Gaps between splitted parts

[uplus2user]

Hello, due to the size of the printer, I divided a large rectangular-like object into four pieces. To fix the pieces serially on a metal plate, I use screw holes. After all four pieces were printed, I tried to combine them into one big piece. 3 pieces are already fixed to the metal plate using screws. When I put in a middle piece, I found gaps. What could be the causes? How can I fix this problem? Thanks.

[DrewPetitclerc]

I would guess you did not allow for shrinkage of the single parts.
Pictures would help.

[uplus2user]

Hello, here are the photos which show the gaps.

[DrewPetitclerc]

To fill these gaps I recommend a visit to your local beauty supply shop and pick up a large cheap bottle of pure acetone (under $5 here) and several empty nail polish bottles with brush in cap (about 25 cents each) and fill the bottles 3/4 with acetone and then snip in some ABS in a single matching color, let set till plastic has melted and then use it to paint, weld or as gap filler.

[pleppik]

Hello, due to the size of the printer, I divided a large rectangular-like object into four pieces. To fix the pieces serially on a metal plate, I use screw holes. After all four pieces were printed, I tried to combine them into one big piece. 3 pieces are already fixed to the metal plate using screws. When I put in a middle piece, I found gaps. What could be the causes? How can I fix this problem? Thanks.

What you're seeing is inherent to FDM printing. The problem is that this printing technique can't make perfectly flat planes and perfectly sharp corners.

[uplus2user]

Hello, due to the size of the printer, I divided a large rectangular-like object into four pieces. To fix the pieces serially on a metal plate, I use screw holes. After all four pieces were printed, I tried to combine them into one big piece. 3 pieces are already fixed to the metal plate using screws. When I put in a middle piece, I found gaps. What could be the causes? How can I fix this problem? Thanks.

What you're seeing is inherent to FDM printing. The problem is that this printing technique can't make perfectly flat planes and perfectly sharp corners.

Thanks for the info. What kind of printing techniques do not have these issues?

[uplus2user]

To fill these gaps I recommend a visit to your local beauty supply shop and pick up a large cheap bottle of pure acetone (under $5 here) and several empty nail polish bottles with brush in cap (about 25 cents each) and fill the bottles 3/4 with acetone and then snip in some ABS in a single matching color, let set till plastic has melted and then use it to paint, weld or as gap filler.

Thanks for the info. May I ask you the following?

1. What the empty nail polish bottles with brush in cap for? Why I will need several?
2. What do you mean by "single matching color"?
3. What is mean by "let set til..."
4. Once I let the acetone to weld or fill in the gap, can the parts be separated easily?

For this set of prints, I used the uPrint SE Plus with ABSplus. I suppose the solution to this problem applies to the printouts of other FDM printers as well.

Thanks.

[pleppik]

What you're seeing is inherent to FDM printing. The problem is that this printing technique can't make perfectly flat planes and perfectly sharp corners.

Thanks for the info. What kind of printing techniques do not have these issues?

I suppose you could try printing it on a powder-based printer, but those cost many tens of $K. You would want to send your model to a service bureau like Shapeways, which is still going to be pricey. Even then you're going to have a visible joint, since the faces won't be perfectly polished smooth.

It may be more fruitful to think about designing the joints in a way that they're either concealed, look intentional, or can be easily filled and smoothed (as some others have suggested). Carpenters have spent centuries figuring out ways to solve these kinds of joinery problems.

[uplus2user]

What you're seeing is inherent to FDM printing. The problem is that this printing technique can't make perfectly flat planes and perfectly sharp corners.

Thanks for the info. What kind of printing techniques do not have these issues?

I suppose you could try printing it on a powder-based printer, but those cost many tens of $K. You would want to send your model to a service bureau like Shapeways, which is still going to be pricey. Even then you're going to have a visible joint, since the faces won't be perfectly polished smooth.

It may be more fruitful to think about designing the joints in a way that they're either concealed, look intentional, or can be easily filled and smoothed (as some others have suggested). Carpenters have spent centuries figuring out ways to solve these kinds of joinery problems.

Thanks. Do you have an example on how to design joints that are concealed? I can't imagine how to conceal the joint of two blocks.

[pleppik]

Thanks. Do you have an example on how to design joints that are concealed? I can't imagine how to conceal the joint of two blocks.

A few techniques I've used are:

• Put the joint along the edge of some feature, so the joint just looks like a corner
• Cover the joint with some bit of decoration
• Arrange the joints in a regular pattern so they look decorative

At the end of the day you can't avoid a joint, so the goal is to make it look like part of the planned design. That probably means planning the joints into your design from the beginning.

If your goal is to have a smooth, flat, featureless face of the object, then pretty much the only way you're going to get there is by filling the gaps with some sort of filler, then sanding it and painting it.

[uplus2user]

Thanks. Do you have an example on how to design joints that are concealed? I can't imagine how to conceal the joint of two blocks.

A few techniques I've used are:

• Put the joint along the edge of some feature, so the joint just looks like a corner
• Cover the joint with some bit of decoration
• Arrange the joints in a regular pattern so they look decorative

At the end of the day you can't avoid a joint, so the goal is to make it look like part of the planned design. That probably means planning the joints into your design from the beginning.

If your goal is to have a smooth, flat, featureless face of the object, then pretty much the only way you're going to get there is by filling the gaps with some sort of filler, then sanding it and painting it.

Thanks. The techniques you mentioned are interesting. Could you please post some sample photos to show us?

[ggeezer]

I print usable machine parts in ABS for my business and have printed hundreds that were made up of joined smaller parts. In fact, you cannot print parts with a footprint of over 4" in any direction without getting warping problems and other printing anomalies; so if you need larger parts, they will have to be made of joined smaller sections.
Edges and corners perpendicular to the printing plane will always have imperfections so gaps will be a fact of life. This is what I do:
1. I know my printer well enough to be able to predict the outcome so I design the parts accordingly. If I need a perfect fit without glue, I print slightly oversize and then, using my milling machine, I plane the surface perfectly flat and to specification. In other words, the printed part is more like a "metal casting" than a finished part.
2. If the parts are to be bonded, I again know how to design and print the part for this process. I use a solvent like MEK or Acetone spread out in a suitable container so the there is about a depth of 1/8". I stand the part on a couple of 1/16" rods, bonding surface down and leave the part in the liquid for 10 minutes or so (you have to experiment). The bonding surfaces are now very soft and when you clamp or force the parts together, the high spots will extrude into the low spots. Force the parts together until the melted plastic oozes out of the joint. Fixture and let dry before removing the plastic that has oozed out of the joint. This is a perfect weld and is stronger than the rest of the part.
3. The FDM printing process is a fairly crude method but it is surprising how good the results can be when you understand the limitations and design around them.

Orv.

[DrewPetitclerc]

That is a great response Ggeezer, I agree with all that you said.

[roller]

As Drew said, awesome answer ggeezer. The only thing I would add for new users is that warping can be quite different between different supplies of ABS and sometimes even varies a lot between colours.

I use the wasted support material, melt it down in acetone as Drew suggested and use this as a bonding filler. The only downside is it is glossier than the finished print unless you use the acetone to smooth the whole print later. MEK is better but I don't like using it as it's nastier than acetone.

[pp3dp.nl]

@ Roller: When I glue something and it has the glossy layers you can use a matte clear coat. It also fills a bit and the print will look way better. But glossy (just a mist) will also make the part uniform..

[roller]

In my case glossy is usually not acceptable for objects so I just wanted to forewarn them joins are a bit obvious due to the different finishes.

[josejuako]

It is best to machine the parts in axes and tolerance in parts to stick , this in done with guides that are required.


J