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  1. #1
    Join Date
    Mar 2014

    Question Advice Moving From Benchtop (G0704) to VMC

    Hello everyone,

    So I decided to go all in on a Vertical Machining Center - I found a Bridgeport TC3G in fairly good condition that I'll be purchasing and moving into my garage in about 3 weeks. While I don't have any regrets on the machine, I do find it a bit daunting to go from the desktop-class to a 7200 pound machine. Here's my main reasons for moving:
    1. Reliability - For whatever reason between computer freezes, Ethernet Smoothstepper communication issues, wiring shorts, noise, I considered myself lucky to pull off a 2 hour job successfully with my old G0704 CNC. Hoping for some good improvements here, although there is still the chance that I'll need to replace the electronics on the new machine as it's been offline for a number of months.
    2. Rigidity - I performed the Hoss G0704 extension and it lost a good amount of rigidity. I was never really able to get the ballscrew mounts and bearings to work as they should have. Ended up with ~.005" backlash on a good day, which would 'slip' up to 0.045" if something came loose, which was about once a month. I also wasn't ever able to machine with anything larger than 1/4" end mills, and though I attempted some roughing end mills, it just wasn't worth my time. I expect the new (to me) machine to be really solid (sorry for the pun) and support better tools and decent backlash values.
    3. Machine Alignment - Not sure if I'll need to modify this much with the new machine, but trying to get the separate joints aligned to get decent tolerances was a pain. And after every move or crash (don't get me started about the Mach 3 pendant I have that decides to keep going if you change axes in the middle of a move) I had to do it all over again.
    4. Spindle Speed. 8k > 2k. Nuff Said.
    5. Tool Changers - YAYYYYYYYYY!!!!
    6. Coolant - Good flood coolant that doesn't leak and is programmatically turned off and on is super nice!

    So, here's what I'm currently faced with / planning that has me a bit uncomfortable. Any advice here would be welcome.
    • Machine Movement - 7200 pounds is heavy! I'm having it delivered to the house, but I'll be responsible for unloading it and placing it. I'm planning to rent an 8k range forklift (not using the range obviously) to position it correctly. In the US, I'm a bit concerned about how to get the forklift here - I'm about 10 miles away from the rental store in a somewhat rural area - can I just drive it down? I think they'll charge something like $400 for delivery and pickup, which I think is really theft. Anyone have any recommendations? How is this normally done?
    • 3 Phase Converter sizing - The spindle max is 20 amps, machine total at 50 amps max. Converting that to HP, it's like 9 for the Spindle. I doubt that I'll really drive the machine anywhere near max power, let alone max power on all axis at once. I'm planning to get an American Rotary 20HP AF model, which follows the general 2x the spindle power in sizing. On the American Rotary product description, they downsize the ratings by half for CNC machines. The engineer part of me says "Even 10 HP should cover 99% of the use, why do they even sell it at 20 HP if it couldn't take it for brief periods". Really thinking they're just trying to upsell, especially after hearing of others on this forum using smaller converters on decently sized CNC systems.
    • Another converter question - it looks like there's a phase filter of some kind inside the unit - should I be forking out additional money for the digital models of the phase converter to provide cleaner power? If this was a new machine, sure, but is it worth it for a fairly well-used machine?
    • Coolant - I'll need to buy a coolant pump for it. Found a couple of models that I think match online, but I'm having a really hard time finding the mesh filters prior to the coolant. The machine comes with the chip bin, but I don't even know what to search for in regard to the mesh filters. Every 'filter' I found on google is more of a detailed post-coolant in-line filter prior to entering the machine. Any suggestions?
    • Coolant smell - I've had the coolant smell pretty awful in the past. I think this was due to not skimming or leaving the coolant stagnant for too long. There may be some months where I might not use the machine - any tricks to help the coolant not grow bacteria? I saw one that recommended a fish pump to move the water and oxygenate it. Thoughts?
    • Machine Interface - hindsight is 20/20 - or in this case, it's a 3.5" floppy disk. Late 1990's were about 3-5 years too early for the emergence of the USB stick. I've looked online at possible 'digital floppy drives' that partition a USB into multiple emulated floppy drives, but it still doesn't really answer my question - how do you get around files that are bigger than 1.44 MB? Even on my desktop, I swear I've tried to run some files bigger than that.
    • Noise - any recommendations to reduce the noise from one of these machines? I'm thinking about walling off the mill in the garage with fake walls and noise insulation. Any better ideas?
    • How hard can I push this machine? It's fairly basic instinct to drop all the RPMs and feeds recommended in Fusion down to my grizzly G0704 levels. Had some experience in college with a knee mill that was really solid and could handle 4" facing tools and all sorts without blinking twice. I'll probably start light here, but can I go up to full feeds and speed levels?

    Anyway, not sure if this is quite the right forum directory to put it in, but I could use some pointers from anyone with experience here.

  2. #2

    Re: Advice Moving From Benchtop (G0704) to VMC

    your tooling is going to cost more for starters... workholding too

  3. #3
    Join Date
    Dec 2020

    Re: Advice Moving From Benchtop (G0704) to VMC

    If your run a business on the G0704 then yes go up to a Tormach 1100 or even a Hoss machineI don know what the problem is with the G0704 conversion. Mine will hold .001 or so which all I need as a hobby. You do know that the G0704 is a hobby machine and is not built to run much more than 1/2 hour at a time. Yep if need to hang the head out over the table to do bigger jobs. Then move up.

  4. #4
    Join Date
    Aug 2014

    Re: Advice Moving From Benchtop (G0704) to VMC

    I had a Torq Cut 22 which is basically what you're getting just a slightly older model. I have also owned a G0704 CNC. There is no comparison of course.

    The Torq cut I had was a 96 and used for 15 years continuously from what I understood. The only issue I had was an endstop trigger had worn down and I needed to shim it out to ensure it worked still. It had a plastic tip that was half gone so 15 years left? Lol. Mine had a 7500 rpm spindle and was ear splitting loud at that speed. I couldn't stand to be near it over 5000 honestly, something about the controller and frequency of the motor driver relationship, hopefully yours is better but it was common with the Yaskawa I had.

    Now for the good stuff. Mine kept 0.0002" or better on all axis with no compensation. Tested using a brown & sharp 0.0001" DTC. The axis moved at 300 IPM no problem and didn't seem to have any play. Spindle felt smooth and the taper was 0.0001" or better. Surprisingly I could push the head laterally and pickup 0.005"+ worth of flex without straining too hard. Seemed to be the leverage I had to flex the column. I've checked a PM45 and they are similar flexing so big VMC doesn't automatically mean perfect rigidity just enough weight and power behind it to take large cuts albeit not cleanly so finishing passes are still needed.

    As for tooling I picked up 5 CT40 er32 holders for $100 I believe. They would all hit 0.0002 or less runout with good collets or OK collets clocked correctly. IMO TTS is overpriced and not very accurate. I'd suggest BT30 over it any day.

    Another plus was my tc22 was easily rewired for 220v single phase. The Yaskawa drive had no issues doing it without mods though I did remove one of the wires for good measure...can't recall which but I have a thread on here talking about it and the guys in Bridgeport section are a lot of help.

    Sent from my BE2025 using Tapatalk

  5. #5
    Join Date
    Apr 2022

    Re: Advice Moving From Benchtop (G0704) to VMC

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