I've completed the 1-23 tooling with final coats of paint until no more sanding is required. I will probably in fact wet sand to 600 grit one more time to remove the gloss from the surface. Having fine scratches from the sandpaper actually helps to allow air to flow over the mold while pulling the parts and ensures that all areas are equally vacuumed to the form - preventing "bubbles" of large area from forming due to the plastic sealing itself some areas of the tooling.
Also shown in the photo below is the nearly complete 1-26E quarter scale tool, also ready for final sanding and coats of paint.
I could feel small defects - flats and ridges - that I couldn't see so decided to go ahead and paint the plug for final finishing. It was much easier to see and feel the defects once the gloss black paint was shot. I sanded the entire plug one more time with the orbital sander and sanding bar to fair out the couple of high or low spots. The two troublesome one were probably no more than 1/32" over less than 2 square inches. Once satisfied they were corrected, I gave it two more coats of the gloss black epoxy paint, wet sanding with 600 grit between coats.
Here is a photo of the tooling on the bench after that process and a third coat applied. I think I will wet sand and paint it one more time. That operation only takes about 30 minutes total and I think the high quality parts we will make from the tooling is well worth the effort.
I also made the tooling for the quarter scale 1-26E yesterday, finishing it with a second coat of West System and filler today after a similar round of sanding it to "final" shape and working out the areas that I was unhappy with. This one will be sanded and spray-painted tomorrow. Don Bailey is building the beta 1-26E quarter scale kit here at Aerosente.
Since Herbert, Mark, and Mike are busy getting their quarter scale 1-23s built, I thought I had better get the tooling done for their canopies so they will be ready in time. The 1-26B model canopies at the same scale that they each have will fit, the crown line curvature being nearly identical, however the aft cockpit bulkhead is more elliptical in the 1-23 and the cockpit opening is deeper. To make sure we have the best quality of fit in production kits, today I made up a dedicated plug to tool for the 1-23 canopy.
I thought some may be interested in the process I use, so I'll be taking photos of my work and will explain each step as I progress.
To begin, I copied the outline of the canopy and cockpit opening from the side view of the plans and brought them into a new file. Next I extended the lines of the top curvature and lower limits of the glazing out about 1/2" or more on front, back and bottom of the canopy to allow enough material once the plastic is formed to allow for trimming.
The next step was to measure the size of the drawing at its greatest extents to know the size of planks I would need to laminate to build the block I will carve for the plug. In this case I needed 12" x 5" planks to be built up to a width of 6", an even 8 parts at 3/4" each.
I cut them out of a scrap piece of particle board (better than pine but not as good as MDF) on the table saw. I applied Titebond II right out of a gallon jug to one side of each, spreading a thin coat with a small squeegee and stacking them as I progressed over some waxed paper and finally clamping up the entire block.
While this was curing, I went back to the computer and made sure I had added enough draft by further extending the lower corner points out another 1/2" or so. Draft is added to the tooling to allow the part to be easily removed from the tooling after thermo-forming each part. I then copied the instrument panel and aft bulkhead outlines to the file and printed the page to use as patterns.
In this photo you can see I left the outline of the canopy glazing limits on my pattern for reference. This shows where the tooling is going to be extended past those limits, irrespective of the what the fuselage does past those points. This allows some tolerance as to where the canopy is trimmed out of the thermo-formed parts which allows test fitting and creeping up on the best fit to the framing during assembly.
Spray mount the side view pattern as shown using a light coat of Scotch 77, indexed from the flat bottom of the block, leaving enough material at the top to cleanly cut the curve in a single pass on the band saw. Take your time to cut the line, backing up if needed to faithfully follow the curve in a single cut. Then while still at the bandsaw, cut the forward and aft draft faces. You can see in the photo above that the more draft the better, while still keeping well within the constraints of your vacuum-forming frame.
