Finding Low Spots -- What's the Best Way to do it?

[Treadhead]

When scratchbuilding, I use the lofting technique. I use multiple cross sections and fill between them with putty. Getting the overall shape is not much of a problem.

The issue that I come across is locating low spots. Obvious ones are easily found. The shallow ones are the most insidious of all. I can get a hint that they are there when I hold the thing under a light and shadows fall in irregular patterns. This drives me up a wall.

So what's the best way to find them?

And here's another prob. When lofting and priming, I see faint lines where the formers are. Sometimes this is a problem that can be fixed with multiple applications of Mr Surfacer -- but I'd like to avoid it if possible.

The only solution that I could think of to avoid both of the above is by using styrene strips across the formers and then filling the gaps with epoxy putty.

But there must be an easier way...

Thanks
Tread

[Digger1]

look at it at a shalow angle in good light. If you have doubts, putty wouldn't hurt. Just sand smooth.

[mech]

Would it be possible to make a negative template of the shape you working with?
Place the template on the model and move it along the peice and when you get to a low spot, it should be seen easily.
I would think maybe. I guess the application would depend on how complex the shape is.

j

[Umi_Ryuzuki]

I spray the model with primer, then sand with a long flat sanding block.
The low spots will hold paint, the rest of the primer is sanded away.

[mech]

I spray the model with primer, then sand with a long flat sanding block.
The low spots will hold paint, the rest of the primer is sanded away.

Much simplier technique. I use that with autobody work, I have no idea with I tried to come up with something more complicated.

Perfect Umi.

j

[Treadhead]

Good suggestions and ideas all thanks

Baba

I try this and have some success. The problem I run into is deterniming the exact boundary of the low spot. I guess just giving it a big dab of putty would help. Maybe I'm just thinking too much.

J-

This technique is a good one, in fact I've seen others do this. With me, I can't figure out if the error is on the negative section or the model.

Umi

This is promising, but I have one question. Can you just apply the putty over the primer? Will it stick? I could mark the spot with a pen, sand away the primer in the low spot and apply putty. What do you do?

Again thanks guys! I'm always amazed by the level of talent and willingness to share ideas on this board

[Andrew Gorman]

Another trick to use is to alternate colors of primer or putty to really make the high and low spots stand out.
Andrew

[DX-SFX]

The auto trade spray a speckle coat of a darker colour (usually black) on top of the grey primer like holding a spray can away from the model and pressing the button for just second or two. When you sand, low spots will stand out easily. You add high build primer or filler to the low spots and just repeat the process until you get an unbroken grey surface all over.

[USSARCADIA]

I find that seeing imperfections is easier in indirect sunlight as opposed to artificial light. For some reason they all pop out that way. I know, not always easy in winter.

[max142]

good info. I have the same problem. prime and sand, over and over again and still low spots. man, this gets discouraging.

[Arklan]

i use the prime and sand technique, but man... sometimes i just couldn't get it right. ...oh well. only i'm gonna know.

[Mr. Badwrench]

I use the same technique as Umi, but instead of primer I use a Sharpie. I've never had the ink cause either paint nor putty to lift. By the time I'm done sanding there's very little ink left anyway. Andrew Gorman's technique works well too. As for the problem of the formers still being visible even after all is said and done, I'm still struggling with that one myself.

[Arklan]

i've had that problem with the formers as well, once... course i've only used that method on that particular model... i'm still experimenting with techniques...

anyway! i solved it by... uhm... heh. saying it was intentional since it kinda looked cool given the subject matter.

[Treadhead]

I use the same technique as Umi, but instead of primer I use a Sharpie. I've never had the ink cause either paint nor putty to lift. By the time I'm done sanding there's very little ink left anyway. Andrew Gorman's technique works well too. As for the problem of the formers still being visible even after all is said and done, I'm still struggling with that one myself.

There are only two ways I have found to get rid of visible formers -- neither one pleasant.

(1) Spray the surface with Mr. Surfacre 500 and this will bring out the formers. Now take a paint brush and paint some Mr. Surfacer 500 onto each visible former and sand lightly until everything blends. This is when I beat myself about the head (after putting down the paint brush and jar of Mr. Surfacer that is) and tell myself that there has to be an easier way...

(2) I build the frame a bit undersize and plank the frame with styrene strip (let's say .040). I use thin strips and purposely leave gaps. I then apply the putty between the gaps and sand.

The former lines are caused by the putty being level with the former and the former not being exactly beveled to the curvature of the hull. The trick is getting a layer of putty to cover the formers -- yet be of a uniform thickness and still conform to the overall shape as dictated by the formers.

The planks give you a guide for the thickness so that you have less problems with low spots.

It's still a hellride in practice, but it works.

Now with that said.....

THERE HAS TO BE AN EASIER WAY!!