CNC router table to cut mostly foam and some light wood.

[rcbamm]

Hi all.


For the people with CNC experience, do you mind reading my post to tell me if I'm going in the right path for my needs? I greatly appreciate it!


I'm getting all my chickens in a row to build a CNC router table to cut mostly flat light foam and some light ply/balsa wood parts.

I saw the Phlatprinter (phlatboyz.com) kit and loved the idea right away, untill I researched it some more and found that the Phlatpriner is just built with parts from the hardware store, and if I wanted a more precise Phlatpriner I would have to mod it for better parts. That made me lose my interest in it. So I thought for around the same price as the RTR Phlatpriner kit, I can build myself a more precise CNC router table.

Like I said, I only plan to cut sheets of foam and balsa/light ply. I'm hoping it will handle up to 1/4" ply, but if not it's no biggie. For right now I want to just cut foam but I do want to build it so in time when I learn more about 3D designing it will be able to have the ability to shape foam parts (I.E. foam fuselages for RC airplanes, foamcore wings etc etc) But for right now my knowledge is only on 2D part cut outs.

My need is for something very precise, quick and easy to use, has the ability to precisely mill foam and wood and precisely cut foam and wood.

What I have in mind for the design: I basically just want an overhead gantry CNC table router that has a cutting area of about 45"-50" L x 25"-30" W, with the Z axis to move about 6"-10". I plan on building the CNC router structure out of aluminum and have it sit on a precisely built MDF table. To keep the cost down, I want to use a open ended belt drive system with pulleys to drive the X and y axis. Allthough, I have no CNC experience other than reading, I'm still unsure if the belt drive system would be good enough for the size of table I want to build and if the belts would possibley stretch under load. Or, the belts might just be enough sense I'm not gonna be cutting hard material.

Here are the parts I have lined up so far.

I wanna get these slides for the X and Z axis because the prices are right. Note: I'm not gonna get the 55" slide for the Z axis. I plan on getting around a 30"-40" slide: http://cgi.ebay.com/55-CNC-Router-Li...item5d262b2c1f

The question I have about these slides. For the size of CNC talbe I want to build would these slides sag? Would it be better for me to get the more expensive fully supported rails or would that not be neccesary for the type of material I will be cutting?

As for the drive system. I was just looking at the driver package Phlatboyz.com is selling for $224 bucks with 3 128oz stepper motors http://www.phlatboyz.com/phlatstore/...product=369624

Would this be plenty for the type of materials I will be cutting and does anyone know if this driver package is very precise? As you all know, there are hundreds of drivers and steppers to choose from on the internet, I'm struck as to which ones to consider. I don't want to spend $500 for a driver package when I could of spent $200 and on something that can get the job done just as good. What I'm looking for in a driver package is reliability, long operating life, and accuracy. I'm not sure as to how many OZ of torque I will need though.

This ebay store sells pulleys and belts. Here is the open ended belt I have found. http://cgi.ebay.com/TIMING-BELT-OPEN...item3ca16af801

Maybe some of you can tell me if this belt would be plenty for my needs? I really don't want to get into ballscrews or acmes screws, I choose the belt for simplicity and cost but if the belt won't do it I will resort to something else. I'm not stuck on this particular belt, some of you may know where I can get better belt drive parts from another website. If you can post up what you know of I would really really appreciate it.

For cutting, I just plan on using the regular Dremel or Rotozip.


Well I think that's about it. I'm gonna continue reading, I'm hoping some of you can guide me through this so I can hopefully do it the right way first without wasting money on parts that won't fit my needs.

All help greatly appreiciated!!!

Thanks! -Dan

[mlabruyere]

Hi Dan,

Keep in mind that a lot of us here have built very good machines with "only hardware" store parts so don't look down your nose too much or see it as inferior....unless you are comparing it to an off the shelf CNC solution (many...many thousands of dollars) Ok....having said this....

If you are going to look into doing 3D type CNC work you will need to go with a traditional gantry style machine. The PhlatPrinter MKII is extreamly precise and very fast but yo will not get the travel in the Z-Axis you are looking for.

The slides look great and your idea of a belt drive is excellent. The 3/8 belt will work but you will be limited on acceleration since you are looking for precision. The belt will stretch and rebound. To limit this you have to slow the machine down or get a wider belt.

The kit from PhlatBoyz will be OK so long as you are not looking for blistering speed or torque. Most other solutions will cost you a great deal more. I've got a 45(x) x 44(y) x 6(z) gantry machine built from 8020 extruded aluminum and Ahren's cncparts. I'm running 628in/oz (dual x) and y and a 282in/oz on the Z. I'm driving it with a Gecko G540 (The elctronics cost me $550 alone). The whole CNC cost about $2500.

