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It was made to comb mail #1: A mahogany foundry pattern

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Blog entry by Patternguy posted 02-17-2017 01:01 AM 1289 reads 0 times favorited 8 comments Add to Favorites Watch
no previous part Part 1 of It was made to comb mail series Part 2: Making use of a layout »

A picture story about building a pattern.

10 years ago, I was the CAD/CAM guy for a pattern shop. We also had a plaster molding shop and an aluminum foundry, where we pressure cast aluminum match plates.

10 years before that, I was on the bench, building the wood master patterns that went on to become match plates.

20 years before that, I was serving a Pattern maker’s apprenticeship in an iron foundry. The master I learned from once ran General Motors, “Tech Center” where the workforce was made up of 400 highly skilled craftsmen from the technical trades, toolmakers, model makers, pattern makers, designers, and engineers.

Anyway,
One day my boss walks in my office, shows me a drawing and asks me if I could machine the pattern out of a piece of aluminum billet. After a few seconds of study, I looked up and said to him, “Yes, I can make it, but WHY would we want to do that?” The amount of money in labor and machine time would be far more than if we just made the pattern “the old fashioned way”. That is, Have a pattern maker make it out of wood and use it to cast a match plate for it.

I think he was just testing me and had already made that decision. I decided to document an example of this “Dying trade” called patternmaking.

The pattern maker in the photos is Gerry Koenig. Jerry is a first class mechanic, trained by a well respected master by the name of Dick Boehm, outside of Reading, Pa.

I’ll start with some images of what Gerry will make.

Next up, “making the pieces.”



8 comments so far

View Kelster58's profile

Kelster58

276 posts in 177 days


#1 posted 02-17-2017 01:12 AM

Can’t wait to see more, thanks for sharing.

-- K. Stone “Tell me and I forget, teach me and I may remember, involve me and I learn.” ― Benjamin Franklin

View Kaleb the Swede's profile

Kaleb the Swede

1753 posts in 1606 days


#2 posted 02-17-2017 01:29 AM

This should be interesting

-- Just trying to build something beautiful

View Bluepine38's profile

Bluepine38

3360 posts in 2722 days


#3 posted 02-17-2017 04:35 PM

Will be impatiently waiting for the next episode. Thank you for the tutorial.

-- As ever, Gus-the 78 yr young apprentice carpenter

View HokieKen's profile

HokieKen

2635 posts in 775 days


#4 posted 02-17-2017 05:23 PM

Awesome idea for blog. I’ll look forward to more!

-- Kenny, SW VA, Go Hokies!!!

View Patternguy's profile

Patternguy

53 posts in 328 days


#5 posted 02-18-2017 01:51 AM

Part 2

A quick disclaimer here…I thought to just throw the pictures up and leave it at that. However, the more I visited this site, the more I realized the level of knowledge and talent of its inhabitants, was pretty dam high.

I have to give the subject the attention and respect that it deserves. That’s going to take me some time.

On to the story… Castings are made by pouring metal into a closed hollow mold made of sand. The hollow shape inside the mold is made by the pattern. Patterns are very accurate wooden replicas of the casting. But, they are more than replicas, patterns are a collection of precise shapes that are engineered to obey the rules of good foundry practice.

good practice means the pattern has the draft needed to mold, that the parting plane is properly located, and that parting lines are smooth and natural, with no abrupt changes of direction.

Draft is the amount of angle, or taper, that is added or subtracted from all vertical surfaces of a pattern.
A pattern must have some amount of draft, or it cannot be removed from a mold without damaging the mold.

The parting plane is the plane that splits a pattern into two. Pattern are not always split in half, nor is the parting necessarily flat.

Partings that are not flat, or planar, are called “offset partings” and are defined by their parting line.

Remember the sand mold?..it must be opened so the pattern can be removed. Ideally, the parting line follows completely around the shape of the pattern. Think of a sphere…the parting line is a flat plane that will always pass through the center.

Now, think about an automotive manifold…where do you split a complex shape like that?
the answer is, at the parting line. In this case, the parting line follows the natural parting line of each feature of the manifold.

All this rambling about partings and lines is for a good reason, because the pattern being made has an interesting parting line. The correct parting line was maintained by the method of construction used to build the pattern. .

After understanding the blueprint well enough to build the pattern in your head…The next step is to make a layout that captures full size views of critical features or dimensions of the pattern. Good layouts are vital to accurate pattern construction.

That is where I’ll start.

I’ll be back to describe what we are looking at.

View Patternguy's profile

Patternguy

53 posts in 328 days


#6 posted 02-18-2017 06:03 AM

I zoomed the picture a little, hoping to show the layout lines.

A layout should be full size, and in this case, its the side view of the fingered ribs. 8 ribs and 48 fingers will be assembled on top of the layout.

You can see wooden stops been glued to the layout on lines that form 3 edges, or faces, of the layout.
You can also see smaller wood stops for locating each finger on the rib. Rib and finger material will be planed to a precise thickness that accounts for draft that will be applied later in construction.

This method of assembly is accurate and consistent.

There is the mindful zen feeling I get into when i’m focused on something like cutting, sanding, and fitting 56 different pieces of material together.

View Patternguy's profile

Patternguy

53 posts in 328 days


#7 posted 02-18-2017 03:44 PM

Unfortunately, I didn’t capture every step of pattern construction and have no image of a rib assembly, resting on the layout.

This view shows the assembled ribs with details such as fillets and radii being added to specific areas of the fingers. The side edges are left untouched at this point.

Also, the only draft accounted for on each piece is found on the faces matching the stops on the layout.

The parting plane for the rib is defined by the line that run along the bottom of the fingers.
The fingers will mold in one direction, and the rib will mold in the opposite direction.

You can see from the layout which faces “draw” up from the parting, and those that “draw” down. The foundry terms are “cope” for up, and “drag” for down.

Draft will be applied to the sides of the ribs, but for now, they must remain parallel for the next step of construction.

View changeoffocus's profile

changeoffocus

463 posts in 1254 days


#8 posted 02-22-2017 12:28 AM

So many memories of trades gone by, please keep up the great work.

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