CR30 3DPrintMill

[Steve_GScale]

Bruce,

Why not make the joint overlapping?

See posts 26-28 of this thread where I did an overlapping joint test of the top/middle/bottom panel.
I had an issue with the thin lap curling, but that was before I had the PLA+ filament tuned in, guess I should try it again. When I removed the lap I found that the butt joint worked well and decided the lap wasn’t worth the effort.

If I do use a lap joint, I still have the issue of hiding that joint at the surface:

I found that if I held the joint flush there is ever so slight a pucker on the edged that will require blending of some sort…

[Bruce_Chandler]

A butt joint would have the same problem, although it would not be as strong.
I haven’t tried it with PLA, but I have had very good results at hiding joints with Bondo glazing and spot putty.

[Steve_GScale]

I’m not worried about strength. If I go back to the lap joint between the top edges of these 4 panels and the window panel it should be more than strong enough. I could also cut a thin piece of (whatever type of ) plastic 28" x 1" and glue it along the entire backside of these 4 pieces for additional strength.

The whole question is how to print them so as to hide the joints.

I did a VERY QUICK test where I sanded the ends with a hand-held orbital sandpaper (400 grit),
glued with superglue, touched up with brush in Dremel:

and applied 2 coats primer + 1 of Rustoleum red:

First, I’ve learned I need a jig for the sander to keep the ends square!

So, Bruce, would the Bondo glaze fill the cracks/imperfections shown in the 1st photo?
Or would purposely creating a crack of about 1/32" - 1/64" give a better surface to the bondo
to grip and level out?

I think this question applies whether I do a butt joint or a lap joint…

[Bruce_Chandler]

Sure…well, maybe. The Bondo glaze is almost a liquid so it will get into the crack, but it’s up to you to make it smooth. If you haven’t used it before, I sure practice a lot first. I think it will work.

[Steve_GScale]

Perhaps this will make my question clearer:

Here I have a lapped joint between 2 of the ribbed panels, with a 0.010" gap.
If I design it with “no gap” there will still be a visible crack …

Would it be easier/cleaner to bondo the hairline crack, or the 0.010" gap?

[Bruce_Chandler]

Nice picture, and great question. The Bondo CAN cover that gap - but I suspect the “larger” gap MAY be a bit easier just because it allows some of the stuff to get in there - though .01" isn’t really very big! How patient are you at sanding?

[Steve_GScale]

Not very … pushing 70 yo, and my hands/eyes are not very steady anymore
That’s one of the primary reasons I like 3d printing, it doesn’t matter…

The 0.010" is arbitrary, I can make it 1/4" if that would be better… A test is printing now:

[manimal (Dan Gilchrist)]

@Steve_GScale

Would it be easier/cleaner to bondo the hairline crack, or the 0.010" gap?

It would be far easier/cleaner if you just used styrene half round. lol

I would not create the gap. I’ve done lap and other joints many times with FDM and find It best to make one side of the joint .1 mm smaller to create a tighter fit. Also, As Bruce mentioned, the spot glaze is like liquid. It can be a challenge to get it in the gap as it tends to pull out due to capillary action. Also, be aware, it starts to dry in seconds!
Here is my “hopper topper” printed in 3 pieces. Joint hidden by 2 coats of spot putty and 2 coats Rustoleum Sandable/filler primer.

[Rooster]

Fluting is a very slippery slope my friend ! Enjoying the progress even though I do not 3D print myself but enjoy watching and learning.

[Steve_GScale]

[Steve_GScale]

@Bruce_Chandler

Sure…well, maybe. The Bondo glaze is almost a liquid so it will get into the crack, but it’s up to you to make it smooth. If you haven’t used it before, I sure practice a lot first. I think it will work.

I reversed the profile from the ribbed panel and printed a “scraper” which may (or may not) be useful for working the bondo into the gap:

[Bruce_Chandler]

@Steve_GScale

Not very … pushing 70 yo,

Well, I can tell you that AFTER 70 it doesn’t get any better…