Making a 10cc Whippet pattern

[bmac2]

Gently tapping the mold I CAREFULY got it open. Not perfect but this is green sand so actually it worked out better than I expected. Of course next I tried to lift if out of the mold and it just crumbled back to what it is . . . sand. I’m feeling great with the way this has turned out and can’t wait to give it a try with sodium silicate.
And the paint job survived! ;D

 

[Cogsy]

I'm learning a lot and it looks like a heap of fun, but I'm still stuck at the point of getting bubbles in my aluminium. I just bought some washing soda so I need to make a degassing plunger and have another go. When the weather dries up a bit I'll drag everything out and have another play.

 

[bmac2]

Cogsy I feel your pain. What type of aluminum are you using? I know I have more trouble with extruded than cast. If you can get just about anything auto related the aluminum is very nice. The better it is when you start the better your castings will be. I’ve messed around with degassing using washing soda a bit and one thing I’ll pass on is Don’t Fill Your Crucible the first time I tried it let’s just say the bubbles got very aggressive.

From what I’ve read the major culprit for pinholes and porosity is hydrogen from any moisture present anywhere. Pre heat everything, the stock you’re melting and all of your tools to drive out/off as much moisture as you can. I wait until my crucible is just starting to turn color before I add any metal. High humidity can affect the casting but if everything is hot you don’t get condensation forming. Pour as soon as you can and try not to overheat the melt. The longer the aluminum is in a liquid state the more hydrogen is absorbed. With me it’s my sand, I still haven’t found that magic balance of sand, clay and water. I’ve read that if you think your sand is a bit wet you can run a torch over the impression in the mold before you close it.

It’s only rained once since May so here humidity isn’t a problem. Having a good chunk of western Canada on fire . . . now that’s a problem. I heard on the news that they brought up a bunch of fire fighters from Mexico and now are looking to Australia. To the guys in the states sorry about the smoke.

 

[bmac2]

Yesterday I made up some SS cores. I’ve had trouble with cores off gassing in the past so I thought I’d try hollowing it out and running a 1/8” vent up the cylinder part of the core. I filled the pattern halves and baked them open faced in the toaster oven for a half hour or so at ~250 degrees.

 

[bmac2]

Once the core felt dry I took it out of the mold and glued the together with regular carpenters glue and put it back into the oven at 350 to dry out.

 

[bmac2]

The core came out a little crumbly around the edges. I’m still messing around with the ratios. Most of the info I’ve read on SS cores use a 6% sodium silicate to sand ratio (by weight). I got my sodium silicate from a pottery supply place so it’s not foundry grade. The foundry SS is a brownish color, thick, and hard to come by in my area. I found one place that had it in small quantities but it worked out to $86.52 for a gallon plus shipping. The stuff I have from the pottery supply is clear, thinner, and you have to use more of it to get a strong core. The up side though is the place is about 8 km from me, open Saturday, and the sodium silicate costs $7.00 a litre.
Mixed up a second 100g batch of core sand this time at 10% SS and just rammed it up solid in the mold and slid a 1/8” rod the length of the core for a vent and baked as before. It cured solider than the hollow one so I‘ll try them both.

 

[bmac2]

Today I’d mowed the lawn, cleaned up the garage, and fixed the little lights my wife has in her flower beds. I have a mostly finished block pattern and a couple of almost serviceable cores and my wife had left me on my own recognizance for the day.
I should have gotten back to finishing the pattern but I just wanted to melt something.;D

Rammed up the drag and then filled the cope about half way and dug out the space for the timing gear mount and rammed it full.

 

[bmac2]

I split the flask and the patterns puled ok but again the sand was looking weak but I decided to give it a go just too see what happens. The two pieces that make up the timing gear mount stay in the mold when I pull the block. The larger one is rapped and just lifted out. The smaller one slides into the void left by the first.

 

[bmac2]

Got the hollow core snuggled in to the drag and the fit looked pretty good.

 

[bmac2]

The pour went good filling both of the riser extensions so I assumed it filled. Now I just had to let it sit for 5 or 10 minutes and I could finally see what I got.

 

[bmac2]

As I expected there is a lot of flash. The general surface finish isn’t horrible in most areas and the core cleaned out well with a little extra work in the cam shaft area.

 

[bmac2]

The biggest problem or lesson learnt on this was that a hollow core will/can float. The dark patch at the top right is just some sand but the bottom left is a hole from the core floating up.

 

[bmac2]

The undercut worked out pretty good though it looks like a lot of loose sand was washing around in there.

 

[bmac2]

I use to feel funny about the next step but now I almost look forward to it.
Cutting it up in the band saw the aluminum is very nice. Not soft and gummy at all with the blade clearing of chips with no problem. The outline of the casting looks terrible but that is mostly due to the fact that I used the flash as a guide line for the cut. The inside finish on this half is a bit rough but not as bad as some I’ve made.

 

[bmac2]

In the cope side the inside is very rough. I’m not sure but this could be from sand washing loose from the core (it did feel soft) and moving around or gassing. The three big black spots in the upper right are actually in the flash so they wouldn’t have been a problem.

 

[bmac2]

Looking at the pictures again I’m starting to think that it’s a gassing/moisture problem with the core. If you look at the cylinder part of the core it’s good. It’s the larger part of the core that’s bad. I’ll try baking them longer and perhaps hotter to see if there a difference.

I’m actually feeling pretty good about this one. The basic shape of the core turned out almost exactly the way I wanted it to. This was the thinnest wall I have tried and it worked (sort of). And I now know that hollow cores can float.

I’m going to add another 200g of bentonite and work my sand some more. I want to see if I can find some fine sand to add to help with the finish. For this one it’s going to be back to the bin to be melted down again.

 

[RichD]

Looks like good solid progress to me.

 

[fourstroke]

Hi Bob
They look good castings apart from the problem with the cores.
Like you I discovered that the cores move, that particular trouble cost me 4 or 5 pours, in the end I used a nail to hold the core in place. I pushed a hole into the core through the crankase boss before I set it with co2, then used a long nail to push through the core and into the sand mould and that stopped all the trouble I was having with the core moving
Hope this helps
Dougie

 

[Swifty]

It’s only rained once since May so here humidity isn’t a problem. Having a good chunk of western Canada on fire . . . now that’s a problem. I heard on the news that they brought up a bunch of fire fighters from Mexico and now are looking to Australia. To the guys in the states sorry about the smoke.

Hang in there, I read in today's paper that a couple of hundred firefighters are on their way from Sydney and Melbourne.

Paul.

 

[Swifty]

Your castings look well on their way to being right, I'm impressed with your efforts.

Paul.