Thursday, September 21, 2017

Getting primer to stick to resin: a primer on mold release agents

In hunting around, I found a number of companies that offer mold release agents. I also found a model hobbyist who makes resins and posted on release agents here. (Let me know if the link stops working, I have saved the file).

This fellow uses a commercial agent called Mann Ease Release 200 (spray) or 205 (liquid). He also makes his own, made up of petroleum jelly thinned with mineral spirits which he then applies with an airbrush ...  anyway the MSDS (here) states it includes dimethyl ether and 1,1-difluoroethane. I figured the fluorine component is likely the part that makes it nice and slippery, but an actual chemist informs me that this is the propellant, and that the actual release agent is not listed.

Mann also lists Mold Cleaner 2508 for removing traces of prior mold release agents. The MSDS for a competing product (here) lists xylene, toluene and our old friend, MEK (methyl ethyl ketone). So whatever the release agent might be (Vaseline?), these are likely the solvents needed.

The next question is what is the impact of MEK on resin parts. Trials with a scrap piece may be in order. As I don't have any MEK on hand, I will report back.

Lancia D50: opening the box

This turned up today as I was putting the clearcoat on Belair, wondering what I would tackle next.

It's the Lancia D50 Grand Prix car driven by Ascari to a win in Monte Carlo in 1955. The kit up to the usual Model Factory Hiro standards in terms of quality. The one disappointment is that it is 1/20 scale; the posting was unclear and I guess I assumed it was 1/24. I'll hang on to it for now but won't start it just yet.

Stay tuned.

Wednesday, September 20, 2017

Getting primer to stick to resin

A while back I described problems I ran into as a result of not knowing about mold-release agents used in resins (here). Atthat time, a bit of research led to the conclusion that a good cleaning in 99% isopropyl alcohol (propanol or rubbing alcohol) followed by dish soap in hot water would do the trick, and indeed I haven't had any problems since, especially when the alcohol bath includes a vigorous scrubbing with a sacrificial toothbrush.

With the current '51 Belair wagon resin body, I ran into some problems with the paint.

I cleaned the body up with isopropyl alcohol as I have done in the past. Then I applied a couple of coats of DupliColor primer/sealer, with no issues around bubbling or any of the other problems associated with applying primer to a resin body which is coated in mold release agent. Finally I put on a couple of coats of Krylon top coat as detailed in recent posts, again with no problems attributable to release agents (although the problems related to using a rattle can were on hand as always).

The problems arose when I started scribing around where the wood-colored paint will go, and was surprised to see the entire paint structure, right down to the primer, lifting off in sheets like multiple layers of old wallpaper. Clearly the primer didn't really stick to the resin. 

So what am I missing? The primer was on for over a week, the top coats for several days, and there has been plenty of time for it all to set. 

Several members of the Facebook group "Model How To's" recommended soaking new resin parts in Wesley's White Wall Cleaner or Black Magic Bleche-Wite tire cleaner. These contain a mixture of an alkaline chemical and alcohol, so presumably they are a more aggressive version of the propanol I have been using. For now I've repaired the flaking bits by carefully trimming with a fresh X-Acto blade dragged along a crease in the body where the step change in paint thickness won't show. 

Then I painted the two wood-coloured portions of the bodywork and some of the chrome parts. The photos show a bit of sloppiness (this is all brush work without tape, so actually it is all pretty good), which will be tidied up; the rest of the chrome will be with Bare Metal Foil. 

Stay tuned -- I will update both the resin cleanup story and progress on the tin woodie Belair. Remember to use the bar across the top of the blog to select Tools & Tips to find this and other posts that are not directly related to specific builds but to generic problem solving approaches.

Sunday, September 17, 2017

1951 Belair: Mating styrene and resin, Part IV

After a fair bit of trimming, I got the firewall and inner fenders to fit, and the chassis is essentially complete with a few minor exceptions such as the radiator. It's all pretty tight and needed a fair bit of carving, which I suppose is better than having to shim up loose bits.

