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Popsicle Crane Update No. 3

The Plan for the Butt of the Crane Boom

Much progress has been made on the construction of the popsicle stick crane.  At the last crane update I had built built the major part of the boom and some pulleys.  Since that time I have figured out how to make the pulleys spin fairly easily.

A co-worker told me her father did woodworking as a hobby and made a lot of sliding wooden parts.  He used beeswax to make the parts slide easily.  I did some searching on the web and learned that the problem with wood is most lubricants are absorbed by the wood.  Beeswax is the traditional method to make things slip because it is not absorbed in the wood.  The problem is I cannot find a source of beeswax locally but I found that candle wax also works well.  Some also recommend silicon spray.  I tried both.  I applied the wax to the sides of the pulleys as well to the shaft the pulleys will be riding on.  This seemed to work well after several turns of the pulley to smooth out the wax.  As I said I also tired the silicon spray on an the 1/4″ dowel rod I will be using as the shaft.  This requires several applications of the spray because the spray is carried by volatile chemicals that evaporate and I wanted a fairly think coating. Before applying the wax and/or spray to the sides of the pulleys be sure and sand them smooth.  The final sanding was with 220 grit sandpaper.

In the future I may experiment with a hard coating on the wood as well.  Possibly urethane may be used, but at this time I wanted to stick with recommended methods.

Building the butt directly on the plans.

The main accomplishments was building the butt of the crane boom and the hinges for it.  This was done by printing out the CAD plans on a 1:1 scale.  This drawing was then mounted on a board and wax paper was placed over it.  I was then able to place the sticks directly over the drawing and glue them in place as shown in the picture to the right.   Although the excess glue did stick to the wax paper, it was easy to peel off once the glue dried.

Clamping the glued pieces.

Because I wanted to clamp the pieces together quickly I normally build at maximum three layers at one time.  Then I put another piece of wax paper on top of the piece and another board and clamped the whole “sandwich” assembly and let it dry overnight.

Because our analysis of the forces on the boom determined that the boom will be experiencing compressive forces and this end of the boom is coming down to a point for the hinge joint I was concerned about the forces wanting to spread the sticks apart.  That is one of the reasons for the cross members to prevent these from spreading.  The other reason is to provide a surface for the end of the boom to butt up against.  Probably three sticks is over design, but I also wanted to keep things centred  and this end of the main boom had two sticks.   This particular project is at this point mostly about “inventing” ways to do the fabrication and not so much trying to design with the minimum amount of material.

The fixed part of the hinges were designed with legs to fit over the 1″X 6″ base board.  Although as we have talked about in the past the nominal size of the board is called a 1″, it is actually 3/4″ thick.  (This was measured and checked before I built.)  My alignment of the sticks was not perfect when I glued them to make the assembly and some of these hinge bases were twisted and not perpendicular to the base board.   This was checked with a square and trimmed as necessary.  I used three sticks for each leg.  This permits a stick to be inserted between the sticks when final gluing is done to attach the unmovable part of the hinge to the base board.

After getting this alignment right I then determined where the hole for the shaft should be so there will be room for the boom to rotate as well as making the shaft parallel to the end of the base board.   I used one fixed end piece as my template and drilled the others based through this one after making sure the pieces are aligned to each other. I started with a 1/8″ drill and then enlarged the holes to finally a 17/64″ drill. This is slightly larger than 1/4″ and the dowel slides easily but is not a sloppy fit. After the 1/8″ hole the rest was done by hand using a pin-vise to ensure I followed the 1/8″ base hole.

Final alignment before anything is glued.

After all the alignment and hole drilling, I then mounted it the first time on the base board.  Nothing is glued in the picture to the left.  Everything at this point is just a friction fit and I can move pieces to get everything in alignment before doing any gluing at all.  I checked and made sure the boom could rotate freely without any binding and then glued the legs of the fixed part of the hinge on one side of the boom.  After those dry I will do the other side.  Then I will have to do the same to the bottom side of the base board.   (The liquid glue wants to fun downhill so there was no way to glue both sides ast the same time.)

Fit of the main boom to the boom butt.

The final picture shows the fit of the main boom to the boom butt. I will cut the excess parts off the butt before the final assembly. To cut all of these pieces I have been using a Dremel tool with a heavy duty cut-off abrasive wheel. The heavy-duty wheel is a little thicker than the normal wheels. This makes it cut a little slower but it is more rugged if you slip. It probably does as much burning through the wood as it does cutting and that is why all the cut ends look black. I may sand these to remove the blackened wood, but probably not. The last thing I will glue will be the butt assembly to the boom and that will be after a final alignment check.



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