Page 1

First a little explanation on what got me to building a shaker table. The roundhouse is going to be built using castings for the walls. Material to be used has been determined.  I was looking for a cut rock with a rough face for the walls. Something like this.

Close up.

Of course these are manufactured stone. What I was looking for is something similar in real stone.  I came across such a product by Chooch Enterprises from Oak Ridge Hobby’s and is no longer available from them. Chooch Enterprises was purchased by Walthers. I checked and they do carry Chooch Enterprises, but don’t carry the products I used. Perhaps at this writing they are out of stock.

Here they are.

From left to right, Medium Cut Stone Wall #8262 HO scale, Small Cut Stone Wall #8260 HO/N scale, Large Cobblestone Street #8658 HO/O scale, Random Interconnecting Wall #8302 HO/O scale. The random interconnecting wall #8302 is a ¼” thick resin casting. The other three are of a printed vinyl and approximately 12” long by 3 ¼” wide. I made two molds of the medium, small and random cut walls.

For the random cut stone wall I built a Plexiglas form to mount the wall in. For the other two wall types I used gator board.

The random stone wall.

And the medium stone wall.

The other two mold boxes behind the medium are for the small stone wall.

Now it was time to pour the RTV. I did the two random stone wall first. I pour from a height of about 12” to just coat the pattern. I let it set for a couple of minutes for the bubbles to rise to the top and then pour the rest of the RTV in. I use Smooth-On 30 for RTV and spray the molds with Mold Release 200.

I let the mold cure overnight and pull it the next day.

So we are up to having the molds made of the rock walls I want to copy. I’ll post the next part of the project in short order.

Bernd

Same here ...

I did the same thing when Chooch  announced they were leaving the business. I made molds of the walls and tunnel portals I had on hand using Smooth On 30.  The initial expense is high to make the molds, but becomes more affordable as more castings are made. I make my castings from hydrocal. 
 

    Tom 

Casting Material

I've experiment with three different casting materials for making the walls, Durhman's Water Putty, Plaster of Paris and Hydrocal. The water putty gets really hard once fully cured. The plaster of Paris is too chalky for what I want to do. But the Hyrocal is perfect. 

I'm not using the wall casting itself. I'm cutting the individual stones out to make a master mold for the roundhouse walls. Once I've got a master made I'll be experimenting with dental stone for casting the roundhouse walls.

Bernd

Page 2

Now that I had the molds made it was on to figuring out which casting medium would work the best. The three I tried are Durham Water Putty, Plaster of Paris, and Hydrocal.

You can get the water putty at any home improvement store or hardware store. Same goes for the Plaster of Paris. The Hydrocal I ordered from the “plasterguys” on E-bay. Same place I got the dental stone powder.

The first two walls were cast using the water putty. I used the recommended mixing ratio. I discovered that it was a little too thick and added water slowly until it reached a pancake batter consistency.

The third mold I used Plaster of Paris mixed to a pancake batter consistency.

After letting them set in the molds over night to cure I demolded the next day.

After a bit of clean up I dry assembled them to see how they fit together.

Not bad. It wouldn’t take much to fill in the seam. If you look real close you can see some small holes where bubbles had formed.

I assembled the three molds wanting to see how they would look when constructing a retaining wall.

Upon closer inspection of the walls you’ll notice many holes left by bubbles. One cause is to vagarious stirring of the mixture introducing bubbles. One remedy is to pour a thin layer first and let the bubbles rise from the shallower pour and then once when no more bubbles rise to the top to pour the rest of the mixture on. Or the mechanical solution of a shaker table, which we’ll build in the next installment of this blog.

Of course along the way when experimenting like this there are mishaps. A closer look at the water putty wall casting shows the holes bubbles left.

Another disaster in casting is thinking you need to make the mix more liquid to pour into the mold and maybe the bubble will surface faster. Not so with the following two pours. One is plaster the other is Hydrocal.

The plaster version had way too much water added. It never cured or got hard. It had the consistency of cottage cheese.

The same happened to the Hydrocal wall.

Now here’s an almost perfect pour, if it weren’t for the bubble holes.

So these test molds is what prompted me into looking at building a shaker table. I also tried putting the mixture under my home made vacuum chamber. It didn’t work to good probably because the mixture was too thick even though it was of pancake batter consistency and I couldn’t pull enough of a vacuum. That’s another experiment for another day.

In the next installment I’ll get into the build of the shaker table. Until then stay save.

Bernd

Link away

As long as you aren't advertising something that you make money on, feel free to link to it. 

@ Jeff

Ok, sounds good Jeff. Thanks. Nope no money involved.

Bernd.

No bubbles using hydrocal

I’ve been using hydrocal for many years in the molds I have made and have never had any issues with bubbles or imperfections. I always wet the mold before pouring the hydrocal in. I don’t have a shaker table or vacuum. All my molds are simple one piece affairs, mostly flat. I have also built some from plastic for things such as abutments and bridge piers.  Going to more complicated multi part molds might cause some issues, or using resin or another material besides the hydrocal might also.

Tom

@ Tom

Thank for you adding your thoughts. Much appreciated.

I've used a mold release and I tried something new. I learned this from watching a Bruce Hirst video's. He uses a dishwater rinse diluted in water to spray his molds before casting. He use it in his dental stone casting projects. Here's the video.

I still have a problem of stirring the mixture to vigorously.

Here's a picture of a casting I did last night using the dishwater rinse.