I've also got a PhlatPrinter MK1 (modded to 1.5). It has the standard 128 in/oz on the X and the Z. I upgraded the y to a 282in/oz. I also upgraded the y to a belt drive. This allows 200 IPM on the X and Y. I am limited to 20 IPM on the Z axis, it's direct drive from the 128in/oz stepper. (24(y), unlimited (x), and 1.2(z)) The full machine with upgrades cost $800

Matthew

[mlabruyere]

One more thing.....if you are looking for precision I would not go with a RotoZip or Dremel. Go with a full size router and get some machined collets and nuts. See here:

http://www.k2cnc.com/2009/09_PC_Collet_Precision.asp

Generally you want to support long rails like that more than on the ends. 20MM is pretty hefty but again if you are looking for precision you will get deflection. You should look for a fully supported rail and open blocks.

Here is the rail and blocks (you'll need at least 4 total (x and y)):
http://cgi.ebay.com/20mm-CNC-Linear-...item1e54334db8

[rcbamm]

Thanks for your reply Matthew.

I'm not looking down on the hardware store built CNC machines. Just after a little research on the Phlatpriner I decided it was not what I wanted. I would much rather have a CNC table. Seeing parts such as slides and what not, are very reasonable in price now, I can build a nice CNC router table for around the same price. Like I said I would much rather have a table. Not taking away from the Phlatpriner because it is a really good design.

Anywho.

I'm gonna research on routers. I really didn't think what router or dremel I used would matter as long as I could fully adjust the RPM. I have a rotozip that I use on restoring cars. I use it to grind away rust and as a cut off wheel. The thing works good but gets way to hot to touch after grinding away underload for long periods of time. The thing I like about it is that it has a fully adjustable speed control. There are no preset stages of RPM speed as seen on other dremels. I don't know much about collets but I knew that I was gonna need something like that other then the stock drywall cutting bit the rotozip comes with lol.

Do you think those 20mm slides will bend when under 128oz of pressure?

I'm coming to some considerations. Trying to keep the budget low, I can go with an x axis cutting length of no smaller then 45". Do you think those slides will still need full support?

[mlabruyere]

Originally Posted by rcbamm Thanks for your reply Matthew. I'm not looking down on the hardware store built CNC machines. Just after a little research on the Phlatpriner I decided it was not what I wanted. I would much rather have a CNC table. Seeing parts such as slides and what not, are very reasonable in price now, I can build a nice CNC router table for around the same price. Like I said I would much rather have a table. Not taking away from the Phlatpriner because it is a really good design.

Cool, no problem. The PhlatPrinter has it's place but it can't be used everywhere...

Originally Posted by rcbamm I'm gonna research on routers. I really didn't think what router or dremel I used would matter as long as I could fully adjust the RPM. I have a rotozip that I use on restoring cars. I use it to grind away rust and as a cut off wheel. The thing works good but gets way to hot to touch after grinding away underload for long periods of time. The thing I like about it is that it has a fully adjustable speed control. There are no preset stages of RPM speed as seen on other dremels. I don't know much about collets but I knew that I was gonna need something like that other then the stock drywall cutting bit the rotozip comes with lol. Do you think those 20mm slides will bend when under 128oz of pressure? I'm coming to some considerations. Trying to keep the budget low, I can go with an x axis cutting length of no smaller then 45". Do you think those slides will still need full support?

128oz will not move the rod too much but you have to keep in mind that not all forces are the dynamic type generated by the motors. You also have to consider the weight it will support (the gantry, router, stepper..etc). My gantry weighs in at about 100lbs (1600 oz) so my rails have to support that with no cutting force.

[stangtjk]

I'm currently building a similar machine to what you have in mind. I'm not sure how well the 3/8" belt will work for you, but you can get 3/4" wide L pitch belt from here and its even a little bit cheaper.
http://shop.polybelt.com/L075-Poly-S...-BL075-MPS.htm

That's what I'm planning on using to drive the gantry and I'm using the 3/8" XL pitch belt and pulleys for the gear reduction.

Here is my basic design. (still missing a few pieces but mostly there)

[rcbamm]

I want to design my CNC table very similar to that. I am trying to figure out if using timing belts is going to be cheaper than ballscrews. At some prices I'v found belts to be $10 a foot and pulleys at $20 a piece. I would rather buy a chinese ballscrew setup for that price. Polybelt.com seems to have some decent prices on steel chorded belts.

I think two 1/2" 3/8" pitch belts, one on each side of the X axis for my CNC design I have in my head seem to be good. I still have no idea as to if certain pulley sizes make a different, and how big of a reduction pulley I need. Instead of using two seperate steppers to drive the X axis, I want to make a pillow block bearing axle that is bolted to the right and left X axis pulleys (pretty much where your steppers are placed) that has a larger reduction pulley system in the center of the axle going to one stepper motor.

