Projects‎ > ‎

Tennis Ball Cannon Jig

This is a jig to help make a CSV19 Tennis Ball Cannon per the instructions on this website.  The cannon is used to raise antennas for ham radio use.  The hardest and most important step in making the cannon is boring the holes in the two end caps.  The plans require the use of a lathe which is not always readily available.  These instructions require the use of a router with a pattern following bit which are much more readily available and affordable than a lathe.  In addition, once the jig is made, multiple end caps can be quickly produced.  Close tolerance of the fit is important for safety to insure a strong joint, especially to the pressure chamber.  This is easily achieved with this construction method.

The plans require one modification to use this jig.  Scroll down on the above website to "Preparing the End Caps".  Where it says "Bore the Barrel 2.5" Endcap to closely fit the outside of one arm of the 1.25" elbow..." - This will not be done.  Instead, a 1.25" coupler will be used to connect the elbow to the barrel.  This is required due to the construction technique of this jig but won't make any difference in the performance of the Tennis Ball Cannon.  It will lengthen the Cannon by a couple of inches.

Photo 1.

Here's the completed jig.  The PVC end cap is held inside the box.  The 4" end cap is held in place by part H (outer PVC) and the 2 1/2" end cap by I (inside PVC).  A pattern following straight bit (11-790B) is used in the router to cut the hole into the end of the PVC end cap.  The bearing is guided by the holes in the top pieces A1 and A2 which are interchangeable (shown in photo 2).

Photo 3.                  2 1/2" end cap held in place.


Drawing 1.

Materials List
 Qty Description
 1 2' x 4' x 1/2" Hardboard
 2 oz 2 Part Epoxy
 pair    Rubber gloves
3 Hot Melt Glue Sticks
 1 Wood Glue
 pckg Plumbers Abrasive Sandcloth
 16 oz 91% Isopropyl Alcohol
 2 Glue Brushes
 50 18 or 22 gauge x 3/4" brad nails if using air brad nailer.
 2 6 x 1" wood screws

Tools Req'd
Tablesaw. 
Plunge router w/ pattern following straight bit (11-790B)  Get 11-081B if you have a 1/4" collet on your router.
Chop Saw.
Jig Saw.
Brad Nailer or brad nails.
Hot Melt Glue Gun.
Straight Edge.


Instructions
1. Pitty the fool that doesn't wear safety glasses!

2. Cut out all hardboard parts per the cut list and drawing 4 and label all the parts with a black magic marker as shown below.
Photo 4.

3. Use a straight edge from corner to corner to mark on X in the center of part G.  Use a compass to draw a light 1 1/2" radius circle and a light 2 1/4" radius circle in the center of part G.  
Photo 5.

4.  Cut out parts H & I on the chop saw.

5.  Center part I over the inside circle of part G.  Draw heavy lines (circles) on the inside and outside.  Repeat for part H. Draw "x"s as shown in photo 6.  

6. Drill 1/4" holes as shown in photo 6 and drill a 3/8" hole in the centerCut out the X's with a jig saw starting from the center circle and working out.  That's four circle cuts.  Cut on the inside of the line (towards the center) on the first cut, the outside on cut two, the inside of the line on cut three and the outside of the line on the last cut.  Epoxy will be used to fill in the gaps.  The donut will be used between H and I and the center will be used.   Photo 7.

7. Dry fit H & I.  The PVC should fit loosely inside. 
Photo 8.


7. Draw the lines and circles per drawing 5 onto part B.

8.  Glue inside the entire square that you just drew on part B with wood glue and glue the back sides of part G, the center and the donut. Spread the glue with a brush.  Align G on top of B and brad nail into place.   The nails are only holding the parts together until the glue dries so you don't need to use a ton of nails.  Align the center and brad nail into place.  Center I by eye and the donut, remove I and brad nail the donut into place. It doesn't have to be exactly centered so don't worry.  Wipe of any glue squeeze out on part B only. Photo 9.

9.  Dry fit (2) E's and (2) F's together.  If E sticks out beyond G (see the pencil tip at the bottom left of photo 10) then trim off this excess.  Trim slightly to avoid cutting off too much.  Tip: Trim both E's at the same time so they're identical.  Also trim F if necessary.
Photo 10.

10. Draw lines on (2) E's and (2) F's glue. Spread glue w/ brush.  Photo 11.  Also glue sides of G per photo 12.

10. Brad nail (1) E and (1) F in place with 3/4" brads.  Photo 13.  Also brad nail the vertical side through F where it meets E.  Brad nail the second E then the second F in place.
Photo 13.

