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JayW

1/18 Scale P-38 Lightning

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Guest Peterpools

WOW

Fantastic work and just knowing how to machine parts is a skill to admire.

Keep 'em coming

Peter

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Uh-oh - the lathe is popping my circuit breakers.  Motor goes into the shop this week.  Please stand by; I will be doing some things that don't require the "machine shop" until I get the motor back.

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What a delay, sorry.  Had to get the lathe motor fixed, and then went out of town.  This may be a bit of a disappointment as far as progress goes, but what you will see here is one of the most difficult parts I have ever made.

 

Here is a fairly simple piece of lathe turned aluminum (.75 inch diameter):

 

  001_zpsc7836052.jpg

 

Anyone following this string knows I am a machine part rookie who has really only done plastic parts.  This is my first large metal part.  I immediately notice it takes much longer to get things done because you can't take as much material, and have had to deal with chatter issues, etc.  This is going to be the elbow fitting of the lower strut.

 

I actually tried this in acrylic with these results:

 

002_zps4417a2cf.jpg

 

Now I had many hours into this part when it cracked as I tried to insert an alum tube into the tight fitting hole.  I should have known.  But it was all for the good, as it served as a prototype for the real part, and I was able to improve the process.  That failure plus the motor breakdown plus the trip are the reasons I have been away.

 

Here is the turned part being end milled to create the clevis lugs for the lower torque link, and also a good tab for clamping for the next milling operation, which was to drill the clevis holes (0.093 inch dia), and the axle hole (.1875 inch dia).  The tab comes off later.  I have found you have to plan how to secure the part when milling.

 

003_zps516a326b.jpg

 

Here is the part just before I clamped it down for hole drilling:

 

004_zps576f12f3.jpg

 

And the finished machining:

 

006_zps672a48e8.jpg

 

I was very nervous about the 3/16 hole.  It was the last operation, and perhaps the most dangerous.  It's a pretty big cut on a small part and it has to be located very close to spot on or it will break out of one side of the fitting.  MOF, truth be told, this part had so much time and sweat in it, I was quite stressed out by this time.  A fatal mistake would be soul destroying.  I didn't enjoy the experience as much as I should.

 

And here is the finished lower strut:  The machined part was bonded to the axle, a 12-bolt pattern added (the bolts attach the axle to the brake drum), a cross bolt added to the axle, and a hydraulic fitting added for the brake line.  Also, a 7/32 tube was slid over the shaft on the machined part, and this will be the chrome plated oleo.  Victory.

 

008_zps556d40e0.jpg

 

007_zps21ed1291.jpg

 

Now for the opposite part, and then on to the upper strut, which has plenty of lathe/mill fittings.

 

See ya later!

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Well done Jay! After just having gone through some similar processes myself on the vampire, I know only too well what you are going through. I find it really interesting how you have to think about the processes you have to do in turn to get down to the desired result. It's really good watching your step by step posts, as I learn a lot each time. I've found sometimes it helps to have some of the holes drilled first, as you have a bit more room for error, but I understand it's the classic "chicken or the egg" paradox as you then have less material to take the machining stresses. In this case it would certainly appear you made the right choice!

 

Keep up the great work mate :)

 

Craig

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JW

 

Your skills are developing quickly and the results are setting a new standard. Micro machining it's an art in itself and your tenacity is most admirable.

 

 

Now about the part you've done. Its just fookin outragious!!! Its for sure a difficult shape and you've nailed it. I'm amazed and duely impressed.

 

Nice going Bud...show us lots more.

 

Geoff

Edited by Ironwing

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"Well done Jay! After just having gone through some similar processes myself on the vampire, I know only too well what you are going through. I find it really interesting how you have to think about the processes you have to do in turn to get down to the desired result. It's really good watching your step by step posts, as I learn a lot each time. I've found sometimes it helps to have some of the holes drilled first, as you have a bit more room for error, but I understand it's the classic "chicken or the egg" paradox as you then have less material to take the machining stresses. In this case it would certainly appear you made the right choice!"

 

Craig - you hit the nail on the head.  It is one thing to visualize a milled shape (or a lathe turned shape).  It is another thing to actually secure the part such that the machining operations can take place on a small part.  On full size parts, there are more options such as tooling holes.  On very small parts, the issue becomes paramount.  For the above part, first there had to be enough excess length on the .75 diameter aluminum rod for the lathe 3-jaw chuck to grab hold of it, that amount (about .4 inch) had to be aded to the total length of stock material, and then machined away once I reversed the part and chucked it from the opposite side.  That added lots of machine time and "chips on the floor". 

 

Then, the shaft you see on the machined part was very important - it served as the clamp feature for the initial milling operations where the clevis lugs were made. Note in that operation I left a substantial mount of material on the opposite side as the clevis lugs are on.  That tab I left became the clamping surface for when I turned the part 90 degrees and did the hole drilling operation.  After that was done, I reclamped to the shaft and milled away the tab.  It took lot of brooding and thinking in the shower to come up with that.  I am all ears for a better way.

 

I have not thought much on the other fittings for the upper strut.  I have the upper torque link fitting, which in the end will be nothing but a tube with a set of clevis lugs.  That one I will do in plastic because it won't be under any load.  And then a real tough fitting for the drag link and side link attach, further up the strut.  That part has two sets of clevis lugs 90 degrees opposed, and will have to be sturdy so it will be metal.  Yikes.

 

I wonder if brass machines better than alum.  Anyone know? 

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I wonder if brass machines better than alum. Anyone know?

 

There are plenty of brass or aluminium alloys, but as a general principle, brass is harder but gives better machining results ...

 

Hubert

Edited by MostlyRacers

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Paul - you are a u-tube star. I will watch them all.  And, I will look into some turning brass - I am with you, the alum sticks to the tool and makes a mess sometimes.

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I'll certainly second what Paul said. Brass machines very nice. I prefer working with it any day. As for your process, I can't really think of any better way to do what you are doing. Sometimes there's no easy way to make a complex part, but that's the price you pay for achieving such impressive detail!

 

Craig

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