I just ordered the Probotix.com 3 Axis Probostep driver kit for my CNC table. These will be the first purchased parts to my CNC project.

[stangtjk]

You can use a long shaft to run both sides of the x axis but don't put the pulley for the gear reduction in the center of the shaft. It would cause way too much deflection unless you support the shaft in the center as well. It would be better just to put it off to one side or the other.

It only cost me around $140 for all my belts and pulleys. I used 10T XL pitch pulleys on the motors that I found on amazon for like $2.50 a piece. They will be paired with 48T pulleys for the gear reduction. I got them off ebay for $4.99 each. He had more but I just looked and they're already gone. The belts for the gear reduction came from amazon as well, they were 11" and cost like $6 each. The pulleys for the driving belts were 12T L pitch and I got them off ebay as well, a lot of 6 for only $15. He upped the price to $18.50 but he still has hundreds of pulleys left. Here is the link http://cgi.ebay.com/ws/eBayISAPI.dll...m=380199077491

Everything but the 48T pulleys are still available from where I purchased them. I can look up the amazon seller if you want. He had good prices on larger pulleys too. Not as cheap as what I found on ebay but better than most of the common online retailers like sdp-si.

[stangtjk]

The 12T L pulleys I'm using have a circumference of 4.5" which is how far the gantry will move for each revolution. With a 4.8:1 gear reduction and 200step/ rev stepper motors that will give me a resolution of .0047" per step. With microstepping I could have higher resolution but I don't know how accurate that is but for wood a foam I think that's good enough.

[stangtjk]

The stuff I got from amazon came from MSC Industrial Supply Co. Here is a link to their site. They have a lot of belts and pulleys and they are pretty cheap. http://www1.mscdirect.com/CGI/N2DRVS...00000125048285

[ahren]

You might consider a rack and pinion drive. Paul Arbo built an excellent machine with our rack and pinion system to drive his foam cutting machine:

http://www.cnczone.com/forums/showthread.php?t=88276

As for those rails, I would be wary of unsupported rails in general. However, you might be able to get away with it since your cutting forces are not all that high. For motors and drives, while I understand the sentiment that you just want something that works, getting something too cheap will leave you without an upgrade path later on, and trust me, you will want more speed once you start a long carving routine in foam. In particular, I would stay away from unipolar motors and drives.

Best regards,

Ahren
www.cncrouterparts.com

[rcbamm]

Stangtjk: Thanks for your replies. They are very helpful when I'm trying to figure out what is best to get. I still have to do my homework on what size pullys I need, what size belts, if fiber reinforced belts will not stretch, or if I need steel reinforced belts, bearings, belt reduction plates etc. I still like the idea of pulleys and belts over all the other options in that price range. I wanna try to get all the belts, pulleys, bearings, I need for under $200.

Ahren: I do like the rack and pinion alot, but still like the belts more. To me, whats gonna win me over in choosing belts, ball screws, or racks, is how much it will cost me to fully equip my table with movement, and how easy everything is to mount to the table and moving parts (and of course, how much accuracy and speed I'm gonna get). I think the rack would be easiest to mount, but I'm wondering if it would be ok to use one rack and pinion in the center underneath the gantry? Instead of using two steppers on both sides of the gantry with two rack and pinion setups.


I just ordered my supported rails. I'v been talking with Chai (his eBay store here > http://stores.ebay.com/linearmotionbearings) the past few days and I cam to a conclusion on what I needed. I told him I wanted the SBR16 supported rails, he told me I can order them in any length I need and he will cut to order. So I told him I wanted two 1400mm rails (55"), two 880mm rails (34" 1/2"), and two 380mm rails (15"), along with two SBR16 bearing blocks per rail. He told me all of this for a price of $167, plus $159 shipping. So he then made me an ebay listing of the rails and amount of bearing blocks I needed with the "buy it now" button. Here is the ebay listing > http://cgi.ebay.com/ws/eBayISAPI.dll...=STRK:MEWNX:IT

To me, $326 shipped is a really good deal on rails. No one else sells the SBR16 rails in the U.S., only a few sell the SBR20 supported rails. The SBR20 rails on ebay are $180 shipped for a 55" (1400mm). I would be spending what I just spent on all the supported rails, and bearing blocks, for the two SBR20 rails with 4 bearing blocks. Yes I know the SBR20 rail are bigger, but after finding a 16mm diameter linear rail in a old 1990's faxing machine, holding it in my hand I decided I didn't need a 20mm diamter rail. 16mm would do just fine as long as it is supported.


So, probotix 3 axis drive package is on the way, and I have all the x,z,y axis slide movement for my CNC table ordered. Now all I need to figure out is what I need to do for connecting those slides to the steppers, and figure out a CNC table structure design.

Can't wait to start building!