Tripod Leg Construction

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Inner Leg Tubes

9/21/2008

Along with the foam work, I made the upper ends of the extendable legs.

Here is the small disk of Aluminum made to fit in the top end of the inner leg tube.  Note the center punch marks around the perimeter to help grip the tube wall.  This disk is epoxied into place.  It is an interference fit.  There is little force on this, so the glue is enough to keep it all together.  I had thought about dragging out the Heli-Arc, but this was faster and easier.

Here is the disk after cleaning up the excess epoxy.  When cured the disk will be center drilled 1/4-20 for the retention bolt to be added later.

Two fender washers allowed me to turn the 0.185" teflon sheet into a disk.

The disk of teflon is secured in place with a 1/4-20 SS Allen bolt and fender washer.  The teflon disk prevents rattling between the inner and outer leg tubes.

Top Cap for Leg Construction

Pattern Making

10/11/2008

I elected to make the foam patterns as smooth as possible and will use my router table to cut the foam parts using 3/8 MDF as a pattern.

Cutting the wood pattern.  Guard has been removed for clarity...

My patterns so far.  The Altoids can was the template for the round pattern, it was used because I was too lazy to cut a wood pattern with a fly cutter or finish the sides of one cut on the band saw.  The MDF patterns are cut on the band saw and finished with a fine flat file.  Double sided tape is used to temporarily adhere the foam to the template.  The tape stays sticky enough to do about 3 parts.  DO NOT use carpet tape, you will destroy the foam taking it apart!  You have been warned....

Shot of cutting the foam disks, all together I need to make 6.  I am going to cut them separately and glue them together.  A 2" long flush cut router bit was a bit pricey and I had the 1-1/2" in the bit box.

Disks glued together.

Cutting the top fork of the casting.  Three of these are made.  They will be trimmed at the base, the thick part was left intentionally long to give me a handle to route the part as well as more surface area for the tape to adhere to.  The band saw cut will be a glue joint, so surface finish is not critical.

A video of the routing process is here:  Routing the foam parts (warning large file!)

The glued disks and the fork patterns prior to gluing.

Pouring sprues.

The finished foam parts, the fork have been trimmed.  Distance between the base of the U cutout and the bottom face is 3/8".  This method is actually pretty fun and I have thought up a great many things to make this way!

10/12/2008

Started assembling the cores using craft glue.  Rubber band holds the cross sprue in place while the glue sets up.  That part as well as the upper half of the forks will be cut away.

Loose-Sand Casting of The Parts

Pattern dipped in gypsum mixture to coat with a hard shell.  Fully coated in this view, the remaining foam will remain  uncoated. This whole assembly will be immersed in loose sand and molten aluminum will be poured into the top end.  When the aluminum sets up the shell is flaked off leaving the finished casting ready to machine.  A video of the pour is here, please ignore my cmplete lack of safety equipment, it's a do as I say, not as I do thing you know....

 Casting Furnace    Pouring tools

Here's my home brew casting furnace based on the Gingery book, I scaled his up and used a small trash can for the housing.  The right picture shows the home brew lifting tongs to get the crucible out of the furnace and the pouring ring to handle the crucible.  It is not advisable to cast over concrete, if you spill the molten metal you could pop the concrete if there is any moisture in the surface.  This was shot after weeks of hot dry weather.

  Hot Pour   Hot Casting

Here is the sand can after  the metal was poured in, the sand gave way and some of the metal from the steel pouring funnel leaked out.  The right side shows the hot casting after it was un earthed and is still damned hot and covered with the remains of the drywall plaster.  Hosing it off while hot makes it easy to remove the coating.

10/18/2008

Cast the first upper leg fitting!

Here it is with the  pouring sprue and blisters removed, then the bottom faced off.

Machining The Leg  Cap Castings

Turning the outside.  I machined the interior on the mill using a boring head, then attached it to the stub of metal on the lathe.  The web across the end was center drilled so I could support it safely with the tailstock. Three of the six setscrews have been installed.

Another shot of the part.

10/19/2008

12/20/2010

Finished machining of the adapter for the top of the leg,  polishing and final finishing yet to be completed.  Note the "legs" of the casting are quite a bit shorter than when I started.  I sawed them down in the horzontal bandsaw, then faced them.  The finished part was edged with a roundover bit in the mill.

Making the adjustable Leg Clamps

The outer legs were machined to accomodate my clamps, three threaded holes and two 3/8" slots were cut in each leg.  The slots hold a short piece of aluminum that the clamping bolts ride on to prevent "bolt divets" on the inner leg.  The force of the bolts (two per leg) are spread out over an inch of the inner tube, giving a very solid clamping force as there are two per leg.