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Posted: Mon Feb 07, 2005 3:04 am Post subject: CNC foam?

check out this link....
http://www.rcgroups.com/links/index.php?id=4063

would it be madness to construct a larger one of these (car size) and then designing the car on the computer and getting the CNC cutter to basically shape the body for you, and then fibreglass over it. its just that i may not have heaps of time to do it and that this would be an ideal way of doing things. when i get home then ill post up some pictures but im travelling round the world for a year at the moment!
cheers

Posted: Mon Feb 07, 2005 3:17 am Post subject: Re:CNC foam?

Thanks for Joining the forum LordFizzer! Like the name...

The cutting tool that you linked to is a 2 axis computer controlled hotwire foam cutter tool. You will find that it is too limiting in that it will not allow you to cut all the shapes you will need for a full-sized car. I used a home made hotwire to cut all the foam on my car and it left a LOT of filling to be done with the plaster. I'm STILL filling! And MAN am I tired of it.

You can see my Hotwire video. If you want to build a car out of foam from a CAD model using CNC then you will either have to build a giant 3 axis CNC mill or hire a company that specializes in this work. Have you seen Dennis Palatovs DP1? www.dpcars.net. Here is a photo of his car under the mill.

later,

Graber
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Posted: Mon Feb 07, 2005 7:15 pm Post subject: Re:CNC foam?

The chassis moncoque bucks were made this way for our FSAE racer. It is pretty expensive though, probably a couple grand (at least!) for a full body. If and when (hopefully when) I build a car I will probably have it done this way.
See: http://152.1.69.247/modules.php?name=Content&pa=showpage&pid=11

Posted: Tue Aug 30, 2005 4:25 am Post subject: Re:CNC foam?

I use a CNC 5-axis router for making Foam Plugs. The machine is scratch built and the cutting area is 3m * 3m * 2m. I use the machine for building aircraft and boat molds. All up it cost me about $3000 AUD ($1500 US) to build. The router is a clasic Ganty style unit. The slides are made unsing 2 pieces of equal angle to form an X with bearings between them. The XYZ axis is driven via a threaded rod suspended on each end with a pillow block bearing. I machined the trhreaded to to attcah a sprocket and run a chain drive to a stepper motor. The Router motor is a 17turn RC car motor running on 12V with a PWM speed control. The motors and stepers are driven from the paralell port of an old PC using interface boards I asembled myself (kits) You can get them at http://www.oatleyelectronics.com/kits/k142.html (prices are Australian Dollars). Software on the PC is Mach2 which is found at http://www.artofcnc.ca/ you can download a free copy. To generate the CNC Gcode I use Featurecam. I design the parts in SolidWorks and use CosmosWorks for the FEA stress and fatugue testing, Cosmos FloWorks for the aerodynamics , Cosmos Motion for the motion and lifepan tests. Obviously my router is not big enough to do an entire plug in one go so I split it into sections using The split feature Solidwoks. To each split section I then add locating dowels. This aids in asembling the plug from sections. The foam I use is stanard 2 part Polyurthane expanding foam. I use a faily large cell foam as it much cheeper. Once the section is machines I spray it with a hibuild undercoat (spray on body filler) and machine it a second time. This leaves very little work to preparts the plug section for creating a mold. Once this is all done the sections are asembled to form the plug. The joins are filled and sanded to complete the plug.

Hope this gives you all a guide on how to do it.

Posted: Tue Aug 30, 2005 2:19 pm Post subject: Re:CNC foam?

Jim, your idea sounds like a real cool thing. Is it possible to see some photos of how it is put together? I would love to build something similar to this. And your method of using the large-cell foam with the hi-fill primer coats is excellent! I really want to try this myself sometime.

Is there a limitation to the size? And where did you get your threaded rod?

If you could email me some photos I would really appreciate it!

Steve Graber
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Posted: Tue Aug 30, 2005 4:53 pm Post subject: Re:CNC foam?

Steve,
A mate took some photos while i was building the machine. I don't have them on my PC but I will get them and email to you.

I'm kind of embarrassed to say but I built the router from scrap steel, well off cuts anyway. I was intending to go 6M square on the bed but I only had enough heavy RHS to make it 3M*2M. I didnâ€™t use any plans for this one but I had already built another simular but smaller cnc machine so its really a bigger version of that. The smaller one was built for CNC Plasma cutting but that makes no difference as you just use a router or die grinder instead of the plasma torch.

