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_Peter_

Repairing Propellers

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I bought a 1/200th Hobbymaster DC-4 off eBay and when it arrived, only three of the twelve blades were still attached :(.  But I do have all the blades.  I've done some plastic modelling before and know enough to know that this is really fiddly and easy to stuff-up.  Any tips on reattaching these little blades?

  • What glue would work best (something reasonably viscous and moderately fast setting I guess?),
  • How to hold them in place while they set,
  • How to get the angle accurate?

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Posted (edited)

I'd recommend a liquid solvent cement such as Tamiya Extra Thin, applied with a small brush. A propeller jig is what you need. You can purchase one or make one yourself. On a piece of stiff card, draw a circle using a drafting compass. Set the radius of the circle equal to the radius of the prop. Draw radial lines through the center of the circle at a 120° angle. In the center of the circle, punch a small hole just big enough to accept the propshaft. At about 3/4 of the distance from the center of the circle, glue small 30°-60°-90° triangles, cut from the same stiff card, on each radial to support the blades. The attached illustration should give you an idea.

 

Print

 

 

Edited by Space Ranger

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That won't be easy, it may be better to return it for a refund (unless you knew it was damaged when you bought it).

Space ranger probably suggested Tamiya Extra Thin because most glue will bulge out at the join and at this scale it would be very difficult to trim off the excess. I'm not sure what type of plastic the props would be on these types of models, but assuming it is a suitable glue, you need to hold the parts together and then apply the glue to the join with a brush. The glue 'grabs' quite quickly but only do one prop at a time on each hub and leave it to dry hanging vertically downwards for an hour or two. You may have to put something under the tail to ensure the prop really is vertical.

Don't try to set the prop angle by eye – it never works.

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Personally I always try to reinforce prop repairs as once broken they are more vulnerable than usual.  Smooth the surfaces of the break, mark the centre with a (very) sharp pin and drill carefully with a pin vice.  You can then insert a piece of fine wire or thin brass rod.  Then adjust for straightness.  This done you can then use the jig method and the pitch adjustment becomes easier before adding adhesive.

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4 hours ago, Vicarage Vee said:

Personally I always try to reinforce prop repairs as once broken they are more vulnerable than usual.  Smooth the surfaces of the break, mark the centre with a (very) sharp pin and drill carefully with a pin vice.  You can then insert a piece of fine wire or thin brass rod.  Then adjust for straightness.  This done you can then use the jig method and the pitch adjustment becomes easier before adding adhesive.

If you can manage that in 1/200 scale, you've got much better eyesight than me. 

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19 minutes ago, Gorby said:

If you can manage that in 1/200 scale, you've got much better eyesight than me. 

Good point well made!

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For some reason, the fact that the props are 1/200 did not register (not enough caffeine in my system, probably). What I proposed works far better in larger scales. And yes, pinning the joint with brass rod is highly advisable, as Vicarage Vee suggests. I forgot to mention that as well. But in 1/200 scale, that's gonna be next to impossible.

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Mount it on a stand, undercarriage retracted and just fit the prop hubs, instant flying aircraft.

Prop discs never really look convincing particularly in such a small scale and the kit props are probably over scale anyway.

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12 minutes ago, Space Ranger said:

For some reason, the fact that the props are 1/200 did not register (not enough caffeine in my system, probably). 

Are we allowed to share that excuse?

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10 hours ago, Vicarage Vee said:

Are we allowed to share that excuse?

It's always worked for me!

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Apart from the small size, there's another potential problem I can see: what plastic are these parts made of ?

If it's the usual polistyrene used for plastic kits then no problem, as this plastic can be glued using many glues. If however they are in the plastic often used for details in die-cast models, then it may be harder to glue than expected... don't know what the technical term is for this, but often the plastic used is softer and more flexible and doesn't seem to like any glue at all.

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This glue takes many "fat" plastic types: https://www.loctite-consumer.co.uk/en/products/specialties/super_glue_all_plastics.html

I used on old Airfix tracks for their tanks and made a test on some small figures from Esci. I glued two of them together at the small plate they are mounted to and had to pull real hard to separate them.

