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AKMac
11-01-2003, 01:25 AM
Hi, let me begin by saying that I know absolutely nothing about CNC machines though I'm an experienced 3D modeler, and I'm pretty sure I can build one with a little help. When it comes to making an actual part from my drawings, I'm a complete newbie.

Basically what I want to know is if my requirements of a home-built CNC machine to much? What I need it to do is to produce the 3D equivalent of what is on my computer screen. Something like is on this site:

http://www.corpcomp.com/weeks1/mb/mb.html

I realize that his machine is about $50,000 but could something like this be done with a homebuilt? I really don't need it to machine aluminum, but it would be kind of nice if it could. Would I need a 3-axis machine (with a rather tall Z-axis), or would a 4-axis machine be required?

I know some of you may say that I need to start out smaller, but a small machine that only engraves, although would be fun to play with, would be useless for my requirements. I would rather build what I need the first time.

As you can see, I'm really kind of lost.

Thank you.

samualt
11-01-2003, 04:49 AM
Looks like a 3-axis machine to me. With a tall Z-axis like you said. Check out CNC Router Plans (http://www.inshorepowerboats.com/cnc%20stuff/CNCROUTER.htm). Its big, 4x8, and has a 9 inch Z. Its what I'm trying to build. You will find the message board for it just under this one called CadCut router.

Good luck!

duluthboat
11-01-2003, 11:14 AM
"I really don't need it to machine aluminum, but it would be kind of nice if it could."

Just a couple things to think about, as the materials get harder the machine needs to be more rigid. The taller the Z axis is, the more difficult it is (more expensive) to make the machine rigid.

For the work shown in the link true 3D is not required. Only a 3 axis machine with 2 axis interpolation is required. 1 axis is positioned and held, while the other two move, this is commonly called 2 Ĺ D. You could find a good metal working mill with 2 Ĺ D capabilities for less than 10K.

If you still want to build your own machine a very good start is to read all the post in this section and check out the links. Then come back with your questions.

Good luck
Gary :D

cadcam
11-01-2003, 02:24 PM
Ok for starters learning about machining is a great start.
this is not some thing you learn over night.

I teach people how to make things like the plane.

I am sorry to say that the stament from duluthboat saying this can be done as 2-1/2 d is way far from correct if you want a smooth contour say over the wing . This will have to be done in 3d surface paths.
the only thing I can see to his statment would be that the code to make one move across this spane would use say "Y" & "Z" moves then move in "X" & "Z" ten once again in "Y" & "Z" .
this does takes time to understand.

What software are you modeling in at this time?

If you want to cut wood this is a great way to get your feet wet and be able to buy a home made routor nd work your way up.

being able to draw the shapes in 3d will help. But this does not make you a machinst.

But with help from freainds and from this board we can help step you thru.

duluthboat
11-01-2003, 03:09 PM
I make 3D parts on a daily basis on a machine that is not capable of moving all three axisís at the same time. It controls all 3 but can only move 2 at a time. That in my mind is a 2 Ĺ D machine. Of course you canít get real smooth finishes with this setup, but you can reduce the scallop size to the point that hand finishing is minimal. 3 axis interpolation will still leave a scallop. We also have a 4 axis VMC, but it seldom is moving in more than 2 axis at a time, maybe for spiral up or down tool paths or thread milling. Still without the ability to change the attitude of the cutter it will leave scallops on a 3D service.

Gary :D

cadcam
11-01-2003, 03:22 PM
Thanks for your reply Gary,Now are you able to do full surfaceing
with this machine.I know that you can not surface at an angle like you stated were you are limmted to 2 axis at a time.
Now is the "Z" moved by hand or is just anly support 2 axis at one motion at a time?

What is the machine if I may ask is it a retro?

As for making thinks work the way you stated there are for sure work arounds .
I use to make some of these shapes on manual machines as per my mold making back round.

But for someone starting out not knowing machineing and cncs at all we are asking for alot.

duluthboat
11-01-2003, 04:29 PM
The machine is an EZ-Trak with an add on Z axis on the spindle. It will move XY, XZ, and YZ, but it will not move XYZ simultaneously. A normal cut path might be a YZ profile, then a X step, or a XZ with a Y step, or XY with a Z step. It is really not that much different than the paths on the VMC, except itís not as efficient. The surface finish can be pretty good if you reduce the scallop height down to say .002, but for most of my work I donít have the luxury of the time that would require. I seldom go below .010. Draft angles, convex or concave surfaces are common. I have been in many shops that do things very much like I do. If you know a better way short of buying new equipment I will be glad to listen.

Gary :D

duluthboat
11-01-2003, 05:42 PM
Iím thinking we may not be understanding each other. It may be I am miss using some terms here. Here are some terms I have used and how I understand them as they relate to CNC.

2 axis machine: May have more than 2 axis but only 2 are controlled by the controller.

