Art. II. Making a Copper Trade Kettle, by J. Gottfred. Photos by A. Gottfred.
In this article I will provide step-by-step instructions for making a copper kettle. The kettle itself is based on the lidded, straight-sided trade kettles sold by the Hudson’s Bay Company in the 1830’s or ‘40’s. It features a 'cramped' (dovetailed) bottom seam and a folded side seam. This seems to have been the style just before the introduction of the 'spun' pot, which has no seams at all. Earlier kettles of this type also used cramped side seams.
I have chosen this model as a beginner's project because the folded side and cramped bottom do not require solder to hold them together. This means that you don’t have to worry about the pot springing open should you heat it up too much during the tinning process!
This project also includes one other minor deviation from the originals– the edge of the lid and lip are simply folded over, rather than wrapped around a wire. Wrapping a wire adds unnecessary difficulty to a beginner project, and on a small kettle it is not required for strength.
The size of the kettle is within the historic range, and is perfect for use as a small personal 'mess tin'. Before proceeding, I strongly recommend you study the techniques described in 'Tinsmithing', Vol. XIV, pp. 1-22.
Copper Trade Kettle— The finished HBC-style trade kettle. Photo by J. Gottfred.
For this project you will need the following tools:
Tin snips (Aircraft aluminum snips are best, since they give more leverage on the thick copper.)
Heavy-duty soldering iron (120 watts)
12" length of 3 ¾" diameter seamless pipe with a ¼" wall, with the ends cut squarely.
12" length of pipe of diameter less than 3 ½" and greater than 2", with the ends cut squarely.
Approx. 4" length of solid steel cylinder with diameter less than 3 ½" and greater than 2".
A hard, flat edge over which copper can be pounded to a right angle. (1/4" X 4" X 18" mild steel bar stock works well, or use the edge of a table saw, &c.)
12" length of 1" diameter steel pipe or solid steel, cut square
Vise capable of holding the largest pipe.
Ball peen hammer
'0000' steel wool
Mask with appropriate filter to prevent inhalation of flux fumes
Marking gauge (not necessary, but extremely useful)
.022 ‘half-hard’ copper sheet.
.040 ‘half-hard’ copper sheet.
¼" copper wire.
1/8" copper wire.
½" copper rivets (available form leather working suppliers)
Safety flux– lead-free.
Pure tin (bars are best).
6" length of 1" x ¾" mild steel bar, ends cut squarely (for seaming tool).
Building the Seaming Tool
You will need to use a special tool to join the sides of the kettle. Fortunately, it's easy to make. You will need a piece of mild steel bar stock 1" by ¾" wide and about 6" long. This should be readily available from metal suppliers.
Clamp the bar into your vise and file the face so that it is nice and smooth. Any saw tooth marks or filing marks will mar the surface of your copper.
Select a 1/8" wide file. (I use the edge of a 1" metal file.)
Carefully file a groove through the center of the face. File it down the long dimension (i.e., 1" long, not 3/4" long). Make the groove 1/32" deep.
Round off the edges of the tool to prevent marking the copper.
Mark your tool as a 1/8" seam tool for future reference.
Seam Punch— The completed seam tool (punch).
Preparing the Mandrel
The next step is to prepare the mandrel that you are going to use to form the kettle body.
For the kettle's main mandrel, I used a 3 ¾" (outside diameter) seamless pipe with a ¼" wall. All of the measurements in this article assume that you are using the same. This pipe is readily available at metal suppliers. I suggest that you avoid using scrap because you need a piece that is cut square and has smooth sides.
Clamp the pipe in your vise and touch up the face to remove any deep saw marks. Be careful not to get carried away and file the face out of square or your kettles will be lopsided!
Slightly round off the outside edge of the pipe. This will help the kettle go on and off the mandrel, and prevent the edge from cutting the copper.
Determining the Correct Material Size for the Mandrel
Now you will need to determine the correct material length to use with the mandrel and the 1/8" seaming tool. You may need to cut several test strips of the copper material that you will use for the kettle, check the fit on the mandrel, and test the seaming tool.
Measure the outside diameter of the mandrel.
Multiply the diameter by 3.14.
Add three times the width of the groove in the seaming tool. For the 1/8" tool, add 3/8".
Add another 1/8" for ease.
Final width of material for the 3 3/4" diameter mandrel is 12 7/16".
Cut a strip of copper 12 7/16" long by 1" wide.
Mark 1/8" from each end of the strip.
Using the straight-edged mandrel, hammer with the raw hide hammer to fold one 1/8" end down 90°.
