tier boxes Tall 4-piece boxes Face grain boxes Needle cases & crochet hook boxes

Tall Box in 4 Parts Not covered but added as an extra. Show maple tall box and mahogany tall box with finial

ON THE WEB On my downloads page: www.treenshop.com/downloads/ This presentation TEW_BoxDesign_1.pps The handouts TEW_BoxDesign_1_Handouts.pps The spreadsheet Lets_Design_a_Box.xls

THE END! Use these examples and Change the assumptions Change the proportions To create your own designs

Contact Info John Cobb www.treenshop.com www.treenshop.com/downloads/ john@treenshop.com 466-3973