Making a 10cc Whippet pattern

[bmac2]

After I ran some filler around the inside and cleaned up the top I wanted to make sure it would pull before I finished it. I did feel like I was getting a bit cocky on this piece. It’s not terrible but it looks like I need to work some more draft.
No worries the forecast for tomorrow is clear and 29 so I can think of worse things than sitting in the shade sanding this thing.

 

[stevehuckss396]

This is really cool. I'm enjoying this one.

 

[bmac2]

Thanks Steve, glad to hear it. I think I must be getting close to a record for the most saw dust on a machinist forum.Rof}

 

[bmac2]

It was a hot day in the foundry (by Alberta standards) 30 degrees and I’m stuck sanding draft angle into the timing cover. I had to setup the tent just to get some shade. Brutal, sand a little check the angle, sand a bit more check the angle. If it wasn’t for the breeze, a cool drink now and then and that nap that snuck up on me while watching some bees I don’t know if would have made it.

 

[bmac2]

But I persevered and the pattern is now pulling from the sand. I had to add a lot of filler to get the inside to pull but finally got it working.

 

[bmac2]

I add the two nubs for the crank and camshafts and it still pulled well so I gave it a quick shot of filler primer and then the blue to finish it off.

 

[bmac2]

There’s something about this part that I really like so I was anxious to see if how it was going to pour. It’s already hot, I know, a lot of you are thinking “Bob 30 degrees isn’t hot” but I have a couple of other things I want to try. I also wanted to check out some changes I’d made to the burner so I thought I’d fire up the Troll.

 

[bmac2]

I had a couple of ideas for the gating I wanted to try so I rammed up the pattern in a small snap-flask. For anyone that’s interested a snap-flask allows you to ram up the pattern and then by undoing the hasps open it just leaving the sand. Great for when you want to do multiple pours and don’t have room for, or just don’t want 5, 10, 20 flasks kicking about.

 

[bmac2]

Now I know I took pictures of both gating setups but since the last OS update my i-pod has started putting the picture into random directories with incipits names and I can’t find them.

Thank you Apple I needed that.

 

[bmac2]

Oh ya.
Back in the first post I’d said “But it may have molten metal, sand, clay, smoke and fire!” This time I remembered to check the batteries in the camera before I started. Not much action I’m afraid but when you’re talking about 3 lbs of aluminum at 671c, 1240f action and drama is the last thing I want.

[ame]https://www.youtube.com/watch?v=24ot6urhnps[/ame]

 

[bmac2]

The first one I poured is just a lid for a little compost canister we have in the kitchen.
The original lid was wooden . . . wood for wet veg kitchen scraps? *bang*

Out of the two timing cases one was a total fail. The gate or channel that carries the melt from the runner to the pattern had shifted out of place and the aluminum never reached the pattern. Dumb mistake and I should have caught it. The second one worked out pretty good and despite some pin holes and loose sand I think is a keeper. Finished the small bolt bosses are only 1/32” high and the two larger ones finish up at 1/16” and 3/16 so no worries there. I’d only let it cool for 10 or 15 minutes so that shake out was still pretty hot!
One of the best things about the shake out is you get to lose most of the leather.

[ame]https://www.youtube.com/watch?v=p_ziIQQL4cs[/ame]

 

[bmac2]

Cut off the spure and did a quick cleanup on the belt sander. I haven’t melted the better of the two castings I did of the block thinking I could use it to check that parts are coming out close to the right size. Back in the sweatshop it looks like all the bolt holes should line up.

Again – Thanks for dropping by

Now where’d those bees go . . . ?

 

[Swifty]

Great job Bob, you will be in to machining it in no time.

Paul.

 

[SmithDoor]

I like the snap flask
th_wav

Dave

I had a couple of ideas for the gating I wanted to try so I rammed up the pattern in a small snap-flask. For anyone that’s interested a snap-flask allows you to ram up the pattern and then by undoing the hasps open it just leaving the sand. Great for when you want to do multiple pours and don’t have room for, or just don’t want 5, 10, 20 flasks kicking about.

 

[barnesrickw]

Nicely done. I purchased castings not nearly as nice.

 

[bmac2]

With my sand finally holding together I decided to work on to see if I could improve the surface finish. My first batch of green sand (about 8kg) I made was with instructions off the internet using sifted Home Depot play sand. It was fun and I learned a lot about patterns and molding but I didn’t think the surface finish of the castings was good enough. Looking at it now it looks a bit like gravel and the only reason I can think of to use play sand is that its silica free and only costs about $5.50 for a 25kg (50lb) bag. I’ll be using it on the ice this winter.

 

[bmac2]

The sand I’m using now is a 50/100 blasting media (also silica free) that cost me around $7.50 a bag. I’ve been getting a pretty good finish but I want to see if I can get it a bit better. If you want to try casting and make up your own green sand spend the extra 2 bucks and skip the play sand.

 

[bmac2]

I’m still pretty new at this so this is just from what I’ve picked up reading. Course sand is great for venting with lots of air gaps between the partials to allow steam and gasses to escape but gives a surface finish like 80 grit sand paper. If you made green sand with just fines it would give a great finish but steam and gasses would be trapped in the mold and generally nothing good would happen to the casting. From what I’ve read what’s best is a mix of sand. One way to think of this like the jar filled with golf balls, then BB’s, then sand and finally water. So I don’t want the golf balls and you don’t want the water.
 
With all this in mind I stopped off on Friday and picked up a bag of 100/200 blasting media, this stuff is like flour.

 

[bmac2]

I started by weighing out 8kg of the 50/100, 2kg of 100/200 and 1.2kg of bentonite clay. Mixed everything together dry (yes dust mask on) before adding just enough water to get it to pass the squeeze test. This is where I wish everything was a different color so it would be easy to tell when it was blended.

It looked like green sand and it felt well sort of soft and silky scratch.gif so I let it sit in the sun for a couple of hours to rest and then mulled the crap out of it before giving it a try. I’ve been having trouble with the head cover so I used it to test the new sand. I set up a couple of different gates arrangements all with the pattern filling from the bottom and one using a knife gate. A knife gate is just a wide thin gate running the length of the pattern. I also messed around with the venting going from next to none to something that looks like the back wall at the gun club.

 

[bmac2]

Fired up the Troll and poured the covers.

[ame]https://www.youtube.com/watch?v=UTxDN8iFs7Q&feature=youtu.be[/ame]