Flip the piece over, and using a thin ruler, continue to work the 90° fold over into a U-shaped channel.
Fold the other end to form a U-shaped channel, but make sure that it bends in the opposite direction. One will go up, the other will go down.
Bend the test strip on the mandrel. Bend it smoothly by pushing your fingers along the copper– this will keep the copper from kinking.
Hook the two U-shaped channels together.
Place the linked copper strip on the smaller round mandrel, and use the seaming tool to punch the seam closed. The result should be a tightly-locked circle.
Test the fit of the circle on the large mandrel. It should fit over the mandrel as tightly as possible, yet be loose enough that the copper will slip easily over the pipe. Continue with these tests until you find just the right width of material required for your seaming tool and this mandrel.
For future reference, mark the mandrel with the material width required and the seam width used.
Kettle Body Template— The kettle body should be cut out as shown above. Fold lines are shown as dashed lines. 'Over' means fold up from the page, 'under' means fold down from the page.
Cutting Out the Kettle Body
You have determined the width of material that is required for the kettle body. You must now decide how tall the body should be. I chose a finished height of 5".
Once you've chosen a finished height for the kettle, add 1/2". For this example, the dimension of the required piece is 5 1/2" tall by 12 7/16" wide. Cut out the piece from the .022 copper sheet.
Mark 1 1/4" in from the top edge.
Mark 1/4" in from the bottom edge and the right edge.
Mark 1/8" in from the left edge.
Cut out the 1 1/4" by 1/8" rectangle on the top left and the 1 1/4" by 1/4" rectangle from the top right. Cut out the 1/8" by 1/4" rectangle from the bottom left and the 1/4" by 1/4" rectangle from the bottom right.
Mark 1/4" in from the top edge.
Mark 1/8" in from the right edge.
Using the straight-edged mandrel and the ruler, fold the top 1/4" over into a U-shaped channel. Set the kettle body aside.
Preparing the Kettle Body Lip
Next, you must prepare the kettle body lip which will be attached to the kettle body. It serves to prevent the lid from being jammed on too tight, as well as to form as tight a fit as possible around the lid.
Subtract two times the seam allowance from the body width. In this example, subtract 1/4" (2 X 1/8") from 12 7/16". The resulting width of 12 3/16" is the width for the kettle lip.
Cut out a piece of .022" copper plate 12 3/16" wide by 1 1/4" tall.
Mark 1/4" in from the top (long) edge.
Fold the 1/4" edge over to form a U-shaped channel.
Gently tapping the U bend, close the gap to form a folded lip. It is best to hammer to the inside of the lip, not right on the edge. Do not flatten the edge, leave it as a stronger 'open bend'.
Fitting the Body Lip to the Kettle Body
Before you can fit the lip to the body, you must be clear on which piece is the inside vs. the outside. On the kettle body, the inside is flat, the outside has the U-shaped fold sticking up. On the body lip, the outside is flat, and the inside has the extra thickness of the folded lip.
Orient the body lip on the kettle body. The body lip piece's inside surface will face the kettle body's outside surface. The body lip's folded edge will be towards the bottom of the kettle, and the unfolded upper edge will slip under the U-shaped channel on the kettle body.
The lip piece should slightly overlap the side edges of the kettle body. Let it overlap about the same on each edge.
Hammer down the U-shaped channel on the kettle body so that the body lip is pinched.
Apply safety flux (lead-free) to the pinched edge, and solder with lead-free solder or pure tin.
Kettle Lip— Detail showing the kettle lip and its orientation with the side seam fold. (The top of the kettle is at the bottom of the picture.)
Forming the Kettle Body
The next step is to form the kettle body and prepare the bottom.
Identify the outside of the kettle body. The inside is flat, the outside has the extra thickness of the body lip.
Bend the 1/8" seam edge (not the portion with the lip) to form a U-shaped channel. The metal must curve from the outside to the inside.
Mark 1/8" in on the ¼" seam tab on the other end, and bend the U-shaped channel from inside curving to the outside. (Looking at the outside of the kettle body, the 1/8" wide seam tab should bend down, and 1/8" of the ¼" seam tab should bend up.)
Using the smaller mandrel, gently bend the kettle body. To avoid kinking the metal, use even pressure and 'knead' the copper around the mandrel.
Engage the two U-shaped edges and place the kettle on the large mandrel bottom first. (It probably won’t go on all the way at this time). Use the 1/8" seaming tool to punch the seam. The resulting seam should be tightly locked.