11.  Dry fit (2) C's and (2) D's.  Trim if necessary.  Draw horizontal lines w/ pencil at the top where C meets E and where D meets F.  Glue.  Be careful not to get any glue above the lines. Photo 14. Also glue the outsides of E and F and spread with brush per photo 15.
Photo 14.

12.  Hold (1) C and (1) D tightly in place and nail with 3/4" brad nails from top to bottom.  Hold the second C in place & nail.  Hold the second D in place and nail.  Wipe off any excess glue squeeze out. Photo 16.

13.  Mark the centers of A1 & A2 by drawing a line from corner to corner.  Draw a 3/4" radius circle in the center of A1 and a 5/8" radius circle in the center of A2.  Photo 17.  Drill the centers out with a 1" diameter spade bit.  If you don't have a 1" bit then draw 1/2" radius circles in the centers and cut out with a jig saw on the line. 
Photo 17.

14. Test fit A1 and A2 into the jig.  Don't force them.  Trim if necessary.  Trim only about 1/32" at a time on the table saw to sneak up on the fit.  Note that it's possible that the left to right dimension will be different than the top to bottom dimension so trim one side at a time.  If this is the case then mark which side goes up with a triangle per photo 18.  There should be no slop, play or movement when inserted.  If the fit is loose then cut new A1 and A2 pieces a little over size, repeat step 13 then slowly trim down to fit.

15. Heavily sand the outsides of H and I PVC to aid epoxy adhesion and so the caps don't fit too tight using plumbers abrasive sandcloth.  Also sand the bottom 1/2" or so of the insides to aid in epoxy adhesion. Clean parts with 91% Isopropyl Alcohol and dry.

16.  Thoroughly mix 2 oz. of epoxy.  Wear rubber gloves. Pour the epoxy into the bottom outside and inside circles.  Photo 19.

17. Insert and center H into the epoxy and give a 1/4 turn twist or so to spread the glue then do the same for H.  Do not use a glue brush because you don't want to get any epoxy on the top outsides so that the caps will fit.  They don't have to be centered exactly so don't despair if they're a little off center.  Set aside and let the epoxy harden over night.
Photo 20.

18. Draw a 1 1/4" radius circle in the center of A3.  Cut out the circle with the jigsaw.  Discard the center.  Photo 21.

19.  Slice a 7/16" ring off of the 1" and the 1 1/4" PVC.  See photo 22 below for how to do this safely on the chop saw (place two PVC couplers FIRMLY on opposite ends of the PVC pipe to hold the couplers securely). 
Photo 22.

20.  Place the 1 1/4" slice over the center of A1 and mark the inside circle with a heavy pencil line.  Photo 23.

21. Cut out the inside being very careful to not touch the line.  About 1/2 way between the hole and the line is fine.  Photo 24.  Place A1 inside the jig.

22.  Roughly center A3 over A1.  Hold firmly and drill and counter sink two 7/64" holes in opposite corners.  Secure with the two 6 x 1" wood screws.  Ensure screws don't stick up above the surface.  Photo 25.

Photo 25.

23.  Center the 1 1/4" PVC slice inside A3 and place a straight edge over the top to make sure the PVC does not protrude above A3 per photo 26.  Trim the PVC down a little more if it does using the same technique in step 19 above.  Hot melt glue the PVC slice centered on top of A1 and inside A3 per photo 27.  

Photo 27.

24.  Chuck the pattern following router bit in the router as you wait for the glue to dry.  Wait at least 10 min. for the glue to dry.  The glue will turn a white color per photo 29 when dried.

25.  Secure the jig to the workbench with clamps.  Adjust the router depth so the bushing rides on the PVC and the cutting edge is adjacent to the hardboard.  Photo 28.  Route in a clockwise direction.  Be prepared for the dust to fly!  Make two or three circles.  Photo 29.

26. Remove the two screws and pry A3 from A1 with a screwdriver.  Photo 30. Remove the PVC slice.  Leave the glue in place inside A3 if it stays there otherwise discard the glue.  Scrape the top of the two holes flat so they don't protrude above the surface.  Photo 31.

Photo 32.      Nice tight fit!

27.  Place A2 inside the jig and repeat steps 22-26.

28.  Remove A2 from the jig and blow the dust out.  Label A1 "2 1/2" End Cap. Inside. Barrel" and label A2 "4" End Cap. Outside.  Pressure Chamber."

