Sheet metal drafting/Chapter 7

by Ellsworth M. Longfield

 

CHAPTER VII
PLANNING FOR QUANTITY PRODUCTION

Objective of Problem on Quantity Production

Problem 28
ASH BARREL

53. Planning for Quantity Production of an Ash Barrel.— In planning for quantity production, a draftsman must consider every item that has to do with the manufacturing processes to be carried on in the shop. In order to do this intelligently he should make a list of these items similar to the one given below:

1. Dimensions of barrel
2. Type of hoop to be used
3. Blank for body:
1. Weight of material
2. Height after deducting hoops
3. Riveted or locked seams
4. Weight of bottom
5. Type of slat to be used
6. Number of slats required
7. Sizes of rivets required:
1. For attaching slats
2. For attaching upper rim
3. For attaching lower rim and bottom
8. Pattern for body:
1. Over-all dimensions
2. Allowance for lock
3. Locating rivet holes for slats
4. Locating rivet holes for upper hoop
5. Locating rivet holes for lower hoop
9. Pattern for upper hoop and lower hoop:
1. Length of blank required
2. Method of joining ends
3. Spacing rivet holes
10. Pattern for bottom:
1. Allowance for flanging
11. Pattern for slat:
1. Miter cut
2. Size and location of rivet holes
3. Size of wooden core
12. Order in which parts are assembled

Dimensions of Barrel.—The dimensions of the barrel would vary according to whether the job was standard, or special size. Different manufacturers have established their own standards. The sizes given below are common to all, and are best adapted to ordinary needs. A barrel 18 in. in diameter by 26 in. high will be treated in this discussion.

Figs. 155–158.—Galvanized Ash Barrel.

Standard Dimensions for Galvanized Ash Barrels

Diameter in Inches	Height in Inches	Approximate Capacity
24	36	72 gallons
20	26	34 "
18	26	28 "
17½	26	24½ "
14	26	16 "

Type of Hoop.—There are several types of hoops that can be obtained from the jobber. Figure 156 gives a full size cross section of the one generally used.

Blank for Body.—The body of the ash barrel is made from No. 24 galvanized steel. The top and bottom hoops fit into the barrel one-half of their entire width, Fig. 157; therefore, the body blank must be ⅞in.×2 or 1¾ in. less than the total height of the barrel. This would make the blank 24¼ in. wide, but in order to use the sheet metal as it comes from the mill the total height would be reduced to 25¾ in., Fig. 157, and stock size sheets 24 in. wide used to make the body. The riveted seam is somewhat stronger, but since the lock seam can be placed under a slat and protected, it is generally used because it can be made more cheaply.

Weight of Bottom.—The bottom of the barrel should be at least four gages heavier than the sides.

Type of Slat.—Figure 158 shows two types of slats in common use. The three-rib slat is made of No. 24 galvanized steel by means of special machinery. The single-rib slat may be made on an ordinary cornice brake and used with or without the wooden core.

Sizes of Rivets.—In riveting the slats to the barrel, the rivets must pass through two thicknesses of No. 24 gage. This will require a 2½ lb. rivet. The rivets for the upper hoop must pass through one thickness of No. 24 gage iron and $\scriptstyle {\frac {3}{32}}$ in. of steel in the hoop. This will require a 6 lb. rivet. The rivets for the bottom hoop must pass through one thickness of No. 24 gage (the body), one thickness of No. 20 gage (the bottom), and $\scriptstyle {\frac {2}{32}}$ in. of steel in the hoop. This will require an 8 lb. rivet.

Drawing the Section.—A section. Fig. 157, showing the hoops, body, and bottom in their proper positions, should be drawn. The Profile.—The profile of the body should be drawn. The profile of the hoops would be larger than that of the body, but since the pattern for the body and the location of the slats are to be obtained, the profile of the body must be dealt with. This profile is divided into eight equal parts. Fig. 155. Using any two divisions of the profile as centers, the two slats are drawn in their proper positions. The profile. Fig. 155, shows the three-rib slat, but a single-rib slat may be drawn in. A straightedge laid across the slats, in the manner shown in Fig. 155, should clear the body of the barrel; otherwise, the slats will not protect the body when in contact with the edge of the ash cart. If the straightedge touches the profile, the slats must be made larger or spaced more closely together.

