Newbie- Design questions

[elz]

I'm very interested in building my own CNC router. Searching the internet and the cnczone forums I came across several designs and plans. Which brought up several questions.

I came across a web site where the authoe first built the jgro design. He said that there were flexing issues. After looking at his one ane only picture of his jgro machine it looks like he doesn't have the upper torsion box. I've also read within the forum where others have had trouble with flexing on this design.

Q1: Has the upper torsion box in the jgro design recently been added? Does this fix the flexing problems? (I'm very impressed with the drawings).

The author of the web site mentioned above then built another machine which looks a lot like Joe's 2006 design.

Q2: I downloaded Joe's 2006 plans and the free viewer. Very nice 3D drawings but I didn't see any drawings showing dimensions and hole layouts. Am I missing something? Don't know how to read the plans? Or are the plans just guidlines where you have to figure out your own dimensions? I like the design - just wondering if I was missing something.

The author of the same web site then built a 3rd, and best, machine. This design uses v-grooved bearings and angle iron instead of the skate bearings which the other designs used. He also used 2 motors to move the gantry.

Q3: Pricing v-grooved bearing I decided that they were out of my price range. I was wondering if anyone has tried using v-grooved tracks with the skate bearings riding in the groove?

Q4: I was going to use 200oz motors. If I use 2 motors to move the gantry can I use 100oz motors and drive them with the same driver?

Q5: It seams to me that the better (more expensive) machines use the 2 motors to move the gantry. Is this a better design?

I want to build the best machine possible within a limited budget. The Joe Hybrid machine seems to get a lot of good reviews but I don't know if I can justify the cost for the plans on my budget.

Thanks in advance for you help.

[Hirudin]

I should mention that I have not built a machine myself... only read about it.

I don't know about Qs 1-3.

4. It depends on the weight of the gantry and how fast you want it to move including how fast you want it to stop moving and start moving (acceleration). Don't forget that the gantry is the heaviest moving section, so it often makes sense to have additional power to move it.
I think Joe himself has said that he experimented with using two motors with a single driver and that it worked, but I doubt many driver manufacturers would recommend it.

5. Having two motors helps in a couple ways. Starting, top speed, and stopping (as mentioned above) are affected by the weight to power ratio of the gantry to the motors. Adding a second motor obviously helps in the "power" department.
Another thing having two motors helps with is to reduce the chance of "binding". I guess if you only have a single screw/motor in the center of your gantry it has a tendency to bind. It's similar to a long drawer. If you push one side more than the other it might jam-up. Also, similar to drawers there are ways to avoid binding: Check out this thread.

It is DEFINITELY possible to build a machine with just a single motor to move the gantry, but it might be more of a hassle than it's worth. First the motor needs to be more powerful than your other motors since the gantry is so heavy in comparison. Therefor the driver needs to be more powerful. It probably wouldn't be a bad idea to reinforce the gantry to help reduce binding (which adds more weight). And if you choose to help reduce binding by using the cable method I posted above that'll mean more money and time invested as well.

[elz]

Originally Posted by Hirudin 5. Having two motors helps in a couple ways. Starting, top speed, and stopping (as mentioned above) are affected by the weight to power ratio of the gantry to the motors. Adding a second motor obviously helps in the "power" department. Another thing having two motors helps with is to reduce the chance of "binding". I guess if you only have a single screw/motor in the center of your gantry it has a tendency to bind. It's similar to a long drawer. If you push one side more than the other it might jam-up. Also, similar to drawers there are ways to avoid binding: Check out this thread. It is DEFINITELY possible to build a machine with just a single motor to move the gantry, but it might be more of a hassle than it's worth. First the motor needs to be more powerful than your other motors since the gantry is so heavy in comparison. Therefor the driver needs to be more powerful. It probably wouldn't be a bad idea to reinforce the gantry to help reduce binding (which adds more weight). And if you choose to help reduce binding by using the cable method I posted above that'll mean more money and time invested as well.

Thanks for the link about using the pulleys - something I will add if I go the single motor route.

[Jack000]

as I understand it dual motor drives are meant to address off-center cuts (think y-axis all the way at one end, and making a cut on the x). When this happens you create a torque on the gantry, which the linear slides don't handle well. By pushing on both ends of the gantry this problem is eliminated.

This is a larger issue with 4x4s and up, I think a single drive for a 4x2 or lower should be fine (especially with a pulley setup).

[Northboy]

Though the torsion box will probably be fine for light work, I decided to go with steel for my jgro.It wasn't much more work,but about 50$ for the steel. I think it is worth the extra.

I used 1 1/2" angle iron and made it adjustable by adding a threaded rod at each corners. My MDF clamp table is supported on this by 4 pieces of 1 1/2" tubing

You can see how I i did mine here

http://www.cnczone.com/forums/showthread.php?t=76277

You may consider using ACME screws with dumpsters nuts and couplers right off the bat. I wish I had.

I spent quite a bit of time making my own backlash setups, used 5/16 threaded rod and used hose couplers. It was real cheap, but...I was unhappy enough with the sloppiness and whipping that I have started the upgrade without even making and real cuts.

Northboy

[BobF]

Can't answer 1 never did a JRGO.
2. There is a measure tool in the viewer that will let you measure anything on the 3D solid works drawing. I think there is also a set of DXF drawings around somewhere.
Can't answer 3.
4. Don't connect 2 motors to the same driver. Use a driver per motor and slave them in software. This is how Joe is doing as well as all the builders of the 4 x 4.
5. Dual motors may be needed on wide gantrys 4 feet or so wide. My Joes model 2006 has 2 feet of cutting area and uses a single motor and works fine.

[dertsap]

i would suggest using vbearings on angle iron rather than skate bearings riding on v track , it's what i used for my y axis along with the vbearings riding square tubing for the x axis , its dead solid and overall not too bad on pocket book