My first sandcasting pattern but I could use some advice.

[knight_toolworks]

Here is my first job making a pattern for aluminum sandcasting. all the edges have a 5 degree bevel. my question is is there a easy way to size things so you make them 2% larger to account for shrinkage? these were made from mdf with three bits. a 1/4" endmill for the bulk pocketing a 5 degree 1/8" endmill to keep the cost down for all of the bevels and a 60 v cutter for the big bevels.

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[Brady Watson]

The only way I know of to account for 2% shrinkage would be to have the part as a 3D file in ArtCAM & offset the entire relief to the outside by 2%. Otherwise...no, unless you somehow build up the entire model with some kind of paint or Duratec.

-B

[Brady Watson]

We made this at Columbia Falls High School in Montana when I visited a couple years back. It was created & toolpathed in ArtCAM, cut on the bot, sealed with shellac and casted. (Posted for inspiration)


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-B

[bob_dodd]

Now a long time ago way before computers (1966), I worked for a pattern maker, in the shop we had 3 different shrink rulers 1 for cast iron ,cast brass , cast alum. & used wax & leather fillets in bottom where it meets the sides to put a radius , the rest was done in lathe or by hand . I would think if you know the deminsions of the finished part, & Times that by 2% in X Y Z & then enlarge your vectors to that size, if I understand your post correctly your doing this as a 2D & machining with different bits hope this helps Bob

[knight_toolworks]

how do you do the math to figure it out? I am math challenged (G)say the ring is 5.865 how to figure it to be 2% larger.

[mzettl]

Steve,

What software did you use to create the vector drawing? I wonder if it would be sufficient to simply enlarge the drawing in x and y dimensions by 2%. With VCarve you would select the entire drawing, then scale it by the 2% factor, being sure that the "Link X and Y" box was checked.

For example, if the original x dimension is 5.865, then you would enter the new X value, 5.982, obtained in the following equation:

5.865 + (5.865 x .02)= 5.865 + 0.1173 = 5.9823

The entire vector drawing would then be scaled by 2%. Not being very familiar with casting, and allowances for shrinkage, I can't say if such a simple solution would suffice. Might be worth a try. Is the size of the finished product that critical that the 2% needs to be factored in at all?

Hope this helps.

-Matt

[knight_toolworks]

I used vcarve to draw it. the only critical parts are the rings in the middle since they need to be fairly close. so thats the part I have to worry about the rest is fine.

[henrik_o]

Or to simplify, 5.865*1.02=5.9823

However, all scaling happens from a reference point (or set of points; a shape). If your shapes are perfectly symmetrical, scaling each from point 0,0 will produce true scaling. If they are non-symmetrical, you can afaik not achieve true scaling from a single origo. Your casts do look symmetrical, so I guess this would not be a problem.

[Brady Watson]

Or...depending on the tolerances you need to hold, just do a cleanup pass on the cast AL part with an end mill. Now you'll be perfectly in spec provided there is enough extra meat there to machine off.

-B

[bob_dodd]

The picture on right top above thats mfd ,The center ring I think needs to be larger on both sides ( both inside & outside ) as this is going to be pressed into the sand mold , so when the hot metal is poured & then cooled it will shrink to the right size, this needs to be figured into the whole puzzle

[thecustomsignshop]

I have never done this before. I have been a shopbotter for years, now I feel like a newbie.

Do you mill the sand? Where do you get the materials? What is the process. Nice job, btw. Thanks..