29. FYI, Hole dimensions in A1 & A2 miced out at:
 PVC Pipe 1.667
 Hole 1.671
 Difference .004
  
 PVC Pipe 1.318
 Hole 1.321
 Difference .003

Instructions on Jig Use using the plunge point bit - link shown above under "Tools Req'd"

1. Adjust the router depth stop so the bearing rides inside the circle of the hardboard when the router is plunged down.  Adjust the router speed according to the diameter of the bit.  Return the router to the up position (not plunged).

2. Clamp the jig down firmly on a workbench with two clamps.  Place a 2 1/2" end cap inside the jig.  Push down firmly to seat it at the bottom.  Place A1 in the jig.  Note that A1 is placed in the proper orientation - see step 14.  There should be about 1/2" space between the bottom of the hardboard and the top of the small end cap and very little space to the large end cap.

3. Wear safety glasses.  Hold the router firmly with both hands.  Turn on the router, plunge, lock it in the down position, cut in a clockwise direction.  Make two to three circles.  Turn off the router.

4.  Remove the end cap.  Tip: Twist and pull at the same time if it's difficult to remove.  Vacuum out the jig and blow out any residual PVC dust.

5.  Repeat the above steps for the 4" end cap using A2 (do only one of the 4" end caps, not both!).








Photo 33.


73's & Happy DXing!
Paul Schultz
KD8KUF

Photo 2.

In the background is the 1 1/4" dia. hole in part A1 for the 2 1/2" dia. end cap.  It requires a slight modification to the plan.  The 1 1/4" 90 degree elbow is not inserted directly into the end cap.  Instead a short length of 1 1/4" dia. PVC pipe is used to join the elbow to the barrel. 

Drawing 2.

Click on any photo or drawing to enlarge.

Drawing 3.

Cut List
 Part # Qty Description Dimensions
 A1 1 Top.  2 1/2" PVC, (Barrel) 8 1/16" x 8 1/16"
 A2 1 Top. 4" PVC, (Pressure Chamber)  8 1/16" x 8 1/16"
 A3 1 Temporary Spacer 7" x 7"
 B 1 Bottom 13" x 9"
 C 2 Outsides - Left & Right 9" x 4 1/2"
 D 2 Outsides - Front & Back 8" x 4 1/2"
 E 2 Insides - Left & Right 7" x 4"
 F 2 Insides - Front & Back 8" x 4"
 G 1 Bottom Inside 7" x 7"
 H 1 Outside PVC 4" x 1 3/4"
Actually about 4 1/2" dia.
 I 1 Inside PVC 2 1/2" x 1 3/4"
Actually about 2 7/8" dia.
A-G is 1/2" Hardboard.


Drawing 4.                ...Click to Enlarge...

 Photo 6.

Photo 7.


Drawing 5.

Photo 9.

Photo 11.

Photo 12.

Photo 15.

Photo 16.

Photo 18.

Photo 19.

Photo 21.

Photo 23.

Photo 24.

Photo 26.

Photo 28.

Photo 29.

Photo 30.

Photo 31.












Instructions on Jig Use using the non plunge-point router bit

1. Adjust the router depth stop so the bearing rides inside the circle of the hardboard when the router is plunged down.  Adjust the router speed according to the diameter of the bit.  Return the router to the up position (not plunged).

2. Clamp the jig down firmly on a workbench with two clamps.  Place a 2 1/2" end cap inside the jig.  Place A1 in the jig.  Note that A1 is placed in the proper orientation - see step 14. Outline the circle with a pencil.  Drill a 3/8" hole in the center of the end cap. Remove A1 and remove the end cap from the jig.  Tip: If A1 is difficult to remove, gently pry a screwdriver between the bottom of A1 and the top of the end cap working front, back, left & right slowly.

3.  Cut out the center with a jig saw being very careful to not touch the line so as not to ruin the end cap.  About 1/4" away from the line is close enough.

4. Return the end cap to the jig. Push down firmly to seat it at the bottom.  Place A1 in the jig.  There should be about 1/2" space between the bottom of the hardboard and the top of the small end cap and very little space to the large end cap.

5. Wear safety glasses.  Hold the router firmly with both hands.  Turn on the router, plunge, lock it in the down position, cut in a clockwise direction.  Make two to three circles.  Turn off the router.

6.  Remove the end cap.  Tip: Twist and pull at the same time if it's difficult to remove.  Vacuum out the jig and blow out any residual PVC dust.

7.  Repeat the above steps for the 4" end cap using A2.

Photo 34.
Comments