Discussion in 'Workshop Tips and Secrets / Tools' started by Mac790, Aug 18, 2009.

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1. Sep 23, 2010

### JerryFlyGuy

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Auto, ok so.. I'm going to do what I said I don't normally do. Rather than figure out the surface area on a 360 and how many molds it would take to build, I figured I'd try making a number that works for per sqr ft. So after some figuring and messing around w/ multipliers etc.. I think [and this is only a rule of thumb mind you] for basic machining you'd be looking at $125/ft^2 for molds that are fairly flat and ~25-30ft^2 or larger, smaller than that it could be more or less just depending on the shape. That is if you have all the CAD work done, and I've simply got to throw it in the CAM and then assemble a mold body to machine into. To have a very accurate rule of thumb price would require a 'volume' multiplier to the costing formula but that would just start to get too complex. There would also need to be setup charges based on how many molds [or setups] would be needed etc.. But to keep it simple you could count on that 125 number as a ballpark WAG and then get a more accurate quote once the molds are designed. Re: some of the other questions. When I machine a mold I try and put every single detail I can into it, such that there is no additional work to completing them. I want all the joggles in the molds, any maint. ports/holes w/ screw locating dimples, part locating grooves etc.. Everything that makes a composite part more 'model airplane' like the better. If you can put a complete plane together and never have to use a tape measure [the holy grail] then it just makes it faster to build. If you can make it w/out a tape measuer and all the parts only fit one way [no left/right issues] then even the most 'un-mechanical' should be able to build it! Of course that would be a tall order to do, but you get the picture. Once a person has the CAD model of the body/surface, your only half done! Putting all those other details into the mold takes alot of time and planning. I've heard it several times where people tell me, oh don't worry about that we'll handle that later. Later comes and I'm chatting to them about it or some other job and they will mention their regret in not putting ALL the details into the mold in the first place. Anyway, I'd better get to work.. JFG 2. Sep 23, 2010 ### Mac790 ### Mac790 #### Well-Known Member Joined: Jun 22, 2008 Messages: 1,529 Likes Received: 19 Location: Poznan, Poland Thanks Jerry one more time for your response, I have account at cnczone already, just in case if I'll have more question, I'll find you here or there btw. Please post some info when you finish your 2-axis head, we would really like to see it. Seb 3. Sep 24, 2010 ### dirk_D ### dirk_D #### Well-Known Member Joined: Sep 23, 2010 Messages: 93 Likes Received: 1 Location: Victoria, Australia. I have had ideas of dynabolting the gantry rails directly to the floor of the shed and using chain pinned at every 5th link as a rack, it would take up a car space but would reduce build cost by using the concrete floor as the structure. (I have even had dreams of building a brick shed as a frame!) When the plane is finished, strip the electronics, grind back the dynabolts and hope the landlord does not notice 4. Sep 24, 2010 ### JerryFlyGuy ### JerryFlyGuy #### Well-Known Member Joined: Sep 7, 2005 Messages: 67 Likes Received: 6 Location: Canada Trouble w/ bolting things down to the floor is that the floor rarely stays flat.. I would think an independant frame would be more 'repeatable' accuracy wise vs bolting to a floor or pad. JFG 5. Sep 24, 2010 ### Rienk ### Rienk #### Well-Known Member Joined: Oct 11, 2008 Messages: 1,364 Likes Received: 190 Location: Santa Maria, CA (SMX) Why half? Or maybe more importantly, which half? 6. Sep 24, 2010 ### Rienk ### Rienk #### Well-Known Member Joined: Oct 11, 2008 Messages: 1,364 Likes Received: 190 Location: Santa Maria, CA (SMX) I sure wish you were closer to me. I have about 20 tons of gantry equipment, much already stress relieved... a whole bunch of 2" and 3" screws, ways, etc, plus a bunch of servos, controllers, etc. I bought out a CNC building shop - mostly for their tools - but also hoping to build these giant mills. I would love to work out a deal with someone to build them for me, and as payment, keep one for themselves. If you're interested, let me know. Unfortunately, a lot of the supplies are rusted/ruined, but I think there is enough there to make it worthwhile. I'll try to get pictures of the stuff to send you, if you want. 7. Sep 24, 2010 ### autoreply ### autoreply #### Moderator Joined: Jul 8, 2009 Messages: 10,732 Likes Received: 2,542 Location: Rotterdam, Netherlands That's highly appreciated. CNC seems to be the stuff where "If you have to ask, you can't afford" seems the common attitude. Ok, so a ballpark of 30-40K US$ for a small 2-seat aircraft. I find that surprisingly high. No offense, but I just don't fully understand why the cost is so high, though other quotes are similar (20K Euro for a similar-sized shiphull for example).
I had a look on several CNC-fora and typical building cost for a usable router (8X4X2') is 10-15K US$. I also spoke to 2 guys (another useful ballpark), doing CNC professionally. Typical hourly cost was around 100-150 US$/hr. I guess, to machine those molds doesn't take 300 hrs of machining time (8 weeks)?
So I'm wondering where those costs are? Is the initial mold building that much work (for me it's just foam blocks)? Or is it the CAM-specific programming that takes so much time by a machinist?
Would construction of a plug be considerably cheaper? (no joggles etc, no negatively bended surfaces)

