The Home Machinist!

Hi All,

I've been wondering about this, but can't seem to get a definitive answer. Any feedback is much appreciated.

Regards,

John

So the core print to support the core can be incorporated into the pattern.

Hi Pat,

Gotcha. I think that would imply that the prints were 'poured' from the boxes, but in industry videos from the 50's where they mentioned the boxes were built first, the patterns still had seperately attached wooden core prints. This is why I was scratching my head..it wouldn't seem to matter which came first since both had to be built from a pattern layout

jlakes85 wrote: ↑Sun Mar 22, 2020 6:17 pm it wouldn't seem to matter which came first since both had to be built from a pattern layout

Keeping in mind that I am not a pattern maker, nor do I play one on TV, from my perspective, which comes first makes no difference, not so long as each is made to specifications. That's the beauty of modern production, whereby parts that must fit one another can be made anywhere and count on to fit when assembled.

One thing that comes to mind that may bear on this is that cores may shrink when cured. If they do (I don't know), if the core location is critical, cores are made before the pattern, so the core print can be made the correct size to properly locate the core.

Any seasoned foundrymen here who might be able to address this concern?

H

I don't know why it would make a difference. Cores to make a round hole for shafts, etc., are often common to many patterns. The core box can be longer than is needed and the core made as long as necessary.

Cover core patterns were the most common type that you would build the core box around the pattern and then add the metal thickness to all surfaces in the box. This assured a perfect uniform metal thickness. At this point either the pattern or the core box could be worked to completion. Type of pattern or shape would determine if things could be "built around". Harold, in my 30+ years as a journeyman Patternmaker the last person you would want to ask would be a foundry person. As I have said previously without the Patternmaker a foundry man is nothing more than a child playing in a sandbox. The days of skilled moulders has long since passed.

How can you build a stable for a horse if you don't have the horse yet, or have never owned a horse? This is similar to: which way would you fit: the rod to fit a bore or the bore to fit a rod? Well, maybe not so parallel questions but both in the same light; one way is hard to do and the other way is much easier.. Measure outside or inside?

https://youtu.be/dqSGTjipFxg

This is the video that got me scratching my head

BClemens wrote: ↑Mon Mar 23, 2020 4:56 pm How can you build a stable for a horse if you don't have the horse yet, or have never owned a horse?

That may have been true more than 100 years ago, but, today, we have the ability to design and build to rigid specifications. If you know the size desired (which you do, thanks to your design), you can make either of them first. It just doesn't matter. I often work that way with other component types, and I did so with the bases I made for gas lamps. I did the core box last in that case, simply because I didn't have a design in mind, I just made what I liked and thought looked good. I then made the core to fit.

This is similar to: which way would you fit: the rod to fit a bore or the bore to fit a rod? Well, maybe not so parallel questions but both in the same light; one way is hard to do and the other way is much easier.. Measure outside or inside?

For me, it makes little difference. I can measure both reliably, and I do. That may or may not be the case for some folks, however, so I get your point.
I still maintain that it makes no difference which one comes first, not so long as one has a complete understanding of the desired size, and the behavior of the core when hardened. If it doesn't change, it simply doesn't matter, so long as your design is correct, and you build to the design.

H

I rarely use core boxes because I have no need, I made the patterns in Styrofoam, and stuffed sodium silicate treated sand in every crevice and opening and then hardened it. All the castings in the first photo required only one core box.

The place I had to make the core box for was the two long holes in the tender truck. I milled a core box in wood, and filled it with treated sand, and hardened. The two rods were then inserted into the Styrofoam pattern which then was invested into the sand.

So, I made the core box AFTER I realized I could not stuff sand to the full length of the hole NOT before!

Wooden patterns would have required a S.H. full of core boxes!