Pattern for the Body.—A line of stretchout, Fig. 159, should be drawn and the spacing of the profile transferred to it, with numbers to correspond. Measuring lines are drawn through each division of the stretchout. One-half inch locks are set off on each end of the pattern. The top and bottom lines of the pattern are drawn 24 in. apart. A distance of $\scriptstyle {\frac {7}{16}}$ in. should be measured in from the top and the bottom lines. These lines will serve as center lines for the rivet holes of the hoops and slats. From Fig. 158 the distance from center to center of the ½-inch edge of the single-rib slat is found to be 1⅜ in. This will also be the distance between centers for rivet holes in the body. One-half of this distance $\scriptstyle {\frac {11}{16}}$ in., is placed on each side of every measuring line in the stretchout. It should be indicated on the drawing that these are to be punched for 2½ lb. rivets. Another line running horizontally through the center of the pattern should bear the same spacing for riveting the center of each slat. The rivet holes for the upper and lower hoops are located midway between measuring lines 1 and 8, 7 and 6, 5 and 4, 3 and 2 as shown in Fig. 159. This allows for four rivets. Therefore, the distance between centers for each pair of rivets will be one-fourth of the circumference. In order to avoid riveting through the seam, the first hole is spaced $\scriptstyle {\frac {1}{16}}$ of the circumference, and the last hole $\scriptstyle {\frac {3}{16}}$ of the circumference away from the circumference line No. 1 of the stretchout. The rivet holes for the drop handles should be placed at ⅔ of the height of the barrel as shown. Fig. 157.

Upper and Lower Hoops.—The upper hoop must be fitted inside of the body. In order for the hoop to go inside, some allowance

Figs. 159–163.—Drawings for Patterns of Ash Barrel.

must be made for the thickness of the metal. Figure 156 shows a "dot and dash" line. This line is called the neutral axis, and takes its name from the fact that the metal at this point remains stationary while that on either side stretches or shrinks as the hoop is formed up. It will also be noticed that this line is not in the center as it would be if the cross-section were rectangular in shape. According to Fig. 156, this line passes the "square corner," against which the top of the body rests, at a distance of $\scriptstyle {\frac {5}{32}}$″–$\scriptstyle {\frac {3}{32}}$″, or $\scriptstyle {\frac {1}{16}}$″. The rule is to double this quantity and add one thickness of the metal body. Following this rule would give $\scriptstyle {{\frac {1}{16}}''+{\frac {1}{16}}''+.025''=.150''}$ or $\scriptstyle {\frac {5}{32}}$ (nearly). This should be subtracted from the diameter of the body (18″−.15″=17.85″) and the remainder multiplied by $\scriptstyle {\pi }$, in order to get the length of the blank for the upper hoop, Fig. 160. This would give 17.85″×3.1416=56.077″, for the length of Fig. 160, The pattern for the lower hoop, Fig. 161, must be shorter than that for the upper hoop, because the lower hoop must go inside of the bottom of the barrel as well as the body, Fig. 157. Using the rule given above:

${\begin{matrix}\scriptscriptstyle {{\text{Diam.}}-}\\\scriptscriptstyle {18\prime \prime }\end{matrix}}$ ${\begin{pmatrix}\scriptscriptstyle {\text{1 thickness body}}&\scriptscriptstyle {+}&\scriptscriptstyle {\text{1 thickness bottom}}&\scriptscriptstyle {+}&\scriptscriptstyle {\text{allowance for hoop}}\\\scriptscriptstyle {.025}&\scriptscriptstyle {+}&\scriptscriptstyle {.037}&\scriptscriptstyle {+}&\scriptscriptstyle {.125}\end{pmatrix}}$ $\scriptscriptstyle {\times }{\begin{matrix}\scriptscriptstyle {\pi }\\\scriptscriptstyle {3.1416}\end{matrix}}\scriptscriptstyle {=}{\begin{matrix}\scriptscriptstyle {\text{length of blank for lower hoop (Fig. 161)}}\\\scriptscriptstyle {55.95''}\end{matrix}}$

Since the ends of the hoops are to be butt-welded no allowance need be made for joining. There are to be four rivets in each hoop; therefore, the distance between the rivet holes on centers would be equal to one-fourth of the circumference. Placing half of this space, or ⅛ of the circumference, at each end would avoid a rivet hole through the weld. The spacing of the rivet holes in Fig. 160 will not be the same as that in Fig. 161, because of the difference in length of the blanks.

Pattern for the Bottom.—The bottom of the barrel has a ⅞-inch flange turned for riveting to the body. This flange can be worked up by hand, but it is generally pressed in a machine. Figure 162 shows a section of the bottom, and the pattern with allowance for flanging. If ⅞ in. were added to each side of the diameter of the finished bottom, the machine would turn a flange deeper than ⅞ in. The rule for finding the correct diameter of the pattern is: Find the total surface area of the finished piece and convert this area into disc inches. Applying this rule,

$\scriptstyle {\text{Diameter}}^{2}\times .7854=(18'')^{2}\times .7854={\text{area of bottom}}=254.47\ {\text{sq. in.}}$

$\scriptstyle {\text{Circumference}}\times {\text{Height}}=18''\times \pi \times 7/8={\text{area of flange}}=49.48\ {\text{sq. in.}}$

$\scriptstyle {\text{Total or combined area}}=303.95{\text{sq. in.}}$

$\scriptstyle {\sqrt {{\text{Area}}\div .7854}}={\sqrt {303.95\div .7854}}={\sqrt {387}}=19.67'',{\text{Diam. of pattern.}}$

The nearest fraction to . 67 in. to be used would be $\scriptstyle {\frac {43}{64}}$ in.; therefore, the diameter of the pattern for the bottom, Fig. 162, would be 19 $\scriptstyle {\frac {43}{64}}$ in.