Punching the Side Seam— The seaming tool is being used to punch the side seam. Note that the kettle body lip does not have a seam, the edges simply overlap
Coax the kettle all the way onto the mandrel. It should go on easily right up until the last ¼" or so, where the extra stiffness of the lip wants to bind. Tap the edge of lip with the rawhide hammer all around the pot rim. This will true up the circular shape of the kettle’s mouth and allow the kettle to slip all the way onto the mandrel.
Remove the kettle and place it on the mandrel top first, allowing the bottom to overhang the pipe end by ¼" (as marked on the kettle bottom.)
Using the rawhide hammer, hammer over the bottom ¼" of the kettle against the ¼" wall of the pipe to form a 90° degree angle. If you are using new half-hard copper sheet, it will take this bending without cracking.
If more than ¼" was folded over in some spots, simply file it off against the inside wall of the pipe. The final bottom should have exactly ¼" all the way around.
Forming the Bottom Lip— The bottom 1/4" of the kettle body is bent over the pipe. The pipe that you select for a mandrel must have a 1/4" wall. Note that half-hard sheet copper will take this bending without cracking.
The Kettle Bottom
The bottom of the kettle is fitted in with a cramped seam (little dovetails) as follows:
Using the drawing compass, scribe a circle on the .022" copper. The diameter of the finished circle should be the same as the outside diameter of the mandrel. For our example, set the compass to 1 7/8".
Cut out the circle.
Draw another circle inside the first with a radius ¼" smaller. For our example, set the compass to 1 5/8".
Draw a line through the center of circle.
Draw two more lines at 60° to the first, dividing the circle into six equal parts.
Draw a line dividing each part into equal halves ; this will divide the circle into twelve equal parts.
On either side of the marks, cut dovetails as shown in the illustration below. (A pattern of only six dovetails is shown for clarity). Avoid the temptation to cut the tabs too deep or you will leak a lot of tin when you get to the tinning stage.
Layout of the Bottom— (Not to scale). The bottom requires a series of dovetails to be cut as shown above. For clarity this illustration shows only six. To be historically correct you should perhaps use eight. For this project I suggest you use twelve as it makes it easier to fit the bottom.
Dovetailed Bottom - The bottom ready to be attached.
If you wish to mark your kettle by punching your name or mark on the bottom, now is the best time to do it. The outside is the side without the lines scratched on it.
Using needle-nosed pliers, bend the tabs up 90°.
Test the fit of the bottom on the kettle. It should be very close to perfect. You may need to adjust a few tabs to get the bottom to nestle just right.
From the inside of the kettle, bend the tabs back over the bottom lip. Place the kettle back on the mandrel and go around the bottom with the rawhide hammer, pinching everything nice and tight.
You have now completed forming the kettle body.
Attaching the Bottom— Bend the tabs back over the bottom lip of the kettle and then place the kettle over the mandrel and hammer around the bottom edge to clamp everything tight. Note that dovetails are on outside of kettle.
The Lid Sides
The next task is to form the lid. We begin with the lid sides.
Cut a piece of .022" copper 1 5/16" wide and an inch longer than you need to go around the kettle rim.
Wrap the copper strip around the kettle rim. The correct spot is just below the soldered part of the rim. (Don’t wrap it around the wider lip 1" below the rim). The overlap along the length of the strip should not exceed about 1". Mark the exact length. For the example kettle, the length marked should be around 12 ½".
Add three times the seam width, plus 1/8" for ease, to the measured length. For the example, it should be about 13".
Mark along the bottom edge of the strip ¼" in from the edge. Mark ¼" in from the right side and 1/8" in from the left side.
Cut out the ¼" by ¼" rectangle and the 1/8" by 1/8" rectangle.
Using the straight-edged mandrel, fold the bottom ¼" over and hammer it down on the other side. As with the body lip, don’t flatten the copper completely, just bend it enough so that the edge touches the other side.
Identify the outside and the inside of the lid sides. The inside is flat. The outside has the folded edge on it.
Bend the seam tabs as with the kettle body. Looking at the outside of the lid side, the 1/8" wide seam tab should bend down, and 1/8" of the ¼" seam tab should bend up to form two U-shaped channels.
Using the large pipe mandrel, bend the lid sides and hook together the seam channels. Using the 1/8" seam tool, punch the seam.
Test the fit of the lid sides on the kettle. It should go on and off easily.
Measuring the Lid Sides— Wrap the side piece around the kettle top and mark in the manner shown above.
Extra Lid tops— Extra lid tops act as spacers so that you can get the lid just the right size. Save these spacers for the next time you wish to build the same size of kettle.
