large casting advice

I'm new to castings and am playing around with designing an iron sand
casting for a machine tool base I have in mind. Could any of you
casting veterans help me with these questions:
(the casting will be about 1500 # and will look like a typical "grate"
style you see for the beds of machines)
1. Is there an avg price per pound for gray iron and also for ductile
iron that I can compare (I can adjust the size of the casting on the
strength of the material)?
2. What is a typical draft angle?
3. What is a typical minimum inside radius? (smaller is better for me
from a weight/cost standpoint)
4. What is a typical minimum wall thickness? (I'm debating going
between more thin walls or less thicker walls).
5. What is a typical shrink factor? Just need an overall, nothing
fancy for thin vs thick areas.
6. I need to have some 3" holes that get bushings pressed in. Should
I just plan on post-machining these or will the holes be accurate
enough as-cast? IOW how close of tolerance can be held for a 3"
through-hole that is about 10" deep (please don't try to impress me
with a GD&T- answer, just a simple tolerance is fine :) )?
7. Can you recommend any casting houses that can do this size of
casting but that are *affordable* (mom-and-pop type foundries)?
Thanks folks.
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Could it be that you have your list of question reversed?
It might be quicker to find a foundry that can pour 1500# for your price and location and then ask them for advice.
Reply to
Yes, that is definitely a consideration. I was hoping to educate myself a little before I started going out for bids though, that way it will keep the estimators from throwing in a "baby-sit" factor if you know what I mean. I searched the web (and of course the newsgroups) and there's a firehose of information out there. I was hoping to narrow it down a bit with some rules of thumb and I know there's a lot of casting folks on this NG.
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Most one off machine bases these days are weldments. One local company makes machine bases from 2" plate, runs the result through an annealing oven. It doesn't take much 1" plate to give you a 1500 pound base unit.
joe_d wrote:
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I think cast iron shrinks about 1/4" per foot. IIRC its 0.0000063 inches per inch per degree F. And think of a temperature of about 2500 degrees at casting time. 2 degrees is a draft number that is often used. Brn Franklin made the plates for his Franklin stove pretty thin, let's say about 3/16" thick.
Price per pound will vary a lot depending on the quality and how much work the shop will have to do to produce it. Think $1 per pound at least.
3" hole. No, it won't be accurate enough. I assume you'll need to core it and you'll be lucky to get close. You have to leave enough metal to machine just to get the hole centered where you want it.
Sounds like a $10,000 pattern to me.
Pete Stanaitis -----------------------------
joe_d wrote:
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This material is relatively expensive ($1 - $1.50/lb IIRC), but doesn't require pattern making skills. The material is typically cast directly into a wooden mold. Metal parts can be imbedded in the casting, either attachment points or functional parts of your machine.
The biggest problem for a do-it-yourselfer would be mixing the material. ITW has a jobber that will do the casting, but that'll be more expensive than cast iron, assuming you make the foundry patterns yourself.
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There have been some discussions here in the past about home brew polymer concretes that'd be worth reading if you're interested in this sort of thing.
Ned Simmons
Reply to
Ned Simmons
If this is a one-off or very limited production think lost foam. You make the pattern up out of styrofoam, and add styrofoam vents, sprues and runners. The foundry can hand ram green or oil sand and when the iron/steel is poured it will flash burn the foam. Makes a hell of a stink and lots of black smoke. Some is toxic so don't breath it. Alternative is to coat the styrafoam with an investment, making sure you have plenty of vents to allow the gasses out. The foundry then can use dry sand around the investment coated foam core for support.
Another alternative is to make the base out of relatively thin sheet/plate [c. 1/4 inch] and fill with high strength [polymer and/or fiber reinforced] concrete. Very strong with exceptional vibration dampening. Used for many of the new cnc machines.
Uncle George
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F. George McDuffee

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