There is a bit of paint to fix under the hood. As I don't have an airbrush, I'd have to do a lot of taping to use the rattle can. Instead, I added some white to Testor's gloss light blue to get pretty close with the brush (not shown in the picture). Also the long air ducts from the radiator bulkhead to the firewall don't fit, because of the injection intake horns on the left and the 6V (!) battery on the right. 

The reason for all the replacement parts (firewall, inner fenders, dash) in the resin kit is slight differences between the resin and styrene underhood areas, mainly associated with the body. Same goes for the hood. I assume the resin molds need to be thicker than styrene, for good filling and stiffness if nothing else. So there are a lot of spare styrene bits, not just the body. 

The stance is fine, and the body colour on the steel wheels is also fine. I had toyed with black, possibly matched by black bumpers (to come), but I think this works. (The resin kit comes with unchromed bumpers.)

The front wheels are the stock steelies from the AMT kit, while the rears are the chrome rears from the drag version, dechromed and painted.  Tires are also big in the fender wells, and the body cleanup will be my last chance to hog them out a bit. After final assembly, the body will sit a bit lower on the left side than in the photo, improving the stance. I'm still of two minds around the baby moons. 

The interior is also complete. I'm going to stick with just the front bench; the resin kit comes with three seats (as shown) which doesn't leave much room for luggage. A luggage rack perhaps? The tan is OK but in retrospect I might have gone for something a bit darker than the Model Master Flat Fabric Tan. And the dash is a bit sloppy but it will do. 

Next is the long boring part: all the sanding, filling and painting to get the exterior up to snuff. A lot of sanding is needed first to smooth it all out, then I'll need to paint on the external wood. This will consist of two shades; the darker will probably be Testor's 1185 Flat Rust applied with a brush. The lighter one will probably be Model Master 1735 Wood, again with a brush, which is a bit darker than the Flat Fabric Tan I used inside. There are some gorgeous restoration jobs on the Interweb, but I am not sure how to make the wood grain look realistic.Finally this will get taped and some more of the baby blue shade will get sprayed on. Still to decide: Bare Metal Foil or chrome silver paint for the trim. Probably the rear fender kick panels will get painted because of the risk of wrinkling the BMF over the large-surface, compound curve, but probably the rest will be BMF. 

Stay tuned!

Wednesday, September 13, 2017

1951 Belair: Mating resin and styrene, Part III

The interior panels have been glued together, and sit nicely in the body with the tops of the door panels just slightly below the window edges. All the interior chrome was done with Bare Metal Foil. The door panels were painted according to instructions from the supplier, Best Model Car Parts, and the light tan (Model Master Flat Fabric Tan) is really not entirely right -- it is all meant to look like a wood panel. The darker brown (Testor's Flat Rust) looks pretty good. Next will be to complete and install the dashboard and firewall, and finish off the rolling components.

I've given the body a first coat of the final colour, Krylon Blue Ocean Breeze. It's a nice '50's pastel colour and it all looks good. I'll probably do the steel wheels in the same colour, and add baby Moon hubcaps.

It'll sit for a few days as I have other projects that will take me away from the bench, so the paint will have time to get nice and hard. I still need to scribe the door gaps which look pretty ratty, then I'll paint on the wood. You can find photos of what these looked like by Googling 'Chevy Tin Woodies'; I'll see what I can find in the way of paints that look reasonable, especially for the light wood colour.

All that's missing is a windshield visor, a roof rack and a surfboard. Stay tuned!

Sunday, September 10, 2017

1951 Belair: getting the stance right

So I got brave and took 2 mm out of the lower edge of the inner door panels. These are resin parts and presumably hard to replace if I screw up. However it all worked out and the chassis now sits where it should, with the tops of the door panels roughly level with the door tops.

