Cast Turrets, Etc.

[neverbuild]

Whos got some good techniques for scrathbuilding cast parts like the the turret on an M103? One guy at a show told me that he uses a technique from the boatbuilding community. He sectioned out the turret, and made guides out of sheet plastic. Then he basically whitteled a peice of balsa down to the shape he wanted, then he cast it in resin. What do you think?

JG

[jimz66]

John what do you mean by sectioned, did make cross sections? Like a balsa wood boat or plane?

[neverbuild]

Exactly.

JG

[jimz66]

Yeah okay I follow, But and here it comes I would guess it would depend on the individual's talent and skill level as well as the depth and quality of their toolbox.

[neverbuild]

Well, isn't that always the case....

JG

[jimz66]

Yup!

[Legendary]

JG and Jim-
                The suggestion to "Section" the turret is just a description of a method you can use to make a shape that is difficult to determine accurately by looking at a two dimensional drawing. The best example I can think of is a boat hull.

Describing this in writing must be the worst way to communicate it but I will give it a shot.

Check out this boat hull plan:  http://www.pt-boat.com/originalhull/pt593.html



Being able to read a drawing like that is key- I tried to explain it in text and then realized you may know this already.

Anyway- using the drawing at the right you can make some hull cross sections. (port to starboard, left to right) You will notice that each cross-section is numbered 0 through 12. You space those along a bow to stern axis as shown in the drawings on the left.

I believe the guy from the show was describing making the cross- sections from styrene and filling the space in between with balsa. There is an important reason for using two different materials- you want to shape the balsa using the styrene as a guide. Basically shape the balsa so there is a smooth transition from 0 to 1, then 1 to 2, 3 to 4 etc. You end up duplicating the shape- old school style- no fancy tools.

You can do this with an X-acto a ruler and sandpaper.

The big hurdle in the case of the M103 would be finding a drawing with turret cross-sections. If you have that - you can make it!

I'll walk you through it if you sincerely want to make it.

Steve

[neverbuild]

Steve:

This is what I was talking about. I forgot to also mention that the guy at the show told me that he would carve the balsa down a bit lower than his guides, then put on a layer of putty to get the thing to the perfect size. He would also then add a layer of Mr. surfacer, and then cast the turret.

I don't have much experience with CAD programs, but I'm wondering if you could scan in a line drawing and then get a three dimenisional figure from that...? You could then add the lines like on your boat hull.

JG

[Legendary]

JG-
       I am not CAD savvy at all- but if you could get the turret drawn in CAD then you could have the turret made by Print-a-Part.

If you find a set of drawings with the profiles then this old school method is the way to go.

Are you really looking to do an M103?  I believe there was a kit of one at some point- I also know that the USMC Reserve Center in Syracuse NY has one on the lawn.

Steve

[neverbuild]

Steve:

No, I'm not looking to do an M103. Accurate Armour has announced that they are doing one...eventually. I have pics of the one at Camp Pendlton on my Picasa Page. Is the one in Syracuse an A1 or A2?

As a matter of fact, what I would like to build (someday) is the line of American heavy tanks that preceeded the M103. Those that came between the development of the Pershing and the M103. The Hunnicut Firepower book has four view drawings of all of those.

Print-A-Part can make parts that big?

JG

[Legendary]

JG-
      you are just like me man! I want to find out what I need to know- but I do not want to tip my hand about my brilliant idea!

I saw this Hunnicut Book years ago-  I remember the turrets you are talking about. The guns were mounted solidly to the turret. The turret rotated in its ring and the gun and the upper portion of the turret pivoted. Neat looking-

I haven't used print-a-part, however I know that the capability to produce parts that large using FDM (stereolithography) exists.

With 4 view drawings the turrets could be made-

I have been in contact with Print-a-Part about doing a seminar at AMPS EAST '09 so I have a contact there if you are interested in making an inquiry.

Steve

[neverbuild]

Absolutley! Please keep me in the loop on the seminar.

Thanks.

JG

[Legendary]

JG-
      something else just occurred to me on this-

IF- you want to give this a shot the "old School" way. Rather than Balsa you should give Aerated PVC a try. As the name implies its PVC which is injected with high pressure air as it cools.

You can glue it with PVC adhesive from a hardware store, or cyanocrylate. It carves really nicely, you can drill it sand it, file it- behaves a lot like styrene.... and when you get the shape you want it takes paint really well too.

Easier to sculpt a block of that down than build up a turret with styrene and putty.

If you want PM me and I will mail you a chunk of it.

Steve

[tlivancso]

Hello Steve,

I find Print-a-Part very expensive for the amount of material used in the SLA machine to create the end result which is still going to take a bit of putty and sanding to get a smooth shape. The SLA produces a stepped appearence and feel as it travels in the Z (up) direction.

Besides the client has to still do all the work to get the file to them so they can produce it.

JG if you can create the model I would be happy to have the part made for you, or if you can get the plans I would be happy to create the model for you and have the part made.

Regards,
Thom

[neverbuild]

Thanks guys for al the offers of help. I'll discuss with you at the show.

JG