Making a 10cc Whippet pattern

[bmac2]

After carefully pulling the pattern I could see that I needed clean up the draft on the back edge and around the one foot.

 

[bmac2]

Worked on cleaning up the pattern and rammed it up again. It pulled better but needs a little work around the core print. I’m having trouble with the green strength of my sand. It always seems that by the time I have it where it will hold the pattern it’s too wet.

 

[bmac2]

Mulled the sand and tidied up around the core print some more and tried it again. I felt confident in the pattern this time and rammed up the drag as well as the cope. The two nails are to keep the sand out of the holes that locate the loose pieces.

 

[bmac2]

After ramming it up I dug down to the pattern using the pencil marks on the cope. Put in the loose pieces and rammed it up again. I guess this is more like a false cope process than a true loose piece but I don’t want to have to make a second core, I think it should work.

 

[bmac2]

Split the flask and the drag pulled great. The edges are clean and the resolution is about as good as this sand is going to give me.

 

[bmac2]

The cope on the other hand just fell apart. The pattern pulled ok and I have now proven to myself that my loose piece idea will work but the sand is just falling apart. I’ve been thinking that I might add a bit more bentonite.

 

[bmac2]

This was the first time I tried a pattern in my snap flask. It works but I think it’s a bit small. The idea is that when I do pour I want to do at least 3 if not 4 of each so if/when I mess something up machining I can just toss it back into the pot and grab a spare. ;D

 

[bmac2]

After reading “Name…That…Green Sand Casting Defect!” (http://www.afsinc.org/files/20020203A.pdf) an article from the American Foundry Society web site, last night I decided to add 100g of bentonite to my 50lbs of sand and mulled the crap out of it. Now with the lid on tight I’ll just let it sit in the sun for a day or so. . . . . . . After watching it for a while I found it just wasn’t very interesting so I got started on the new mold for the core. I wasn’t really happy with the first one so while going over it to correct the dimensions I made a couple of changes that I think will make it easer to remove the core. I got the wood cut to size and glued up with newspaper then mounted the patterns to the 4 pieces that will make up the bottom part of the mold. Clamped the bottom parts and drilled the holes for the bolts that will hold everything together when it’s finished.

 

[bmac2]

On the first mold I used my band saw and I think now that may have been a mistake. I had predrilled the corners to avoid having to cut the tight radius but even with the table tilted I had to file/sand the draft in the corners and I was never really happy with it. This time I opted for the scroll saw and with the table tilted a couple of degrees cut out the patterns. This just felt right. As long as I cut in the right direction I knew I would have plenty of draft angle in the pattern. I then replaced the blade with a strip of cloth emery (I hate sanding) and it was a breeze to clean up.

 

[bmac2]

With everything cleaned up it was ready for glue. The 1” dowel in the upper left has a taper on one end and I wrapped it with sandpaper to get the draft in the big hole for the core print.

 

[bmac2]

Bolted everything together and used a ¾” dowel to help align the parts and waited for the glue to dry.

 

[bmac2]

Once the glue was set I cleaned it up on the belt sander and split it apart. Then filleted the edges in the area that makes up the water jacket with a five-point-trowel.
With a bit more sanding it was ready for paint.

 

[bmac2]

All painted up I’m feeling pretty good about this one. Once the paint has dried for a day or so check it with some green sand. If that works it should be no problem with a sodium silicate core.

 

[Swifty]

Really looking forward to you pouring these castings, I've got my fingers crossed for you that it will all come out OK.

Paul.

 

[RichD]

Looks good to me. I'm learning. Thanks

 

[bmac2]

Hi Paul I’m actually feeling good about the patterns so far, it’s just the condition of the sand that keeps me up at night reading articles with chemistry I barely understand. The one thing I have learned since I started messing with casting back in November is that if I can get the hole in the sand right I can fill it with aluminum. I’ve got my fingers crossed too.

 

[bmac2]

Rich, I think the reasons I decided to post this slightly odd thread was that I found it frustrating to find much information on pattern making that I could relate to. Don’t get me wrong there is a ton of good information available out there but most of it is related to commercial foundries and other than “with aluminum make your pattern 2% bigger than you need” and “provide adequate draft” most of the examples shown, I think because of the diversity of patterns, are pretty general . So if one person can take away something from this I am very happy. Thank you.

 

[bmac2]

On with the show.
I jumped the gun a bit today and decided to try out the core mold. I justified this to myself by thinking that if it needs more work I’ll have to repaint it anyhow and if it does work I want to paint it in something smooth and high gloss anyway. So with a total disregard to the relatively fresh paint I rammed it up.

 

[bmac2]

The back of the mold came off as just as planned. The small button is only about 1/8” high with a filleted edge so I wasn’t expecting any drama. My idea here was to expose as much of the core as I could. If I bake it this will help it to dry out and if I gas it with Co2 I should get a good flow through the sand with the 1” opening on the front that forms the core print.

 

[bmac2]

There is no way in . . . . well you know the place. . . that I was going to be able to pull a 1” diameter ¾” long plug of green sand so what I did was hold it in place with a dowel and slide the front piece up. The sand crumbled a pit around the edge but there is no way this would have worked before I added that 100g of clay. My sand is better but not there yet. More reading and mulling . . . . :wall: