CriCri MC-15 in NZ

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proppastie

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matched hole assembly
that is when you drill the holes in two separate parts and assemble them using the "matched holes"......rather than say clamping the parts together and "drilling at assembly"......to match hole assemble you need very accurate position of the holes so you would need a high end (expensive) CNC machine......drilling at assembly assures the holes line up and can be done by hand layout (pencil and ruler) and simple drilling equipment (hand drill or drill press). Often the top part is pre drilled and the bottom part is drilled at assembly.
 

BJC

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John Thorp developed the “matched hole tooling” method for his T-18.

Excessively brief description: when rivet holes are drilled, an extra strip of metal is simultaneously drilled, then used as a template to transfer the hole positions to mating metal. No CNC involved. Anyone contemplating scratch building a sheetmetal airplane should get a copy of Thorp’s description and study it.


BJC
 

Mayank

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Actually i am planning to make parts using a cnc.can all the parts be made without using a CNC?if it can be made without a CNC,can you please tell the tools needed for making the parts?
 

proppastie

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can you please tell the tools needed for making the parts
that is an open ended question...."you can never have enough tools" as they say.... the minimum would be an accurate scale (ruler), Combination set for layout of angles , hand drill, RH LH Straight Cut tin snips. hack saw. Most people would want more than that. Next It would be nice to have a drill press, and table saw with a carbide blade for cutting thicker aluminum and a steel blade or abrasive cutoff blade for steel. Belt sander would be useful to round the edges.....CNC router for skin and holes on the top skin. (not accurate enough for matched hole for the bottom skins in my opinion, but more expensive ones could be accurate enough. )
 

Mayank

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that is an open ended question...."you can never have enough tools" as they say.... the minimum would be an accurate scale (ruler), Combination set for layout of angles , hand drill, RH LH Straight Cut tin snips. hack saw. Most people would want more than that. Next It would be nice to have a drill press, and table saw with a carbide blade for cutting thicker aluminum and a steel blade or abrasive cutoff blade for steel. Belt sander would be useful to round the edges.....CNC router for skin and holes on the top skin. (not accurate enough for matched hole for the bottom skins in my opinion, but more expensive ones could be accurate enough. )
Will the stm1325 CNC work out for this purpose?
 

TFF

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A CNC makes repeatability easy. Help prevents carpal tunnel. You can make it with a hacksaw, a hammer, and some files.

Hopefully the weather has cooled off down there and madrocket can start wowing us again.
 

1Bad88

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Hopefully you can slow the spindle down enough to get workable feeds and speeds. I had difficulty getting a Komo to spin slow enough for cutting aluminum. Onsrud does make single fluted bits for cutting aluminum iirc.
 

Jay Kempf

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Single O flute bits work really well. Smaller is better if you have high speed spindle. I cut aluminum at 20,000 RPM normally. I was surprised how hard I could push a coated single flute bit dry with just a lot of compressed air to cool and remove chips. My machine is 48" x 48" but you can reposition a sheet and do it in halves if you are clever. So far I haven't seen much difference between expensive and cheap bits. If you screw up you can break or weld both. If you run them conservatively they last a long time.
 

Fiberglassworker

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Some Commercial kit builders are now using large format CNC Multi head Routers, with different sized cutters and added drill motors, to put all of the required holes in all of the kit part sheet metal components , so that the builder only has to make sure the holes are deburred then Cleco the parts together and start riveting. No jigs and perfect fit.
 

proppastie

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Some Commercial kit builders are now using large format CNC Multi head Routers,
Those are high end and very expensive........I am most familiar with Amada turret punch press
 

MadRocketScientist

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First up. Last week I cut some more flanges for the exhaust pipes on the CNC. I cut the outlines 1mm deep and will cut them to final size once they are welded onto the exhaust tubes. I leave the flanges wider to allow some metal as a heatsink when welding to keep the shape, otherwise the narrow flange tends to melt into a blobby mess.
DSC00390 (Medium).JPG
I was considering making the final exhausts in stainless steel or maybe even aluminium, although both metals fatigue, but for now I am going to make the exhausts in mild steel and see if I get around to changing over once it is flying. I have ordered some more 32mm exhaust bends to make another couple of Y pipes. Hopefully I do a better job of welding the next ones.

Today I finished another little job that was thought through some time ago. These are more of a test fit as they only fit the propellers for use on the test stand, but the idea seems to work pretty well.

Yesterday evening I started out making up some CAD (cardboard assisted design) patterns around the propeller blade roots.
DSC00403 (Medium).JPG
I took these home and made a 3D model of the spinner flange shape needed to clear the prop blades and when I came to the shed today I cut these handed mdf patterns on the CNC.
DSC00401 (Medium).JPG
Which I subsequently stuck onto the spinner with double sided tape. I made a small mistake somewhere with the size of the mdf pattern and I had to lift it up a mm or so from the bottom edge of the spinner for the right clearance. Not sure where I went wrong on that one but no real consequences in the end.
DSC00405 (Medium).JPG
After marking the inside edge of the pattern and allowing around 3mm for the flange I removed the pattern from the spinner.
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And then cut the opening out with a drill and tin snips.
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I stuck the mdf pattern back onto the outside of the spinner and carefully hammered to flange into place. I had to use a combination of panel beating hammers and some round solid steel bars of varying sizes to get all the corners formed.
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Then I removed the pattern and carefully filed to flange to an even depth all around and a taper at the lower edges.
DSC00415 (Medium).JPGDSC00417 (Medium).JPG
Fits the propeller pretty well with a small clearance but not touching.
DSC00419 (Medium).JPG
I have hit the picture limit for this post so onto the next one!
 

MadRocketScientist

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And finally a spinner, prop and backing plate.
DSC00422 (Medium).JPG
And the other one on the engine on the test stand.
DSC00395 (Medium).JPGDSC00398 (Medium).JPG
I am still working out the screw pattern for holding the spinner in place. If I use 6 screws the prop will be able to be indexed around on the hub but if I use 8 screws then the propeller orientation is fixed once the screw locations are drilled. The plans do show 8 screws so I am leaning towards that if possible.
 
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