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JayW

New Shoes for Miss Velma (Lots of Lathe Work)

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Hello fellow master modelers - I am going to hopefully take you through a pretty challenging scratch build of some 1/18 wheels and tires for a P-51 Mustang using primarily a Unimat mini-lathe.  At the time of this posting, I am not done, and there is some risk that it will be a failure.  But here goes.....

 

A few years ago I dove into a 21st Century Toys 1/18 scale P-51 Mustang, made extensive modifications and improvements, and called her Miss Velma.  Here is a picture of her after the two-year project was completed (some of you know of this giant project):

 

89final16.jpg

 

I have a 4-part article on Miss Velma on LSP, if interested.  

 

The main landing gear were a big part of the project.  I scratch built the struts, brakes, and gear doors but used the existing toy's tires and wheels, although heavily modified.  Here are some closeups:

 

DSC04847_zpsyulo0coc.jpg

 

DSC04846_zpsbfy3s5zj.jpg

 

It may be evident to you from the pictures that the original tires were split (sawed) in two right along the centerline, and a good bit of plastic sheet material added in the middle, and then the diamond pattern re-cut.  At the time that was all I could think of to get the tire width correct.  I lived with the inaccurate tread pattern, and also the inaccurate diameter of the rims (they are a little too large but the tire OD is actually about right).  The outer wheel half was mercilessly whittled on in and attempt to make the "spokes" look somewhat accurate, with marginal results.  The inner wheel half was modified too, to accept the scratch built brake housings.  Here is what the wheels and tires are supposed to look like:

 

DSC04850_zpsp4osu7dj.jpg

 

Meanwhile, I purchased a Unimat mini-lathe in support of my P-38 "Lucky Lady" build (look for an article soon), and learned how to make pretty good tires and wheels as machined parts.  Here is an example (main gear P-38, 1/18 scale):

 

DSC04817_zps673cgzcm.jpg

 

So now I mean to give Miss Velma some new shoes, which better represent the real thing.  Off come the old:

 

DSC04849_zpslfovrrhj.jpg

 

Geez - it's a bit damaged but nothing I cannot fix.  

 

And I will get on with the new.  Stay tuned!

 

 

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At the risk of boring you all I am going to show some of the lathe operations.  Some of you have seen this little jewel:

 

DSC04833_zpsyfjrjbfk.jpg

 

This machine is almost as old as I am I think.  And I just retired!  So there is the Unimat SL1000 mini-lathe, with a chunk of 1-inch diameter brass chucked in its jaws, and a .125 inch hole line bored through the middle.  You can see the drill chuck on the right (drill bit is lying on the wood base to the left).  There are also three other chunks of brass in the foreground.  The four pieces of raw material were cut with a circular saw from a large and expensive piece of rod I bought from a metal house on line, and are intended to become the four wheel halves.  Little did I know at the time that it would take all four to do the inner wheel halves, as I ruined a couple of them in the middle of the machining processes.

 

I have decided to start out with the wheels first, and do the tires last.  The tires I know I can do (incidentally you will see they will be turned from acrylic).  The wheels I am less sure of, so if I fail then I have minimized the effort wasted.

 

P-51 MLG wheels in real life are 15.0 inches outer diameter and about 10.0 inches wide (a touch wider than the 9.5 to 9.75 inch wide tires).  That scales down to .833 inch diameter by .56 inch wide.  My wheels will differ slightly but not by much, mostly to be compatible with the existing struts and brake housings.  They have ten "spokes" separated by familiar looking teardrop shaped cutouts on the outer wheels, more circular shaped on the inner wheels (see pictures in my previous post).  The basic wheel shapes can be turned on the lathe, and the cutouts machined by end mill.  This will give me the "end plates" so to speak.  They will be separated by simple machinings which will give the finished wheel its proper width.  Also some inner stiffening ribs will be added, cut from thin plastic sheet.

 

Here is the machining plan for the inner and outer wheels:

 

  • Start with 1.0 diameter brass material cut to .6 - .7 inch length (could be much shorter but I need material in which to chuck the part).
  • Drill .125 inch axle hole.
  • Turn OD (.86 inch diameter; a bit larger than a perfect .833 inch diameter)
  • Angle the lathe's head stock to 37 deg, turn the basic coned surface of the wheel (this angle is for the inner wheel; is more like 14 deg for the outer wheel) 
  • Re-align head stock to zero deg, flip part, re-chuck, machine the axle housing diameter
  • Remove part, convert lathe to end mill configuration
  • Secure part in vise, drill or machine cutouts between spokes
  • Remove part, reconvert to lathe configuration, re-chuck part
  • Turn rough cuts to approximate the inside coned surface (unable to do this with turned headstock)
  • Use hand file on spinning part to obtain final inner shape
  • Flip part, re-chuck, machine of excess to obtain final part width of .24 inch
  • Finished

 

Next post I shall show each of these operations and the finished machining.

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OK here we go with the lathe and the inner wheels.....