The Lid Top & Attachment to Sides
The lid top will not have the same diameter as the kettle bottom. You will find that it needs to be about ¼" larger in diameter than the mandrel that you used to form the bottom. The best method to find the perfect size is as follows:
Cut out a circle of copper ¼" larger in diameter than the diameter of the mandrel. (E.g. For the 3 ¾" diameter mandrel, set the drawing compass to 2".)
Place the copper circle over the end of the pipe so that it overhangs evenly all around. (This is easiest to do if you set the pipe vertically in the vise.)
Hammer down the edges of the copper to form a 90° lip all around the circle.
Test the fit of this circle on the lid sides (it won’t fit!).
Place this 'undersized lid top' back on the pipe, and measure the diameter of the pipe with it in place. Go back to step 1 and keep adding more and more lids to the pile until you get to the size that fits the lid sides the best. (Probably about the fourth one or so will work)
Keep the 'extra' lid tops for future use. In fact, leave the first one on the mandrel to help prevent scratching the real lid during the next step in the process.
Nestle the lid sides within the lid top and place it on the mandrel, top down. Work your way around the lid top's rim, gently hammering in the edge to pinch the lid sides firmly. Close up all the gaps. You will need to go around several times until it is perfect.
Apply safety (lead-free) flux to the inside edge of the lid and the seam. Solder from the inside using only 100% pure tin. You must not use plumber’s solder for this work ; it contains antimony as a lead substitute, to allow the solder to melt at a lower temperature than pure tin. Antimony is less toxic than lead, and is safe in small amounts for water systems, but it is not recommended for cooking pots!
Forming the Lid Top— Using extra lid tops as spacers, hammer down the edges to form a lid with a 1/8" lip.
Attaching the Lid Top to the Sides— Hammer around the edge of the lid lip until the gap between the lip and the side of the lid top is gone.
Soldering The Lid — Solder the lid using only pure tin and safety flux. Apply the flux to the inside of the lid. Heat the lid from the outside with the torch and apply the tin to the inside. The heat will draw out the tin, making a perfect seam every time. (Note the use of welders gloves for handling the hot metal)
The Soldered Lid — The soldered lid is now ready for the attachment of the pull ring. Later, you will tin the whole lid.
The Kettle So Far — The kettle is now ready for the attachment of the bail and the pull ring on the lid.
The bail (handle) is made from 1/8" solid copper wire. It is attached to two lugs, which in turn are attached to the kettle body.
Form an eye in the end of the 1/8" copper wire. This is easiest to do if you wrap the wire around a nail a couple of inches from the wire's end, then cut off the excess wire just at the point where it overlaps to form a complete circle. You can then easily form the final eye.
Determine where on the kettle you wish the bail to be attached. It should be between 1/4" and 1/2" below the lip. Hold the kettle below the large pipe mandrel, then hold the bail end where you want it on the kettle. If you bend the bail wire above the mandrel and down to the other side of the kettle, the final length of the bail will be perfect.
Form the second eye in the other end of the wire, cut off the excess and check for fit.
From the thicker .040" copper sheet, cut two bail lugs 1/2" wide by 2" long
In each lug, drill three holes just large enough for the copper rivets to fit through. Place one hole in the center, and one 1/4" from each end.
Using the snips, round off the ends of the two lugs. Don't worry about making the ends perfectly round. The originals were apparently cut out with chisels and left quite rough (The same applies to the 'dog bone' later).
Using a file or drill, widen the center of one of the rivet washers so that it will fit all the way down the rivet shaft.
Place a 1/2" copper rivet through the center hole of the lug, and place the bail eye over the rivet followed by the widened rivet washer. Using the 4" diameter solid round mandrel as an anvil, use a ball peen hammer to peen the rivet end, thus locking the bail and washer to the lug. Don't peen it so much that the bail will not move, but do peen it to the point that the bail moves stiffly– you don't want a 'floppy' bail. Repeat with the second lug.
Using one of the mandrels, bend the lug so that it follows the curve of the kettle side.
Hold the lug in place on the kettle side and mark the position of the two lug holes. Drill the two lug holes through the kettle using a bit just large enough for the rivets to pass through.
The 1/2" rivets are too long to use for riveting the lug to the kettle body. You must cut the rivet short at about the spot where the rivet shaft begins to taper. (Cut off the final 1/8").
Using the small round mandrel as an anvil, use the two shortened rivets to attach the bail lug to the kettle. Repeat with the other lug.
The Bail Eye — The bail ends should each have an eye like this.