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7 hours ago, Giorgio N said:

Apart from the small size, there's another potential problem I can see: what plastic are these parts made of ?

If it's the usual polistyrene used for plastic kits then no problem, as this plastic can be glued using many glues. If however they are in the plastic often used for details in die-cast models, then it may be harder to glue than expected... don't know what the technical term is for this, but often the plastic used is softer and more flexible and doesn't seem to like any glue at all.

Good point. I was assuming this was a regular polystyrene kit (once again, not enough caffeine). Further research reveals this is in fact a die-cast model.

 

I'm off to have some coffee.

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1/200 props are so freakin' small and besides, matching each broken blade to its hub would be impossible, I would imagine. I would suggest you contact Hobby Master via their website and see if you could get or purchase a set of props for your model... or you could always feather the props on the three bad engines, if you were really desperate!

Mike

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If you have a complete prop, get some Plasticine or soft modelling wax and carefully press the prop with equal pressure on all the blades, into the modelling material.  Ensure that you have a good impression when you take out the master prop.

 

The impression is now your jig..  Make three more impressions. Check each blade to see if you can match each break.  Use a gel type super glue to stick the blades back onto the hubs. allow to set and then trim off any glue seepage.

 

This I think will be your simplest way.

 

 A cruder way would be to buy some pressed metal Dinky spare three blade props and file them to size and shape  Steve Flowers of Leicester www.model-supplies.co.uk  make Dinky Toy Car and Plane spares.

 

John

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Thanks everyone for the great advice. Really helpful.  Serves me right for not building it from a kit like God intended, (but I do need it 1/200th scale and I' pretty clumsy with fine-paint work :( )

 

This is the beast BTWhttps://hobbymastercollector.com/HL2005.html

 

I think that's wise advice about getting spare props from Hobbymaster.  (Even buying another DC-4 -- doesn't matter what livery really, as long as it's cheap and the props are silver.  Hello eBay.)

 

I take the point about setting by eye never works -- especially, I'll venture when you've got three other props right there to compare it to.

 

I have considered cutting off al the blades, or putting disks on ( https://oikofuge.com/how-to-model-rotating-propeller-discs/ )and going for the spinning blades look, but I'm not desperate enough yet.

 

I feel the blades are polystyrene -- I mean they're not metal and I can't see why you'd bother making them of anything else except ploystyrene, but I'll bear the posibility that they're not in mind when I glue the first one.

 

I don't have a complete prop, but I have one with two blades, which could be used to make a three bladed plasticine jig.

 

That Loctite superglue looks the go https://www.loctite-consumer.co.uk/en/products/specialties/super_glue_all_plastics.html  (would you say that's a gel type superglue?)

 

As has been noted these things are *bloody* small.  I'm wondering if I should cut them off the shaft -- afix the blades without having to deal with a cumbersome aircraft, and then glue the complete three bladed prop back on (I don't care about them rotating -- in fact as far as I can see the props were always synchronised and fixed in same position is more realistic than higgldy-piggldy positions).  Or am I just making extra fiddly work and increasing the scope for things to go wrong?

 

Edited by _Peter_

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If it is not polysytene Tamiya released also a new cement for ABS-like plastic, 

https://www.tamiya.com/english/products/87137cement_abs/index.htm

I have not used it but they said it can glue some difficult to glue plastics

Regards

J-W

 

Edited by JWM

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I did discs on an old Revell Boxscale Connie.... it's around 1.125 scale so a fair bit bigger than yours, as I wanted her sweeping in just before the tyres squeal. 

I was fairly pleased with the look, considering what I started with. 

IMG_20190712_221635

 

IMG_20190713_122115

Thin clear poly sheet and a compass cutter. 

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I’ve scratch built a couple of props.  Not saying you should do so but this is the rig I used to get the angle the same on a three bladed prop.  The blocks are balsa slotted to the same angle.  You wouldn’t have to clamp the blocks, just glue them in place and slide the blades in.  Food for thought maybe.

 

Dennis

 

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