Joining resin printed parts

[Kevin-the-lubber]

Can I pick the brains of this community. I need to join two resin printed parts as a T-joint. The main body is printed such that the jointing face is supported, meaning I lose some precision. The edge of the part to be 'T'ed is the side of the print so nice and sharp. I have very little tolerance to play with, 0.2mm max, otherwise it adversely affects the fitting of various dependant parts. As per the screen grabs, currently I'm using a dowel approach but this is unsatisfactory as the dowel holes get distorted during printing and re-boring tends to shift the centre by maybe 0.1 - 0.2mm. I'm scratching my head for a better approach and just thought I'd see if anyone has suggestions.

 

This is the assembly, the two sides get joined to the main plate. The 'webs' are actually floors and are part of the sides.

 

A close-up of the dowel method. The 2mm dowel is part of the main plate, the socket part of the side.

[Egilman]

Ok, the pins become locators for the side parts as well as attachment points... Mechanically complex with little room for adjustment...

 

Why not a simple ledge structure inset along the edge, on either part, where the side part is simply laid along the edge and glued in place? would look like a square trim block in the corner when standing vertical and would be hardly noticed?

 

Mechanically simple, easily adjustable and will work as locaters much better than pins....

[Kevin-the-lubber]

Yes, I've been thinking along those lines myself. I should have made clear, I can of course sand down the bumpy resin face very easily and the problem itself is not that problematic - the quest is for the best solution in the context of resin printing.

 

Ledges, which probably is a better approach than pins for all sorts of reasons, still doesn't address that one mating face will be as smooth as the proverbial while the other mating face will still be a spotty teenager. Though easier to smooth accurately than the dowel method. The grail is to somehow get two perfect mating faces.

[Egilman]

1 hour ago, Kevin-the-lubber said:

...still doesn't address that one mating face will be as smooth as the proverbial while the other mating face will still be a spotty teenager

Taming the teenager and their rough edges... {chuckle} If I had the answer for that I would be a billionaire.

 

Seriously though, what is making the edge rough? shouldn't there be a way to arrange the print so both edges are smooth?

[Kevin-the-lubber]

I didn't explain this very well and should have used photos;

 

 

The 'pins' side is the underside of the print and it has LOADS of supports. This face doesn't show on the model so finish doesn't matter much. This one is partially cleaned up and of course in practice this is relatively easy but unscientific. I don't think there's any way around this, this face has to be the underside as I need the A grade finish on the topside.

 

The side piece has to be printed with supports on the face shown for the same reason. However, as the dowel sockets are on the side, their faces are perfect and, in engineering terms, this face comes out as designed, except that the dowel holes lose integrity as the tops are unsupportable.

 

A ledge system (which I'll try this evening) will yield a perfect mating surface on the main body (but a rough top edge, which doesn't matter). But the mating face on the side piece will be an underside so imperfect. I can think of a few convoluted ways of getting two perfect mating surfaces which I doubt I'll even play with, they are that daft, but maybe someone here will point out something obvious or clever - it's easy to miss the obvious when you have your head buried in these things.

[Egilman]

I do have a question, why are you printing the side pieces flat? if you printed them vertical you will need fewer supports... these are the side galleries correct? since they taper off to the hull going forward, print the aft side against the build plate and let the exterior just form itself in free space...

The only thing you will have to clean up is the mating surface and interior which is very easily done......

 

Just a suggestion off the top of my head..

[Kevin-the-lubber]

See, I knew someone would see something I'm blind to now! Thanks, I think I'll try that, it should also solve the dowel hole issue and save me redesigning that aspect. There's some important detail on the outer face but there are ways around that.

[Egilman]

1 hour ago, Kevin-the-lubber said:

See, I knew someone would see something I'm blind to now! Thanks, I think I'll try that, it should also solve the dowel hole issue and save me redesigning that aspect. There's some important detail on the outer face but there are ways around that.

Excellent... There is an easier way to design the mating surfaces as well which will use less resin and give you more gluing surface for a much cleaner look.... The look doesn't really matter cause it will be inside I know... but it will also make your design simpler and faster to execute...

 

Let me know how it turns out my friend...