JayW Posted May 27, 2020 Author Share Posted May 27, 2020 Calling all modelling experts - I have a challenge with material selection for the ignition wiring harness for this version of the R-2800. The harness is a round cross section circular tube as shown: Scale this to 1/18 scale and the diameter seems to be about 0.080 inch or just over 2 mm. Also note that the lower end of the harness has a very tight bend. And note that it has welded-on ports where the spark plug wires protrude (two per port). First - does anyone actually know the basic cross section diameter? All I have done is scale multiple pictures of it. I'll bet Tamiya got it about right in 1/32 - that could be another good check. Second - assuming .080 inch is about right, then 5/64 inch material (0.078") would be OK, and 2 mm (0.079") would also be OK. And of course .080". What material would be suitable for this part? It must be the right diameter, bendable, and be drill-able so I can properly attach those little ports. That tight bend is the problem. I actually have some 5/64 brass tubing, but it cannot stand that bend. Even if I fill the ID with material, the wall fractures when it is bent. I have .080 diameter plastic rod that also cannot stand the bend. Perhaps I could heat it and try again.... I can obtain 2mm solder which will form just fine. But it is going to be a little pliable so I worry it won't retain its shape well. I have .070 solder and it bends rather easily; I also have .118 solder which is much stiffer. Also, I am not real confident the ports can be attached to solder especially with the pliability issue. Any ideas? daHeld and ctayfor 2 Link to comment Share on other sites More sharing options...
easixpedro Posted May 27, 2020 Share Posted May 27, 2020 No idea on the correct size, but I'd peruse the jewelry making aisle at the local craft store (Michaels/Hobby Lobby) next time you get drug to one. I've seen things like aluminum wire that's pretty thick and holds up better than solder. My wife used to have rolls of the stuff, that I have appropriated over the years and I'm pretty sure she got it at one of those stores. HTH -Peter JayW 1 Link to comment Share on other sites More sharing options...
airscale Posted May 27, 2020 Share Posted May 27, 2020 I used copper electrical wire for this in the past - there are some bits of house wiring like ovens etc that carry high load so the wire is chuffing huge (and all ranges inbetween) - don't know if its 0.80, but that is where I would start simply because copper is malleable and holds its shape once bent around a former.. hope that helps Peter daHeld and JayW 1 1 Link to comment Share on other sites More sharing options...
Landrotten Highlander Posted May 27, 2020 Share Posted May 27, 2020 3 hours ago, JayW said: Calling all modelling experts - I have a challenge with material selection for the ignition wiring harness for this version of the R-2800. The harness is a round cross section circular tube as shown: Scale this to 1/18 scale and the diameter seems to be about 0.080 inch or just over 2 mm. Also note that the lower end of the harness has a very tight bend. And note that it has welded-on ports where the spark plug wires protrude (two per port). First - does anyone actually know the basic cross section diameter? All I have done is scale multiple pictures of it. I'll bet Tamiya got it about right in 1/32 - that could be another good check. Second - assuming .080 inch is about right, then 5/64 inch material (0.078") would be OK, and 2 mm (0.079") would also be OK. And of course .080". What material would be suitable for this part? It must be the right diameter, bendable, and be drill-able so I can properly attach those little ports. That tight bend is the problem. I actually have some 5/64 brass tubing, but it cannot stand that bend. Even if I fill the ID with material, the wall fractures when it is bent. I have .080 diameter plastic rod that also cannot stand the bend. Perhaps I could heat it and try again.... I can obtain 2mm solder which will form just fine. But it is going to be a little pliable so I worry it won't retain its shape well. I have .070 solder and it bends rather easily; I also have .118 solder which is much stiffer. Also, I am not real confident the ports can be attached to solder especially with the pliability issue. Any ideas? Have you considered 2mm aluminium Bonsai wire? It is easily bendable yet has sufficient stiffness, and with proper support can be drilled. It comes in different lengths, so I assume for your application you only need the smallest package available (not the 0.5kg roll). If you want I can send some over... JayW 1 Link to comment Share on other sites More sharing options...
Lee in Texas Posted May 27, 2020 Share Posted May 27, 2020 Does it really need to be drilled? If you use copper or brass wire, couldn’t the ports be short sections of tube soldered in place? JayW 1 Link to comment Share on other sites More sharing options...
JayW Posted May 27, 2020 Author Share Posted May 27, 2020 26 minutes ago, Landrotten Highlander said: Have you considered 2mm aluminium Bonsai wire? It is easily bendable yet has sufficient stiffness, and with proper support can be drilled. It comes in different lengths, so I assume for your application you only need the smallest package available (not the 0.5kg roll). If you want I can send some over... I certainly have not! That could work. Yeah I need about 6 inches of it. Ha! If you can conveniently send over a foot or so (to account for mistakes) that would be awesome. Can you send me a private message? Landrotten Highlander and ctayfor 2 Link to comment Share on other sites More sharing options...
JayW Posted May 27, 2020 Author Share Posted May 27, 2020 4 minutes ago, Lee in Texas said: Does it really need to be drilled? If you use copper or brass wire, couldn’t the ports be short sections of tube soldered in place? Thanks for the reply Lee. Well I have not fooled around with brazing/soldering copper tube in a very long time! Now I call the plumber. I think in the end, it would be hard not to avoid some sort of hole, if for no other reason than to firmly attach the spark plug wires themselves. Link to comment Share on other sites More sharing options...
Lee in Texas Posted May 27, 2020 Share Posted May 27, 2020 Do you have or have access to a small mill with rotary table? That and a sensitive drilling attachment would be ideal for drilling in just the right place. JayW 1 Link to comment Share on other sites More sharing options...
