8020 and gas pipe design thoughts

[jvanick]

I don't have much experience in using cad software yet, so I really can't show pictures of what my thoughts are... And i'm pretty much a total green newbie when it comes to cnc machines, but I've been lurking here for a bit now and seeing everybody else's designs... and I've got some ideas that I'd like to kick around with people that know millions of more times what i know right now:

I'm thinking of building my first machine out of a combo of mdf, unistrut, gas pipe and roller bearings, and 8020.

I'd like to use 8020 for the X rails... with gas pipe mounted on the top and bottom, kinda like the Joe's 4x4 8020 prototype.

I notice that it looks like he's using the 3060 dimensioned 8020 stock 3" x 6" and mounting the gas pipe on the top and bottom of it.

i'm thinking of doing gas pipes just like that, but mounting it on a strip of mdf with a v-groove cut in it and then attaching that on the top and bottom of the 3060... since I don't have a way to cut the holders.

my question is this tho... can I go down to the cheaper 1530 or 1545 (1.5" x 3" or 1.5" x 4.5" ) dimensioned material and still maintain rigidity on a 60 inch span?

What's the best way of mounting the gas pipe. I'm thinking flathead screws countersunk into the gas pipe and then screwed into T nuts would be the easiest mounting method. Using 1" or possibly even 1.5" gas pipe to add a bit of extra rigidity and make space for the rollers to run past the screw heads...

I can't afford the THK rails right now, and already have the roller bearings.

My overall thought for dimensions at this point would be 60" long by 30" wide, allowing for a cuting dimension of at least 4' x 2'.

the work space would be either 8020 1515 or unistrut supports running across between the X rails with a piece or 2 of MDF on top.

The gantry would be driven by a single acme 1/2" lead screw in the middle under the table and would ride on the gas pipes with the (now standard?) aluminum angle and roller bearings with tensioning provided by a pressure system on either the top or bottom of the gantry arms.

I'm thinking of using a piece of 8020 for the gantry as well, again, either the 1545 or 3060 depending on what the consensus is here.

Can anybody offer any suggestions or thoughts on these design thoughts?

I've got a 3-axis Hobbycnc controller and their 305 oz steppers, along with 2 6' sections of acme 10 tpi 1/2" rod and some lovejoy couplers. Going from MDF to 8020 should lighten things up, so I'm guessing this will be plenty of power to at least start to run this beast, right?

Thanks in advance!
-J

[DistortedDesign]

I am fairly new at this as well but from what I have seen the 2040, and 1545 should be ok for 60" spans, but I am not for certian. I have researching the cnc designs for more than a month now. I have looking into joes 4x4 design a lot. I love the design but I don't like the rails because of the mounts that you have to custom make for them. Ahren here on the forums makes a low cost rail system for 8020. Something else you should know about joes 4x4 is that he is running dual motors and screws for his y axis. He has them linked together. The only problem is with the design is you have to have a cnc to make it...... I am currently redesigning a hybrid version of the jgro, joes wood cnc and joes 4x4 design. Simplifying the designs, so that it could be made at home with no cnc machine.

[jvanick]

I looked at Ahren's site and couldn't see any linear bearings for rail or shaft...

however, I did see a link over to kelinginc .. they have some linear rod bearings for pretty cheap.

how do you mount the rod to the 8020 tho? and... can I get away with just one bearing rod on top, or will I need an additional bearing on the bottom to stabilize things.

I'm thinking that with my machine being only 30" wide, I can get away with driving the gantry from the bottom in the middle, however, if that doesn't prove to work well, I can always add a fourth motor.

-J

[joecnc2006]

I am using 72" 2x4 80/20, with my new design now, I use V-bearings, altho the gas pipe worked, it is much easier to fit angle iron for the v-bearings instead. I just finished the Z-Axis so you can see a little of the angle iron used.

if you do go with the gas pipes, i would not use mdf as standoffs, use some other material, remember you only need to support the pipe every 8 to 10 inches, a rule of thumb i use is do not go wider than your gantry.

Joe

[jvanick]

so... to get back to my original question then...

if I go with V-bearings and angle iron, I should be able to get away with even dropping to 1530 dimension material since the angle iron on the top and bottom of the X rails will stiffen things up a bunch... I'm guessing a 60" span should be no problem with this type of configuration.

hmmm.. starting to look pretty promising here.

now i have to learn how to use some cad software to draw this all up... and order some materials to start my build.

-J

[joecnc2006]

Also remember its not just the 80/20, pipe rails or angle iron, when you get your cutting bed installed this also will stiffen up the machine, I even stood on my machine, an extra 200lbs, with no effect to the machine. so this configuration will work because the bed is attached several places along the 80/20's length. Look at my 4x4 you will see what i'm talking about. I also will have plans coming out soon of the new CNC 4x4 Hybrid.

