Fitting a Barbie waist to a Slim LM body

cross sections of Barbie waist and Slim LM waist The slim version of the Ladies Mission body has a somewhat odd shape: wide waist with narrow hips, in fact its waist has the same circumference as its hips have. This not only looks a bit odd but also makes it hard to find clothes that fit properly.
By contrast recent Barbie play-line 'Bellybutton' bodies have a beautifully shaped waist but have very limited articulation.
The image on the right shows the cross sections of the waist of a Bellybutton (top) and of a Slim LM body.

After completing Julianne I had a left-over Barbie Bellybutton body with a skin tone close to that of the Slim LM bodies, so I decided to try and replace the waist and hip section of the Slim LM body with that of the Barbie body (the body I used was marked ©2015 and had catalog nr. DGY58 inside).
Fitting a Barbie waist to the LM body did mean trading some articulation for looks: no more lower waist joint and hip joints with reduced range.

At first I felt reluctant about cutting up a perfectly good Slim LM body but some careful measuring convinced me that the two bodies could successfully be merged.
It does require making some accurate straight long saw cuts, I put some tips for doing so on a separate page.

In theory, the plan sounds simple:

In practice I ran into some interesting problems that took some out-of-the-box thinking to solve.

This page is divided into sections:

Tools and materials used:


dissected bodies When cutting up the Barbie body I made the first cuts some distance away from where I wanted the actual cuts to be as I knew nothing about the construction of the body or what the wall thicknesses of the parts would be. It turned out that the Barbie body has quite thin walls (about 1.0mm) whereas the upper legs have surprisingly thick walls (about 4mm on average).

I cut the LM body halfway through its waist section (where the waist is at its widest) and cut the legs just above their axial pivot lines (i.e. the joints in the top of the thighs that allow for twisting the legs).

LM upper body Then I carefully took the halves of the LM waist apart and lifted them off of the chest joint.
Only the waist parts of the LM upper body were modified. By reducing the depth of the waist parts, the gap between the upper body part increases slightly but trying to reduce the gap might impair the functionality of the chest joint. In fact, the slimmer waist increased the range of the chest joint slightly.

Making the body parts fit

test fit of bb waist with top of LM waist To mate the LM body parts to the Barbie body, first the Barbie body was shortened to arrive at a similar total length as the bodies used to have (about 94mm from top of the shoulders to crotch).
I chose the angle of the cut so that the front of the LM parts lined up with the contour of the Barbie body in side view.
I left a raised tab (10mm wide by 4mm tall) at the rear of the body, this tab should help with locating the LM parts and also preserves the contour and some of the details of the Barbie back.

cutting lines for reducing depth of LM waist planned result after reducing depth of LM waist To fit the Barbie body the depth of the LM parts needed to be reduced by 5mm.
The depth at the top of the LM parts should remain about the same to enable the chest joint to function, so a wedge shaped cut was made in the sides.
I used the pictures on the left and the image editor on my PC to determine where to cut so the length of the join line would remain the same on both halves.
The sides of the rear LM part have a flat section, so most of the wedge was cut out of the rear part. That way the width remained constant.
The mounting pegs on the inside of the LM parts were also cut down and re-drilled.
After the sides were cut to shape, the lower edge of the rear part was cut to fit and a cut-out was made in the rear to fit the tab on the Barbie body.
With both edges it was a matter of repeatedly trimming and test fitting to arrive at a perfect fit.
reinforcement strips inside parts reinforcement strips inside parts Some of the left-over bits of the Barbie body were cut into strips that were fitted inside the body parts along the join lines:
a wide raised strip at the front of the body to locate and support the join, a curved strip inside each of the sides to add wall thickness (the outsides of these areas needed to be sanded down later) and a strip in the upper part behind the cut-out.
After the glue had cured, the strips in the sides were trimmed to be level with the edges and the strips in the front and rear were trimmed until all parts fitted perfectly.
On the pictures the LM parts are fitted together without glue.
LM upper body reassembled Next step was to reassemble the chest joint by sliding the LM parts around the spring-loaded post and gluing the halves together using Plastruct Plastic Weld glue.
I also glued some reinforcement strips along the insides of the join lines.
The separate parts of the body are easier to handle than a complete body is, so I decided to wait with joining the LM upper body to the Barbie waist until after I modified the neck and fitted the legs.
The picture was taken after the neck was modified.

Making the legs fit

plug for fitting LM leg to Barbie leg Whilst cutting the Barbie legs I noticed a problem: the legs of these play-line bodies are made of a type of plastic (probably polypropylene) that is very difficult to glue.