 

The OD is turned, axle hole bored:

 

DSC04834_zpshmnev7f1.jpg

 

The flat common to the brake housing is turned:

 

DSC04835_zpsvhwvlp0c.jpg

 

Lathe head stock rotated to 37 deg, coned surface turned:

 

DSC04838_zpssx9drmcu.jpg

 

DSC04836_zpsmzyv1qac.jpg

 

Part flipped over and re-chucked:

 

DSC04842_zpsmux3rwfo.jpg

 

Axle housing diameter turned (ALOT of material disappears here):

 

DSC04843_zpssuckphqp.jpg

 

Part removed, lathe converted into end mill, cutouts drilled into part:

 

DSC04844_zpskkxi0wws.jpg

 

Lathe returned to lathe config, part re-chucked and inside surface machined and filed to match outside surface (several steps here):

 

 DSC04845_zps6p7eoimp.jpg

 

Part flipped again, and sawed off to right width (no pictures of this simple operation).

 

And the finished parts:

 

DSC04851_zps2sk4kphd.jpg

 

I will add a .010 or .015 inch thick plastic disc to the flat surface to serve as the actual brake housing mounting plane, sand and file a little more, paint and then the parts will really be done.

 

Then it is off to go do the outer wheel halves.  Stay tuned (they are started yet).  Hope this is interesting for you.

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Dude

 

HAPPY RETIREMENT!!! Welcome to life where your greatest decision is to decide which chair to sit in next. I love it!!

 

Anyway, I'm glad your showing this operation. The inner hubs look super. Now I'm going to have to buy a lathe. Your a bad influence...but a really talented one.

 

Tell me, why aren't we casting these? :)

 

Show us more...please

 

G

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Thank you thank you.  So the topic is interesting; good.  Now, I need to come through, which is far from certain.  On the P-38, the nose gear wheels are the same size, but there are only six cutouts.  That is much easier, as tolerances are not very noticeable.  These wheels have ten spokes with a thin amount of material making up each "spoke".  Much more challenging.  I would not be totally against doing the inner rims over again.  They have flaws, the worst of which is poor angular tolerance between cutouts.  But each one takes several hours of machine time, so more likely I will just use the ones you see.  Geoff - I know what you are after.  I could send you a set and you could mold them, since I don't have the equipment.  Let me know.

 

Tires, BTW will have a block tread.  Its a fixture of sorts to do diamond tread patterns.  I will reserve that for my Thunderbolt.

 

Oh, and BTW Geoff - I have lots of big decisions to make in the near time over and above "what chair to sit in".  Like Part B supplements, pension payout methods, proper investment strategies, etc - all sorts of things that were not on the radar a couple years ago.  Making me a nervous wreck.  Soon though - life will be MUCH easier; beginning to feel it already.  Modeling helps!

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Decisions..decisions... maybe this will help: all the money gets Auto deposited into your checking account.. Supplement B is cheap.. get it. Supplement C is good too if you don't have prescription coverage. Investment strategies...spend it. You can't take it with you. Most importantly.. Relax and enjoy it.

 

Poor angular tolerance... how could you let this happen? To tell you the truth.. Casting the new rims would be nice, but the longevity of resin, over time, and given the weight of the Mustang, I don't think resin could handle it. Now I'm forced to buy a lathe. Why do you bait me so? :)

Edited by Ironwing

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Finally - a little progress.  I have been working on a little son-of-a-gun machined part.  You have seen the inner wheel; let me show you the outer wheel.

 

First, in an attempt to improve accuracy I made a template of sorts out of thin plastic sheet to help align the spoke holes better.  Here it is bonded on a partially machined piece of brass:

 

 DSC04852_zpsklmiasul.jpg

 

Here is a shot midway through end mill machining of the spokes and slots:

 

DSC04854_zpskobbrx0k.jpg

 

If it looks a little sloppy that is because it is.  My concerns about tolerances were well founded.  These features are small, and my machine just isn't that accurate.  Another shot with the basic machining done:

 

DSC04856_zpspcpbzboh.jpg

 

From there it was back to the lathe to turn in the dished surfaces (14 deg dished).  Pretty straight forward:

 

DSC04857_zpshzr5mtek.jpg

 

Reverse, and cut away a ton of material.  Then rotate the head 14 deg and turn the inside:

 

DSC04860_zpsubiiptuh.jpg

 

And here is the rough finished part, along with most of the material I removed to make it:

 

DSC04861_zpspbw6qolw.jpg

 

Buy-to-fly ratio must be about 10 or 20 to one!

 

A little sanding and filing and it looks fairly good.  Here it is along with the inner wheel.  I am hoping the imperfections are less evident to your eyes than to  mine.

 

DSC04863_zpsj8m2i07i.jpg

 

That part was very difficult and time consuming to produce.  Now I have the other one to do, and then I will machine the tires.  Stay tuned!

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I have just got my first lathe and this is exactly what I wanted to learn how to do - thank you for sharing it Jay

 

they are incredibly powerful assets, but as I am finding they need a very disciplined approach and actually some confidence and experience - both of which I lack :)

 

I can see school is in session here though so again, thank you for talking through what you are doing and how you go about it

 

Peter

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Oh yeah! More juicy lathe operations! Glad to be following another of your gems Jay :)

 

You're making a great start on it so far. Do you grind your own tools? I need something with a small tip like what you have but I'm not really sure where to start with grinding them down. I'm sure there's a whole heap of youtube videos out there though that I should look at....

 

Bring on the awesomeness mate!

 

Craig

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Wow, Jay, nice work!!! That looks like a pain in the ass. Personally, I am waiting for 3D printing to get simpler and cheaper!!!

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