Joe

[jvanick]

I was more concerned with the properties of the aluminum extrusion... the 8020.net's deflection calcuator says that a 60 pound load on a 60" unsupported 1530 says that you'll get a 0.017" deflection. .. changing to the 1545 tells me 0.005" ... and going up to the big stuff... the 3060 tells me 0.002".

I am concerned that with the 1530 I'm going to get enough deflection with the gantry to make uneven cuts over the length of the X axis, and I'm hoping that the angle iron will help stiffen up that deflection. Or am I really just worrying about something that I don't need to worry about?

-J

[DistortedDesign]

If you are thinking about going to v-bearings you better be prepaired to drop a lot of cash. Good V-bearings are $25 per bearing and the cheap chinese stuff is $15 per bearing. You will need 4 bearings per rail. There are 4 rails just for the y axis, 2 rails for the x, and 1 for the z...... OUCH!!! 7 rails x 4 bearing x $25 each = $$Holy Crap

I am looking for the post where I saw pics of what he is selling. Here is his website and just send him an IM and tell him you were intrested in his railing system. (Ahren
cncrouterparts.com) They look very promising.

From what I have seen it is a valid worry and better do it now during the design phase rather than after it is built and not working the way you want it to. It depends on what you are planning on cutting with it.
The 1530 might be a little thin for 60" span. 2030 , might be better. I guess it depends on what you mount to it, will add regidity to it. Joe would know more than I would though.

[jvanick]

You're exactly right about how expensive the v-bearings are... that's why I'm trying to come up with a solution that I can use the gas pipe and roller bearings that I already have on... but I'm not 100% sure yet... if I do the $15 bearings, at 12 of them, I'm looking at approx $200 in bearings including the bushings... and the mounting will end up much easier than the roller bearings...

As far as the 1530 or 2030 or 3060 goes... I'm now just thinking about biting the bullet and buying the 3060 for the x rails as well as the y gantry... like you said.. doing it right now will save me time and frustration (more important than time) later.

it's all a tradeoff... and I can really see how this hobby just starts to consume $$$ faster and faster and faster.. I don't even want to think about how much Joe has spent during all his R&D time.

It's pretty cool to think that you can design and build a machine for less than $2500 that will perform as well as a machine that costs 4x the cost.

-J

[ahren]

Hey all. Thanks for the bump on the rails, Distorted -- they aren't quite ready yet due to a supplier delay, but should be on sale this weekend. I can't say much more, as this isn't the proper forum to advertise in, but look in the product announcement section towards the end of this week.

As for your beam, I would go with the 3060 for a 60" span. Deflection is one concern, but you also could potentially have significant torsion depending on how tall your z is under heavier cutting loads. Torsional effects are hard to calculate, but the amount of deflection is proportional to the length of your axis, the applied torque, and the polar moment of inertia of your cross section. A wider cross section significantly (more than linear -- I think it's a squared function of the radius) increases this moment of inertia, and reduces deflection.

Another benefit of a super stiff gantry beam is better resistance to racking (if you aren't driving your system on both sides). Spend the money -- you'll be glad your system is super tough, and the frame is the most annoying thing to upgrade in the future. My $0.02.

Ahren
www.cncrouterparts.com

[DistortedDesign]

Generally when using a rail you don't have just one on each side of the x and y axis. You would have a top rail and a bottom rail just like the gas pipe design. I am pretty sure this is essential so that you don't get any torsion in the gantry. The only one that can have just one rail is the z and it needs to be failry wide like 4 to 6 inches. So basically instead of gas pipes you would just put a rail in its place. You don't get to subtract rails.

"You're exactly right about how expensive the v-bearings are... that's why I'm trying to come up with a solution that I can use the gas pipe and roller bearings that I already have on... but I'm not 100% sure yet... if I do the $15 bearings, at 12 of them, I'm looking at approx $200 in bearings including the bushings... and the mounting will end up much easier than the roller bearings..."

You would need nearly double that amount. That is why I put this (7 rails x 4 bearing x $25 each = $$Holy Crap ) 7 rails x 4 bearings x $15 = $420 just for bearings + the rails which are $100+ per 6' section and you would need 6 or 7 of them. Usually they are more than $100, more like $140 per 6' section cause it is hardend steel. You can make your own or use v channeling some how. I don't know how joe has his new one cofigured cause there are no pics yet with the v bearings installed.

[joecnc2006]

all 16 of my v-bearings were $186 shipped, so for simplicity and ease of installation, it was a simple discission.

Joe