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Originally Posted by ItBites
David,
I thought you were the Engineer... Musta been Tom?
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Thomas is a mechanical engineer. What I lack in paper I have worked to make up with books and experience.
Quote:
Originally Posted by ItBites
David,
If you're not gonna re-heat treat, two things:
1. Your strength, especilly yield strength will be low in the center of the billet. Period. Further, your hardness will be down as well. These may not be any issue if you have put the thickness in the right places. Any aluminum billet above a T-4 condition and thicker than 6" suffers from property degradation in the center. Billets 12" thick can be real bad in the center, but depends on your source a little bit.
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Indeed the center will be somewhat softer than the outside. Our billet just over 9 inches thick. We cut the entire bottom end off the motor to minimize the softness in the center. Also, we are using an Aerospace forging house with extensive experience with large billets. We spoke with their engineers quite a bit aobut it.
Quote:
Originally Posted by ItBites
David,
2. Your block will warp when you unclamp it from the CNC bed, even taking small amounts of material per pass (unless you unbolt it to allow relief between passes). You can mitigate some of this by unbolting from the CNC bed after each or a couple of passes and re-truing you datum (or even shimming your datum). To properly do this you need to index off of other important features (bore centerlines, crank centerline, and cam centerline...) and measure the block again in the 'free' state. Determine the average of how things moved and adjust your datum accordingly. I have done this, but it is very tedious to do right, and at the end, you still have, at best, an average of tolerances and dimensions.
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We are certainly aware of stress relieving and the associated problems of dimensional creep. That is why we are holding on to one end of the block to do the machining. The other end is free to move around as the A axis unclamps and repositions. (The pillow block unclamps with A axis movements and re-clamps before machining to keep the system rigid.) Each time the pillow block unclamps, the block can move.
Quote:
Originally Posted by ItBites
David,
Not knocking what you're doing (trust me, I am not, I see that you guys do some very cool stuff). Just hoping to share some advice from someone who has been there and also interested in learning, if y'all have found a way to do what you're attempting, without dimensional walk. I could use that mojo!
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Thank you so much for your advice. We certianly don't have all the answers and are always willing to learn from anyone else who can help. Time will tell. We will see how it turns out in the end. If we didn't try, we wouldn't know. "What's the worst that can happen? We learn something." Bob Ross.
David