Pattern for Slat.—The top and bottom of the slat are "cut back" on an angle of 60° as shown in Fig. 163. An elevation showing the miter cut at a 60° angle should be drawn. Extension lines are carried from the profile to the miter line. A line of stretchout is drawn and upon it the spacings of the profile are set off. The measuring lines are drawn in. The intersections from each point in the profile are traced to the miter line, and thence to the corresponding line of the stretchout. These intersections are connected by straight lines to obtain the miter cut. If the wooden core is to be used, some means for closing the end must be provided to prevent the core from slipping out. If the proper machine is available, an end may be "pressed on" the metal slat. Another method is to provide laps as shown by the dotted fines on the pattern. These laps may be fastened by one rivet. Holes for riveting the slats to the barrel must be laid out to correspond exactly to the spacing of holes in the body pattern, Fig. 159.

Assembling the Barrel.—The body blanks are cut from sheets of No. 24 galvanized steel 24 in. wide by 120 in. long. Rivet hole centers are transferred from the master pattern, and holes are punched in each blank. Locks are then turned in the stovepipe folder, after which the body blanks are formed in the rolls and grooved in the grooving machine. The slats are riveted to the body. The upper hoop is then riveted on. The bottom and the lower hoop are then placed in the barrel and riveted in place. The drop handles are attached to the barrel and it is then ready for final inspection.

54. Related Mathematics on Ash Barrel.—In order to estimate the cost of the article to be made by quantity production methods, each item must be considered separately.

Sample Problem.—Figure the cost of stock entering into the manufacture of 500 ash barrels such as shown in Fig. 157.

Item 1. Cost of 500 Body Blanks. Fig. 159.

Size of sheets 24"×120", No. 24 gage

Area of sheet 20 sq. ft.

Number of sheets required—250 (2 bodies from each sheet)

Total area of 500 body blanks 250×20 = 5000 sq. ft.

Weight of No. 24 galv. steel per sq. ft. =1.156 lb.

Total weight of bodies, 1 . 156×5000 = 5780 lb.

Cost of 500 bodies at 8.5¢ per lb. = $491.30

Item 2. Cost of 500 Bottom Blanks.

Size of blank = 19 $\scriptstyle {\frac {43}{64}}$" diameter

Size of sheet required, 24"×120' , No. 20 gage

Number of blanks from each sheet, 6

Number of sheets required, 500÷6 = 84

Total area of each sheet = 20 sq. ft.

Total area of 84 sheets (84×20)=1680

Weight of No. 20 galv. steel per sq. ft.=1.656 lb.

Total weight of metal required (1680×1.656)=2782 lb.

Cost of 500 bottoms at 8.5¢ per lb.=$236.47

Item 3. Cost of 4000 Single Rib Slats.

Size of blank, 24"×2⅞", No. 24 gage

Size of sheet required, 24"×120"

Number of blanks from each sheet, 41

Number of sheets required, 4000÷41=98 sheets

Weight per sheet, 23. 12 lb.

Weight of 98 sheets, 98×23.12=2265.76 lb.

Cost of 4000 metal slats at 8.5¢ per lb. =$192.59

Item 4. Cost of Hoops.

Length of upper hoop=56.07"

Length of lower hoop=55.95"

Combined length of upper and lower hoops=112.02"

Total length of 500 upper and 500 lower hoops,

$\scriptstyle {\frac {(500\times 112'')}{12}}=4666$ ft.

Weight of 4666 ft. at 1.195 lb. per ft.=5575.87 lb.

Plus 5 per cent for waste=5854.66 lb.

Total cost of hoops at 11¼¢ per lb.=$658.65

Item 5. Cost of Rivets.

Total number of 2½	lb. rivets required	(500×	52)	=	26,000
Total number of 6	lb. rivets required	(500×	4)	=	2,000
Total number of 8	lb. rivets required	(500×	4)	=	2,000
Total number of 1½	lb. rivets required	(500×	16)	=	8,000

Flat Head Tinner's Rivets are sized by their weight per thousand; i.e. 1000 rivets of 2½lb. weigh 2½lb.

Weight of	26000-2½	lb. rivets	(	26	×	2½	)	=	65 lb.
Weight of	2000-6	lb. rivets	(	2	×	6	)	=	12 lb.
Weight of	2000-8	lb. rivets	(	2	×	8	)	=	16 lb.
Weight of	8000-1½	lb. rivets	(	8	×	1½	)	=	12 lb.
Total weight of all rivets								=	105 lb.
Total cost of rivets at 40¢, average price per lb.=$42

Item 6. Drop Handles.

Total number of handles required, 500×2=1000
Weight of 36 handles and lugs, 15.66 lb.
Weight of 1000 handles (1000÷36)×15.66=444.18lb.
Cost of 1000 handles at 30¢ per pound=$133.25

Summary of Costs.

Item 1	$491.30
Item 2	236.47
Item 3	192.59
Item 4	658.65
Item 5	42.00
Item 6	133.25
Total cost	$1754.26
Cost per barrel	$3.51