Help on deciding which CNC :)

[woox]

Hey guys I am new to the CNC world but I have done my research

The main reason for CNC is 2d cutting, and text ingraving on plastics mainly.

My budget is $1000 for CNC machine excluding software

I am not going to be really using this CNC for too much fancy work mainly for case designs like the ones here:
http://www.cnczone.com/forums/showth...548#post493548
I have came across a few on eBay and I was wondering what you guys think is a good one:

#1:
http://cgi.ebay.com/Hobo-Jr-rev-B-3-...QQcmdZViewItem

#2:
[Not Buying]

#3:
http://cgi.ebay.com/ZENBOT-CNC-ROUTE...QQcmdZViewItem

What do you guys suggest is the best of the 3?

[xcayba]

I just bought the Zenbot. It came in a couple of days ago and appears to be a good machine. I have not cut anything with it yet though. The biggest thing to consider with that one is that it is tiny. The other two machines you listed are larger. I can't speak for them since I don't own them. The only thing about #2 that strikes me is how you plan to hold your work down on the table. With a smooth surface like that, you may end up drilling some holes in it first. You might want to ask that guy what the hold-down setup should be (carpet tape perhaps???). I do like a moving table design though. Implementation is key. It can be a great design, but if the guy is a sloppy builder, it all goes to crap. That is kinda the risk you run in buying something from ebay. The first machine I bought via ebay looked good in the ad, but when I got it, I found out it was built crappy and didn't perform well. My new Zenbot looks good so far, but I have not put it through it's paces yet.

[woox]

Yeah I pretty much am settled on #3 the guy is willing to make a whole package too putting in everything i would need including motors etc.. how do you hold down stuff with the zenbot? not sure how to do it with #3 either

[xcayba]

I bought mine with motors as well, but you'll still need a 3-axis controller board to run the motors. I have a Xylotex controller which has been good to me and is more than enough to drive the Zenbot (I just hooked up last night...woot, watch that thing fly!!). I actually had to dial down the current on the Xylotex board to not overdrive the motors on the Zenbot since they are rated at 2 amps per phase. The Xylotex boards have a pretty good following and good support, as well as an attractive price. You'll see it mentioned a bunch of times in CNCZone too.

The Zenbot has a matrix of threaded inserts that are drilled into the table. they are actually flanged and inserted from the bottom, so they won't be pulling out easily. I bought a length of 1/4-20 threaded rod from the local hardware store today that I plan to cut into small pieces that I can screw into the threaded inserts in the table. I'm going to combine that with my step block set to make a complete hold down solution. You could also just use some pieces of wood with holes / slots in the middle of them in place of a step block kit to make hold-down jigs with the threaded rod. The main thing is having something to attach to on the table, such as t-slots or, in this case, the threaded inserts.

The Zenbot has almost no slop in any of the bearings that I can see and each axis has very little resistance, so much so it feels like they are gliding on ice. That is how he can get away with using only 75 oz motors. That really drives the speed up too.

[woox]

Originally Posted by xcayba I bought mine with motors as well, but you'll still need a 3-axis controller board to run the motors. I have a Xylotex controller which has been good to me and is more than enough to drive the Zenbot (I just hooked up last night...woot, watch that thing fly!!). I actually had to dial down the current on the Xylotex board to not overdrive the motors on the Zenbot since they are rated at 2 amps per phase. The Xylotex boards have a pretty good following and good support, as well as an attractive price. You'll see it mentioned a bunch of times in CNCZone too. The Zenbot has a matrix of threaded inserts that are drilled into the table. they are actually flanged and inserted from the bottom, so they won't be pulling out easily. I bought a length of 1/4-20 threaded rod from the local hardware store today that I plan to cut into small pieces that I can screw into the threaded inserts in the table. I'm going to combine that with my step block set to make a complete hold down solution. You could also just use some pieces of wood with holes / slots in the middle of them in place of a step block kit to make hold-down jigs with the threaded rod. The main thing is having something to attach to on the table, such as t-slots or, in this case, the threaded inserts. The Zenbot has almost no slop in any of the bearings that I can see and each axis has very little resistance, so much so it feels like they are gliding on ice. That is how he can get away with using only 75 oz motors. That really drives the speed up too.

Thats great! I would totally by Zenbot if it was bigger though...do you think you can post up pics on when your securing something? I think i would get a better idea with a visual example

[xcayba]

Sure thing. I just got done cutting my first piece on the Zenbot. I went for the gusto at 100 inches per minute and had good results. I started with a 1/16 ball end mill, then finished up with a 3/64 flat end mill. Results are good. Just have to remember to program little bites on each pass. See attached pic of my hold-down. I should have put a hold-down on the other side of the work in addition to the two you see pictured, but this was just a trial run.

[woox]

Thats a neat idea, so did you make that holder your self or buy it from a hardware store?

[xcayba]

I bought those black pieces used on Ebay. You can see the rest of the kit in the background. It normally comes with several sizes to fit most any job. I use them on my drill press as well to keep things still. Nice handy thing to have around the shop. I'm sure they are the same thing sold by Harbor Freight. See this link for pricing and more about Them. Harbor Freight Step Block Clamping Kits

[CNCadmin]

Any pics on how the linear bearing are set-up?

[xcayba]

On the Zenbot machine, the linear bearings are a bit difficult to take a picture of since you have to dissassemble the machine to get to where the bearings are. In short though, there are two square tube rails on the X and the same is true for the Y axis. There are four plain sealed ball bearings per side (two front, two rear that ride on two faces of the square tube). They are fitted with pins that run through the middle of the bearing assembly and mate up with slots cut in the HDPE. They are not adjustable, but I've run mine for a while now and it is still without slack and running very accurately. Not sure that helps a whole lot, but that is what I saw the two times I took mine apart. This design requires that you have a dust collection system since chips on the rails will bind up the ball bearing assemblies that roll across the flat parts of the square rails. That is why I had to take my apart twice since the chips had gotten on the rail and caused the axis to bind up. The Z axis is made with hardened rods and bushings, so it doesn't suffer the same chip binding problems as the ball bearing design of the X & Y axis. As long as you keep the rails clean, this is an awesome design with very little resistance.