Puget Sound Knappers

How to Make Copper Cap Boppers¹

By James C. Keffer

Materials:

1. Copper plumbing caps, sizes 1/2" to 2"* (available at most major hardware stores).
2. Wood for handles, sandpaper in 80, 100 and 220 grit for handles.
3. Wood finish - polyurethane (my preference) shellac, or varnish for handles.
    This keeps wood from shrinking, reducing the chance that the cap will loosen.
4. Hardened lead: Hard lead resists deforming and helps keep the bopper end round and uniform.
    Wheel weight lead is harder than pure lead - adding antimony, zinc or tin.
    increases hardness. I use my own homemade lead alloy - pure lead and about 10% zinc.
    This gives me an alloy hardness of 33-35 on the Brinell Hardness Scale (BHN) as compared to pure
     lead.
    that is 5 on the Brinell Hardness Scale (using a Lee Lead Hardness Testing Kit).
5. Epoxy - Loctite Heavy Duty Professional Grade (available at most major hardware stores).
6. Sandpaper (80 grit) or Sandblaster and sand for inside of copper caps.
7. Sandpaper (80, 120 & 220 grit) for finishing handles.
8. Acetone and paper towels for epoxy cleanup.

Tools:

1. Doming punch set or doming anvils. .
     a. Example of doming anvils (homemade).
         i. 1/2" and 3/4" round bar with rounded ends.
         ii. Hitch balls rounded to size, 1-1/2" and 2".
         iii. Ball peen hammer 1" (1-1/4" not shown).

2. Hammers for doming, ball peen or auto body hammers.
3. Wood lathe or carving tools for handle.
4. Pot to melt lead in, burner with which to melt lead (propane torch, propane burner or a
gas stove will work).
5. Mixing cup and stirrer for epoxy.
6. Clamps for holding caps to handles while epoxy dries.
7. Paint brushes for applying wood finish.

Procedure:

The Cap

First, start by doming the copper caps.

The objective is to get the copper cap as round and smooth as possible. The more round the
cap is the better control you'll have in striking flakes. You want to be able to strike the rock
with a single point of the bopper end as shown below.

Procedure Using an Air-Over-Hydraulic Mini-Press (Home made)

First, select the doming punch for the copper caps. Note the difference in caps, the ones on the right are taller and will have more area to either add more lead or suface area to glue.

This is the Air-Over-Hydraulic Press I built and use to press the domes on the caps. I prefer to use the press as it says wear and tear on the punches caused by hammering

Doming block in the Press

Fit the cap in the block

Fit the punch into the cap

Press the air actuator on the press

Voilà - perfectly domed cap every time!

Filling with Lead Alloy - I make a harder lead alloy by adding about 10% zinc. Zinc weights about 80% as much as lead but is much harder. Pure lead is a 5 on the Brinell Hardness scale, my lead alloy is 35 on the Brinell Hardness scale as tested by a Lee Hardness Tester. The harder lead is less likely to deform, especially on harder rock.

I use wood block to hold the caps when I pour the lead. The block allow me to level the caps and get a consistent, balanced weight! For the larger caps I place them in a vice and level them.

To test that the lead is even in the cap I test them to see if they will stand upright without tipping:

Next clean the inside of the cap with sandpaper or a small sandblaster (I use either a small
cabinet sandblaster or an inexpensive siphon sandblaster).

Siphon sandblaster ($20):

Level the cap and secure (I use a vice and bubble level).

Then melt some hard lead/lead alloy and pour into the cap. Leveling the cap helps to balance the weight
distribution of the lead creating a more consistent bopper.

Be sure and only fill the cap up to the end of the dome. This serves two purposes, it allows
sufficient area on the handle and inside the cap for the epoxy to adhere and also places the
weight forward making the bopper more efficient at delivering the energy to the platform on
the rock.

Caps filled with lead just to top of dome:

Let the cap/lead cool. There is a high degree of probability that the lead will not adhere to
the copper, particularly if using hard head. I find the easiest way to secure the lead to the cap
is with epoxy applied when attaching the cap.

Other means of securing the lead involve 'tinning' the cap with solder prior to pouring the
lead. This doesn't work as well with hard lead containing either zinc or antimony.

Another technique is to 'punch' the lead. Place the cap on a sandbag or similar surface and,
using a blunt punch (or carriage bolt), hammer the lead to where is swells within the cap
thereby creating a tight fit. Again, this also doesn't work as well with hard lead. Since epoxy secures the lead to the cap and the hardened lead doesn't deform, I prefer to use harder lead and epoxy.

Roughen up the interior of the cap with sandpaper or sandblasting one more time to take off
any residue or glazing cause by the hot lead. This will help insure the epoxy has the best
opportunity to create a strong bond.

The Handle

Making a handle can either be very simple or quite elaborate. Handle styles are a matter of
personal preference but most are usually 3-5 inches in length and made of hard wood. Oak, walnut, maple, alder, fir or any other wood that does not contain oils (such as teak which does not take glue well) will work for a handle.

A wood lathe allows for fast and easy turning of custom-fit handles. A variety of shapes,
sizes and styles can be created relatively quickly. Alternatively, carving/whittling can
achieve the same end although with considerably more work. The simplest and fastest way
to make a handle is to start with a wood dowel and whittle one end to fit the cap snugly.

Turning a handle on a wood lathe:

Checking the fit - a handle that allows the cap to fit flush is more comfortable to use. The
caps should fit snug but not too tight to allow enough area for the epoxy to form a strong
bond.