I did take a moment to marvel at the design of these legs: a hollow, thick walled, single-piece casting (it looks like it was spin-cast using a multi-part mold).

To provide a base for attaching the lower part of the legs to I decided to fit a plug, made from thick polystyrene rod, inside each leg and use epoxy resin to hold the plugs in place.
I did have to leave the Barbie legs longer than I initially planned to provide enough of a container to securely hold the plugs and the epoxy.
This meant that the remaining part of the Barbie legs tapered towards the cut, so filling the insides of the legs with epoxy glue should anchor the plugs in place.
The LM legs can then be glued to the ends of the plugs.
Leaving the Barbie legs longer, meant that the legs ended up a bit taller and that the contours of the thighs are not perfect.

plug fitted to Barbie leg I started by making the inside surfaces of the Barbie legs more rough using a motor tool fitted with a small grinder, the rough surface should help the epoxy adhering to the surface.
Then I cut two 22mm pieces of 12mm diameter polystyrene rod and used the motor tool to grind the pieces down to match the shape of the inside of the legs.
A 1mm thick spacer strip was glued to the outsides of the plugs to keep the plugs in the center of the legs.
Once the plugs had the right shape, I wiped the insides of the legs and the outsides of the plugs with some acetone applied to the tip of a rag.
I cut two 10x10mm pieces of 5mm thick polypropylene foam (PPE) and firmly stuffed one piece into the top of each leg, this will stop the epoxy glue from getting into the hip joint or leaking out through the small hole in the top of the leg.
Then I mixed up some 2-component epoxy glue, poured some glue into each leg, pushed the plugs into the legs and let the glue cure. Before the glue had cured I moved the hip joints to check if these were clear.

After the epoxy had cured for 24 hours I verified that the plugs were firmly mounted, then I sanded the plugs down until the LM legs would fit seamlessly.

Change of plans

To be able to mount the plugs in the Barbie legs I had to leave the legs about 8mm longer than planned. I had hoped the extra length would not be noticeable, but a test picture revealed that the thighs were just too tall (the knees should be exactly between the hip joints and the heels). Apart from the overly tall thighs, the LM legs taper a bit at the top and that spoiled the look as well.
So I cut 8mm off of the top of the LM legs, stood the body up on the legs and took another test picture. The length of the thighs did look right to me now and the taper near the join line is less noticeable as well.
The 8mm tall part I cut off of the top of the LM legs included the pivot joints, so I had to fit new pivot joints to the insides of the LM legs.
Unfortunately the existing pivot joints proved unsuitable for trimming and fitting inside the legs, so I had to find or make new pivots.
On the positive side, the join line between the Barbie part and the LM part of the leg could now be used for the pivot joint line, so there was one less seam to take care of.

On the inside of the LM thighs were two pairs of alignment pins, one pair was about 2mm below the cut, the other pair about 15mm.
I cut away the pins closest to the cut, leaving a depth of 15mm to fit both the pivot and the plug from the Barbie leg.

creating new pivot out of polystyrene tubing and strip After considering a number of options, I decided to make new pivots out of polystyrene tubing and strip.
I sanded the plugs in the Barbie legs down to protrude 2mm beyond the edge of the legs and decided to make the pivots 12mm tall, leaving 1mm for clearance between the alignment pin, the pivot and the plug.
The picture shows the parts used to construct the pivots: a 12mm tall inner tube (Evergreen 234, 11.1mm diameter) that was locked up by two 1mm tall rings inside a snug fitting 10mm tall outer tube (Evergreen 236, 12.7mm diameter).
A set of six strips (3x2x9mm) were glued to each outside tube and the strips were interconnected with six more strips to form a stable construction.
The interconnecting strips were cut at 60° angles, so my accurate JLC miter block with 60° groove came in handy.

The remains of the upper alignment pins were removed from the insides of the LM legs using a motor tool with a small grinder head.

pivot fitted inside leg Then the strips were trimmed to fit the insides of the LM legs, making sure both strips in opposing pairs kept the exact same width to keep the pivot centered inside the leg.
The top of the LM legs is slightly more narrow than the part where the pivots should be mounted, so I carefully cracked open the top of the rear glue seam of both legs.
Then the pivots were put into position and carefully glued to the legs by letting some Plastic Weld glue run between the strips and the inner surface of the legs. Some Plastic Weld was applied to fix the legs rear glue seams.

tubing for connecting pivot to leg To achieve a sturdy connection, a 10mm piece of tubing (Plastruct TB-12, 9.5mm diameter) was cut to mount each of the LM legs pivots to the end of the plugs in the Barbie legs.
The tubing was temporarily inserted into the pivot, so the outsides of the parts of the leg could be aligned.

inserting foam to make tubing stick out of pivot Before glue was applied a piece of PPE foam was temporarily inserted into the top of the tubing. The foam made the tubing stick out of the pivot slightly (to make applying glue easier), yet allowed it to be pushed into the pivot completely.
Then Plastic Weld glue was applied to the plug and to the edge of the tubing and the LM leg was positioned against the Barbie leg and aligned.
Once aligned the LM leg was slid off of the tubing, the foam was removed and the glue was left to cure.

