CNC mill beam deflection

chrismp · Post by **chrismp** » Mon Sep 20, 2010 2:39 pm

Well, I might be building a CNC router over the next year and I'm currently in the process of making some design choices.

Here's a couple of renders (sorry for the bad quality, the Rhino renderer takes some getting used to):

My main concern with my current design is the strength of the y-axis gantry beam.
Currently I'm planning on making it of 45x90mm aluminum extrusion, like this:

The only data I have on it is this:

moment of inertia x: 19,07 cm4
moment of inertia y: 79,35 cm4

My other option would be using square steel tubing (e.g. 100x50x3mm).

The load it's going to take will be up to 200 Newton.

Which one's better? (sorry if this is a really dumb question for most of you, but I'm nowhere near an engineer type of guy, so please bear with me)

COsurfer · Post by **COsurfer** » Mon Sep 20, 2010 6:15 pm

Hey Chrismp, I started off trying to design a CNC router because it seemed like the least expensive way to go. I ended up with a splitting headache and wasting a lot of time. I would recommend buying a kit. There are so many pitfalls with these machines and you can end up throwing away many thousands of dollars. I am not sure if you read my thread I started a few weeks ago:

http://www.skibuilders.com/phpBB2/viewtopic.php?t=2514

The post has some great info. Make sure to read Head Monkeys CNC blog, it is very thorough.

FYI-my gantry is made og 80 20 aluminum. I dont know the size off had but I can check for you. It works great.
Best of luck!

OAC · Post by **OAC** » Mon Sep 20, 2010 10:00 pm

Check this one: http://www.automatedwoodworks.com/
I was planning for it this year, but my focus changed. I even bought the plans...
It's belt driven which I think is an advantage.

chrismp · Post by **chrismp** » Tue Sep 21, 2010 2:51 am

Thanks guys!

@COSurfer: sure I read all the links you suggested! Thing is, I can get most of the parts like the steel and linear rails (Igus Drylin W type) for free. Buying a kit would be nice, but much more expensive.
Could you do me a favor and measure the dimensions of your gantry beam?

@OAC: I know his webpage

His design is the reason I'm asking whether to use those 8020 sections or rather use some beams like he did.

BTW: the beam length is 110cm! Forgot to add that.

falls · Post by **falls** » Tue Sep 21, 2010 2:58 am

If you're going to 110cm you might as well go a little bigger so you can get a whole 120cm x 240cm MDF panel on there.

chrismp · Post by **chrismp** » Tue Sep 21, 2010 3:26 am

110 is just the total length. cutting area will be about 82cm

OAC · Post by **OAC** » Tue Sep 21, 2010 3:44 am

What shall you do with that?

What ever happened with G-man's? http://www.skibuilders.com/phpBB2/viewt ... ne&start=0

chrismp · Post by **chrismp** » Tue Sep 21, 2010 6:44 am

OAC wrote:What shall you do with that?

What ever happened with G-man's? http://www.skibuilders.com/phpBB2/viewt ... ne&start=0

It's main use will be snowboard building, so making cores, templates, molds, cutting bases (maybe fibreglass).
The only other use I would have for it would be trying to make a surfboard out of a foam block.

OAC · Post by **OAC** » Tue Sep 21, 2010 8:04 am

But 110cm in length? Is that enough for snowboards? Just curious

chrismp · Post by **chrismp** » Tue Sep 21, 2010 8:15 am

nope, thats just the gantry beam length.

cutting area will be 2300x820x180mm.

OAC · Post by **OAC** » Tue Sep 21, 2010 8:23 am

Ok, got it. I mixed the "lengths"

COsurfer · Post by **COsurfer** » Tue Sep 21, 2010 5:39 pm

FREE is the best way to go! My entire frame(including the gantry) is built with 3"x3" 8020 aluminum. Here are some pics:

G-man · Post by **G-man** » Wed Sep 22, 2010 12:14 am

What ever happened with G-man's?

Geesh... been so long since I've been on the forum, I had to spend a bit of time trying to find my password.

I run my CNC machine for a number of hours pretty much everyday. I've never had to do anything to it except for a slight backlash adjustment to a drive nut once or twice over the last couple of years. The machine is surprisingly accurate. I can set up a dial indicator, take a reading, then jog all three axes all over the table, then send all axes back to zero, and end up within .001 inch of where I started. I'm in the process of building 3 additional cnc machines. If I had the time to focus on just building a machine, start to finish, I could build one in about one week. It takes less than a day to cut out all the parts for a new machine. So, I'm a real fan of building my own. I never have to call a tech rep for assistance when something isn't working correctly. Admittedly, it was a very steep learning curve, but if you're going to spend much time making stuff on a CNC machine, you'll have to go through the learning process at some point in time. Two years ago, I didn't even know what g-code was. Now, I write the code for about half of the stuff I cut. Oh, I've never regretted building out of MDF. The machine is amazingly solid. It runs so smooth that, if I rest a hand on the table, I can hardly feel a vibration, even during quick maneuvers.

So, both G-man and his machine are still kickin', but the machine is a lot better lookin'.

Cheers

OAC · Post by **OAC** » Wed Sep 22, 2010 1:13 am

Great to hear that you and you're machine are well! Have you reached you're wife's limits? Or are you still in the livingroom?

Just curious, did you file your work over at cnczone?

I'm not in the "zone" right now. I have to postponed the cnc project till next season. No room...not even in the livingroom..

Cheers

G-man · Post by **G-man** » Wed Sep 22, 2010 10:35 am

Have you reached you're wife's limits?

I think I shouldn't answer that question because it'll only make you feel bad for asking. I suppose the CNC machine wasn't totally at fault. Truth be known, I think that having the CNC machine to focus on, helped me get through all those difficult months. It was definitely weird going back and re-reading the stuff I wrote on the link that you posted... like a totally different world. Anyway, life is tough sometimes, and 'that's all I have to say about that'.

No, I never did post a log on cnczone. Things just got too crazy, and they're still too crazy. Who knows, maybe I'll get around to it someday. And no, I'm not still working out of the living room. I built a nice two story full-on ski building 'factory' over the past year, but alas, I feel like I'm outgrowing it already.

Okay, I think I'll go back into hiding now (actually just too busy to be very involved with the site)... which means that I'm not in a good place to be an effective 'moderator' for skibuilders.com. So, if anyone wants to take on the title, just let the forum administrator know that you're interested.

I'm getting enough word-of-mouth ski orders at the present that I don't want to put up a web page just yet, but I'm sure that eventually I will. Then ya'll can see what I've been up to.

QAC, you're a thoughtful and energetic contributor to the site. The questions in your post were totally well meant. It's okay.

Cheers to all,

G-man

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CNC mill beam deflection

CNC mill beam deflection