Long Hood Version 2

Test printed a V2. I had a lot of problems with it – but I suppose that like anything else if is relative .. as I can see where I need to modify the design.

Printed in PLA at .3mm layer height .. a ‘draft mode’ I suppose. The mass of supports at the front are just that .. a solid mass .. problem. The supports at the bottom when removed also broke off part of the bottom of the shell. Lots and LOTS of supports inside. I need to rethink .. perhaps instead of a single shell .. print multiple parts like the top and end separate and then glue everything together after.

The opening for the fan was fine .. the fan snapped in easily. The exhaust not so much as I had to open up the hole some for the part to fit.

Long Hood Version 3

Trying a different method, split the hood into multiple parts. The sides will print much better flat. The other parts will print with shorter supports. The nose should print better with the notch nice and clean. See how this goes.

V3 Test Print and Assembly

This is the result of breaking the long hood into parts and printing that way. Came out pretty good. Not too concerned with the rough surface .. was printing at .15mm layer height and .4mm nozzle. This is in any case .. prototyping. If I ever get it like I want it I can always see if I can get it printed in resin.

  • Issue: The parts have a 1mm step (with matching 1.1mm ‘slot’) .. while this worked it was difficult to align the parts when I used super glue to assemble.
  • From that I think I need longer step/slots to align everything. I increased that to 3mm and 3.1mm in the follow-on model. To that end I shifted the two fans forward 2mm to give me room
  • Super Glue .. hmmm. I was going to do a smallish test print and see how well epoxy worked – that would give more time to align but will need bracing while it sets. Doing a little research and found what I hope is a better solution, Weld-on 4 appears to work well with PLA (see below)
  • I made small lips on the openings for the fan. This worked ok .. but I realized that if I want to fill/sand the hood the lips would be a problem. In the follow-on model I removed those lips and just opened up the dia of the fans. See how that works.
  • I also modified the part that connects to the cab to fix some problems there.

Cementing PLA

I did some research on a better way to cement PLA and found a link to Weld-on 4. A post on a 3D community on Reddit indicates that … yes .. it works well with PLA.

Click the image to the left links to the product on Amazon.com for a 4 oz. can. I figure that will last a long time. I also read a comment that you shouldn’t remove the little metal plug (if there) under the cap but punch a hole just large enough for the applicator needle.

I also ordered a Weld-on 25-gauge Syringe Applicator. Comments on Weld-on that come with a plastic bottle syringe were not good .. all said to purchase this syringe.

The Weld-on 4 is evidently very thin and you use the syringe to apply the cement to a joint where it wicks into the space between the two surfaces. It does require a fairly tight fit since this does not act as a filler.

Long Hood V3C

Jigs to help align the top and sides of the long hood for my On30 Narrow Gauge Road EngineMade all the modifications I mentioned earlier and did a test print. I also created a couple of jigs to hold everything in place while the cement sets

Here’s how the jigs will work. The little notches up top are placed where the top and side seams meet .. that is to keep any cement from wicking through to the jibs.

I am going to stop here for a while until my Weld-on and syringe get here.

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