Still some bubbles, but not bad. More practice at stirring the mix is needed.

Bernd 

Up-date

Jeff gave the okay to link roundhouse build page of the forum where I saw the modeler build a look-a-like of John Allen's roundhouse. You'll find the updated link in the intro to this thread.

Bernd

Bubbles

I'm not sure I would have spotted those, or at least not all of those, if you hadn't circled them. They sort of look like the kind of damage an industrial building accumulates over the years. 

Those bubbles

Jeff,

They are hard to see on the picture since you are not looking at them at full scale. I did another casting last night. It came out much better. Conclusion is that 1) I was stirring the mix to vigorously. 2) there seems to to be lost of air in the powder mix. As you pour the powder into the water it releases lots of bubbles. On this pour I let the mix soak in the water, then placed the bowl on the vibrating table while not stirring so vigorously. Then poured the mix into the molds while they were on the vibrating table. After several hours I de-molded the castings and had better results. Here's the picture to prove it. Also this wall has smaller blocks than the previous walls I cast.

I'm satisfied that I've got it down to just a few. As I said before I'm not using the walls themselves, but am cutting out individual blocks to build a master pattern for the roundhouse walls.

I hope to have the build of the shaker table posted by tonight.

Bernd

Page 3

At the start of the roundhouse project when I started to cast the first walls that are going to be used for building the master pattern for the roundhouse walls I discovered I was going to need something to remove bubbles from the castings. A member on another forum made a good suggestion that I build a vibrating casting table. I did as he suggested and searched the Tube. Found some interesting setups. I took the idea of one I liked and modified it to the size I needed.

So, let’s get started. First you'll need a motor that will vibrate when something on the shaft is offset from center. I had the perfect motors. Back many years ago I got very interested in building model air boats. Both gas powered and electric powered. I started to build an electric one to retrieve the gas powered one when the engine quit. I didn't get too far before I lost interest and went back to model railroading. Anyway I had started to build the electric powered one with twin 12 volt electric motors. I got as far as building a frame work to mount the motors and two pontoons to support the batteries and motors. The first picture shows what's left.

The motors are out of one of those little plastic cars that kids first learn how to drive with. They have two motors a bunch of plastic gears, a charger and two 6 volt batteries. I think this is how they get two speeds out of the vehicle. I happen to be two driveways up from the towns transfer station. The guy that is there on duty is my neighbor and allows me to bring back any purchase I don't deem useable. The motors are quite powerful and run at a fairly high rpm.

Before mounting the motor to the table I needed to find a power supply. The computer power supply didn't like the motor at all. It would start but the power supply would shut down. One of two things happening here, either too much amperage being pulled or the motor is way too noisy (electrical spikes back feeding into the supply). The old train transformer worked okay but would pop the circuit breaker. I lubed up the bearings a bit and the supply seems to be able to handle the motor at around 9 to 10 volts.

When I had built the motor pods I used some PVC piping I bored out to the motors outer diameter. The motor is a tight slip fit. I did that so I could pull the motor out without having to unscrew it from the frame. Also the hold down band didn't squeeze on the OD of the motor.

In order to get a vibration out of the motor I took one of the blades and dismembered it.

The motor was mounted on one to the plates. I purchased two sets of four springs that I thought would work. The set on the right have a larger diameter wire to make the spring a bit sturdier. I turned four pieces of square wood to the ID of the springs for a snug fit. At this stage of the project I couldn't find the dowel I knew I had hid somewhere.

The turned pieces were glued and screw to the bottom of the table.

By the time I got around to doing the bottom part of the vibrating table I had found my dowel. Here I'm marking where the round dowels will get glued to. I was going to drill a pilot hole and  screw the dowels down but found it wouldn't be necessary.

I just glued them on with white carpenters glue. Waiting for the glue to dry so I can take the table for spin.....ah vibrate.

And the finished vibrating table. Works quite well except it doesn't vibrate enough. I'm going to have to add more weight to one side of the abused prop to give it a bit more vibration or make something on the lathe.

I increased the weight on the one side of the prop by adding 3 more nuts and cut off the remaining part of the prop on the opposite side. There is a lot more action now.

I am also using a product mentioned in one of the video’s I post by Bruce Hirst in his casting videos. He used a dishwater rinse product in a water mix that he sprayed into the mold to help shed the bubble off the mold. Works pretty good.

Here's a comparison with what I was getting before I made the vibrating table and last part I cast last night.

Before:

Last night:

Take note that the blocks on this wall is the smaller block wall version. The dimensions are the same in length and width as the large block stone castings.

So that just about wraps it up for this project. I’m going to take a break here for now. Next will be the building of the master pattern for the roundhouse walls. This will take some time. If there’s interest in this part of the project I’ll post updates as I work on the pattern.

Bernd

Improvement added for leveling

I made a slight improvement to the shaker table. Every time I set something on to shake the bubbles out, the material would shift to one side of the mold. I had to put a shim under one side. After not finding that same shim the next time I needed it I decided it was time for a slight improvement of the table so this is Ver.1.1. Now I can adjust the level both ways by just turning the wing nut.

The parts for one adjustable leg. 3/8" bolt, two washers, one nut and one wing nut.

The sequence of the assembled leg.

The top side with the legs installed.

The bottom side.

Everybody understand the three leg principle of support so you get no rocking? Four legs would be to hard to adjust the level. Remember the three legged milking stool? Same idea. Except your not milking a cow.