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Wood Patterns for Metal Castings


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  #21  
Old 06-20-2014, 09:12:59 PM
J.B. Castagnos J.B. Castagnos is offline
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Default Re: Wood Patterns for Metal Castings

Very nice work Terry. I'm using the same method on the core but instead of the plaster I'm using a two part plastic called Replicate. I made the positive core stick, will try to mold a negative with the Replicate. You have to use a release agent and time it correctly, it wants to grab hold of what's in it.
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Old 06-29-2014, 08:04:18 PM
J.B. Castagnos J.B. Castagnos is offline
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Default Re: Wood Patterns for Metal Castings

The core box is almost finished, it's coming out OK.
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  #23  
Old 06-30-2014, 05:24:44 PM
tharper tharper is offline
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Default Re: Wood Patterns for Metal Castings

Looking good!
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Old 03-10-2016, 10:54:41 PM
Gary A. Craig Gary A. Craig is offline
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Default Re: Wood Patterns for Metal Castings

Where can I buy letters to use on a sign I want to have cast, they need to be 2" to 2 1/2" wide and 3" to 3 1/2" high? Any help ? Thanks Gary!
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Old 03-10-2016, 11:36:58 PM
Thaumaturge Thaumaturge is offline
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Default Re: Wood Patterns for Metal Castings

Saw a real interesting video on youtube about "lost foam casting". Basically you make patern out of styrofoam and just leave styrofoam in sand. When liquid metal is poured styrofoam vaporizes leaving a clean casting that follows styrofoam shape. Watch it here: https://www.youtube.com/watch?v=tH-PaNugz9w
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  #26  
Old 03-11-2016, 09:15:11 AM
Doug Tallman Doug Tallman is offline
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Default Re: Wood Patterns for Metal Castings

Quote:
Originally Posted by Gary A. Craig View Post
Where can I buy letters to use on a sign I want to have cast, they need to be 2" to 2 1/2" wide and 3" to 3 1/2" high? Any help ? Thanks Gary!
Check Lowes, Menards, maybe even the hardware store and look for the letters they sell to put the address on your house or mailbox. They come in a lot of different sizes and styles.
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  #27  
Old 03-12-2016, 09:02:01 PM
51cub 51cub is offline
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Default Re: Wood Patterns for Metal Castings

I hate finding excellent posts like this from before I was a member here. Lester Bowman's story near about brought tears to my eyes
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  #28  
Old 03-15-2016, 05:26:08 PM
TomBall TomBall is offline
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Default Re: Wood Patterns for Metal Castings

excuse my ignorance but what is the reason for the split pattern?
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  #29  
Old 04-07-2016, 05:22:40 PM
tharper tharper is offline
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Photo Re: Wood Patterns for Metal Castings

Hello Tom,

The split pattern allows you to lay one half of the pattern flat on the mold board and allows the mold to be split so you can add cores, gates etc. and pull the pattern. Otherwise you would have to "cope" or dig down to the center plane of the pattern. Some patterns are in multiple pieces to deal with under cuts etc. that my hinder removing the pattern from the mold.

In this photo the drag has been rammed-up and flipped over. Next the other half of the pattern will be attached, the cope or other half of the mold rammed-up. Once that's done they will be split and the pattern removed, gates cut and vents etc. added.


Since the finished piece will be hollow a core made from sand mixed with a binder will be placed and aligned with the core prints. and the other half of the mold put in place. When poured the molten metal will fill the void around the core. After casting the core will be broken up and removed leaving a hollow casting.



Here is a very simple pattern. This one uses split patterns and a follower board. The follower again defines the part line and in this case allows multiple patterns to be cast at once.



That was the short quick explanation. I hope it helped!

Best regards,

T
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  #30  
Old 04-08-2016, 05:42:32 AM
ChipTosser ChipTosser is offline
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Default Re: Wood Patterns for Metal Castings

Gary, If there is a Hobby Lobby craft store, near you they have many different sizes and founts of letters.
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  #31  
Old 04-08-2016, 04:49:07 PM
TomBall TomBall is offline
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Default Re: Wood Patterns for Metal Castings

Thanks for the explanation on the split patterns. Would it be the method to use if one wanted to make a pattern for an engine piston? I know cores are involved and I'll deal with that later.
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  #32  
Old 04-08-2016, 06:42:27 PM
tharper tharper is offline
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Default Re: Wood Patterns for Metal Castings

Hello Tom,

Yes. You would use a split pattern.

