Author Topic: Going over to the dark (CNC) side!  (Read 5251 times)

Offline kvom

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Re: Going over to the dark (CNC) side!
« Reply #90 on: April 14, 2019, 12:32:06 PM »
The bi-directional feed rate is good, but for aluminum I use only climb.  That allows air blast to clear any chips and prevent welding during the non cutting move.

Offline Jasonb

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Re: Going over to the dark (CNC) side!
« Reply #91 on: April 16, 2019, 07:13:32 PM »
To finish the sandwich construction of the engine base some form of filling was needed and as I have quite a few off cuts of Corian I decided to use that rather than metal.

The sequence was much the same as the top and bottom plates but I tried out peck drilling for the 3mm holes as they were quite a bit deeper than before, I could have gone faster with the retract speed and not lifted so far out of the work, drill was running at 5000rpm.

I used a chip breaker feed for the larger holes, you can't see it that well on the video but can hear when the drill pauses the feed which if I was drilling steel or Ali would shorten the swarf, dropped down to 1000rpm on the 6mm and 7.8mm holes.

Finally machining the contour where you can see the tool ramp down and then start cutting in 2mm deep passes before it starts to get lost in the swarf which is when I stopped filiming and got the vacuum running. The 3-flute Carbide cutter romped through this at 5000rpm and 350mm/min feed.



I did not use any tabs this time as the material was thicker than needed, bottom milled off afterwards.



Quite pleased with the cut edge, no sign of cutter marks when held upto the light, this was a full depth finishing pass



I used a 50mm face cutter to thin the work down to 10mm moving the clamps to complete the ends, only downside to working with Corian is the mess.





I'll bond it all together with JB Weld but that won't be until the bearing supports have been fabricated and silver soldered to the top plate but could not resist a quick trial assembly.






Offline Admiral_dk

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Re: Going over to the dark (CNC) side!
« Reply #92 on: April 16, 2019, 09:46:33 PM »
Nice progress so far and I like the combination of the different materials  :ThumbsUp:

Offline Jasonb

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Re: Going over to the dark (CNC) side!
« Reply #93 on: April 18, 2019, 06:49:00 PM »
A post on another thread brought up the subject of the "Star Wheel" used on the Alyn Foundry "Sphinx" engine which is an alternative to timing gears and operated the exhaust valve on alternate strokes. A casting is supplied but I happened to mention that  it would be something worth trying to cut on the CNC. Well that was all it took to get me trying it out.

Video firstly shows the adaptive clearing, I speeded things up 20% after filming so that was a 6mm Carbide 3-flute cutter at 3600rpm, 150mm/min, full 8mm height cut with a conservative 0.25mm DOC. I went with Andrews suggestion of cutting both ways which reduced the time quite a bit. It was cutting very nicely and I did not bother with brushing on anymore suds which only seemed to make the swarf stick to the work.

There is then a clip of a 4mm dia cutter clearing further into the internal corners which went well but during the final contouring cuts it went pop which almost made me go poop. It was a cheapie and at a cut height of 2D I was probably asking for trouble. I had drawn in a corner radius of 2.1mm but that probably should have been more.

Video ends having reverted back to the 6mm cutter for the final contour cuts which I slowed down so that it would not chatter in the corners.


This pic shows the star wheel after the first clearance cuts, you can see the faceting of the curves.
 

 
This is after all the milling where the curves flow better. Interesting to see the three height bands left by the tool, although it has not done much they show the wear from the 2.5mm plate, the 1/4" flat bar and the best finish at the top which can be seen better in the video is unused edge.
 

 
All that remained was to file out the internal corners, casting shown alongside. Just need to put it away somewhere safe and resist all temptation to do more on this engine for a while.
 


Simulation of the cutting


Online Johnmcc69

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Re: Going over to the dark (CNC) side!
« Reply #94 on: April 18, 2019, 07:03:03 PM »
 :ThumbsUp:
 Pretty cool stuff Jason! Modeling the parts, creating the program, & watching it work, is pretty exciting.

  :popcorn:

 John

Offline kvom

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Re: Going over to the dark (CNC) side!
« Reply #95 on: April 18, 2019, 10:07:17 PM »
That is the type of part I prefer to make from stock vs. the casting as well.

Thoughts:  The big nut on top meant that your tool stick out was higher than it needed to be.  Generally you want the collet to be clamped as close to the flutes as possible and the profile cut to be as high on the flutes as possible.  4mm mill got deflected too much.

According to G-wizard, if the stickout were 12mm, a DOC of .25mm would allow a feedrate of 800mm/min in 6061 for a MRR of 1.68 cc/min.  But a DOC of 40% of tool diameter (2.4mm) with a feed of 213 mm/min has a MRR of 10.25.

Offline Jasonb

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Re: Going over to the dark (CNC) side!
« Reply #96 on: April 21, 2019, 05:26:56 PM »
Just a small item today in the form of an elliptical gland flange, used an aluminium specific cutter as they also work well in other non ferrous metals and a split point Dormer stub drill for the 2mm holes.



I cut another star wheel but took the different route of drilling 2mm holes at the root of all the internal corners which made filing to final shape a lot easier than leaving the 2mm radius from the 4mm cutter.