Author Topic: Colibri Hummingbird Dynamic Sculpture - WIP  (Read 1637 times)

Offline crueby

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Re: Colibri Hummingbird Dynamic Sculpture - WIP
« Reply #30 on: December 02, 2017, 01:56:29 AM »
Wow - this is going to be a great looking sculpture!

 :popcorn:

Offline 10KPete

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Re: Colibri Hummingbird Dynamic Sculpture - WIP
« Reply #31 on: December 02, 2017, 02:33:01 AM »
I had no idea one could mill such small threads! Wow.
 :ThumbsUp: :ThumbsUp:
  :popcorn: :popcorn:

Pete
Craftsman, Tinkerer, Curious Person.
Retired, finally!
SB 10K lathe, Benchmaster mill. And stuff.

Offline kvom

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Re: Colibri Hummingbird Dynamic Sculpture - WIP
« Reply #32 on: December 02, 2017, 12:43:59 PM »
The place I bought that thread mill sells one for #0 threads.  :o

Offline crueby

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Re: Colibri Hummingbird Dynamic Sculpture - WIP
« Reply #33 on: December 02, 2017, 02:23:38 PM »
I don't get how an internal thread can be milled, any diagrams out there??


Offline kvom

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Re: Colibri Hummingbird Dynamic Sculpture - WIP
« Reply #35 on: December 02, 2017, 03:36:35 PM »
That video is a bit deceptive.  The tool shown has multiple teeth and as such can cut only threads with the same pitch.  It can cut multiple diameters, limited to the size of the hole for internal threads.  These tools are be fast as they need to go around the work once if the thread depth is less than the number of teeth.

In my example, the cutter has only a single cutting edge with three teeth, so it can do multiple pitches, obviously limited by the width of the teeth vs. the diameter of the shaft.  In this case, I can mill only a bit more than 1/4" of threads.  I also have to make a complete turn for each pitch depth.  In this case, 32 tpi x 1/4 means 8 times around.  I also make 3 passes, similar to single pointing.  In brass I could get away with 2, but I also make a spring pass to clear up any burrs and to compensate for any flex in the tool. 

The single tool cutters have a ramp angle in the tooth profile that limits the pitch range.  The tool in the picture can do down to 56 tpi.  The feed rate needs to be much smaller for internal vs. external threads.  One starts with the required SFM for the material to be cut to determine the RPM.  Then you use that plus the chip load (inches per tooth) times the number of teeth in the tool to determine a linear feed rate.  Finally you convert the linear feed rate to actual taking into account the diameter of the tool path.  In essence, you want the time to complete a single circuit of the work to be the same regardless of the diameter.

I have a larger thread mill that can cut 1/2" internal threads.  I used it on the Joy engine to make all the 1/4" studs. 

I also have a 27 TPI NPT thread mill I used to thread brass tube 1/16-27 and 1/8-27 for piping the loco.


Offline crueby

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Re: Colibri Hummingbird Dynamic Sculpture - WIP
« Reply #36 on: December 02, 2017, 05:52:44 PM »
Thanks Bill/Kvom - makes sense to me now, clever use of CNC control. 

Back to watching the project!   :popcorn:

Offline kvom

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Re: Colibri Hummingbird Dynamic Sculpture - WIP
« Reply #37 on: December 05, 2017, 09:56:00 PM »
Some progress after getting a shipment of aluminum via eBay.  Alloy is Mic 6 (cast);  I like it since the finish on both sides is good, and as well drilling causes the swarf to be little chips rather than stringers.  I tried to get 5 parts from one piece of material, but one was too close to the edge and broke off.



I also got the other two hypocycloidal gears back from Shapeways, this time in the polished material.  While it's a bit smoother than the first one, I wouldn't call the surface polished.  Also, the center hole is a bit smaller than the first, probably about 2 thou, so the eccentrics will need to be turned to fit.

Offline kvom

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Re: Colibri Hummingbird Dynamic Sculpture - WIP
« Reply #38 on: December 08, 2017, 11:45:49 PM »
Another batch of parts machined from a single piece of 1/2" cast aluminum.



The part on the lower left, labeled "wing frame support right", while it won't be used until fairly late in the assembly, proved instructional.  The plans call for a 7/16" (.437) countersunk hole for the needle bearing, whose diameter is .439".  I assume that would be a press fit in wood, but too tight for metal.  Given that there are 16 such bearing in colibri, I'll need to keep this dimension in mind for similar counterbores.  I intend to machine a sliding fit and secure with loctite.

The same part has a 5/64 hole (obscured by the bearing) that's used along with the bearing diameter to connect the part with its mate while they are glued together.  The plans specify a #2 wood screw though both parts ;  I will actually be screwing the parts together with a 2-56 screw, so this hole needed to be a #2 clearance and drilled with a #43 drill.  The mating part will need it's hole to be tapped.  That's a lesson to go back to the assembly drawings to see how each part is mated and modify the DXF and machining instructions where needed.

I located a piece of stock with dimensions large enough to make the main frame but not too large for my mill.  It's 5/16" thick while the plans call for 3/8".  Originally I didn't think the frame thickness was critical as the datum for most of the mechanism can easily be the face of the frame.  However, reviewing the assembly more closely I see that the body parts of colibri are centered over the frame, meaning that I'll need to offset the mechanism spacers by an additional 1/32" or do some shimming, and the bird's head needs to be the same thickness as the frame.

One other painful lesson this week is that even with peck drilling and .06" pecks, 1/16" drill bits don't care for a vertical feed of 22 ipm instead of the recommended 2.  Need to proofread the CAM entries or the g-code a bit more closely.


Offline kvom

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Re: Colibri Hummingbird Dynamic Sculpture - WIP
« Reply #39 on: December 10, 2017, 06:49:28 PM »
More parts as a result of the past two days in the shop.


Online b.lindsey

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Re: Colibri Hummingbird Dynamic Sculpture - WIP
« Reply #40 on: December 10, 2017, 06:57:20 PM »
All the parts are looking great Kirk. Are you getting close to doing any of the sub-assemblies yet?

Bill

Offline crueby

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Re: Colibri Hummingbird Dynamic Sculpture - WIP
« Reply #41 on: December 10, 2017, 07:19:39 PM »
Looking fantastic! It would make a great puzzle - hand someone the box of parts and see how long it takes to figure out what/how to build it!

 :popcorn:

Offline kvom

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Re: Colibri Hummingbird Dynamic Sculpture - WIP
« Reply #42 on: December 10, 2017, 07:55:10 PM »
All the parts are looking great Kirk. Are you getting close to doing any of the sub-assemblies yet?

Bill

Many of the sub-assemblies involve gluing or otherwise hard to undo assembly.  My plan is to dry fit everything first.  to re-check vertical alignment.  There are 15 different spacers, mostly round disks with center holes needed for this purpose.  I will turn these from either aluminum or brass as I go.  I have stock being shipped that will be used for the 4 main "frames" and the long tail cam follower.  Once the frames can be put together I'll have a basis for attaching the sub-assemblies.

I'm still debating on what to use for the larger center gear.  Brass in that size is too expensive.  I may end up with Lexan or similar.

In the mean time I still have some smaller parts to machine out of the aluminum sheet I already have, not to mention more acrylic parts.