8. Sep 26, 2010

### Rienk

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Everything always takes longer than you think... designing the plug, cutting it in layers or with 5-axis, recutting mistakes, prepping the plugs for molds, surfacing, sanding, polishing, waxing, etc. We easily have 300 hours of machining time into the Solo.
Good luck making it for less :ermm:

9. Sep 26, 2010

### JerryFlyGuy

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Just a quick note, I'll reply more in-depth here tomorrow. [I just got back from a 3 day trip.]

Rienk, where are you located? I'm interested

Auto, simple math for you.. A typical mold needs to be cut twice [minimum]

First pass @ 0.125" to 0.375" step over [depending on setup etc etc] also dependant on machine, cutting speeds are 100-300ipm [inches per minute] so an average of those and we're looking at 37.5"^2/min [the amount of surface area covered in 1 minute of machining] so, a lancair 360 has [rough guess] 600sqr ft of molds [sounds like alot but it's probably not that far off] 600sqr ft = 86400 sqr inches. 86400/37.5=2304 minutes or 38.4 hrs ... just to rough cut..

Second pass is generally 0.005" to 0.020" step over again depending on several things. Finish feed speeds are ~75-150 ipm. So averaging those we're covering ~1.406" ^2 /min.

So 86400"^2 of area / 1.406=61450 minutes or 1024hrs of machine time to finish cut the molds. So w/ your proposed rates of 100-150/hr [we'll guess middle of the road at $125] your looking at [38.4hrs+1024hrs] x$125/hr= $132,800. [and thats not including tooling charges and material!] And you know what, companies DO charge those rates for large machines. I personally know of several shops who charge large dollars for a simple mold, simply because large and accurate machines are few and far between. I'd like to see one of these$10-15k machines! If your interested, I've got some ocean front propert in Az I'm trying to move too , all kidding aside.. I've heard of these cheap machines, I'm not convinced! Know why? I built one and have the reciepts to show that it cost me over \$100K! I design stuff like this for a living [my flying job is part time]. I've been there, done it and have two of the tee-shirts. Also remember, your quoting a 8 x 4 machine, make it 2.5 x as long and 2.5 x as wide and you'll spend 10x as much [check my previous note to this effect]. A 8 x 4 machine, isn't large enough to build the molds or bucks needed for a airplane [well other than a larger model/RC unit].

No offense intended here Auto, I'm just giving you my biased experiance and/or opinion.

Fwiw

JFG

10. Sep 26, 2010

#### Moderator

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Well, as for the price discussion, I asked before to leave the above considerations out (since most homebuilders can do those theirselves and I was interested in the lowest realistic expense for a homebuilder that can do the rest himself)
I don't know what your definition of "offense" or "quick" is, but it obviously is far from mine, I'd qualify your post as very informative, lengthly and extremely helpful
Those numbers and explanations clarify a lot and also give a good answer to my fundamental question (Why is CNC so expensive and can it be done cheaper). Ow, and the name is Jarno, "auto" sounds so... automatic
The Legacy has (link, is wetted surface comparable to mold area?) something like 400 sqft external area, so I guess the 360 is closer to 300 or so. Doesn't matter for your comments (it's still bloody expensive), but it gives me a good idea of actual prices. My smallest design is probably closer to 150-180 sqft
Ok, so the biggest factor is the accuracy of the mold. I see a factor of 4 in the second pass step over.