Be sure to use dust collection and facemask while using the bandsaw as the dust from particle board and especially MDF can be extremely toxic and cause a severe reaction in your throat and lungs.
Note here I decided to leave even more material at the front since I had extra stock. My draft line is still on the pattern here but I figured that another 1/2" or so would make the part more fair in the shaping and easier to trim the best section for final canopy construction.
Now trim out the fore and aft patterns, net at the top curve to simplify placement, and fold them in half and mark the center points. Again use the Scotch 77 to cement them in place, indexing them to the top of the plug, on the center line in the glue up.
One MUST leave at least a half an inch of stock in the tooling below the limits of the trimmed out clear parts that will be formed over it. This ensures there is no distortion in the part along its lower edges.
With the patterns mounted, begin to remove as much material as quickly as possible to reach the final curvature of the sides of the upper canopy. I placed the tooling in a bench vice and used a large drawknife. Going directly to rasp or sanders at this point is futile and a waste of time.
After the squared corners are removed to within 1/4" of so of the pattern lines, I switch to a 2" wide farrier's rasp to rough the tooling down to shape, removing the faceted cuts left by the drawknife. The cut of the coarse side of this tool is very aggressive so be careful not to get too close to the centerline at the top of the plug. The bandsaw cut here is net to the finished part, plus or minus a small fraction and should be finished with sanding blocks or fine rasp to avoid leaving gouges with the rasp that will need to be filled.
Good sources for hand tools suitable for woodworking are eBay and thrift and antiques stores. Vintage tools may be much less expensive than new ones of the same or lesser quality. Tools available through hardware and home centers today don't possess the quality of tools made pre-1950. And, a good cleaning and possibly re-sharpening or re-handling is all many need to be put back into years of good service.
Brands such as Stanley (hand planes, spoke shaves, scrapers and chisels, Disston (saws), Nicholson (files and rasps), Starrett (rules, squares and calipers), Miller Falls (hand drills and braces), Buck Brothers (carving, bench and lathe chisels), Irwin (drill and brace bits) are among the finest tools one can use. They were made long before the modern disposable culture took over for men and women that actually used these tools to make a living. These "antique" tools used better materials and employed ergonomics (before the science was invented) and so are more durable, hold edges better, cut more cleanly and accurately, and can be used for prolonged periods without bringing up blisters or drawing blood!
An added benefit of using hand tools is that they don't raise dust and are quiet to use - so no safety glasses, ear, or breathing protection is required.
Once you've reached the stage above, you may either use the fine side of the rasp to further refine the shape or switch to an orbital sander with about an 80 grit paper. This will smooth out the marks left by the rasp but be careful as you approach the lines of the patterns to work slowly and constantly turn the plug in hand and work the sander in circular motions over the curved sections.
The next step which I will do later this evening or tomorrow is to completely coat the plug in West System epoxy. The slow curing of this epoxy will allow it to soak into and impregnate the surface, hardening it for the final shaping and sanding before pulling the first part. (West System actually lists this as a fast cure since it is the fastest in their system but it would be considered slow by most hobby adhesive standards.)
This morning I coated the plug with epoxy. I used it without the filler for the first coat, deciding to get the best penetration and then re-coat later today when its nearly cured, or sand the first coat when fully cured and then coat again. The West System epoxy I am using is the 105 resin and 205 hardener. This is a six-eight hour cure system and allows plenty of time to coat out the part and excellent penetration. I just went out to the shop once more and found some spots that looked flat because so much of the liquid had penetrated those areas, and re-coated them.
I coated the bottom first, then the two ends, finishing with the upper curved surfaces. Don't worry too much about the product sagging to the bottom of the plug. This will actually help fill in and build up the lower edge of the plug which can be sanded flat once cured. I use foam brushes which are cheap and disposable since the epoxy cannot be cleaned out of a bristle brush well enough to save and reuse. You may also use the small foam paint rollers and frames which apply a much more even coat and are especially useful for finishing coats. Its also a good idea to use nitrile gloves to protect your hands. If you happen to get it on your skin, wash it off with waterless hand cleanser first, then soap and warm water. You can download information about this and other products from their web pages including the MSDS for each.
