lmagna

Evening all,   some more progress  -  I added a few more details  to the engine bay,  then I decided to have a go at the drivers compartment,  I wasn't too  sure how this would  turn out as I had  used  some of the parts  for my Chally  build,   one of the  main areas  was the  right hand bulkhead  - this I managed  to  manufacture  using  some other parts from the kit,    the rest of the parts  are mainly  there  - still needs an instument panel making up  from scratch.
 
OC.

Oh come on Ken. You know you miss SOME of it. People pay perfectly good money to do many of those things.

Got to lay out in a hammock. The chair things just aren't as comfortable and over time put a lot of strain on my busted back! Besides one looks much more regal while laying in a hammock.

I'll be right back I ran out of hammocks! Don't do to much before I get back!

Got to lay out in a hammock. The chair things just aren't as comfortable and over time put a lot of strain on my busted back! Besides one looks much more regal while laying in a hammock.

Got to lay out in a hammock. The chair things just aren't as comfortable and over time put a lot of strain on my busted back! Besides one looks much more regal while laying in a hammock.

I'll be right back I ran out of hammocks! Don't do to much before I get back!

Oh come on Ken. You know you miss SOME of it. People pay perfectly good money to do many of those things.

It's not fair Mark. As I was just a lowly door gunner not a crew chief I didn't get any of that cool type of training! Our stuff after volunteering was pretty much "Here's your gear. Don't walk into the tail rotor. Do you have a next-of-kin you want us to send your stuff to? " Oh yeah, a couple of weeks learning to clean an M-60 and which  end the bullets came out so you would be less likely to shoot your own chopper out of the air. At least that seemed to be the reasoning. Mostly they seemed most interested in filling the right back door with a warm body. Pretty much the way everything went in the Army I guess.

The main thing I’ve been printing in FDM is a four section 500mm long deck with staggered, interlocking joints using the plank lines to disguise that there’s a joint. As there’s only 0.2mm clearance the elephants foot effect meant I couldn’t do this successfully in resin on the plate. But I have to admit it didn’t occur to me to reduce the cure time for the initial layers so I might try that next time round. I also had another problem that I simply couldn’t figure out; when printing large rectangular sections on supports and tilted, the straight leading edge was not coming out straight, it always had a slight curve to it, regardless how hefty the supports. It’s as though the resin shrinks slightly during the print and gradually pulls the outer edges towards the centre.

I'll be right back I ran out of hammocks! Don't do to much before I get back!

Oh come on Ken. You know you miss SOME of it. People pay perfectly good money to do many of those things.

Fellows on The Ship Model Forum have been experimenting with printing large flat surfaces without any supports - just flat on the print platform. This produces very flat thin pieces like decks. The initial long exposures for the base layers will create a small wider bead around the part on the print platform,  but this is easily filed/scraped/sanded away. Because the contact surface on the plate is so large you don't need many long exposed base layers. Some have made successful prints without them.

I did these a week or so back, just to see if it would go, which it obviously does. The wire is 0.5mm dia, the stems a very generous 1mm or thereabouts. The wire holes closed up during printing but there was enough of an indent to make drilling out easy. I wouldn't want to have to do 500 though! I think I only broke one stanchion head along the way.
 
As you can see I've gone back to FDM for some parts. I'm finding that it is better than resin for larger flat surface parts and comes up well with a little light sanding. 
 

 

Pat,
 
Nice railings. I have been thinking about how to make railings for the OK City model for about 12 years. They have extremely small diameter sections. I have been planning the purchase of a small high tolerance milling machine just to drill 0.008" holes through 0.013" brass wire to make the stanchions. Even with a very good mill I foresee a lot of broken bits and scrap pieces. There are between 450 and 500 stanchions that will have to be prepared!
 
****
 
I ran the chain prints again, using a 0.04 mm step size and 3 second exposure (as opposed to the earlier 0.02 mm step and 2 second exposure). Half as many exposures but 50% longer exposure time.
 
The design diameter of the chain "wire" was 0.66 mm. The horizontal links came out 0.75 mm to 0.84 mm thick, 14% to 27% oversized. The vertical links were 0.63 mm to 0.66 mm, or 95% under size to 100%. Most of the links were free or slightly fused, but when I gently twisted the chain around the long axis almost all of them separated. So this was near the limit for getting a flexible chain. However, I printed three chains and one did not print completely.
 
I think the 2 second exposure was better because it have thinner vertical layers - even though I was printing layers twice as thick as before, so only half the number of exposures. I can see no visible difference in the surfaces of the 0.02 mm vertical step and 0.04 mm step parts, so 0.04 mm is adequate. Actually, these things are so small that if there was a difference it wouldn't be noticeable.
 
There really wasn't much difference in the thickness of the vertical links between the two runs, so the longer exposure time made no difference there. But it certainly did make the horizontal link thickness greater even though there were only half the number of exposures. And that was causing the links to fuse.
 
So it looks like the optimal settings for these tiny parts 1s about 0.04 mm step size and 2 second exposures with the Anycubic Basic Grey Resin - which they call "Colored UV Resin" on their web site - on the Photon Mono printer.

What resins are you using for parts that will be machined, Pat? I guess if the wall thickness is substantial enough you don't run into problems with brittleness. Unfortunately I don't have a hobby lathe/milling machine and although it would certainly solve many problems, I'll leave that until / if I reach a point where it would be more worthwhile.
 
