1/18th Jaguar D Type

[hot ford coupe]

This looks pretty interesting. True , 1/18 is not large scale but in this case, I wouldn't count this build out yet. Let it serve as the experimental or prototype build for the larger scale kits. If this comes out like I think it will, it will do even better in 1/8. I like the guide coat technique. When you sand the material, it still looks grainy even though it's perfectly smooth. This will help avoid the confusion.

[John]

Hi guys,
I find the whole subject of rapid prototyping fascinating. But I do have a question. I have noted that regardless of scale all the bodies or engines I have seen have a set of grooves on them which are part of the manufacturing process. The question is, if I have a body in front of me do I sand down to the valley of the groove or do I use a high build filler to build up to the ridge line and then knock the whole thing back to the high line?
I think that we are looking at the future of modelling with rapid proto and look forward to seeing many more projects coming to the fore.
Regards,
John

[Daytonatim]

Good question John, and one that has come up a few times these past few weeks.

I have been thinking on this matter some and I think it just comes down to this. The 3D printer is just a machine that has a manufactured in accuracy. I figure it is just as likely to over spray an edge as it is to under spray and edge. Therefore I figure that the "true" edge probably lies somewhere in the middle.

Therefore I don't think it is wise to sand the RP material down to a smooth surface nor do I think you should just build primer on top of the rough body. We need to wind up in the middle somewhere. Keep in mind, the individual layers are only about .004 inches thick, so there aint a lot of height difference between layers and the rough "error spray" is only about .010 to .015 inches and sands off very easily.

This is why I decided to shoot the body with a standard primer (ie NON high build) for the first sanding . What I intend to do is to sand the primered body down untill I have about 75% of the primer removed. This allows me to knock off the high spots, but as long as I have black still showing in the low spots I know I have not sanded past the minimum surface level.

I will then shoot a layer of high build primer (grey), let it dry, and then shoot another layer of high build primer (red). I will then start wet sanding with 400 grit paper untill I get a pretty even distribution of RP material color and the first primer coat (grey). Any red primer I have left are "extreamly deep" grooves that I will apply spot primer too and sand till smooth.

I will then repeat the last paragragh again to obtain a perfect surface finish.

This is pretty much the same process I used on the parts of the Offy I wanted a perfect finish on, like the valvecovers and exhaust pipe. It sounds like a long process but it is not bad. The 400 grit paper cuts through the primer /RP material like butter.

[ScaleMotorcars]

Always loved this body style. Picked up a 1/32 multi-media kit about 10 years ago and had a great time building it up. 1/18 scale ??? Ill let it slide.

[Don Garrett]

Dan, keep in mind it could be done in 1/8th....just costs a bit more.

[hot ford coupe]

Good question John, and one that has come up a few times these past few weeks.

I have been thinking on this matter some and I think it just comes down to this. The 3D printer is just a machine that has a manufactured in accuracy. I figure it is just as likely to over spray an edge as it is to under spray and edge. Therefore I figure that the "true" edge probably lies somewhere in the middle.

Therefore I don't think it is wise to sand the RP material down to a smooth surface nor do I think you should just build primer on top of the rough body. We need to wind up in the middle somewhere. Keep in mind, the individual layers are only about .004 inches thick, so there aint a lot of height difference between layers and the rough "error spray" is only about .010 to .015 inches and sands off very easily.

This is why I decided to shoot the body with a standard primer (ie NON high build) for the first sanding . What I intend to do is to sand the primered body down untill I have about 75% of the primer removed. This allows me to knock off the high spots, but as long as I have black still showing in the low spots I know I have not sanded past the minimum surface level.

I will then shoot a layer of high build primer (grey), let it dry, and then shoot another layer of high build primer (red). I will then start wet sanding with 400 grit paper untill I get a pretty even distribution of RP material color and the first primer coat (grey). Any red primer I have left are "extreamly deep" grooves that I will apply spot primer too and sand till smooth.

I will then repeat the last paragragh again to obtain a perfect surface finish.

This is pretty much the same process I used on the parts of the Offy I wanted a perfect finish on, like the valvecovers and exhaust pipe. It sounds like a long process but it is not bad. The 400 grit paper cuts through the primer /RP material like butter.