Checking the fit:

Attaching the Cap to the Handle

Mix a good two-part epoxy according to the directions. Use only enough epoxy for the
number of caps you can attached in the curing time specified by the epoxy instructions.

Liberally coat the inside of the cap (if using the epoxy to secure the lead, coat the entire
inside of the cap and then place back the lead). Also apply epoxy to the end of the handle
where the cap will be attached. Place the cap on the end of the handle and twist back-and-
forth several times to even disperse the epoxy. Clamp firmly and clean up excess epoxy with
paper towels and acetone. NOTE: for boppers larger than 1-1/2, epoxy alone is not
sufficient to hold the cap securely to the handle. I use two 1" copper rivets but nails will
work.

Clamping the cap:

2" boppers with caps pinned with copper rivets;

Once the epoxy sets, sand the handle and apply a good wood sealer/finish. I use regular water-based polyurathane (easier clean-up sith warn soapy water). Sealing the wood helps prevent the wood from expanding or shrinking with changes in humidity, one cause of caps becoming loose.

One the finish is dry you have a bopper!

Drying Boppers (a drying block helps!):

The Finished Boppers (Walnut and Maple)

Maintenance:

All that is require to maintain the boppers is to occasionally re-seal the handles with your finish of choice.

Repair:

When a copper cap wears through - and if you use it a lot - it will, you can remove the cap from
the handle by applying medium-high heat (I use a standard size propane torch). The epoxy will
soften and, using gloves, you can usually twist the cap off. I simply form a new cap of the same
size, put it in a vice, level it, set the old cap on top and melt the lead out with a propane torch.
This insures that you have just the right amount of hardened lead in the new cap. Leveling the
new cap prior to pouring in the lead is critical to assure the best balance. Once the cap is cool to
the touch you can re-attach in with epoxy. Removing some of the old epoxy first using some
coarse sandpaper should provide an adequate bond.

Potential Problems:

I've only had a handful of caps come loose in over 500 boppers I've made. None of the caps
have come completely off and those that came loose had to be heated in order to remove them.
Once removed, I just re-glued with epoxy and none have come loose a second time.

From what I've observed the primary reasons for caps becoming loose:

1. Inadequate epoxy coverage. Solution - use extra epoxy and twist the cap several times to
disperse the epoxy evenly.

2. Too smooth surface on cap/handle. Solution - roughen the inside of the cap with sandpaper
(better still, sandblast the interior of the cap) and roughen the part of the handle that goes
into the cap. Clean with denatured alcohol.

3. Wood shrinkage - wood shrinks or expands with humidity. Solution - seal the handle with
wood sealer, shellac, lacquer or polyurethane.

4. Too much lead in the cap resulting in insufficient glue surface area. Solution - fill the cap just to the top of the domed area.

5. Too tight of a fit between cap and handle, not enough glue area - solution - make sure the gap
between cap and handle is large enough for adequate gluing - not too loose but not tight. Clamp
and let set for 12-24 hours - regardless of the 'advertised' set time.

¹Bopper Cost (as of 9/27/15)

Material Cost

Making boppers can be cost effective - IF you already have most of the materials on hand. Otherwise it can be much less expensive to purchase a bopper or set of boppers than make them yourself. The following is a material cost breakdown of making a set of 5 boppers, sizes ½” , ¾”, 1”, 1¼” 1½”. This is the material cost for the least amount of material you can reasonably purchase at your local hardware store – most cost come from Home Depot. Although the amounts and types of materials are the least cost, you will end up with more than you need, especially polyurethane and epoxy. Unfortunately purchasing smaller amounts may not be possible or at least practical. Also scrap lead, if pure lead, is too soft. It needs to contain an alloying metal like tin (wheel weights) or zinc or antimony. Each of these alloying metals can add an additional cost.

1. Polyurethane (water-based, water clean-up)– ½ Pint (water clean-up) $5.98
2. Copper Caps
    a. ½” = $0.63
    b. ¾” = $1.36
    c. 1” = $2.91
    d. 1¼” = $4.25
    e. 1½” = $6.12
    Total = $15.27
3. Chip Brush 1” Economy = $0.97
4. Scrap lead 3 lbs @ $1/lb = $3.00
5. Sand Paper 9 in. x 11 in.
    a. 80, 150, 220 Assorted Grits Advanced Sanding Sheets (6-Pack) $6.97
6. Steel wool
    a. 12 pad Steel Wool, Coarse, Medium, Fine $3.98
7. Epoxy
    a. Loctite 8 fl.-oz. Professional Job Size Epoxy $15.67
8. Acetone (cleanup) 1-pt = $4.97
9. Paper towels (cleanup) Basic 1-Ply White Paper Towels $1.00
Total cost of materials1 = $57.81

This does not include the cost of sandblasting sand that I use to clean and roughen the inside of the caps to insure good glue-up. Silica sand is $8.47/100 lbs

Labor Cost

It takes about 2-3 hours of actual labor time to make a set of five boppers. This includes time for doming the caps (assuming one has doming blocks/punches), melting lead, pouring the lead, sandblasting the caps, turning and sanding the handles, gluing and clamping the caps to the handles, applying the three coats of polyurethane and sanding with steel wool in between coats. This does not include the time it takes for the lead to cool or the polyurethane to dry. It also does not take into account the amount of time or the cost it takes to get the materials. At the Federal minimum wage of $7.25/hour the cost of labor would be about $18.12 (2.5 hours of labor).

Total cost for a set of 5 boppers - $75.93