[adam_m]

First post, "Hello"...

I've seen a lot of different designs and am curious about the 8020 setups that I've been seeing. I downloaded a pic of a table that looked interesting and wanted to ask some questions about it to the forum, hopefully the owner can chime in. (sorry for not remembering the link)

It appears that there are already custom parts that are made to order for building a CNC out of 8020, does anyone have a link to that site(s)?

What kind of performance/accuracy are you getting from the build?

In the pic I attached it appears the builder is using ACME rod but what type of linear bearings? all that I see are UMHW type do they make anything different? are they really that good as opposed to a roller type?

The steppers are mounted on brackets I assume these are manufactured as well?

Why the need for the multiple 8020's banded together - does it flex too much? does it really not make a good CNC setup?

I'm reading as much as possible but there is so much to learn for a neewbie.. hopefully you guys can help me out.

AJM,

[ben_jackson]

I'm working on a design for a similar router right now and I have some notes for a "build thread" post including these references, which you will find useful:

Ahren's R&P development
jsanto's 8x5' build
Arbo's 24x80" build
lunchtrayrider's small but scalable build
Joe's 4x4 Hybrid megathread where it discusses R&P

The pic you included appears in one of those threads.

Why the need for the multiple 8020's banded together - does it flex too much? does it really not make a good CNC setup?

At 8020.net you can download a deflection calculator. I think most people are overbuilding their 8020 routers. A length of 3030 (3" square) is about the same weight as .120 (nearly 1/8") wall steel tube in the same size, and significantly stiffer. However, overbuilding is always a fine policy with the possible exception of the gantry, which can easily weigh upwards of 150lbs in a 5' wide design. A 5' length of 3060 weighs 40lbs and the 7" steel plate on the front weighs 30lbs. Cutting back to 3030 and 4" plate cuts the weight to about 40lbs total. Unfortunately no one has done the FEA on the 3030+plate combo to really know what the deflections would look like under various loads, whereas the 3060 alone is definitely good for only a few thou deflection.

One other motivating factor for not overbuilding with 8020 is that it's pretty spendy. My design puts a flat 8020 table on a steel frame. The frame will be about $200 in locally-available tube steel and the 8020 in the router is over $1000.

(working design shown below with all-3060 gantry which will be reduced at least to 1545 sides...)

[DIYaholic]

adam_m,
Welcome to the Zone. :wave:
The answers to ALL your posted questions are answered here on the "Zone" in the various threads. The threads ben_jackson provided links to, are good places to start.
My advice to you is to determine what you want your machine to be capable of: ie. material to be cut(foam, HDPE, MDF, exotic woods, aluminium, even steel), size/thickness of material to be cut (this will determine your working envelope), tolerances needed for various materials, cutting feeds, rapid speeds, to name a few performance criteria. Along with performance criteria, you need to consider your budget, design skills, available tools, your building skills, electronics skills and your time constraints. The budget is usually one of the most critical aspect of any build. Who couldn't build the perfect machine(s) with time and an unlimited budget.
Once you determine your desired performance criteria, you then set out to design a machine to meet or exceed those criteria.
While doing your research, keep your performance criteria, build & design skills and budget, in mind. You have come to the right place to research/learn all there is to know about DIY CNC routers. The people here on the zone are ready, willing and able to share their knowledge and expertise.
Again, Welcome to the "Zone". Have fun reading/researching.

Randy,

[lunchtrayrider]

take a look at the builds listed at cncrouterparts.com too. a couple of different styles that you can look at.

[adam_m]

Thanks for the reply's. I see now that CNCRouerparts is where some of the supplies came from for jsheerin's CNC build or if he has a thread avaiable?

So does anyone know what he used for linear motion bearings on that setup?

I realize that critiquing designs isn't a polite thing to do but if you were to do it how does jsheerin design measure up, is it worth repeating?

DIYaholic, I've been doing a lot of thinking about material/feed/size. Since this is my first CNC I really don't want to bite off more than I can chew. I think MDF/Hardwoods and maybe Aliminum might be in the mix.