Bluntly thinking:
(I nicked Mac's excellent picture to clarify myself a bit)

Why not raise that step size much further. If we're cutting a fuselage in the length direction (lower right to higher left) a too large stepsize immediately results in "stairs" in the fuselage sides. If the cutter head moves in the spanwise direction though (lower left to higher right) I guess that even a stepsize of a quarter of an inch wouldn't result in visible "stairs", since the change in width and height are very gradual in the lengthwise direction, of course only, if the cutting tool is sufficiently large. A stepsize of 0.1" would result in almost a tenfold less cost.
Is the above reasoning wrong?

Another question; more to the experienced builders; is there anything against relatively rough molds (stepsize 0.02"-0.05"), cut in the traditional (lengthwise) direction and sanding the steps away?
I think, our (homebuilders) luck is that many people want a 8X4 working area since it's a standard size MDF. Given enough Z-axis, that might make the market for us just big enough.

Last edited: Sep 26, 2010
11. Sep 26, 2010

### Tom Nalevanko

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To confirm the adequacy of the 4 x 8 size, David Algie is doing a very nice job on his plane with it. And it is fairly well documented on his website and Yahoo group. http://www.woodward-aerospace.com/david-algie.html/

I think that the opportunity cost has to be taken into consideration. The notion that this is zero is false and will be realized when you run out of money; LOL. After all, you could work at McDonalds or be a bodyguard for super-models and get paid instead of working on your plane.

Last edited: Sep 26, 2010
12. Sep 27, 2010

### JerryFlyGuy

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Jarno, I you can pretty much take any mold size and it would be nearly a linear comparison in dollars.

The big advantage of cnc is simply that you can't duplicate to the accuracy of a cnc by hand, for the cost of getting it done [or the time]. There would be little point in machining a mold w/ lots of little scallops [due to a larger stepover value] in the surface, just to cut cost. The impact on aerodynamic performance would be huge, if you decided to finish it by hand, you'd kill the accuracy and your time to finish would be large.. hardly worth starting it out as a cnc job in the first place!

The easy [relatively good guess anyway] way to figure out what your step over needs to be [if you have access to a simple 2D cad] is to draw a section view of the tool on the surface of the mold. Now, decide what your max variation [or scallop height] would be [0.01 is easily seen in paint or felt by hand], offset your mold line/surface by this amount. Now take your tool section [say 3/4" diameter] and insert a copy of it beside the first. By moving it back and forth unti you find where to radius of the tool nose cross's itself, on your variation line. Then measure the spacing between the tool centerlines and thats your stepover value. To have a mold that is smooth to the touch and needs little to no hand work afterwards, you have to run the tool path down to a small spacing, there is no other way around it. [Well, either that or use a HUGE tool, but that brings in other limitations]

This means that you end up w/ a very dense tool path w/ a small stepover and it takes a long time to run it. In my situation, I often start a machining job after I get home from work. I let it run all night and this way I can get in an ~15-18hr machining job every night. I've got my shop set up w/ wireless webcams so I can log in from work and look at whats happening. However, to date, I've not used them for this as I'm not yet comfortable leaving it running while I'm that far away. I have left it in the hands of the wife many times while I ran to the shop or store but I'm usually back home w/in 15-20 min and she can hit the Estop if need be [which now that I think about it, has never been required--> the hitting of the Estop I mean].

This means I can run my machine for cheaper than most shops out there as my labor time is less [I'm not baby sitting it all the while it's running]. Not only that but I'm not looking to make a killing doing this work, paying off the machine over it's lifetime, while helping out other homebuilders is really all I'd planned on doing. Well.. and if I can use it for my own projects in the mean time.. thats good too

I've built molds where there was more than one part and it was assembled. It does work, but it's certainly not optimum. It does require some hand work at the end of it all to get things exactly perfect. Typically I'd only recommed making 'bucks' this way and then pulling molds from these to be your working articles.