It's a good thing I saw this post. I've been sanding down to the deepest defects and then smoothing from there. Everything I've done so far on the TDR 426 has needed the textured surface. One valve cover is another story. It should be fine because of the thickness of my paint, but it's going to make my job a lot easier. Thanks Tim for the new info. The thing to remember is that this technology is in its infancy. If anyone out there has some good suggestions, let me know. It may take a little time to perfect the handling but we'll get it right soomer or later.

[Don Garrett]

That's the way it goes when you are at ground zero. Had the same problems when they introduced Metal Flake and Candy paint (full size). Major learning curve involved, but look at what was accomplished with it. New toys, new finishing techniques, it's all part of the learning curve and you guys will be the experts that the newcomers go to for advice.

Somebody had to it.

[Daytonatim]

That's the way it goes when you are at ground zero. Had the same problems when they introduced Metal Flake and Candy paint (full size). Major learning curve involved, but look at what was accomplished with it. New toys, new finishing techniques, it's all part of the learning curve and you guys will be the experts that the newcomers go to for advice.

Somebody had to it.

Man Don, you are older than metal flake paint!!!!! YOU ARE OLD.......

Well I did about and hours worth of sanding on the D type. Thought I would post up some pics to show what I have been talking about.

The next thing I am going to do is re-scribe the seams again, to make them deeper and more accurate. Then I will shoot it with the two coats of highbuild primer .

Here they are

[Don Garrett]

Clear coat it and it would like it was carved from bleched out wood.

[hot ford coupe]

Congratulations Tim. You've just figured out how to do the world's first simulated petrified wood paint scheme. Just shoot a coat of clear and polish.

Sometimes I crack myself up.

All kidding aside, it looks like that's the best way to handle the roughness. It takes a lot of torture out of working with this stuff. A 1/8 scale body although more labor intensive because of its size shouldn't be too difficult to get nice and smooth. Let's keep experimenting. We'll get this down sooner or later.

[strevo]

Guys,
To help clear up some of the issues with where the design surface is on a rapid prototype part, maybe I can explain it another way...
The part is "grown" in the rapid prototyper from the bottom up, one layer at a time. The layers are about .0035" thick on the machine that you are using. The software creates the layers as 2D slices through the part, and then prints them one by one on top of each other to build up the part. As such, anywhere on the part that has a slope that is not exactly 90 degrees to the layer plane, will be created by "stairstepping" the layers. It is my understanding that the machine goes equally above and below the design surface when creating the "stairs". As you can see in the example I created, the steeper the slope of the part, the more stairstepping is evident in the final surface.
I hope this helps clear it up a little.
-Steve

[Daytonatim]

Steve, that makes it perfectly clear. Thanks.

So it looks like shooting for the middle of the layers is the right approach.


As far as the wood grain look goes, maybe I will just put some minwax stain on it and call it done!!

[strevo]

Tim,
I hate to muddy up the waters now, but I was going over my product literature at work and it seems that I was slightly off in my description. When the software creates the 2D layers, it moves up the part .0035" at a time, and takes a 0 thickness slice which it then uses to tell the printer what shape the layer will be. Because of this method, any undercuts on the part(in the as-grown orientation) will be below the design surface, and any positive drafted surfaces will be above the design surface. See my attached example for a better description. Also, I have included a picture showing how humidity, temperature, and bleed compensation settings can effect the final surface in either direction.
So I guess what this means is that in some areas you need to fill in to the top, and in other areas you need to sand down smooth. In the end though, keep in mind that these layers are extremely thin, and any amount above or below the design surface will be negligible, so do whatever makes the part fit and look good to you.
-Steve

[Daytonatim]

In the end though, keep in mind that these layers are extremely thin, and any amount above or below the design surface will be negligible, so do whatever makes the part fit and look good to you.
-Steve

LOL.......I am going to go with your last sentence Steve........My head is starting to hurt!


If you scale out the maximum predictable error (.0035" * 8) it comes out to be less than 1/32" in the real 1:1 car. So yes the most important thing is to just make it look good to you, the modeler, because you are the most important judge.

Oh, Steve, have you ever worked up any model stuff on Pro/E? If so, please feel free to post some up on the "Digital workbench" forum and share them with us.