I actually had to cut off, sand and re-glue the right hand tubing twice because the gap between the parts of the leg was uneven.
Cutting through the glue join within an hour after gluing takes much less effort that after the glue has fully cured.

rod for reinforcement To reinforce the join between the tubing and the plugs a length of rod (Plastruct TB-2, length 9mm plus the depth of the hole in the center of the plug) was epoxy-glued into the hole in the center of each plug, then the inside of the tubing was filled with epoxy glue.
tubing filled with epoxy

improving shape of LM legs In the meantime I turned to sanding the LM legs into shape.
Three things I wanted to do:

In the picture the leg on the left still needs to be sanded, the one on the right is done and ready to be fitted.
I did not make too many changes to the legs, I limited myself to sanding the plastic without using any putty, filler or paint.
Besides the plastic of the legs is just 1mm thick so there's only so much to sand down.

Another change of plans

I had planned to use glue to attach the posts I fitted to the Barbie legs to the tubes inside the pivots in the LM legs, however these have a snug fit (which was intentional to improve alignment and stability).
Usually I attach snug fitting parts by assembling them first and then applying some thin liquid glue to the mating edges, capillary action will then distribute the glue between the parts.
However in this case the outsides of the legs hide the parts to be glued so I have to apply glue before assembling the parts.
Fortunately I thought of testing this with some scrap pieces first and found that none of the suitable types of glue I had (Plastic Weld, thin cyanoacrylate, acetone) allowed the snug fitting parts to be slid together over the full 10mm distance.
So another bit of out-of-the-box thinking was required...

In the end I tried fitting magnets to both parts of the legs instead of using glue.
I settled for magnets of 6mm diameter size as that was the largest size I had that could be safely inserted through the hole in the center of the pivots.

To create a flat mounting surface for the magnets I used my motor tool fitted with a flat tipped cutter head to carefully flatten the top of the alignment pins inside the LM legs.
Next I turned some spare tubing into a little tool for inserting a magnet into the LM legs (to reduce the risk of dropping a tiny magnet with epoxy glue applied to one side).
Then I used a marker pen to mark the magnets so I could tell if these were right side up.
Finally I mixed up some epoxy glue and used that to stick the magnets to the tubing and to the insides of the legs.
After the epoxy had cured I test-fitted the legs.
The legs remain attached and remain fairly well aligned, however the magnets are not strong enough to tighten the gaps between the parts of the legs completely, oh well...
legs fitted with magnets

Final assembly

body parts ready for assembly

body assembled Before joining the halves of the body I modified the neck by rounding off its edge, drilling a hole through the neck pin, fitting a piece of vinyl tubing and securing it with a cloth pin.
I also made the seams along the upper body and the arms smooth and sanded the front lower edge of the chest piece down a bit.
Then I glued the body halves together using Plastic Weld glue. I made a paste by dissolving some of crumbs of plastic in acetone and applied that to the seams (on the back, the front fits seamless) and let it cure for a day.
After the glue and the plastic paste had cured I carefully shaped the contours of the LM part to match the Barbie part (spine, subtle shape of belly).
Then I sanded all seams smooth and buffed the sanded areas.

Gluing Polypropylene

Polypropylene (PP) is not effected by solvent based glues (e.g. Plastic Weld, acetone) and its smooth surface makes that contact type glues (e.g. CA, hot melt glue, rubber cement, epoxy) do not result in a strong bond either.
Two types of glue that can bond PP are Loctite Super Glue-3 For All Plastics and polypropylene-based hot melt glue.
I do not like using hot melt glue for scale model purposes.
The Loctite All Plastics Super Glue is a type of CA that comes with a separate activator.
As CA is usually not able to withstand shear stress and the legs are to be joined in between two rather stiff joints (Barbie hip joint and LM leg axial joint) there will be quite some stress on the glue joins when the legs are posed, so I decided to try the 'plug with epoxy' method first and kept the Loctice glue as a last resort method.

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