The Bail Lug—The shape of the bail lug.
The Bail —The bail is attached to the kettle with two bail lugs. Note the rivet washer on top of the bail wire. Also, the bail rivet does not go through the kettle.
The Pull Ring
The next step is to make the pull ring and attach it to the kettle lid using a 'dog bone'.
Bend the 1/4" copper wire around a 1" diameter round mandrel to form a ring. Solder the join.
Cut a piece of .040" copper sheet 3" long by 7/8" wide.
Using the drawing compass, draw a 7/8" circle at each end of the rectangle.
At the center of each circle, drill a hole just wide enough for a rivet to fit through
Scribe a line 5/16" wide from each edge.
Cut out the resulting 'dog bone' shape.
The 'Dog Bone' — The shape of the 'dog bone' (actual size).
The 'Dog Bone' — The 'dog bone' after bending to form the U-shaped channel to hold the pull ring.
Bend the dog bone in half around a 1/4" round mandrel, then bend up each end around the 1/4" mandrel to form a U-shaped 1/4" diameter hump in the middle of the dog bone (see photo).
Position the dog bone over the center of the lid and mark the position of the two dog-bone holes.
Drill the holes in the lid and cut down two rivets as you did with the lugs.
Insert the two rivets, place the ring in the 'U' bend of the dog bone, and place the dog bone over the rivets.
Using the 4" solid round mandrel as an anvil, peen the two rivets to tightly clinch the dog bone to the lid. The ring should flop around loosely.
To add the final touch, you may wish to stamp the volume of the kettle on the lid. (For this size I use '1 Q' for one quart– which is close enough for rock 'n' roll.).
Tining — The kettle must be tinned with 100% pure tin. Bare copper is not food safe for cooking pots, nor is lead-free plumber's solder containing antimony.
The most challenging step is tinning the kettle. (If any members actually know how to do this the 'right' way, please let me know!) This is the technique I use for struggling through the process.
Make sure that you are using only 100% pure tin and safety flux for this process. I have been told that plumber's 'lead free' solder, which contains antimony as a lead substitute, is okay for water pipes but is not safe for cooking pots. Pure tin bars can be obtained from metal alloy suppliers.
Put on some work clothes and boots that you don't mind having liquid tin splash on.
Prepare your work area. Plug in the heavy duty soldering iron and safely secure the propane torch. (I clamp mine to the work bench so that it can't accidentally be knocked over.)
Using safety flux, put a thin coat over the entire inside surface of the kettle body and lid.
Don your goggles, vapor mask (safety flux flumes should not be inhaled), and welder's gloves.
Holding the kettle by the bail (which should be stiff), heat the outside of kettle over the propane torch. Rub the bar of tin on the inside of the kettle until it just begins to smear a thin coat of tin on the inside. Do not overheat the kettle. Apply a little flame at a time as you work your way around the kettle. The kettle bottom is likely to drip a small amount of solder– be careful that these drips do not fall into the nozzle of the torch or you will wreck it.
Once you have gone around the kettle body, the coating of tin that you have applied will be very rough, with patches of bare copper. Continue going around the kettle heating the tin with the torch, and then immediately switching to the soldering iron. Use the soldering iron to smooth out the tin and to fill in any bare patches. When the copper cools too much, reheat it with the torch. Work your way around the kettle in this manner until you have an even, smooth, shiny coating of tin over the entire kettle.
Repeat this process with the lid. I use a pair of vise grips to hold onto the lid at the 'U' bend of the dog bone.
Scrub out the inside of the pot with soap and water to remove the flux residue. Check for water tightness and carefully inspect for bare patches of copper. (You will no doubt find a few). Continue with the tinning process until all the leaks have stopped, and the bare patches have been coated.
The kettle at this point will look horrid. The copper will be various shades varying from dull copper to black. You may have one or two rather large blobs of solder frozen in mid-drip from the kettle bottom. You can deal with the drips by attacking them with the soldering iron. I sometimes prefer to simply file them down and smooth them over with some fine sand paper.
As to the color, you have several choices. You can pickle the pot in an acid bath to remove the oxidation, or you can just scrub it with '0000' steel wool. If you have a polishing wheel that works wonders too. I suggest that you simply attack it with the steel wool or polishing wheel. The discoloration will rapidly disappear.
Wash the final kettle well to remove sanding dust and flux residue. Congratulations! It's now ready for the fire!
Thanks to Randy Chappel for helpful tips when I began working with copper, and for sharing his historic research.
Copyright 1994-2002 Northwest Journal . May I copy this article for my class?