Here is a very informative link to a father and son team in England who are working to bring back to life a WW1 era Thornycroft lorry. The whole thread is amazing but they provide a top notch view of how to fabricate the pattern and core box for casting pistons

http://hmvf.co.uk/forumvb/showthread...oration/page83

Best regards,

Terry
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  #33  
Old 04-08-2016, 11:16:59 PM
Craftsman56 Craftsman56 is offline
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Default Re: Wood Patterns for Metal Castings

I have a sandwich cart,original cast iron.I wanted to have 3 more cast for my other engines.I went to a foundry in 3 local cities and they wanted me to pay 5000 to 15000 for just the patterns.I went to a business with 3 D printing.he could make all the split patterns for 2000 but the examples he showed me had lines.ridges I would have to fill and sand.So,would finding a pattern maker that uses wood be an option or are they all high cost? Then would the foundry accept "my" patterns?
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  #34  
Old 04-09-2016, 01:17:03 PM
tharper tharper is offline
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Photo Re: Wood Patterns for Metal Castings

Fabricating patterns is time consuming and thus expensive if your hiring someone to do it. - that's why I taught myself how to make them. Its not hard given a bit of wood working experience and access to some basic wood working equipment - though a lathe is very helpful. If you make a mistake you have only wasted some time and a bit of wood.

Many times a foundry can use the actual original part as the pattern. (Depending upon the shape etc.) They have to compensate for shrinkage so the cast part comes out a the correct size. They can use anything from bondo to tape to build it up and plug any holes etc. Cattail Foundry in Pa. use this technique frequently and their prices are very reasonable.

They also are willing to work with "loose" patterns as opposed to many commercial foundries who need to meet certain volume and require the pattern halves to be mounted on match plates.

In regards to 3D pattern - people tend to overlook the time and expertise required to model the part 3D and adapt it to pattern work versus the actual printing and cost of material. I teach CAD and 3D modeling for a living - modeling a part can indeed be a swirling black hole of time.

If you want to try it yourself I strongly suggest creating a full size drawing of the pattern. I frequently use the 2D drawings as a template to assembly the patterns and core box masters. There are cheap if not free CAD software available or... draft it out the old way by hand.

Water manifold pattern under construction. Its setup on a follower to keep the correct angle of pull and to define the part line. When using the lathe I laminate the halves together using Elmer's wood glue and a layer of brown wrapping paper in between. Once the lathe work is done its easy to split the halves apart



Finished pattern - note male masters for the core boxes


Intake manifold patterns and core boxes. Core boxes are plaster-of-paris castings of male pasters


Finished intake manifold castings ready for assembly


Best regards,

Terry
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  #35  
Old 04-09-2016, 08:31:14 PM
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Default Re: Wood Patterns for Metal Castings

Beautiful Work Terry !

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Old 04-09-2016, 09:53:46 PM
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Default Re: Wood Patterns for Metal Castings

Lester Bowman,

Your post misses a major point. Back in the old days patternmakers made patterns the way they did because that was what they had available to them to make as many patterns as quickly as they could. They weren't going for the experience, they were going for stuff. So in that sense the new ways of doing things, plywood and 3D printing, are more true to the original patternmakers' intent than the people who are still working with mahogany and jelutong. I'm sure those old timers would be all on board with the new technology once they saw its productivity and precision. Or so say I.
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Old 04-10-2016, 09:52:00 AM
TomBall TomBall is offline
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Default Re: Wood Patterns for Metal Castings

tharper,I went on the link and the piston pattern looks to be one piece. It does give me good ideas though, especially the boss on the end to chuck in the lathe for machining reasons. I like the suspended core also. I might have to get ahold of Cattail and see if it would be acceptable to them.
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Old 04-10-2016, 01:30:12 PM
tharper tharper is offline
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Default Re: Wood Patterns for Metal Castings

Excellent Tom,

You could do it as one piece but they would have to cope (dig) down to establish the part line. Its just extra work on their part. It not hard to make a split pattern. Laminate up your wood, Glue together with brown paper in between - turn than before splitting drill through for the locating dowels, split, add the dowels and fill the remaining holes.

I usually turn my pieces long than cut off one half at each end so I have a flat surface to rest the pattern on when I drill the dowel holes. or pre-drill the dowel holes before you turn the piece.

For fillets you can use the old school wax fillets, bondo or Durhams Water putty (my favorite.
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Old 05-09-2016, 10:04:02 PM
tharper tharper is offline
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Photo Re: Wood Patterns for Metal Castings

I posted some of this over on my on-going Big, Big Wisconsin thread on the Antique engine forum, but I though it might be good to do a little post here as well.

The following is an example of a non-split pattern. In this case its a gear box for the drive for the oil pump. Since all I have of the original is a bit of smashed bronze including the stem and thrust bearing I had to create a pattern and have the part cast.

Rather than using my traditional method of wood patterns and since I have the technology available (I teach Drafting & Engineering Technology) I decided to model it in 3D using Autodesk Inventor Professional and then 3D print the pattern and core box.

