Official Luthiers Forum!

I have been watching this topic, but just have not had 3 minutes to chime in ...

Anyway it is very interesting. CNC has come a long way since I used it in the early 80's. I am in the process of learning some CAD and noticed the nice perspective drawing of the rails was done in Rhino. (3d modeling S/W ~$800)

Don mentioned that a shopbot would be 16K. Not quite, but it can add up depending on what you want to do. The benchtop model (still fairly big) will be about $5k. You can really do a lot with that. You can carve in 3 dimensions too.

Stuff that does add to the cost is the spindle (you can use a router and keep the cost down) the software and drive motor upgrades. Shopbot has new alpha motors which will travel quite fast and retain accuracy better than servos and steppers. I believe they use resolvers for feedback.

Clamping is a topic for another thread at some point. Vacuum clamping seems to be the way to go with CNC and many other things for that matter.

Keep posting the build pix, I think it is really cool that you are doing that.

Thanks for the encouragement John. I would have liked to have gotten a shopbot but 5k is still out of my league. After I build this one then I'll think about building another unit in aluminum like the shopbot with the rails on top, besides, what else can I do while the glue drying on my guitars.

As far as clampinng goes, Alot of people just use double sided carpet tape. I'd like to make a vacuum holder but we'll see how it goes.

Super glue (CA) is a great clamping tool for machining also. It's amazing what a couple small drops will hold. I usually hit the part to be clamped with accelerator so the bond isn't quite so hard to break using a knife wedged between. MDF makes a good sacrificial work board for holding parts and will usually last for quite a few parts. The CA usually pulls up a little piece of the MDF where applied which can then be scraped off the part. Aluminum fixturing is a step up in that CA can still be used and then the spots scraped clean before loading the next part. I have found that roughing the aluminum with coarse sandpaper gives a good bond for machining.
Vacuum works good for larger workpieces.
Nelson

webcast
This is a free webcast comparing servo to stepper if anyone is interested.
Nelson

Here are some more pictures.





Here is a close-up of the x axis adjustable rail supports.

Adjustment bolts.



Mock-up of y axis skate bearing slide.


Bearing rolling on rail (Very Smooooth!!)

Here is a couple pictures of the incomplete z axis.





I'm currently working on the table, I should have it complete within a few days. The price has gone up becuase I decided to go with much larger 640oz steppers and Gecko g202 drivers. this upgrade cost about $400 more.

So far with everything purchased including Mach3 software I'm right at about $1000.00 As I said, this could still be done using the xylotex controller and 269oz steppers for about $400 less. The stepper I am using are stronger than those found on the shopbot.

Looking good, Ed!
Nelson

Nelson,John, What cad software do you use to produce the design and g-code?

Ed--I use Autocad for most of my 2D design work and ProE for solid modeling 3D work. These take care of the CAD part of the CAD/CAM equation.
For 2D work I then export the shape as a dxf file into Maxnc which is the proprietary CAM software that comes with a Maxnc machine. It's very basic but produces accurate results.
For 3D work, I export the shape as a STL file into CAM software such as MillWizard or VisualMill. That said, I don't do a lot of 3D work and have only used trial versions of these packages.
I do have digitizing capability with a probe mounted in the CNC router spindle and used this to develop the cut program for roughing out my archtop plates.
There are a lot of inexpensive CAD programs "out there" for creating the shapes that will export a dxf file. I'm at a loss, however, for what's available for the CAM part.
For simple parts, you can write the Gcode manually but it takes some study to get familiar with how to code an arc.
Nelson

Nelson

Nelson, how well does the digitizer work? what brand is it and was it very expensive? I bought the Mach3 software for the cam part of the equation.

[QUOTE=EBarajas] The price has gone up becuase I decided to go with much larger 640oz steppers and Gecko g202 drivers. this upgrade cost about $400 more.

So far with everything purchased including Mach3 software I'm right at about $1000.00 As I said, this could still be done using the xylotex controller and 269oz steppers for about $400 less. The stepper I am using are stronger than those found on the shopbot.[/QUOTE]

The shopbot alpha has a 2-phase, hybrid, step motor and driver package, which eliminates missed steps, a common problem with stepping motors. The new AlphaStep uses a built-in feedback device that constantly monitors the motor shaft to detect and correct for loss of synchronism. It has about 560 oz/in holding torque, the motors will deliver about 60-70 lbs of linear cutting force at cutting speed and will jog quite fast ~ 30in/sec. The alphas are expensive though, about $1k/each, so we are really starting to get away from the forum topic of cheap CNC.

The progress looks great, you'll be cutting part soon!johno38669.9287037037

I use Rhino and VisualMill. Like Nelson, I do very little 3D. Mach2 has built-in cycles, macro capability, and offsets, so with a little practice, you could create some fairly easy to create and complex routines without any other software.

The problem with the ShopBot is not with the motors. It's the rack and pinion drive system. Innacurate and difficult to pre-load. I think the starting price is closer to $10k when you add up everything you need. For that money you could get into a used Techno-Isel, which is a "real" machine (ball screws, linear guides).

"which eliminates missed steps, a common problem with stepping motors"

I have to disagree, John. What are you basing that on?John Watkins38670.4001736111

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John Watkins
CNC Guitar Parts

Ed--I get a little confused sometimes on the CAM part. I think the Mach3 is considered the controller software. CAM software would be what converts, for example, a dxf file output from CAD, into Gcode ready for the controller.
I guess VisualMill and Mill Wizard etc. are consider CAM.
Maybe someone can chime in here to clarify this.
Nelson

That's right, Nelson. Mach2/3 is the NC software. Some packages do it all, such as Gibbs or MasterCAM

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John Watkins
CNC Guitar Parts

See guys I told you I was a newbie at all this cnc stuff.