The stance as shown here is with the dropped kingpins, the rear axle in its standard position, and with two types of whitewalls from the parts bin. The fronts are from one of the aftermarket companies supplied through Model Roundup (I forget which one), and are the same size as the black walls that come with the AMT kit. Note they are very large inside the fenders and would not steer at 1:1 without fouling the fenders. The rears are from AMT's MH Racemaster slicks parts pack and are both taller and wider. While they raise the rear, the stance is actually quite nice, and furthermore they now fill out the fender wells a lot better. I suppose another approach will be to go for the down in the weeds look by lowering the rear. To be decided.

It also appears that the chassis needs to move rearwards slightly relative to the body (the wheels look to me to be a bit forward in their fenders), which will allow the body to drop a bit more over the chassis (it's hanging up on the top of the dashboard, and just inside the rear bumper). Too much and I'll have to cut clearance for the headers peeking out from under the right side rocker panel.

Incidentally I had problems getting the color coat, a Krylon automotive paint, to sit on the inner fenders, even on top of Tamiya primer. This is interesting because the Tamiya rattle cans and Testor's bottled paint all took fine. This could be because the solvent used in these auto paints is a lot more aggressive ('hot') than Testor's or Tamiya. Anyway I stripped it all off with paint thinner, then cleaned it up some more with isopropyl alcohol and put on a couple of coats of DupliColor primer-sealer. That seemed to do the trick. I've given the body some added scrubbing with alcohol just to be safe.

So progress is being made! As this is my first transkit, as opposed to the multi-media resin items from Profil 24 or Model Factory Hiro, I am pleased with the state of it at this point. So far (says I, knocking loudly on wood), the trimming and adjusting needed has not been horrendous. Stay tuned!

Saturday, September 9, 2017

1951 Belair: Mating resin and styrene, Part II

I started by cleaning up the resin bits in isopropyl alcohol before putting on some Tamiya primer. No long brown stringy bits of goop surfaced, and the primer stayed on the resin bits, so that all worked out. 

The front end went together reasonably well. The AMT kit offers standard and dropped kingpins, but for some reason the kingpins don't have pins to socket into A-arms at both ends, just at one end. A 1/16" drill and some brass tube fixed that, but this would be a problem for a beginner. Also the tie-rods are glued in place, so while the wheels steer, they won't steer together -- both will have to be posed separately. The photo shows the underside of the front end, with the brass pins visible at the ends of the A-arms.

It's hard to see how low it will be, with the rear at its standard height, because the interior needs to be built up, and I suspect this will lead to lots of filing and resulting changes in the relationship between the body and the axles. 

But two things stand out at the start: the front track is wide enough that the front wheels can't steer (interference with the inside of the fenders); and the rear track is very narrow making the wheels look lost under the fenders. It's a porky little thing seen from the rear. Comparing the AMT and resin bodies, the resin body, measured across the rear fenders at their widest, is 0.150" wider (3.6" at scale) than the AMT styrene body. So lots of room in there for wide tires. At the front the two are the same, meaning the resin body is narrower inside the fenders due to greater wall thickness. 

I've also got a choice between two aftermarket sets of whitewall tires: the narrow whitewalls in the photos are the same height and width as the black tires that came in the kit. I've got another set with wider whitewalls which are both taller and wider. The wide ones are also going to raise it all, and in any case don't fit inside the front fenders. Finally I've got some whitewall slicks from the AMT parts packs. More decisions... I will say, though, that engine looks darned good! 

OK, it's not a small block V8, but it looks good, is unusual, and it probably made close to 200 hp with the headers and injection. (Wikipedia says the Blue Flame version of the 235, with hydraulic lifters, the siamesed head and a single carb, as used in cars with the Power Glide trans, made 136 hp, and 150 hp with three carbs as installed in the base C1 Corvette.)

Stay tuned. The interior will be next, with lots of trial fitting into the body. How low the body sits over the interior will impact the choice of tires, and whether I need to do some cutting to sit the rear lower over the leaf springs.