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Popsicle Crane Update

Cutting a Popsicle Stick

 

Details, details details.  Details seem to be everything, but sometimes you don’t even know the details you need to know.  Since constructing the popsicle test tower I have learned a lot.  Unfortunately, there is not yet a lot to show because I am working slow and methodically to do a much better job constructing this time around.  That tower did serve its purpose because I quickly got some experience with some of the problems constructing with craft sticks, and that is really the most important lesson of all. “You will not know what you don’t know until you try.”  Or, said in my most convincing Rocky Balboa voice: “Hit me again Murphy… It don’t hurt”.

The fixture to build the boom.

One of the problems with that tower was it was not square or consistent.  I attempted to build it square but the problem with trying to do that is the clips get in the way of measuring properly.  This time around I have constructed a fixture to ensure the frame is square.   Not all of the lattice bracing will be installed while it is in this fixture, but enough is glued in place to set the spacing on the fame.

Holding the ends of the columns against the ceiling tile.

This fixture consists of a 2′ X 4′ acoustic ceiling tile (Between $3.00 and 4.00) for the flat surface and some wooden yardsticks (Less than $0.70 each) bolted to a similar yard stick on the other side of the ceiling tile to serve as a guild for the beams. This was easily checked to make sure the two yardsticks were parallel and that the end piece was square to the other pieces.  The soft ceiling tile allows for easy insertion of finishing nails to hold the columns firmly against the yardsticks.   Rubber bands and tape can hold the columns against the tile.

A partial cut using a wood chisel.

I have decided that the next tower will be 3″ thick X 4″ wide.  This was decided upon because it “looks” more like are real crane boom. and this should make it achievable to obtain the compound angles necessary as the boom narrows in two dimensions at the pulley end of the boom.   These dimensions make it necessary to cut the sticks.  I have tried many methods but the easiest is to use a wood chisel as shown in the first picture.    The picture above shows a partial cut using the chisel and shows how nice the cut looks.  I use the flat side of the chisel toward the piece of wood I will using because the wedge part of the chisel does compress the wood on that side.  I simply press on the chisel with the stick placed on a hard surface and do not use a hammer or mallet.

Using string to help prevent flexing of joints on the sides of the sticks.

At 30 lbs compression on the test tower I heard something break loose.  It was only later I determined what that was.  It was the same diagonal piece that had broken loose earlier.  There are several things causing that problem.  First, there is not much surface area on the narrow side of the sticks for the glue to adhere to.  The second problem is if the tower tends to twist first one of the sticks breaks loose and then the second half easily breaks loose.  The third problem is the sticks have any curvature, one half of the joint will be very weak.

I will be addressing all of these problems.  First, I will be very critical in my sorting of sticks.  I had not been too worried about the curvature since the sticks are only 4 1/2″ long.  During some of my other testing I have found cases where gluing sticks to the side of a double stick section the stick has ended up being 10 to 15 degrees off of perpendicular because of curved sticks.

The second problem, twisting, is a head slapper. “Duh!”  I had worried about using angle pieces to keep the boom from flexing lengthwise, but I did not think about twisting of the cross-section area.   I will probably install string X bracing inside the tower.   The internal hoist rope should be well above the center of the X.

The final fix is tying sting above the joint as shown in the picture.  I first glue and clamp the joint, then once the glue has dried I then place and tie the string and then apply glue to the string. The sting is 1/3 of a twisted mason’s twine.  I have since tried jute twine and I think it works better because it actually absorbs the glue where the mason’s twine is designed to repel chemicals.

Crane boom angles. See text for the assumptions.

The final thing being worked out is the dimensions.   The tower columns are 31″ long.  I assume I will probably add about six more inches at the butt end of the hoist making the hinge joint.   The pulley end will probably add about twelve inches more to the total length.  I created the very rough sketch of the boom.  The bottom line of each colored pair represents the 40″ boom. The top line represents the rope that controls the boom height and I set it at 10 degrees angle from the boom at the pulley end.   The blue pair is a boom angle of 45 degrees above horizontal. The green pair is 35 degrees, and the red pair is 55 degrees above horizontal.  The question I was trying to determine was if the rope angles intersect and where is that point located from the center of the crane hinge point.

Close-up view of the intersection point.

I determined a point for the green and blue lines.  The red line misses this point and will create a smaller angle to the boom, but that will be acceptable because it will not be holding as much of the actual load weight at that point because more of the weight will be resting on the boom hinge.

Things are going slowly in the actual construction, so the next few posts about this subject will be more theory.

A few announcements:

I have loaded a new version of the e-mail subscription program.  Before, people that registered to this blog could opt out of receiving e-mails on all categories.  I have a few people that opted out of everything.  The new version makes some categories mandatory.  I have chosen to make all the theory categories mandatory.

Very soon I will be creating two new pages.  One will be called subscribe to make it easier for people to subscribe to this site.  The second will be called projects and will provide an easy way to locate all the information related to a project.  For example,  the popsicle crane will have methods to find all the construction as well as all the structural theory posts.

If you find this blog site interesting please consider subscribing using the RSS feed, Facebook or the E-mail subscription service.

Thank you,

Gary

 

 

 

 

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