I looked at having the main body of the stern I made for the Victory professionally printed as I was having endless difficulty at this end, but it was too expensive. Eventually I found a way, as you do. Likewise I looked at making the vic stern available via shapeways but I wouldn't have been willing to pay the net price so wouldn't expect anyone else to either. When I go back and finish it off I'll look at another, more affordable way.
 
Phil, one thing I learned on the Vic stern was that resin either shrinks or loses accuracy in the printing. I was losing about 0.5% with elegoo ABS-like. I haven't measured the loss with syratech but think it may be more as I've had a couple of parts that wouldn't fit as intended, but I think Pat's approach - treat as needing machining - is the best solution. I chased my tail a lot on the Vic trying to compensate through scaling but, in the end, adapted the design to work around the issue and am doing the same with the Cutty Sark.
 
I think once you're printing walls/objects down at 0.3mm or so, they'll be fragile whatever resin you use. However if anyone is going to find the work around it'll likely be you, with this methodical approach. 
 

The "wire" in the CAD model anchor chain is 0.6615 mm diameter and a circular cross section. The printed parts are oval in cross section, 0.62 to 0.65 mm on the vertical and 0.71 to 0.74 mm on the horizontal. So I am getting about a 2% to 10% reduction in the width on the film, but an additional 10% to 12 % thickness on the vertical.

I expected the parts to be a bit too thick on the vertical dimension. From past experience I knew that the very thin parts are translucent so additional resin gets cured on the upper surfaces of very thin slices.

But I can't explain why the parts were thin on the horizontal dimension. I would expect resin to be cured over the entire pixel width but this apparently is not happening.

Increasing the exposure time probably would increase the horizontal width, but it might also cure more resin in the vertical dimension. Increasing the step size would reduce the total exposure time, and perhaps reduce the vertical thickness.

I am happy with the results I got - no one (except me) is going to be taking a micrometer to the chain on the model. But I might try printing them again with a different step size and exposure time.

With a model diameter of 0.66 mm the 0.02mm step size gave 33 slices and exposures. A 0.03 mm step size would give 22 slices, 0.04 mm would give 16 and 0.05 mm would give 13 slices.

So I might try the 0.04 mm step size to halve the number of exposures and try to reduce the vertical diameter, but use an exposure time of 3 seconds to expand the horizontal width a bit.

****

The reason I want to control the printing better to get a circular cross section is that there are many yards/meters of life rails on the model. They real parts were made of pipe 1.25", 1" and 0.75" diameter. At 1:96 this comes out to 0.013", 0.010 and 0.008", or 0.33 mm, 0.25 mm and 0.20 mm. This is less than half the chain link "wire" diameter.

I have successfully printed 0.20 mm diameter pieces, but they are extremely fragile. I really don't want the parts to come out any smaller, but 10% oversize would be OK. But I want them reasonably close to cylindrical.

I have been reading up on some of the flexible resins. I would think these would be less susceptible to the accidental bumps that happen while assembling models. But several sites say they are not suitable for thin walls, and the minimum thickness should be 1 mm, or 125 times the thickness of the smallest pipes!

Furthermore, because they are flexible they may not separate from the plastic film evenly and become bent while printing. This is also probably true for regular resins, so lots of supports will be needed!

Pat,
 
Your DUKW "duck" drive train brings back memories. I grew up in Hot Springs, Arkansas. It is a tourist trap - it had about 270 hotels and motels (individual businesses, not rooms) when I was a kid in the 1960s. The town is surrounded by lakes on two sides (actually it has grown around the lakes these days). There was a company with a fleet of "ducks" to take tourists on rides around the lakes.
 
I never rode on one. But I worked for an auto parts house in high school and college driving a delivery truck. The DUKWs had a bunch of universal joints in the drive train (I don't remember the actual count but I can see eight in your model), and they wore out fairly quickly. And of course there were the engines and lots of other parts. I made a delivery or two every week to the "duck barn." Hauling the engine blocks back and forth for rebuilding in our machine shop was the most difficult part.
 
I think they are still using some of those things that are older than I am!

And let's not forget another thing you can do- print metal parts! 
Actually, you have a service print waxes for investment casting, and they outsource the parts to a casting house. You can also print your own waxes at home, but have to deal with the casting process yourself.
Here's a 3 inch Federal-Mogul "weedless" prop for that same DUKW, cast in bronze:

Another use for printing: Rubber tires, as shown above. 
There are some flexible black resins, but they are difficult to work with and produce a material more like vinyl.
Instead, I printed a mold for the 5 inch OD tires, and had a friend pour polyurethane rubber into it.

 

Oh come on Ken. You know you miss SOME of it. People pay perfectly good money to do many of those things.

Accurate? More accurate than anything we whittle in wood!
Smooth? As with wood, allow all surfaces to be sanded or scraped smooth. Molded plastic parts from Tamiya are smooth, but those steel dies have been laboriously polished to achieve the smoothness. Someone is going to do the work somewhere.
 
For precision parts, I treat printed parts like metal castings... which need to be machined for precision work.
Here's a 1:8 scale DUKW axle printed in pieces on a little Photon Mono. Parts were machined for fit and for bearings, and glued together. Works fine.

 

Foremast.

The foremast is mounted on the cruiser's hull.

Brett - alternatively look up Gerald A Wingrove - he has written an number of books and you can find some of his work on MSW. Sadly Gerald is no longer with us. RIP.