How to make clean oval holes

[Red Dog]

Doing a conversion of Airfix's 1/72 Spitfire Mk.I/IIa into the Type 300 Prototype.

Most of the differences I'm confident of scratchbuilding myself but its the exhausts that I'm having no success with.

Need oval holes.

Are there oval hole punches out there like Waldron's punches?

If not how do others punch oval holes.

Need six per side in a perfect line with very little room between upper edge, lower edge and each hole.

Using Rogerio "Rato" Marczak's fantastic article from Finescale Modeler, great info except for how he made the holes for the exhausts. http://www.finescale.com/~/media/import/files/pdf/a/a/8/build_172_scale_spitfire.pdf

                         "Using sheet styrene, Rato scratchbuilt a master for the flush exhaust stacks of the Type 300 and cast resin copies to be used on the model"

Cheers

Edited September 14, 2018 by Red Dog

[Corsairfoxfouruncle]

If i were going to try and make an oval hole i would drill the center at its maximum diameter. Then use either an triangle or round file of a smaller diameter, & stretch the round hole into an oval.     

[Doolie]

47 minutes ago, Corsairfoxfouruncle said:

If i were going to try and make an oval hole i would drill the center at its maximum diameter. Then use either an triangle or round file of a smaller diameter, & stretch the round hole into an oval.     

 

That sounds like a good suggestion, but I know I would have trouble keeping them consistent.  I wonder if drilling the holes at an angle would give acceptable ovals.  It may help if you had a drill press or some other means of keeping consistent alignment.  This may actually yield a realistic appearance, because without looking at a picture, I'm guessing that the reason the holes are oval may be that the round pipes are at an angle?

[Corsairfoxfouruncle]

Hello @Doolie ... Thats likely the pipes were at an angle. You could do a thin plastic card master using a photocopy to keep them consistent. Or do like i do count how many strokes you file in each direction. If you file/sand 5 forward then do the same backward to get a consistent angle. Though that might require a practice run on scrap to keep the pressure consistent ? In 1/72 shouldn't take but a couple strokes to get the shape correct. 

 

Dennis

Edited September 15, 2018 by Corsairfoxfouruncle

[Doolie]

For me, this is one of the aspects of this hobby that keeps it interesting.  I enjoy trying to figure out these little challenges, and it's often helpful to get "fresh eyes" or some one else's perspective on it.  I'm not always the best at lateral thinking, and there have been many times when somebody has a solution that makes me go: "why didn't I think of that".

 

Cheers, Tom

[Bozothenutter]

looking at pics of the real thing, they are not oval ie have a radius on the top and bottom as well as on the left and right.

apparently it's a stadium:https://en.wikipedia.org/wiki/Stadium_(geometry)

 

this would make it easier for you to make the shape, drill two holes and remove the middle bit.

[Black Knight]

I drill the centre of the hole and then tip the drill to each side using the flutes as a reamer. Whet the oval is at the width I need I then use the drill as a 'file' cutting the edges parrallel with the flutes rather than turning the drill. With this method I've been able to make oval holes as small as 0.3mm wide.

For a row of holes, eg exhaust ports, I use a pair of dividers to mark the centre of each with a small divot pressed into the plastic

[FinnAndersen]

What about doing it with printed decals?

 

HTH Finn

[72nd SQN]

Hey Red,

 

I have had some luck using brass tube, re- shaping one end into the shape you want (ie oval, flat sided oval etc) then file the edges until they are sharp and either using to mark out your template pattern and drill out (stay in the lines) or if the plastic is thin enough - can punch through. There are also some 1/72 conversions for the Spitfire prototype (Aeroclub and Paragon) which you may be able to pick up second hand ? They will do the job for you including the exhausts and will also will have the canopy, rudder and the original radiator (angled at rear) that you need to make the prototype.  Chrs, Paul

[dnl42]

Instead of drilling the holes, perhaps a hole punch, like the Waldron you mentioned. You could punch the two end holes and then remove the excess with a knife to produce the stadium mentioned above. If it truly is elliptical, then a needle file with a crossing shape should be able to provide a sufficient approximation of the major arcs with a smaller punch providing the minor arcs..

[Red Dog]

Cheers, Thanks guys.

Plenty of ideas there, that's just what i was after.

Will give the drill two outer holes and cut out middle section (although that now means 24 holes altogether without mishap).

Round hole by trusty Waldron punch and sand or drill outwards sounds useful too.

Thanks again

 

[Parabat]

Might be an idea to use a scribing template in conjunction with the above technique. I.E. scribe your 12 ovals, then you can drill the 24 holes and have scribed marking outlines for the cutting/filing to join the two holes. 

Hasegawa and Lion Roar do some good scribing templates. 

[Rob G]

Thin the kit plastic from behind, it's easier to get consistent dimensions in thin material, and practice a few times on sheet or a scrap model.

 

I'd actually be considering making a couple of panels with the holes in them, then cutting out/modifying the kit to suit. That gives you more than one go at making the holes.

[Badder]

Looking at the link, then the holes ARE 'stadium' shaped : correctly called an obround, or discorectangle

I'd take @Rob G's advice and forget about making holes in the kit. Get some very thin plastic and make the holes in that, using one of the techniques already mentioned. It may take many attempts, but you'll get there in the end.  Then cut the panel out of the kit and insert your scratch-built one. You can always thicken the scratch panel up again (on the reverse side)  if that is required.

 

Good luck,

Rearguards,

Badder

Edited September 15, 2018 by Badder