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Firefly build-along

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Firefly build-along

Postby Feral Donkey » Tue Sep 25, 2007 6:37 pm

Ok. I'm copying this over from the old board so bear with me for a bit. We'll start off with a few cad file pics to tell the whole story. This build-along will show the making of the center red riser body, not the limb pockets.
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Re: Firefly build-along

Postby Feral Donkey » Tue Sep 25, 2007 6:41 pm

Let's start off today's lesson with one word; CONSISTANCY. When doing multiples of anything you always do everything with consistancy. I take a lot of time and care in the prepping of the blocks.

I square them up and make them as close to each other in size and as straight as I can. That way I can set a stop, put the part in the vice, and perform an operation on each part with minimal checking of the ordinate(X,Y,Z zero). I know that when I put that part in the vice, slide it against the stop, close the vice, and give it a little love tap on the paralells with a dead-blow hammer, that it is in the same spot within probably .001" as the last part was. Since the parts are all squared to the same size, I can flip the part over, and perform operations on the other side and everything lines up perfectly. This saves tons of time and money. Well, far more perfectly than a bow needs to be. So by doing this I have some milling and drilling operations done on 3 sides of our blocks. All the fixtureing holes, stabilizer hole, plunger holes, dampener holes, and AMO sight holes are in place on all 11 riser blocks now.
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Now, when I square up the blocks I leave stock on all sides usually adding up to a really round number. I make compensations for this when I touch off my tools. I also use the center of the block as my X/Y zero. That's how Mold Makers do stuff. That way the error acumulates from the inside out and minimizes the mis-match of cutting operations from different sides as well as minimizing mis-match of mating parts. This really isn't necessary because we're not trying to make a mold with a contoured parting line shut off air-tight, we're just making a friggin bow. Please pardon me being anal and obsessive/compulsive. Z zero is the top surface below the stock left so I make adjustments in my tool length offsets to compensate for the stock.

Ok. With me so far? Here's some pictures.

This is one of me pretending the riser is finished but it's not. It's a big, square block with holes. Notice the dampener hole, sight holes, and plunger holes.
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This is what I was talking about with setting a stop. That strap clamp has been modified by me to have a nice, clean, square, radiused corner. I bump the machined end of the riser blank up agaist that with each one of these set-ups that I use a vice with.
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And this is that set-up in action. I had to be fast with taking the picture so I didn't get sprayed with coolant. The coolant nozzles are pointed at different heights because the drills and cutters I used with that program are all different lengths.
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Re: Firefly build-along

Postby Feral Donkey » Tue Sep 25, 2007 6:44 pm

Anyway, you see all the tapped holes and the 2 outside untapped holes in the back side of the riser blanks? The tapped inside holes are both for the Stab hole but also for fixturing. Those holes will all be machined away with future operations. I sneak them in places like right over the shelf or in where the limb pockets will be. The outside holes are reamed .251". The fixture shown assembled with the part has 1/4" dowel pins press fit on locations coresponding with the .251" holes on the part. The tapped holes on the part have coresponding clearance holes, countersunk for socket-head-cap-screws from below. So basicly all of those blanks will pop on to that fixture, back side down, and be screwed in with a repeatability error of .0005"/side. Now I take the assembly shown and put it in a nesting fixture where the back-to-belly profile will be cut out with a long inserted cutter with a step-down of about .065-.070"/pass, leaving .005/side on the part to be finished with a long fluted 3/4" solid carbide end mill just like we finish the pocket walls on a mold. No less that .005/tooth and about 1/3 the speed of what the book says. Nice lead-in/lead-out moves and the part comes out straight, uniform thickness, and smooth as glass with only one deflection pass. That won't be done for a few days because I have to do some of my day-job stuff in that machine. Anyway, I colored in with the Sharpie what's going to be left when I do that operation.
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Remember not to do that type of milling with the gold coated end mills. Those are great for certain things but for real precision machining they suck. You want a sharp cutting edge, sharp enough to cut god. That titanium nitride is nice and slipery but it's also thick and rounds off the cutting edges of the cutter. What this does is slightly rub and smear the surface of the metal, pushing heat and stress into the part, but also making more deflection than you want. They hold up a long time but I don't like them for that reason. The purple coatings are better because they're more of a stain in the surface of the cutting tool and not a chrome-like coating like titanium nitride. For making thousands of mounting brackets for the air-ride system for Peterbuilt trucks, that coating on cutters is great but for making a size come home the way you want, it sucks the big one.

Remember when doing a deflection pass when side milling, to either pick the cutter up or drop it in the neighborhood of .03 to take out lines left by imperfections in the flutes of the cutter. Hell, we'll do pockets in 4140 steel 5" deep to a uniform width that you can check by sweeping with guage blocks from top to bottom. And it'll be centered in the mold base and from one half to the other to within a half a thou. I mean, that's the stuff I do for a living all day. That's the easy stuff. You should see what I get paid for. With that little machine you see in the photos, if I warm the machine up to a point where it's stable, checking different points on the machine with an electric thermometer, then get the room temperture to to be stable, I have made electrodes on that machine where I have held .0002" for size and location. And that machine is a cheap, bottom of the barrel, disposable machine. It's a beer-can with servo motors and a tool changer. I told my boss if he goes out of business I'm taking that machine with me. :P
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Re: Firefly build-along

