Thread Tools
Nov 29, 2020, 01:01 AM
AvB
AvB
Wind, hill, ... I'm keen ...
AvB's Avatar
Thread OP
Hey guys, it’s taken a long time, but we’re making progress on Synergy Mk II. It’s happened in fits and starts over the last couple of years, with. Geoff did a heap of computer crunching on developing new improved foils, but things stalled for a long time as lots of family and works stuff got in the way of Synergy stuff for our CAD gurus Will and Geoff. Earlier this year Will finalized the drawings enough to start on some moulds using a borrowed 3D printer. Then Alex and I begged Geoff to have a look at a few minor details and once he got stuck in, he went for it like a dog with a bone and a couple of weeks ago he emailed me the final Rhino mould drawings.

So as you can see it’s likely that we’ll hopefully see slightly different versions … a Syn2AU, and a Syn2UK in the air in the next year!

I haven’t cut any model aircraft moulds for maybe 2 years now. Haven't been building and have hardly flown at all either. Dirt bikes have been the hobby but I'm backing off that to a degree now. Most of my CNC efforts (which can be very intermittent) have been making signs or machining motorbike things, or other things that are mostly fairly simple 2.5D. So I’m a bit scared about trying to get my head working on 3D stuff again, and worried how much I’ll forget … and whether it will all end in tears. It’s sort of harder too than when I did the last Synergy moulds, because I now use a different CAM program, and also different CNC controller software. So there’s more potential for getting a bit confused.

Anyway, I procrastinated as long as my conscience allowed, and got started preparing for cutting the first moulds today. Naturally I went for the horizontal stab moulds as they’re the smallest and least complicated part!

First thing is to work out the material size. So I opened up the drawing in Rhino and worked out the size of each mould half, plus what we need to allow for hold-down screws around the edge. I worked out the minimum workpiece size if the halves were side by side, and also if they were end-to-end. Then I had to un-bury the stack of heavy Laminex Freestyle that we moved up to our new place a year ago. It’s been stacked really straight-edge flat, and fortunately the stuff is incredibly UV resistant. The Freestyle is hard to get and expensive, and I go to a lot of effort to minimize wastage. I decided to bond a couple of long narrow bits together, in order to save the larger slabs for bigger moulds to come. This sounds rough, but actually works well for vertical joins and the worst outcome is we may see one very fine line across the parts, if anything. I set up a very flat bed, sanded the edges of the Freestyle pieces flat and flush, applied plenty of medium CA (which has been in my fridge for at least 4 yrs, but from the way it burnt my nostrils I’d say it’s working) then pressed and clamped it. I like to leave it a good day before screwing it down to the bed.

Next I got onto Rhino and set the mould halves out to match the workpiece. Then started making toolpaths … first, just facing the whole piece down with a flat end 8mm 2-flute carbide endmill. Then roughing into the wing shape cavity. That’s as far as I’ve got so far.

They say the hardest part of a job is starting, so I’ve done well.
Sign up now
to remove ads between posts
Nov 29, 2020, 03:15 AM
Everything’s A Compromise
Larrikin's Avatar
Quote:
Originally Posted by AvB
They say the hardest part of a job is starting, so I’ve done well.
Yes Andrew .... yes, you have!

Nov 29, 2020, 04:12 AM
Registered User
Well done Andrew, I guess it depends on, if you are a complete newby or know what you are doing. You have done it before so you know what you will face the next years... And the good thing about it is also you actually don't know all the things that will go wrong... I wish you a good way and a nice flying plane in the end. And even though it is a hard way, but in not too many hobbies you can create such nice real things that you can see feel in flight and touch than in designing a DS plane.
Go for it Bjoern
Nov 29, 2020, 03:37 PM
Registered User
sll914's Avatar
Good to see you back on it Andrew! Do you find CA works better than lam resin for joining the pieces?
Last edited by sll914; Nov 30, 2020 at 06:00 PM.
Nov 29, 2020, 03:48 PM
Remember... Fly for fun!
ALEX HEWSON's Avatar
The material is an acrylic resin base, which is why cyanoacrylate (CA) works great as its the same family. We haven't tried acrylic resin itself, but am sure that would work just as well, if not better assuming the surfaces are prepped satisfactory
Nov 29, 2020, 08:49 PM
AvB
AvB
Wind, hill, ... I'm keen ...
AvB's Avatar
Thread OP
Actually the 30mm Freestyle is polyester based - it's a bit unusual in that regard. I think it's just a cheaper quality product compared to the Corian type acrylic based products. But the CA does seem to bond the Freestyle really well.

Geoff and I did put a lot of leg work into sourcing some acrylic glues, but the stuff was pretty expensive and I can't remember why exactly but we tried it and gave up. You can also get litle tubes of colour matched joint glues that are suitable for butt joining kitchen bench sections, which are also really expensive and you need a special applicator gun.

Our main goal at the time was to be able to flat laminate big pieces of 12mm Corian-type stuff. We decided that cheap CA was as good as anything. But it hasn't been terribly successful as it seems impossible to avoid bubbles or voids here and there and the shallow wing surface cuts through the join often got wafer-thin blistering popping out over the join line area, after a while (like my current Scratcho wing mould).
Nov 30, 2020, 05:45 AM
Registered User
Geoff_S's Avatar
The acrylic glue we tracked down was a very thin solvent type glue (IPS Weld-On #4). Despite being advertised as specifically designed for acrylic, it seemed to have almost no effect on the Freestyle. Perhaps it has too much solid filler to dissolve sufficiently?

edit: just read AvB's comment that Freestyle is polyester. That probably explains it
Dec 01, 2020, 02:54 AM
AvB
AvB
Wind, hill, ... I'm keen ...
AvB's Avatar
Thread OP
I got stuck into it today. I get really sh#t scared when I get back into tricky CNC stuff after not doing it for a long time - worrying about forgetting some basic thing or making a stupid stuffup. I have to force myself to just keep going and know that when the first one’s done, it will all seem a lot more do-able!