Thanks for the clarification John.

Nelson, please tell us more about the digitizing probe.

Sorry, forgot about the probe.
I use the probe from Maxnc as it's probably one of, if not the, least expensive I've found.
It has a 1/4" shank that is chucked or colleted in the spindle. The single signal wire connects to the input on the controller box. Mach2/3 that John mentions above have a digitizing "Wizard" which allows one to select the size, orientation and origin of the digitizing rectangle in the XY axes as well as the travel speed while digitizing. Other parameters to set within the wizard are Z retract height after each probe cycle as well as the maximum probe depth in case the probe doesn't hit anything going down. The probe cycle moves the spindle/probe over the preset distance and then down until the probe touches the part being digitized. The X, Y and Z coordinates are captured at this point into a text file of your choice. The cycle then repeats up, over and down. At the end of a row of such cycles, the spindle moves over a preset distance and proceeds to do the next row.
So when it's finished with it's rectangular shaped probe pattern, you will have a "point cloud" file showing every point that was probed.
This point cloud can be used as is by adding appropriate header information such as G80, G00 etc. manually to the file.    Or the file may be input into CAM software, such as MasterCAM that can convert it into a surface and then generate various cut paths for machining a part.
Whew! What did I leave out?

[QUOTE=John Watkins]
"which eliminates missed steps, a common problem with stepping motors"

I have to disagree, John. What are you basing that on?[/QUOTE]

I am basing that on the fact that stepper motors run open-loop and will not detect a missed step. There is no feedback. It is part of the design and that is why many machines use servos. Servomotors provide feedback in positioning. Some Hybrids Steppers use a "resolver" type system to get the feedback. I believe that is what the Alpha motors on the Shopbot do.

This will be that last time I mention ShopBot in this forum since John W feels the need to trash them. Yes they do use rack and pinions but not all ball screws are created equal. I have seen some really accurate cuts made on Shopbots. As far a Techno goes, yup nice machine, but they will cost.

I use Rhino for 3d CAD stuff and export it to Mill Wizard for 3D toolpaths (CAM.) MillWizzard appears to generate toolpath formats for about 50 different NC controllers.

MillWizard seems fairly limited, but it is all I have used for 3D and it works quite well. For example a 24 inch wide spherical bowl to match guitar back (or top) radius is easy to generate tool paths for.

Whoa. I think "trash" is a little strong. All I said was that rack and pinion is not as good as a ball screw and that in my opinion that's the weak link in the Shopbot system.

I really don't want to argue about any of this. I'm not here often enough to keep up with a debate.   

But, for anyone who's seriously considering diving into this, I will point out that the inability of a stepper to correct a missed step does not, in itself, mean that missed steps commonly occur. They in fact do not. Most problems that are blamed on missed steps actually have to do with other problems in the system. Further, most missed step problem do not have anything to do with oz/in power.

I'm not trying to be the expert here, I've just had every possible problem and blamed them all on a) not having servos, or b) not having 600 oz/in motors. Neither of those things ever ended up being the problem. John Watkins38670.7394675926

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John Watkins
CNC Guitar Parts

John

I am not trying to get in a arguement either ... it is not worth it. I come to the forums to relax and seldom even have the time to post so when I do, I don't like to get "fired-up."

Regarding drives: rack and pinion may be a weak link in some eyes. On the other hand some ball screws are not that good. I have also heard that ball screws also have problems with dust. By no means I am saying rack and pinion is superior, just that can work quite well. For the sake of letting this go ... let's let it go.

Back to the steppers. I was not saying CNC with steppers miss steps all the time, but stepper motors in general will miss steps. It is in their nature. It may not be a problem in most cases. Heck for "most" of the cutting in guitar work, there is little need for much "power" and if speed is not an issue it should be fine.

Remember this thread was about "Cheap CNCs" and these homemade CNCs are great. In my eyes they are "real" machines whether made of MDF, steel, ball screws steppers or servos. Remember the main idea is to make guitar parts and if these things do it accurately enough, they are quite "real."

Back to the probing post above--should mention that this type of digitizing is mainly for contour work as opposed to probing the perimeter of a part.
Also, going directly from digitizing to machining a part usually requires that the probe tip be the same size and shape as the tip of the cutter that will be used.
Probing is widely used in industry for inspecting parts on a Coordinate Measuring Machine. Part features such as planes and holes are probed to establish their true position.
Might mention that Mach2/3 also has a routine (Gcode?)for probing several points inside of a hole and then establishing the centerline coordinates of that hole. John W. is better versed on Mach2/3 than myself and may be able to shed some light on this.
Nelson

Sorry, Nelson. I don't do any digitizing.

I think the key to effective, low-cost CNC is to do as Ed appears to have done; build the system in as precise and sturdy a manner as you possibly can with whatever materials you've elected to use. Doing this alone will not assure success, but not doing it will surely bring failure.

_________________
John Watkins
CNC Guitar Parts

Hi guys, I just wanted to let you know that I just finished buiding the table, whew! what a job! I built it using 3/4" extira for the bed and torsion box ribs and I used 1/2" ply underneath. I decided to test it's strength and deflection so I enlisted the help of my 15yr old daughter and there was no deflection what so ever! My daughter pretty petite so I decided to go for broke and give it the ultimate test, all 315lbs of me and the deflection was almost unnoticable! I'll post more pictures after I pretty it up a bit with paint.

Hi guys, I will no longer post to this thread but rather I will and have posted pictures and links to videos in the new CNC sub-forum.