Building a set of mold boxes #1: Wood boxes designed to fit together.

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Blog entry by Patternguy posted 03-04-2017 03:15 AM 1402 reads 0 times favorited 3 comments Add to Favorites Watch
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You need some kind of molding process in order to make a casting. The size of the casting determines the appropriate process. Those processes require different kinds of pattern equipment.

This casting is made in a process called “air-set”, where sand is combined with a chemical binder and packed into a set of mold boxes that contain the pattern. The binder reacts and causes the sand to harden, the molds are removed from the boxes, fit together face to face and clamped tightly together. The mold is filled with molten metal and allowed to solidify. The mold is broken open and the casting is removed.

This is the casting we want to make.

Mold boxes are not just wood tubs, they are built so that the shape of their bottom face form a means of accurately “matching” both halves of the mold together.

Look closely at the cross section of the bottom faces of the boxes. One mold is constructed to form a pocket on its face; the other mold box is constructed to form a raised pad on its face.

I’ll let the images speak for themselves.
However, I’d be happy to clarify what is going on in a picture if anyone had a question.

Unfortunately It’s another sad story about a declining trade.
This was awesome wood pattern making work before the machines took it over. I’ve built patterns like this both ways and I’ll take my shop apron over my keyboard…anytime.

3 comments so far

View socrbent's profile


906 posts in 2870 days

#1 posted 03-04-2017 04:27 AM

Thanks for this post. Brings back memories of my youth. While in college in the late 60’s I worked in a local foundry – Morris Bean that produced ductile iron and aluminum castings using this process. Their molds were made entirely of wood by some very talented pattern makers. Those molds weren’t just boxes but also the positive image of the part (the red items in your photos). No CNC mills back then.

My first task was in knock out where we removed castings from the sand molds using sled hammers and picks. A very physical, hot and dirty job. I remember picking out the hot chills from the sand which were placed in the sand molds to cause certain areas to cool quicker. The castings were as small as your hand to huge tire molds for earth movers. The binder they used was was acidic. I remember the sand dust getting in my hair causing my eyes to burn as I rode my tiny Honda motor bike home in the rain. Gave me a good reason to wear my helmet.

I moved up to cutting risers off of castings with a huge radial arm saw, to running the aluminum and ductile iron furnaces and pouring the castings in the sand molds, to running an early vacuum tube spectrograph analyzing the metal being cast. After graduation I left to become a high school teacher.

-- socrbent Ohio

View Patternguy's profile


66 posts in 1293 days

#2 posted 03-04-2017 03:06 PM

I’m glad you enjoyed your walk down memory lane. I started this blog with the hope of doing that to some readers, bringing an aware of the subject to other readers, and especially, to document the skills and craftsmanship of a once, highly respected trade.

Years ago, foundries and manufacturers were in every community and everyone was familiar with the “trades” that worked for them. I doubt that most people today have any clue. (Unless of course they watch, “How it’s Made”)

Technology may be the driving force behind today’s manufacturing, but it was the hands and knowledge of the craftsman that made the Industrial Revolution happen. (Well..maybe that, and the output of a reliable source of energy:)

View socrbent's profile


906 posts in 2870 days

#3 posted 03-04-2017 04:22 PM

I agree with what you say. Too bad that the skilled trades of past generations are being lost. Thanks for your blog.

-- socrbent Ohio

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