2 Ĺ axis machine: 3 or more axis, the controller can not operate more than 2 axis simultaneously, but can control all axis.

3 axis machine: The controller can operate all 3 axis simultaneously.

To me it is how the controller functions not how many axis the machine has.

Gary :D

Mr.Chips
11-02-2003, 12:03 AM
Gary,
The 3 axis machines that most people are building here can operate all 3 axis simultaneously, isn't this so.
Being a newbie I just assumed they would, after reading your comments i'm kinda unsure.
Hager

AKMac
11-02-2003, 12:18 AM
I'm currently using 3D Studio Max as my 3d software, but I will hopefully be switching to solidworks sometime this month.

The machine that samualt posted is about the right dimensions that I'm looking for. I don't think making it sturdy will be to much of a problem since my dad is a certified welder, and I have access to a bunch of 2" square tubing that can be used as supports/gusets/etc.

One question that I can't find an answer to is how does the machine know what type/style of bit to use? Is this in the G-code or is this calculated by the operator?

If anyone knows of a beginners guide to CNC machines, that would be very helpful.

Thanks

ger21
11-02-2003, 08:06 AM
The software that generates the G-Code will let you choose what bit you want to use, and then figure out the code based on what type of bit you're using. You also need to consider that a large z-axis won't do you any good if you don't have a long bit to cut with. I'm assuming you're going to use a router, and you won't find much over 4-5 inches long, with cutting lengths of only 2-3inches max.

Gerry

duluthboat
11-02-2003, 11:47 AM
It seems I am guilty of causing the post to drift off a bit Iíll try to stick with the topic. I just want to urge all who are interested in CNC to read as many of the post on this site as they have time for, before they start spending money. The best machine and the best software will not substitute for lack of knowledge. The other point I wanted to make was that if you want to machine metal, you can likely buy a decent mill cheaper than you can build one sufficient to do the job.

Most if not all the software I have seen for home built PC based controllers will run 3 or more axis simultaneously.

In most cases that I know of you need at least 2 types of software. 1 to control the machine and one to write the code. If your parts are simple you can write the code by hand. If you want to cut complex parts than you will need some type of CAM software to write the code. Prices range from free to over 50K. You will need to understand the code that you are using, so you can edit. Even the best software will not do it all for you. You first have to get the part information into your CAM, if it is already drawn digitally in a vector format it might be a simple import. In some cases you can convert raster images to vector; but you will most likely need to redraw it. Once you have your part in the CAM you need to make many decisions, what you want to cut, how it will be arranged on the machine, what size cutter you will be using, what direction will you be cutting, how fast, and so on. The better the program the more options you will have. Now you have the CAM write (post) the code for your machine. At this point you will want to run a simulation if you have that option or do a test cut on some scrape. In the beginning you will find errors in the code and you may need to adjust the post processor, change the way you cut the part, or manually edit the code. As you gain experience with your setup the errors will start to diminish.

Not sure if I have helped here at all. Itís much easier for me to cut the part than explain how I do it. In the future if you ask a question Iíll try to be specific and not drift.

Gary :D

dcd121
11-02-2003, 11:57 AM
Akmac,
1.create model (sounds like you have the hard part well in control)
2.create toolpath ( you need to learn this no matter what machine you have)
3. machine ( a machine does nothing except cost money until you create 1.,2., above.

Suggestion: Down load Visual mill (free Demo) from this site and try making some of your parts virtually. Its free and fun and the time spent is not lost. Its just part of the cnc learning curve. I don't know 3d Studio file transfer abilities but there must be a way. Solidworks is an exellent program to move to.

Regards

cadcam
11-03-2003, 12:33 AM
(It seems I am guilty of causing the post to drift off a bit Iíll try to stick with the topic.) I don't feel this your fault by any means .

these are all important thoughts and samples of thinks he will run into..

You have been playing well with others keep it up.

(Not sure if I have helped here at all.) I would say you are doing a great job.

fyffe555
11-03-2003, 12:30 PM
AKMac

If you're familiar with 3DSMax then have a look at http://groups.yahoo.com/group/CNC_Toolkit/

or

http://www.rainnea.com/cnc.htm

It's a clever set of maxscript functions to create, edit and export toolpaths from a 3DSMax, Gmax or VIZ model for use with 3, 4 and 5-axis machines.

The Author posts here on occasion.

I'm a 3DSMax novice but have had some fun and education using it on my homebuilt 3 axis (where all three axis can run at once.....)

rgrds

Rekd
11-03-2003, 12:47 PM
Originally posted by cadcam
(It seems I am guilty of causing the post to drift off a bit Iíll try to stick with the topic.) I don't feel this your fault by any means .

these are all important thoughts and samples of thinks he will run into..

You have been playing well with others keep it up.

(Not sure if I have helped here at all.) I would say you are doing a great job.

+1 Cadcam