For table size I'm thinking 36 x 48 or somewhere in that range...

Thanks,

[adam_m]

Any reply's to my earlier question(s)?

For electronics it looks like I can't go wrong using:

Gecko G540
KL23H2100-35-4B 381 oz motors
KL-350-48 48V/7.3A power supply.

There are also some auctions going on EBay with motors any thoughts as to which is better/worse 380, 381, 640?

http://cgi.ebay.com/4-Axis-CNC-Gecko...item3efcc47070

http://cgi.ebay.com/Gecko-G540-w-Fou...item1c10e2da8f

Any thoughts?

Adam,

[lunchtrayrider]

I am using cncrouterparts.com motors, power supply, cables, and got a g540 from them. the coolest part about them is the motors come with connectors prewired with a current set resistor in them already for you. also the red cables make hook up a breeze. think long and hard about saving a few bucks and all the pain of making your own cables.

[adam_m]

Any input into the above selections that I've made?

I'm also thinking about using 20mm supported linear rod for the x, y and z axis.. thoughts?

Thanks,

[lunchtrayrider]

im guessing that the 380 oz/in motors from cncrouterparts along with the geckodrive g540 are going to generate the highest rpm. the cncrouterparts motors and the kelings are going to be the same. the other ones i have no idea. mine from cncrouterparts just fly with their rack and pinion system.

here is my setup that is what cncrouterparts ebay auction is for:

[ame="http://www.youtube.com/watch?v=c42czVwDRl8&feature=player_embedded"]YouTube- 1264735178.mov[/ame]

[adam_m]

lunchtrayrider - I like the speed...

Do you have a link to your table assembly or some more details on what you used for your build, etc.?

It looks like its an 8020 build, what type of bearings did you use for the gantry and how is that assembly completed?

Thanks for any light you can shed..

Adam,

[ben_jackson]

Are you reading the replies? lunchtrayrider's build thread is one of the links I posted.

[adam_m]

Missed that, sorry.

Adam,

[jsheerin]

Yeah, that is my router. It has issues, but I think the biggest one is the router (PC892). I would recommend one of the Chinese spindles and a vfd. Next up is lack of shielding of the linear rails - Ahren's carriages tend to compact the dust onto the 1018 CRS rails which can lead to stalling of the motors (or lots of time spent cleaning), so it would be better to protect them with some sort of enclosure. I have the Keling 425 motors on there which have lots of low end torque but drop off fast as speed increases. They really need more voltage than the G540 can handle, so I'd say that your choice of a smaller motor is good - it will have more torque at higher speeds. I'd also recommend going with the rack and pinion drive. It should give you a better force vs speed curve so you can cut faster. You'll also eliminate screw whipping problems which currently limit me to around 200ipm.

The best part of my machine is the mechanical structure, imo. It's pretty stiff. I plan on reusing a lot of the pieces for other machines after I get my new router going (still in the design phase). The one downside to my mechanical design is having the X rails below the work surface. This gives a longer moment arm from the gantry to the bearings so any force in the gantry applies a larger moment to the X bearings leading to higher deflection. It also tends to accumulate dust on the rails that flies off the table. So I'd recommend putting the X rails above the part and ditching the vertical legs of the gantry. There are good examples of that using Ahren's parts.

[lunchtrayrider]

i have plastic guards that are 4 inches tall to protect my rails along with an actual dust collection system. that is sort of a minimum needed to keep the rails clear. other rail systems are less susceptible to build up.

[adam_m]

Since this will be my first CNC I think I will be using ballscrew(s) 1 maybe 2.

2 questions,

How do I determine which screw(s) to get and how many? I realize that table design will have a lot to do with how many but is 2 ballscrews always better than 1?

The other question is in regard to speed which I believe impacts the 1st question. Do I determine the ipm that I desire for my materials to work on and then work backwards or go for a ipm range and work towards that?

Thanks,