Size of CNC Router to make

[sdantonio]

Hi,

The first thing I have to decide on is the size of machine to make. I have plans for the HobbyCNC and the JGRO machines. I was planning on building 2 machines eventually, a small hobbyCNC and a larger JGRO.

My applications. I am a violin maker (all insturments of the violin family and guitars). I envision the HobbyCNC fixed with a dremel mototool router to do fine applications like mothor or pearl inlays (see link below for a guitar fingerboard). The carving would involve typically cutting a 2mm depresson into the wood and cutting out the parts in mother of pearl.



I envision the JGRO machine with a 2ft X 4ft bed, fixed with a 2 or 3 hp router to carve the backs and tops of instruments. In the worst case this would involve carving a piece of maple about 24" X 48" X 2" down to a shell (like a soup bowl) of about 7mm thick (double bass instruments).

I suppose the first question to ask is: Is it worth building 2 machines or should I just build the large one and use it with the two different routers?

All the electronics can easily be swapped from one machine to the other, so there is not much extra expence here and most of the HobbyCNC parts I already have laying around the house (including the steppers).

Thank you for your input on this. I assume more questions will follow as I start building.

Steven

[Lionclaw]

You'd be looking at quite a hassle to switch out the electronics between the two machines. I'd opt for one large machine. If you build it stiff enough it will do the fine inlays just fine.

[2muchstuff]

I'm with Lionclaw on this one. Take your time and build it the way you want to suite your needs. There are several people here that have the capability to swap routers heads out.

[sdantonio]

Hi Andy (Lionclaw),

Thanks. I was thinking of the computer, stepper controller and power supplies as stand alone boxes with long cables going off the the stepper motors. Couldn't one set of steppers (one router) just be swapped out for the other set (the other router) by dusconnecting the three sets of cable bundles?. Remember, I'm a rank amature beginner here and may be asking a dumb question. But this setup does sort of seem logical to me. Or is there a whole initialization and calibration thing that I am missing in my thinking?

[sol]

It is relatively easy to switch out machines if plugs are used for the connections. Mach2 allows for setting up and opening in different configurations so the dual machine idea is workable. I do it with my machines. However the machines will need to use similar steppers if the same controllers are used since the controllers have to be adjusted to match the steppers, and that process is something that no one wants to do on every switch over.

That said, it is a tough call on the two machines. A large one with quality components that can do fine inlay will easily be well over $1000. If the larger one does not need the precision why pay for it?
A smaller machine that can carve that kind of detail will cost much less and its smaller size will also eliminate some of the flex that is endemic to homebrews.

However, I suspect that both of the plans you mentioned, if built as drawn, will not satisfy the perfectionism that runs in the instrument building profession.

[jeffs555]

I don't think I would plan on using one stepper controller and switching it between two machines. Most of the plug type connectors are just not designed for constant plugging and unplugging. They will wear out quickly. Also, if you ever forget, and unplug it with the power still on, the voltage spikes can kill the controller.

[carlnpa]

I don't think the JGRO machine will meet your accuracy needs. I built one and am still chasing accuracy, the frame is not that rigid and the roller bearing is very hard to set up. I have a K2 3925 with servos, it will meet your accuracy needs with some modification to strengthen the frame, cost wise will go over $5K. I'm working on a new design using aluminum extrusions and milled UHMW bearings that should address many of the JGRO issues.
Just build one machine unless space is at a premium for you. You will develop a feel for the single machine that will allow you to be much more productive.

[sdantonio]

Hi Carlnpa,

Have you seen JGRO's modifications to his second machine (the first was desrtoyed in a flood). He is using oil impregnated bushings instead of the roller bearings and a 1" tube steel frame with steel angle crossmembers for support. It's bolted, not welded. I am planning something similar, but welded.

Their on his personal web site, not on the drawings.

[carlnpa]

Instead of multiple posting I'll put some pictures of my mods in my thread in the JGRO section. The idea seems to work but the machine is not all back together yet.