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IndustryArena Forum > MetalWorking Machines > Benchtop Machines > New CNC Project for University Research
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  1. #1
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    New CNC Project for University Research

    Hi. I have been tasked with putting together a CNC milling machine for research at my university. The real meat of the research will be measuring forces and determining tool life while machining as well as integrating STEP-NC. Everything in the project is supposed to be open source. Right now we're planning on using LinuxCNC along with Mesa electronics and stepper motors probably driven by a gecko brand drive. We are thinking that the best route will be to buy a manual mill and convert it to CNC. Lead time is an issue as the machine must be operational by mid December. I have been looking at the Grizzly G0704 and G0619. Since the project is not centered around building the mill, I would like to find an option where I can just slap some steppers on a mill and begin cutting. I have experience with Taig mills but I would be concerned about their rigidity. The budget for the machine is $4-5k USD. We have serious reservations against buying used equipment or equipment without warranties. We intend on spending a minimal amount of time assembling the mill initially. Hopefully as the research progresses we will get more funding and can switch over to servos and nicer ball screws etc.

    Initially we will not be doing any high speed machining, does this mean I can avoid installing a new ball screw on the G0704?

    We will need fine control over spindle speed from LinuxCNC. The 2250 rpm of the G0704 will probably not cut it.(hah) How easy is it to upgrade the spindle / motor? We will primarily be cutting aluminum.

    I'm sure I had other questions but I can't think of them right now. I intend on documenting the process and sharing it.

    Thanks

  2. #2
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    Re: New CNC Project for University Research

    I did not read anything about HOW you plan to measure forces.

    I think there will have to be some serious changes to the machine to measure forces at the tool tip.

    Don

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    Re: New CNC Project for University Research

    Got me. The easiest sensor to include will be a power monitor and tachometer/encoder for the spindle. I assume a platter type dynamometer would be sufficient for measuring other forces. I have no experience with these but it should just secure to the table with T-slot hardware. I haven't done much research on the measurement side of things yet. The budget for machine + sensors is $8.5k USD.

  4. #4
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    Re: New CNC Project for University Research

    If time is an issue, you might rethink the Mesa electronics - last I heard they were taking 4-6 weeks to fill orders, and that's when they responded at all: http://www.cnczone.com/forums/linuxc...ectronics.html

    Most people retrofitting G0704s change out the leadscrews to get rid of backlash and slop; it's not just necessary for high-speed machining. But cheap ballscrews just introduce more inaccuracy. If you do this, get good ground ballscrews, not rolled ones.

    The spindle, as you point out, is slow, with considerable runout; this will impact tool life, especially smaller tools where the runout is a large fraction of the diameter. Fine control of the speed will require hacking into the speed controller, which is set up to use a potentiometer to control the DC motor. The other alternative would be to swap out the spindle motor for a 3-phase motor controlled with a VFD, which you can control from LinuxCNC.

    If the idea is to start with a mill that you just have to slap some steppers on and be ready to go; the Taig would be a better choice (although you'd still have to swap out the spindle motor). Converting manual mills to CNC often takes a lot longer than anticipated, as many here can attest...
    Andrew Werby
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  5. #5
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    Re: New CNC Project for University Research

    Thanks for the info. The Taig did seem like a good choice but the small size and light weight worries me. There's a CNC Taig mill where I work that we use for mold finishing. It's pretty nice when you're not trying to move lots of material. I will have to find out if we can use such a small mill. Do you know what their lead times are like?

    I also use a Smithy 1240 CNC at work which is the size I'm looking for. It's a medium sized stepper based mill similar to a Tormach. Are there any machines like this (stepper driven) that are sold without controllers? Or with a controller but cheap enough and easy to interface with LinuxCNC?

  6. #6
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    Re: New CNC Project for University Research

    The tormach 440 is listed right at $5k and is a turn key mill. not sure when the release date is, but might be worth looking into.

    Also, the taig mill is a great little mill. I have one that i have filled the base and column with epoxy granite, and added a brace for the z column. its surprisingly rigid for its size.

  7. #7
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    Re: New CNC Project for University Research

    Ah that's a good idea. I was worried about its weight. Have you done anything with the spindle? I'd like to have something at least 1/2 or 3/4 HP and variable speed.

    Also where do you see the 440 for $5k? Their website says $7k. That would be a good choice at $5k as long as the software and controller is open source enough that we can interface with it. The project is on implementing STEP-NC.

  8. #8
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    Re: New CNC Project for University Research

    Yes i have upgraded the spindle motor and pulleys. I'm using a treadmill 2hp motor and mc60 controller with a single timing belt.It's now controlled with mach3 as well.

    I keep seeing adds on this forum for a preorder of only $5k.

  9. #9
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    Re: New CNC Project for University Research

    found the tormach mill pricing in the FAQ:

    "Only the packages are available for pre-order, but mill only purchasing will be possible in the future. The base price of the PCNC 440 is $4950."

  10. #10
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    Re: New CNC Project for University Research

    Taig has been shipping mills pretty quickly of late; they just about always ship within a week of ordering. But a 1/2 hp motor would be a bit heavy for them; that's why they use 1/4 hp motors. Why do you need such a big motor?
    Andrew Werby
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  11. #11
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    Re: New CNC Project for University Research

    I don't know that we need all the horsepower but we will need to control spindle speed through the software. I'll have to ask the key stakeholders in the project if they really need more HP or not. I assumed if we were going to find a motor to use with a VFD we might as well find a beefier one.

    Edit: And yes, I emailed Taig and they estimated delivery within 7 business days.

  12. #12
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    Re: New CNC Project for University Research

    Take a look at some of the Chinese spindles; they seem popular here. They range up to 2.2 kw and are controlled by a VFD. They would be lighter than the standard Taig motors. You can easily make a dovetail mount for one that would interface with the standard Taig mount plate, so you could slide off the regular spindle assembly and substitute the high-speed one. Here's a company that imports them, who checks them out, programs the VFDs and stands by the ones they sell: CNC SPINDLES
    Andrew Werby
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