Postby Feral Donkey » Tue Sep 25, 2007 6:49 pm

Ok next phase. One thing that makers of machine tools do is make the clamp slots straight with the travel of the X axis and always a nominal or constant size. With Bridgeports it's 5/8". With the Fadal, it's some other obscure #. As a matter of fact, the fadal does not take regular T nuts like every other machine known to man. The T nuts have to be cut narower at the top to fit in the slots. Anyway, As you see below, I have some precision ground hardened steel blocks inserted in the slot clamp slot. This acts as a fence. The strap clamp bolted to the left side of the table acts as our stop.
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Now I take the assembly of the part and fixture that you saw earlier, make sure it's oriented properly, and put it in the machine against the hardened steel block and slide it to the stop. This located it in X and Y axis.
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Then I put the clamps together and make sure there's a shim of either a small piece of brass or paper between the fixture and the clamp to knock down on torquing of the part when I reef on it with a wrench. With one hand I put pressure on the part towards the stops and the other hand is tightening the clamps hand tight. Then the 2 in the middle are tightened snug with a wrench before letting go of the part. Then I tighten all 6 clamps like one would the head on an engine. The tools then get touched off on a probe block so the machine knows the Z offset of every tool. I didn't take a picture of that. but here's the fixture clamped down.
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Now to do some rippin' like we mean it. What I'm doing in this picture is profile cutting the part with an inserted milling cutter. Each pass it takes, it drops another .070". It's programmed for 3500 rpm at 40 inches/minute. It was singing a little bit so I turned the rpm down to 95% and the feed rate up to 120% and it quieted right down and cut nicely. This operation leaves .005/side of stock on the work piece which gets removed with a long carbide endmill I talked about earlier.
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And here it is after the finishing operation.
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Re: Firefly build-along

Postby Feral Donkey » Tue Sep 25, 2007 6:52 pm

Then I loosten the clamps and slide out the workpiece/fixture assy, clean the table, reload a new part on the fixture and do it all over again.

Here I miked 2 oposite corners of the part for size. One was down by the fixture and the other end up at the top of the part.
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Re: Firefly build-along

Postby Feral Donkey » Tue Sep 25, 2007 6:57 pm

We had an idea today that's nothing short of pure cheese-eating genius!!! Well, it was Chad's idea. Chad is my coworker who's working off a new Firefly by helping me. He was also Contestent #1 in the Black Sheep stress test.

Anyway, you know how we're making both left and right handed risers? Well, that means I have to make both left and right hand fixtures. I was thinking I could make them ambadexterous but I can't because my fixturing/dampener holes are not evenly spaced from the center of the part. so that idea got knixed and I was looking at doing 4 different fixtures. Then Chad walks over to the pile of parts and lays the lefty over the top of a righty and the holes line up perfectly. The only differenece is the sight window goes left on one and right on the other.

So fixture #1, which will have the RH part laying on it's side with the sight window down. This fixture, with the adaptor plate will then be Fixture #2 for the LH risers. Then Fixture #1 for the LH risers in turn will double as fixture #2 for the RH risers. All we need to do is make a block that is twice the distance from the inside of the sight window to the outside of the grip, 1.125", and punch a clearance hole for a 3/8 inch bolt with a slip fit for a 5/8" tube dowel on each end of the hole about 3/8-1/2" deep.

So now I'll be able to do 4 set-ups with 2 fixtures and one adaptor plate!!! YAY!!! Jump for friggin joy!!! I can even have both fixtures loaded in the machine at the same time and perform program #1 on one part in fixture #1 and then program #2 on the other side of a different part in fixture #2 that had been previously in fixture #1.

Can you smell it? You know what that smells like?

Ok. What I said earlier, here are the pictures to go with the words. I'm pooped and a lot of this is self explanatory. I have to go back and do the rest in the morning after the broad head shoot at the club.

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Re: Firefly build-along

Postby Feral Donkey » Tue Sep 25, 2007 7:04 pm

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I got over to my friend's house last night and we sat out on his patio drinking beer while I sat there finish assembling the Firefly. I got 3 beers in me and I passed out. His wife woke me up at like 3:00am and told me to go crash in the guest bedroom.

First impressions are: It's the Black Sheep's angry little brother. It's a little more of a wild pony than the Black Sheep. I posted more on the main page.

Here's some more pics. The first one is of after I got all the operations done exept for the milling and drilling of the limb pad ends.
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And here is a few pics of my fixture for holding the work piece at 18 degrees. I can change it over for 5 degrees for Ernie's stuff too. It's nothing fancy, it's just a large precision ground angle plate with a steel bar and a stop bolted to it. I hold the parts to it with cant-twist clamps.
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And that, ladies and gentlemen, is how you build the Firefly. :D
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Re: Firefly build-along

Postby Fiddleback » Thu Sep 27, 2007 2:48 pm

Yes yes. How do you BUY the firefly?
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Re: Firefly build-along

Postby Feral Donkey » Thu Sep 27, 2007 6:51 pm

Well, you don't quite yet. There's a few things I want to try and test before taking orders.
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Re: Firefly build-along

Postby Cutty » Wed Oct 03, 2007 12:15 pm

Again, awesome thread, Aaron. Kudos to you for letting everyone in on the process. I see mine in the middle in that one pic...it's the one all the rest are scared of :evil:
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