Once the individual components are modeled I created a working drawing. The part I needed to cast is B1B.



Next I created the models for the pattern, core print and core box halves. Since molten metal shrinks as it cools, I needed to apply a shrinkage factor. This means that the pattern and core box will be larger than the actual finished casting. If I made the pattern and core box the same size as the finished piece than the resulting casting would be smaller than its supposed to be.

Every metal alloy has a different shrinkage rate. For the bronze alloy I chose to use its 0.18" per foot so I have to scale-up the size of my pattern by 1.015%. Seems like a small amount but it is important and does matter. That's why if you use an existing part as a pattern it should be built-up with a skim of bondo, paint, tape etc.

I also had to provide for machining allowances for surfaces that need to be machined. For instance the drawing calls for a certain distance (.550") from the face of the flange to the center of the stem. Since the flange face as cast is rough and un-even I would need to face it (machine smooth) this means I am removing material. If I didn't increase the thickness of the flange (1/16" to 1/8") to provide machining allowance, by the time I faced the flange so it was nice and smooth, I wouldn't be able to hold that critical .550" distance to the center of the stem. In addition to adding machining allowance to the flange, I would also had to add it to the thrust bearing surfaces which need to be milled and the diameter of the stem since that needs to be turned and threaded.

Next I had to think about draft. Draft is an angle that is applied to all the vertical faces that are parallel to the direction of pull. Hmmm.....so what's that mean..........Picture a square block. We place a frame around that block and pack sand tightly all around it. Then we flip the frame over. Once its flipped over we see only one side of our block sitting flush with the surface of the sand. As we try to pull the block up out of the sand (direction of pull) the sand wants to stick and cling to the vertical sides of the block wrecking our nice square hole. Now imagine if we shaped the vertical side of our block so it was slightly wedge shaped. As we pulled it from the sand there would be more and more clearance between the pattern and the sand - the sand wont stick to it.

That's exactly what had to be done to this pattern. Since this particular pattern will be laying flat (flange down) with the rounded part up when the drag (lower halve of the mold) is rammed-up the direction of pull is... well flange first. All the edges of the flange including the flats of the round piece and the stem need to have draft. I use 2.5 to 3 degrees.

So... to recap the pattern must include:
Shrink Factor
Machining Allowance
Draft

Now lets talk about cores. cores are moldings made of sand that create the cavities in a hollow casting. In other words as molten metal flows into the mold it flows around the core. Once the casting is removed from the mold the sand core is broken-up and removed and you are left with a nice cavity in your casting.

Here is an example: This was a failed casting of the gear box. It cold shut on us which means the melt was not hot enough. But you can see how the sand core was used to create the hollow cavity.



To core is made of sand mixed with a binder - in this case sodium silicate (water glass). Once mixed the sand is packed into the core box which serves as a mold to create the desired shape. Remember that core boxes need draft as well. In this case I made a split core box that has studs to hold the halves firmly and accurately together while the core sand cures.

Once cured the core will have consistency of a very hard cookie. Cores made from multiple pieces can be glued together.

Here you can see the 3D model of the pattern (green) core print (yellow) and core box halves (red).


The core print leaves an impression in the green sand mold which allows the core to be precisely positioned and held in place. Sometimes the core prints will be part of the pattern. In this case, since the pattern had to lay flat on the mold board. I created it as a separate piece. After the Drag is rammed-up and flipped over the core print is attached to the pattern with dowels. Than the cope or top half of the pattern is rammed-up. Then the pattern and core print are removed. In this case the core print leaves a 3/8" impression for the core to sit in.

If you flipped the failed casting shown in the above photo over you would see that the core projects a bit beyond the flange of the casting. That's the portion of the core that locks into the core print.

One other item. Since this is not a split pattern and we have that round stem which is not at the part line (face of flange) after the drag is rammed-up we have to cope or dig down into the sand to establish a part line at the centerline of the stem. Otherwise it would undercut the sand and not pull cleanly. I could make a follower which would establish the part line and eliminate the need for coping but I decided not too.

Here is a photo of the completed pattern, core box halves and core print.


Once modeled I 3D printed all the pieces. It took 17 hours to print the pattern and 20 to print the core box halves. Since the printing process I use leaves little tiny ridges denoting each layer I had to fill, sand and paint each piece. Its important that the pattern is as smooth as possible.

I hope this helps. Again, I am far from an expert - just a fellow trying to get a project done and learn some new and fun skills along the way and I am sure there are easier or better ways but this is what works for me.

Best regards,

Terry
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Old 05-10-2016, 04:11:58 PM
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Default Re: Wood Patterns for Metal Castings

I find your methods a great example of technology. Compared to your way I sometimes feel like a caveman carving out a wheel.
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