Sunday, 26 December 2010


My wife has assembled her own Christmas crackers from kits in recent years. She puts in much better gifts than even the more expensive commercial ones contain. It did backfire one year when she put a handkerchief in one and it ended up with a powder burn from the explosive!

This year she asked me to make some reprapped boxes instead to contain the usual cracker contents and look decorative on the table. The explosive element to be provided by a party popper. This is what I came up with: -

Having zero artistic ability myself: the star is Christmas star by andrewar from Thingiverse and the tree was grafted from the frame vertex of the Holiday Prusa Mendel by kliment.

My contribution to the design is the box. The base dimensions were determined by the hats my wife wanted to use and the height by the party popper diameter. This one also contains a magnetic bookmark, two chocolates, two PLA snowflakes and a charade instead of the usual bad joke or motto.

The lids had to be printed hollow side down because of the raised design on top. The gap is too big to be spanned without a lot of droop, so I used the support facility in Skienforge. I set the "support gap over extrusion perimeter ratio" to 10 to make it easier to remove and waste a little less plastic. I have no idea why the ends of the support are all in slightly different places.

It was still quite tedious to remove, so I tried Adrian Bowyer's technique of using oil to reduce the bonding. I knew the roof of the lid started at 8mm, and my host software prints the height of the current layer, so I just waited until it had finished the support and painted it with machine oil using small paint brush, while dodging the head. It worked very well and made the support easy to remove.

Here you can see the scars left behind, probably where I missed with the oil: -

I removed the scars by waving a hot air gun over the plastic.

The unsupported area sags a little and that makes a visible pattern on the top as there are only three solid layers. I think that actually makes it look more decorative by adding a textured border: -

The removed supports could be glued together and used as streamers.

These cracker replacements went down very well with both our families. They make a lot less mess on the dinner table and could also be reusable, but they all asked to keep the boxes, which was of course our original intention.

The files are available here.

Merry Christmas!


  1. So to fully automate the process, is the next step an oil dispensing head to coat the support material?

    Merry Christmas to you both.

  2. Yes Adrian's idea is to use a felt tip pen.

  3. Wonderful! I wish you and your wife happy holidays!

  4. Cool - Liquid Soap, I think would be easier to clean up (cleanup wasn't really even necessary in my experiment)

    1. I don't remember having to clean anything when using oil. I think possibly the plastic absorbs it while molten.