The size of the machine is totally driven from what you want to do w/ it. I've built 21ft kayak parts on mine, I can machine a 20+ wing spar in 1 pc. I've got an airplane design which will fill the machine [just]. This was really the guiding factor in my building mine as large as I did.

Keep one thing in mind [ I learned this the hard way]. If your building a cnc machine to use to build an airplane, just go build the airplane. You'll end up spending more time and money on the machine, than is really worth it. I've been working on my machine for several years, I've got tons of money invested and no airplane to show for it . If I would have invested my time and money into an airplane instead of the machine, I'd be flying by now!:tired:

Fwiw

JFG

13. Sep 27, 2010

### Tom Nalevanko

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Originally Posted by Tom Nalevanko
Hey, if anyone needs 1/2 of a Lancair 360 fuselage, I have it hanging from the ceiling of my hangar... No kidding. LOL

From Rienk
Why half?
Or maybe more importantly, which half?

I went to the hangar today and it is a right half. When Hi-Tech Composites in Oxnard was sold, I picked up all the Lancair pieces that were going to be scrapped.

The Horizontal and rudder in the picture are for a Stallion.

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14. Oct 24, 2010

### Atomic_Sheep

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I posted this on the CNC Zone forum but I also wanted your guys opinions since I'm more in tune with this forums understandings of accuracy and your awareness of properties of various materials...

I've had a look at a few build threads and I'm really liking what Ernie has accomplished so far with his build...

New 4x8 Steel CNC router build - CNCzone.com-The Largest Machinist Community on the net!

I've got a few questions though...

1.) Just wondering how one might weld the top 4 pieces into the rectangle in such a way that there is no warp? How would you find a surface flat enough for this?

2.) How do you know if the 4 steel tubes that he used are not bent in anyway i.e. they aren't sagging from the get go?

3.) How important would the straightness of the tubes be in terms of being a base for a perfectly flat top? Would you sand it somehow to ensure that they are perfectly flat?

4.) Lastly, how do you ensure that the side rails... if drilled with a basic hand drill, are installed horizontally with the guide rail not having any wavelike motion? Sure there's a lot of bolts holding the side rails but I dunno.

Like overall, it seems like a really cool looking project but I'm just not sure about hard it would be to create something that is perfectly straight and true if you know what I mean with these sorts of dimensions (and also how would you go about selecting your vendors for materials to ensure that you get straight bits of a high quality for this sort of job?)

Obviously all this depends on how accurate you want this thing to be and although I said I'm not looking to build anything ridiculously accurate, I'm starting to think I want something that's pretty **** accurate after all. I read that most hobby CNC machines range in accuracy from 0.01" to 0.001" in accuracy. I think I want to go for the 0.001" accuracy and better if possible but at this stage I'm totally in the dark in terms of understanding how one would derive such accuracy i.e. how you can design in a particular accuracy.

Also, does anyone have an opinion on this?

http://joescnc.com/gallery/albums/Joe's 06 Machines/cnc router1 1.jpg

There are free plans for it on the website, I was thinking of maybe modifying it to make it from metal but I'm not sure.

Last edited: Oct 25, 2010
15. Nov 19, 2010

### K-Rigg

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got my torch table done, built it over the past couple weeks. Well see what ill do with it.

16. Aug 12, 2011

### Mac790

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Seems it works now.

Seb

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17. Aug 14, 2011

### berridos

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Hi

This is my 4 axis cnc hotwire cutter.
The machine does the job but gave me too many headaches...

Building now another cnc machine would be straightforward.

18. Aug 29, 2011

### N15KS

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Router Bits

I'm purchasing a 4ft x 8ft CNC router later in the year. I'll be using it to cut MDF plugs and I'm having trouble finding suitable router bits. The machine has 200mm of vertical travel but I don't see any router bits this long... any suggestions? What kind of bits are you guys using?

19. Aug 29, 2011

### Tom Nalevanko

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Why would the router bit have to be that long?

20. Sep 1, 2011

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