JayW Posted June 2, 2020 Author Share Posted June 2, 2020 (edited) While I wait for the aluminum picture wire (2 MM) to arrive in the mail - I selected this material to make the ignition harness - I set to work on the reduction gear case. The detail is going to be a fully machined part, first on the lathe, and then on the end mill. Here it is in the middle of the lathe turning work: The lathe part finished and primed and sitting atop the cylinder banks: Then came the nerve wracking work of milling slots into the turned part so that inserts can be bonded in, in which to mount accessories. The work went pretty well, resulting in this: You see three mounting pedestals - Magneto, prop governor, and oil scavenge pump. You also see one of two large holes where the distributors go. Right before another coat of primer, epoxy was added to the inside edges, a couple more inserts, and a bolt ring around the nose (turned from brass): And the primed part: Now - to make those accessories. The scavenge pump, the prop governor, the magneto, and two distributors. Also, lots and lots of Meng nuts! Stay tuned. Edited June 2, 2020 by JayW easixpedro, Landrotten Highlander, patricksparks and 13 others 16 Link to comment Share on other sites More sharing options...
JayW Posted June 2, 2020 Author Share Posted June 2, 2020 Do any of you have any good info on the Bendix-Scintilla distributor used on this engine? I have literally nothing to go on besides photos! Link to comment Share on other sites More sharing options...
brahman104 Posted June 2, 2020 Share Posted June 2, 2020 I love seeing your machining efforts Jay! I wish I could help with some distributor info, but I know considerably less about this engine than you do! I have not turned acrylic before but it looks like it comes out really well. Quick question, do you make your own custom cutters for your lathe? I'd really like to make some for myself but I haven't had any experience in this. This engine is absolutely brilliant! Craig Link to comment Share on other sites More sharing options...
TwoHands Posted June 3, 2020 Share Posted June 3, 2020 Can I suggest you use Mr. surfacer 500 and stipple the reduction gear case? JayW 1 Link to comment Share on other sites More sharing options...
JayW Posted June 3, 2020 Author Share Posted June 3, 2020 13 hours ago, TwoHands said: Can I suggest you use Mr. surfacer 500 and stipple the reduction gear case? Now there is some stuff I have never used, and wondered about. Would this be for the purposes of filleting inside corners, or for filling very small imperfections, or for general texturing? I have some fairly thick flat or semi-gloss gray paint that is going to cure a few ills so to speak. Whereas the primer is very thin. Later on. ctayfor 1 Link to comment Share on other sites More sharing options...
JayW Posted June 3, 2020 Author Share Posted June 3, 2020 (edited) 17 hours ago, brahman104 said: I have not turned acrylic before but it looks like it comes out really well. Quick question, do you make your own custom cutters for your lathe? I'd really like to make some for myself but I haven't had any experience in this. Craig - acrylic is a wonderful material for machining. It is tough plastic which doesn't melt except at much higher temps. The only thing I dislike is that it doesn't respond to model glue! I am no machinist for sure. But I have been using my little lathe for several years now on and off. And have learned usually the hard way what tends to work and what doesn't. The cutters I have were all purchased on E-bay I think. Even some basic uncut ones, where I attempted to grind my own on a couple of occasions (not very successful). I believe there are some pretty simple basic rules for designing a shape depending on what you want to use it for - a "Lathe Cutters 101" of sorts. But I have not been able to find it. Here is a shot of my favorite cutters: There are cutters for cutting the RH side of a part, and others for cutting the LH side of a part. Here is a not so favorite cutter I have - a "parting tool": This piece is the kiss of death for me. It is intended to quickly cut a part off from its stock material. I don't use it anymore, but on the one or two occasions where I did, I was rewarded by a violent jam where the cutting edge dug into the part, which stopped the motor in its tracks, nearly bending the rails that the carriage travels on, and ruining the part. To this day I am mystified why that happened. It must have to do with the local shape of the edge and its width (a much narrower would take less material and be less likely to cause a jam). Here I include two pages from the machining manual I got with my Unimat minilathe: It describes some of the different basic cutter shapes that can be had, including the dreaded "parting tool". I have learned a few things. One - the cutting edge needs to be very narrow to lessen the likelihood of a jam. Two, you cannot have a cutter side be perpendicular to the motor axis of rotation. What that does is essentially turn the long side of the cutter into a very long cutting edge. It results, as the cut deepens, in excessive and sometimes violent vibration if not an outright jam. So the cutter must be positioned so that the long side of the cutter is at some angle off perpendicular to keep that long edge from digging into the part. I wish I could explain it more clearly, but you already have some lathe experience so perhaps you know what I mean. Three - The point where the cutter touches the part needs to be level with the rotation axis if not a touch below. If it is too high the cutter will tend to try to dig in, and potentially cause a jam. This is more serious the smaller the diameter of the part. Motor speed is also important, but I know very little about it. I do know that with acrylic and other softer materials, lower speeds are OK. And with real hard stuff like brass, you need higher speeds. To me, a novice, lathe turning is a mysterious artform, where I am enjoying a bit of success, but also much frustration and failure. I would love to attend a hands-on class. It is also a bit dangerous - I cannot imagine the hazards of a larger machine with a more powerful motor. The worst that has happened to me is getting knuckles torn open by rapidly whirring chuck jaws, and one time those same chuck jaws jamming a small file into the palm of my hand. I use safety glasses of course - a brass filing does not need to find its way into the eye. Edited June 3, 2020 by JayW Greg W, Derek B, daHeld and 2 others 5 Link to comment Share on other sites More sharing options...
REJ Posted June 3, 2020 Share Posted June 3, 2020 Don't know if this is of any help, but this is an R-1820 radial....of coarse my work isn't near as detailed as yours...but I try. This, incidentally is the 1/18th scale SBD 3/4 kit from Merit. JayW and ctayfor 2 Link to comment Share on other sites More sharing options...
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