Its not necessary to use the West System epoxy, any good quality product will work, but I have found that for the applications for which I am using these, that their products far exceed that of inexpensive products sold for general modeling and are well worth the expense if using larger quantities.
If you know you have developed sensitivity to epoxy resins, you may also use water-based polyurethane, shellac, lacquer or similar liquids to seal and build the surface for sanding and finishing. However, these products may or may not provide the tolerance to heat required to thermo-form a sheet of hot plastic over the tooling more than once or may cause the plastic to stick to the plug. Only one good pull is required though if you plan on using a pourable product to fill that part to make a permanent resin- or plaster-based tool.
I'll post more images as I complete the tooling.
This morning I sanded the plug with a sanding bar to work out any high spots left by the the previous sanding around the glue lines. Working in a circular motion similar to the way a lens is ground, the flat of the bar will span low area while working down the high spots. The key here is not to work a finite area but to move about the plug while sanding in this fashion and to rotate the plug to come at the high spots from different angles with the bar.
After satisfying myself that most or all of the high spots were faired into the curves of the plug and the entire glossy surface was removed to show the entire piece had been sanded, I again went over the entire piece with the random orbital sander. I flattened both ends and the bottom once more to remove the gloss and quickly went over the curved upper surfaces. When fairing a curved surface such as this, the best way to find high and low spots is to close ones eyes while rubbing your hand slowly across the surface. The hand remarkably, is very sensitive to what the eye can't see.
Finally I gave the plug another coat of epoxy, this time mixed to the consistency of mayonaise with micro-balloon filler.
I've now sanded this last coating, using the same procedure with the orbital sander, only this time I added bevels at the forward and aft bulkhead points to allow easier release of the formed plastic from the mold. I then applied a third coat of epoxy, this one mixed with even more filler, laying it on very thick and allowing it to float out, dripping off the raised tooling.
The next photo shows it sanded only on the bottom, to remove the drips, and the fore and aft flats. A note here on sizing. It is not crucial to make the mold exactly the same size as the drawing to get a good fit. If you note in my steps above, I've never made any other measurements or taken any dimensions. Other than matching the fore and aft bulkhead shapes with the side view shape, it is not required to get the final dimensions exact to have the finished plastic parts fit the canopy bow formers from the kit.
There is probably as much as 1/4" of variance that can be tolerated in the plastic part or in the size of canopy bow frames that can be glazed from a given plug. Since the general shape is correct and to scale, the clear plastic at nominally .030"-.040" thickness will easily conform to the bows by pressing it down from the top while marking out the final cut lines to fit the part to frames. Likewise, when its time to glue up the part to the frames, only slight pressure is needed to pull it down to contact the entire circumference of the framing and to tape it in place for cements to cure. There is more on this in my post regarding canopy construction.
In the closeup image above, you can see that their is only a very fine texture left on the toolng in the un-sanded final coat. This will be taken out with 400 wet and dry paper and water to leave a glass-like final finish. The only way to improve this plug beyond that would be to use a very high-gloss two part paint system to apply a finish coat, preferably in black. Gloss black is the easiest color to wet sand to perfection by making any blemishes extremely easy to see. I've found that the rattle can epoxy appliance paint sold at hardware stores will work very well for this without the need for spray equipment, coats and flows out very well and is extremely durable, wet-sands exceptionally well to a high gloss finish and can be vacuum formed over several times before the tooling becomes too hot and causes issues with sticking.
In this case, since I am going to pull only a single good part and then make a casting inside of this, that its better to do the final sanding on the permanent final cast tooling, rather than spending the time required now, only to have to repeat this operation later.
When I pull my first parts over the plug, I will post the images of them here.