The blocks are solidly bonded as one, and I screwed it down to the bench, countersinking the screws deeply. The first cut was just to face the whole workpiece down by 0.75mm to give a flat smooth and level surface, using an 8mm flat endmill. Cutting a stab mould is simple compared to wings, since the stab’s datum line is on one plane so the faced off surface can remain as the Z zero and the finished surface for the flanges.

Then a simple roughing path with the same cutter to take most of the material out of the wing cavity area. I always think contoured roughing cuts make the most beautiful CNC patterns!

I use the noisy big vacuum for the above cuts which remove a lot of material. But then I do the finishing cuts with no vacuum as there’s so little waste material.

I put quite a bit of work into tinkering with options for the curved wing surface toolpaths. When you do the main finish cut, you want smoothness and accuracy so I set a fine 0.35mm stepover with the 4mm endmill. That means there are thousands of parallel cuts, so I play with the options to avoid having extra “moves” at each end of each pass. We use a “fake leading edge lip” that sticks out and above the LE, to make the cutter move about 1mm up above the flange before doing its side move. Also, you want to get a super accurate shape in the LE area, so in addition to the main cut I create extra cut sections at the tips, in which the parallel passes are more square-on to the tip angle - to avoid having the cutter contour across the LE area and leave terracing lines. By having the cutter run up and down the LE with a fine stepover you get a really smooth sharp accurate LE shape. Takes a bit of fiddling but it’s worth it.

Finally I got the finishing cuts running, but it was frustrating. This new UCCNC controller software I’ve switched to a couple of years ago is good in some ways, but it has this stupid behaviour of travelling too slowly in arc moves. So it would run slowly over the front part of the wing path then fast out towards the TE. It wastes so much time. After the first half had been finished I stopped it and created a test section to “air cut” and I mucked around changing tolerances and settings both in the CAM program and in UCCNC. Absolutely nothing made any difference (I stopwatch timed 10 paths and it took 33 seconds every time). If you do the maths that’s about 2 hours to cut these two small shapes out!

So I gave up and let it run the second cut. BUT … DRAMA! Almost at the final tip, with only a few minutes to go, the machine stopped moving. Just sat in the same spot spinning, with the servos off. I got it moving again (jogging) but every time it went to move side to side (in the X axis) there was a clunking noise and the servos shut off. Hmmm. The lead screw wouldn’t turn freely. I pulled the cover off the drive belt area and there were bits of broken belt everywhere. So we’re now stalled till I can get a new belt. It’s an automotive timing belt … “Megadyne T10.400”.
It's a pain that the cutter stopped on the finish surface - it left a small circular mark - just what you don't want.
Dec 01, 2020, 05:56 PM
AvB
AvB
Wind, hill, ... I'm keen ...
AvB's Avatar
Thread OP
This shows how far it got yesterday before the breakdown.

I'm pretty impressed with how good the little wing bolt bumps look, just after this parallel cutting. They'll be finished much smoother with a fine 1mm cutter doing concentric steps around them later.

I'm onto ordering the belts. I decided I should replace all 3 of the drive belts at this stage.
Dec 02, 2020, 12:45 AM
Everything’s A Compromise
Larrikin's Avatar
Quote:
Originally Posted by AvB
I got stuck into it today. I get really sh#t scared when I get back into tricky CNC stuff after not doing it for a long time - .
There's not a lot of difference between fear and excitement. Try telling yourself that you're EXCITED to be working on the CNC!
Quote:
Originally Posted by AvB
I'm pretty impressed with how good the little wing bolt bumps look, just after this parallel cutting. They'll be finished much smoother with a fine 1mm cutter doing concentric steps around them later.
Very swish indeed ... and probably more accurate than what I did with the Rubicon.
Quote:
Originally Posted by AvB
I'm onto ordering the belts. I decided I should replace all 3 of the drive belts at this stage.
Sage wisdom born of experience
Dec 02, 2020, 03:28 AM
Registered User
Geoff_S's Avatar
Can you just re-cut the entire mould surface ~0.5mm lower to remove the defect?
Dec 02, 2020, 06:51 AM
AvB
AvB
Wind, hill, ... I'm keen ...
AvB's Avatar
Thread OP
Yes, definitely could Geoff. Although with this slow UCCNC cutting I'd kinda hate to have to do it (about another 3 hours running time). I'll see how it looks when I've done my best job of finishing it. Perhaps a 4mm circular spot on the paint on top of the Synergy Stab can be a unique identifier of its DNA. And makes a good story.
Dec 02, 2020, 01:35 PM
the occasional flyer
rothlisburger's Avatar
^^^Yes..
Dec 04, 2020, 11:23 PM
Score board:Rocks-2,Carbon-0
Thurssday1's Avatar
Keep up the good work Andrew, looking good.
Dec 06, 2020, 07:59 AM
608 km/h!
josh18's Avatar
Good to hear its coming along guys!


Quick Reply
Message:

Thread Tools