Saturday, June 13, 2015

I still hold a large amount of dislike for you, bear.

As with any relationship, problems aren't just one of the party's fault. You both have to be willing to compromise and make changes. Either that or you must decide to give up and go your separate ways.

I'm not ready to give up on the bear just yet. I took a little "me" time to reflect following our last encounter. Time to think about what I could be doing that is contributing negatively to our relationship. When I came out of this time of reflection, I felt better prepared to face "our" problems.

<shudder> That got a little to real for a moment. I feel like I've had that conversation way to many times before.

Anyway, I did come up with two things that I could change or do better.  The first thing was I gave up on trying to draw the bear with the inner portion made as part of the drag. Instead, I decided to make a "core" for inner portion separately.

I say "core" in quotations because I wasn't making it like you would a proper core which would be from a separate, baked material. I had actually this before with several different recipes and had about as much success as I did with my greesand, that is: none. I think that's overkill for this project anyway but it is something I will certainly come back to on a project when required.

For this pattern I felt I could just mold one out of the Petrobond and dump it out like you would a sand castle. I used and excessive amount of parting dust, crammed it full of PB, and the first one came out quite nice.

The only issue I had was with its legs which tended to break at the narrow portion when demolding. I've noticed this tendency before with this pattern so for the second attempt, I decided to try to reinforce the area lengthwise. A popsicle stick broken in half seemed to be almost the perfect length to make him some internal splints.

The problem, I discovered, was that they interfered with the ability to compact the surrounding area sufficiently. This led to the legs deteriorating even worse when dumped because it would crumble rather than be a clean break. So, in the end, I made it the same way as the first (i.e. without sticks).

I figured two cores were sufficient. I only plan to make one actual mold since I don't have that much available PB. So just having one and a backup would do. With that done, it was time to enact my second change. 

Previously, I'd been digging away half the depth of the pattern to get to the parting line. I realized that is silly. I decided to just adjust the pattern depth by placing some spacer boards around it when I go to ram the first flask.

Of course, the boards didn't match the contour of the pattern so a small rectangle of sand was left around. This was much easier to dig out though than the way I was doing it before.

One additional change I had to do (as a result of the pattern being offset) was now I needed to dig the runners in the cope instead of the drag. This meant I had to completely flip the cope over whereas I usually just set it on it's edge.

Everything was going relatively smoothly until I had almost flipped it over and... my hand slipped. Too much parting dust (yeah, that's it). It of course landed against the drag jostling both patterns a fair amount and creating a small fracture line where the fresh Petrobond is backed by used PB. It didn't appear too bad so I decided to keep going. I tried to repack the areas that were obviously damaged as best I could. I dug the runners and I thought I was out of the woods.

I set the bear back over the core to be able to handle it and placed him back in the drag. This went surprisingly well and it wasn't until I went to lift the cope and turn it over... (no I didn't drop it again!) I realized how bad the damage from before was. Most of the surface where the old and new PB mated sloughed off onto the counter.

At this point, I'd already been at this for almost four hours. Well, I had be doing other things along with this but either way, it was too late to make another pattern so I decided to keep going with what I had. I figure that the inside of the pattern would be okay and about half the outside pattern would come out intact. I could use that as a guide to clean the rest of the casting on the band saw and sander. It'd be like cutting off and cleaning where the sprue would normally be just much, much wider.

Since there was much more to cast now, I definitely knew I need more aluminum than I had available. Time to start collecting (i.e. emptying) fresh scrap and getting it melted. Here's some now warming by the furnace before being immersed.

The more I thought about it and melted scrap, the more concerned I was getting that the pour would be short. My crucible was about as full as I felt I could safely get it with aluminum, I just had to hope it was enough. It wasn't. 

Since I already have a "short bear", I'll call this guy "inside-out bear" because the areas where I actually wanted aluminum are bare and vice-versa.

Despite this being yet another failure, there is a glimmer of hope here (albeit slight). The parts of the cast that came out actually do look like I intended. Making the "core" for the inside as a separate piece is definitely the way to go. Offsetting the pattern, not so much. Well, it wasn't the offsetting part, it was that I had to dig the runners in the cope instead of the drag that I didn't like. I will have to rethink that approach but at least I did learn a few new things in this approach.

In fact, I think I'm going to withdraw my earlier statement calling this a failure. I didn't fail, I just discovered a
new way not to do something.

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