I have the original plans for that one in Solidworks which I will email to you. You can get the 3D Solidworks viewer from www.solidworks.com This will allow you to view all the components and take the machine through all it movements as well as get the dimensions. Send me your email so I can forward it along

This is how you do the axis slides on the cheep

My advice is to build a 3 axis machine first then upgrade that to 4,5 or 6 axis later. The one in the pic in this thread is a 5 axis. With 3 axis you cant effectively cut anything along the edge without gouging. IE it depends on the length of the cutter and how deep you can go before the Collet hit the job. A 4 or 5 axis can get around this a fair bit but it still has limitations. You also have to have some very good software to generate Gcode for more than 3 axis. Its also a lot harder to get the Gcode right for more that 3 axis, IE a lot more learning to do.

If you approach CNC as 2.5D (3 axis) all you need to do is make sure that
1. You have a flat surface on the underside
2. The cuts donâ€™t allow the spindle to hit the job by cutting too deep. You can cut deeper if the cut slopes away at an angle
3. No undercuts

If what you are cutting fails in any of these conditions you simply have to split the job up into smaller pieces to get around it.

You can use anything you like to machine your parts from however the harder the material the longer it takes. I use foam because its cheep and quick to machine although I have to do and extra finishing pass after applying hybuild undercoat but again thatâ€™s cheep. There are lots of materials to use such as MDF, Clay, Wax among others. All have advantages and disadvantages. With foam I have no storage issues as I make it up when needed, Its light which is great for big molds, Its quick to machine and cheep to make. Foam is mot as good as say wax for the finish but after a filler is applied there is no real difference. Best of all foam is cheep.

To prepare the foam I have to make up the blocks. I use box to make the blocks. The base is an MDF sheet to which I screw on the sides. The sides are removed once the foam sets leaving the Foam Bonded to the MDF and ready for machining. I change the size of the walls depending on how big a foam block I need. The foam is split from the MDF at the end with a hot wire cutter that runs along the X axis.

Jim

Posted: Wed Aug 31, 2005 10:02 am Post subject: Re:CNC foam?

Hy,

This whole subject is very interesting.
Is it possible to get the files (and pictures) as well?

Maybe Steve is able to host those on his webspace. If not maybe I can find some place on my webspace.

Best regards,

Geoff

Posted: Wed Aug 31, 2005 11:02 am Post subject: Re:CNC foam?

I'm emailing a buch of stuff to Steve. In the mean time here are some screen shots from Solidworks. This is Plasma cutter version I did first. The main diference is the size of the bed and the height of the gantry. The bed on theis ine is made from cut lengths of flatbar which allows the molten steel to fall through. For foam you can just make it a few crossbars to hold a sheet of MDF.

Post edited by: ozroder, at: 2005/08/31 14:07

Post edited by: ozroder, at: 2005/08/31 14:22 Post edited by: admin, at: 2005/11/24 19:20

Posted: Wed Aug 31, 2005 11:13 am Post subject: Re:CNC foam?

This is the sdlie on the X Axis. It runs on the Equal angle welded to the side on the bed.

Post edited by: ozroder, at: 2005/08/31 14:15 Post edited by: admin, at: 2005/11/24 19:21

Posted: Wed Aug 31, 2005 11:17 am Post subject: Re:CNC foam?

This is the Carrage or Gantry on the Y Axis

Post edited by: admin, at: 2005/11/24 19:21

Posted: Wed Aug 31, 2005 11:20 am Post subject: Re:CNC foam?

This is the Y axis Rail setup, it attaches to the the X axis carrage. You can see from this and the previous pic how the slides work using equal angle. Nice and cheep to make, no need for those expensive linear slides.

Post edited by: admin, at: 2005/11/24 19:21

Posted: Wed Aug 31, 2005 11:43 am Post subject: Re:CNC foam?

Nice stuff!

I have however still some questions. You probably welded yourself the equally angled bars. What did you do to have the appropriate accuracy?
The wheels/bearings are rolling on the angled bars but is there something that is holding them â€œexactlyâ€? on their place? I mean hereby that the carriage shouldnâ€™t move into any direction except the rolling direction.
What is the total accuracy you can achieve with your CNC machine?

Geoff

Posted: Wed Aug 31, 2005 12:48 pm Post subject: Re:CNC foam?

Geoff,

I designed the CNC Plasma to use all off the shelf steel and simple cuts. IE the RHS is all 50mm*50mm and the flatbar is 50mm. All the cuts are at 90 or 45 deg and all the welds are the same. So with simple welding acuracy its easy to put together. The Hardest part is adding the equal angle To do this I made a few jigs which clamped it all together then I stich welded it in place.

For the bearings you can either use track rollers or I just used plain bearings and a spacer. The spacer is to make the contact pacth as wide as possible on the equal angle. In practice I just used a bunch of washers for the spacers. The wider the carrage the less you have to worry about accuracy in your drilling. I drilled the holes on my mill so they are dead on position. All you have to worry about is the distance from the peak of the angle. IS both are the same height off the center line. If you find you cant do that acuratly enough another trick is to slot the holes till you can tigten them in place. If the head of the bolt is on the carrage you can then tack the bolt in postion.

The carages move by turning a thraded rod. Attached to the carrage is a plate that has a nut welded on it. Acuracy overall is a function of gearing. A steper motor has 200 steps per turn for a 1.8 deg stepper. I used M10*1.25 threaded rod a simple calculation

1.25mm / 200 = 0.00625mm

On my foam router I also gear the stepers down by 5:1 using a chain and sprocket, but that was done to increase the power of the stepers due to the weight of the carages. I also used M20*1.5 Threaded rod so that one is
1.5mm / (200*5) = 0.0015mm

Posted: Sat Sep 03, 2005 8:15 pm Post subject: Re:CNC foam?

Jim, I have decided that I would like to build one of these routers, so if it's possible to send me the Solidworks file I would really appreciate it!

Steve Graber

OZRoder wrote:

Posted: Sun Sep 04, 2005 10:18 am Post subject: Re:CNC foam?

Hi Jim,

Can you tell me more about the specifications from the step motors and the sprockets you are using?

Geoff

Posted: Sun Sep 04, 2005 2:11 pm Post subject: Re:CNC foam?

Geoff,

I designed the Plasma for Type 24 Steppers (direct drive) but I upgraded them to Type 56 ones. I used the same type 56 ones on the big router with gearing. Just for reference it does not matter really which steppers you use its just a question of speed and resolition. If you are driving a threaded rod or ball screw you already have enough resolution for most aplications. A small stepper may need some gearing to get mor power out of it however theis will also slow the machine down. A bigger stepeer has more power at a given speed. So the bigger the stepper the faster you can go. Its all a question of speed and how much you want to spend on steppers.
BTW I used the type 24's on a mill to upgrade that to 3 axis cnc so they did not go to waste. The Type 56 units I used were Japan Servo Model KH56QM2-961.

The KH56QM2-961 is a double shaft one you can also get the KH56QM2-951 as a single shaft. As per the data sheet they are 4 volt, 2A, 1.8 degree step. However I drive them at up to 36 Volts and a constant 2A. Relating to speed again you get max spped at max power if the stepper motor driver bard is a constant current type. The Standard "Chopper" type gives you less power the faster you drive it. Check upot the link to the driver boards I posted earlier.

Posted: Sun Sep 04, 2005 2:14 pm Post subject: Re:CNC foam?

Steve,

The solidworks files are on the way via email. They are in Solidworks 2005 format as well as edrawings. The solidworks viewer and edrawings can be downloaded for free at www.solidworks.com

Posted: Sun Sep 04, 2005 4:14 pm Post subject: Re:CNC foam?

Jim,

Thanks for your information.
The only thing I have been asking myself for some time now is the following. You have been telling us you built a 5 axis CNC router. 4 axis are possible as a standard functionality on the driver kit you mentioned in a previous reply. Did you add another card or did you use the additional auxiliary I/O to drive that 5th axis?

Posted: Sun Sep 04, 2005 4:47 pm Post subject: Re:CNC foam?

If you download the documentation from Art's site on the link I posted earlier it will explain everything about interfacing the steppers. The sofware will drive up to 6 axis, Torch Contoler for Plasma, Digitiser, Servo or Steppers, Encoder feedback, and lost more.

As for my setup I use Lpt1 for the XYZ axis and linit switches and LPT2 for the AC axis. LPT 2 is also used for the THC (Torch height control) on the plasma but that does not use the AC axis.

If you use the controlers from oatley you need one constant current psu per axis plus one controler per axis. IE I have 5 controlers, 5 cunstant current units, 2 switchmode PSU (12V & 36Volt), PWM motor Control, THC, breakoutbaord with 4 relay outputs mounted in a 19in rack case.

As for Art's software you can use
2 lpt ports (5 inputs per port and 12 Outputs per port)
USB (Up to 32 inputs and 32 outputs)
Keyboard Emulation (any KBD switch)
Joystick (USB or Game Port) for Jog functions

Their is lots more options than that but thats the basics. As I said download the Software and Manual its all explained their.

Posted: Mon Sep 05, 2005 4:44 am Post subject: Re:CNC foam?

I downloaded the manuals and read up on the electronic components. It's so well explained and so straightforward. Way cool.

The only things that I have to clear up in my mind is where to get the stepper motors for "cheap" (ie;not new) and to see the solidworks drawings so I can understand how you put it all together. I wonder why you used threaded-rod instead ball-screws.

If you sent me the drawings I haven't gotten them yet. info@grabercars.com (or grabercars@gmail.com)

Do you mind if I make your drawings available to others on my website? I would like to host the files and links to parts.

This is such a cool project it really deserves it's own little website... But I am happy to host the information here if you don't mind. Smile

Steve
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