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G0678 CNC Conversion Build Log

Posted: Fri Nov 24, 2017 3:04 pm
by Dave_C
I bit the bullet today and ordered a Grizzly G0678 Mill for the purpose of converting it to a Centroid Acorn CNC mill.

The mill won't be here until mid December of 2017 so stayed tuned. I'll post as much detail as I can so others can do the same or a similar project as well. For those who have done these, you'll be bored but for those who haven't, you can see how one is done from the ground up. Feel free to ask, why did you do it that way, and we can discuss.

The next big decision is do I go with closed loop steppers (like I used on the lathe project), Clearpath closed loop servos or DMM closed loop servos. Each one has its own charms and drawbacks.

Thoughts?

Dave C.

Re: G0678 CNC Conversion Build Log

Posted: Sat Nov 25, 2017 6:54 am
by BClemens
That's an excellent mill to convert to CNC. I converted the Enco version of that mill with ball screws and fabricated the antibacklash ball nuts for it. I used Litton servo motors with encoders - (used Mach3). The headstock was a bit of a chore figuring a way to counterweight the spindle so it wasn't hanging on the motor - used a flat wound spring. This mill has been a joy to operate. Don't know how I got along without it.

This one had the step pully arrangement on the headstock so I replaced the motor with a three phase and used a VFD - works great. It's controlled by the operating system for speed but still have the ability to change the belts too. (Use Accu Link belts - much smoother operation)

I'll watch your build log and 'kick in' now and then. I took many photos while converting and still have some of the build data and drawings if you may need assistance.
BC

Re: G0678 CNC Conversion Build Log

Posted: Wed Dec 06, 2017 7:01 pm
by Dave_C
Oh boy! Grizzly called today, the mill is here. So off to the warehouse to pay for it, over to U-Haul to rent the truck, back to the warehouse to load the mill then home to disassemble as much of the weight as possible so the wife and I can get it into the garage for now.

2 1/2 hours later, the mill is in the garage! I'm actually pretty impressed with this mill as I see hand scrapped ways when I took the table off!

Lots of cleaning to do so the disassemble with make that a lot easier.

Step 1 is done, just getting this part done was a major accomplishemnt.

Step 2, stop and have some coffee!

Step 3, now move all the parts to the shop, but no rush, no truck to return, plenty of time and many methods and tools available.

Re: G0678 CNC Conversion Build Log

Posted: Sun Dec 10, 2017 1:46 pm
by Dave_C
Moving day!

The wife and I were able to move the last of the mill into the shop today with the help of my home made low boy cart and the lawn mower. Then just lifted it off of the cart and placed it in its new home.

Now to start the cleaning and reassembly with all the new modifications that will make it CNC.

Almost time to order the Acorn as the control panel is well on its way to being together!

Later,

Dave C.

Re: G0678 CNC Conversion Build Log

Posted: Tue Dec 12, 2017 11:16 am
by Dave_C
Short video mainly showing work on the control panel!

https://youtu.be/DeBQihMp2Pc

Dave C.

Re: G0678 CNC Conversion Build Log

Posted: Wed Dec 13, 2017 12:57 am
by BClemens
Centroid Acorn is interesting..... If that had been offered back when this machine was converted it would have no doubt been the choice - after some study. Mach 3 has been fine for the machining operations accomplished with the machine - it is a small milling machine to be sure. I have often wished that I had converted my 'Baby Bridgeport' since it is much more robust with lots more table and travel.
I was never a fan of stepper moters. Going to a commercial CNC operating system then using steppers seems a step backwards IMO.
The quill should be Z axis and is somewhat short in travel but that is compensated for in the programming - most all contour machinging is done in steps anyhow.
Is the spindle speed control on the machine controllable from the operating system? Like a variable 0 to 10 volt control voltage...

Re: G0678 CNC Conversion Build Log

Posted: Wed Dec 13, 2017 9:53 am
by Dave_C
Yes the drive will uses 0-10 vdc control. The 4" quill stroke is not an issue for me as the knee has 20" from spindle nose to table. I'm not actually using "steppers" as they are called "hybrid servos" and are closed loop. I've used them before and they are fast, quite and accurate. They have dropped in price from $500 for a 1,200 oz in to around $200 for both the motor and the drive.

Sure I can throw thousands of dollars at DMM servos or Clearpath servos but the clearpath motors are somewhat slower in rpm and don't have the constant torque the hybrid has.

I bought all three axis for around $600 and you'll pay that or more for one motor from clearpath or DMM. And for a home hobbyist, it just doesn't make sense to me.

IF it were just ordinary steppers, I'd say it was a step backward as well but then Tormach is still using just ordinary steppers and they are selling tons of the PCNC1100's!

Dealers choice I suppose,

Dave C.

Re: G0678 CNC Conversion Build Log

Posted: Wed Dec 13, 2017 12:47 pm
by BClemens
Sounds like you have a pretty good handle on what you're doing. Do you have a plan for your ball screws and nuts? I modified a couple of simple ball nuts into preloaded ones using belleville springs on threaded collars keyed to the nut housing blocks. This sort of stuff may be more reasonable now than back then but that saved a good bit.
Something to keep in mind: coolant. The machine is not really set up for flood coolant nor even mist. If you keep that in mind as you build your machine you can make it ready for coolant without having to take it back apart. Seal the bearing housings on the table ends as it goes back together. I use mist coolant often and it is a mess after making a lengthy run. It is mighty nice to be able to walk away from the machine during the contour machining of a steel part instead of dabbing a brush at the cutter and blowing chips. But then they are mesmerizing to watch....
Keep up the grand work...and I'm certain that you will never regret the time involved in completing your mill conversion.
BC

Re: G0678 CNC Conversion Build Log

Posted: Wed Dec 13, 2017 1:07 pm
by Dave_C
I did the same thing on the lathe conversion with the belleville washers, and it worked like a charm. Pain to do but I had some space limitations and nothing I could buy commercially would fit. So necessity was the father of invention! This time I'm buying zero backlash nuts and all I have to do is make the ball nut Carriers and possibly remake the table ends as the center line height will most like be different.

Coolant, yes, this is going to be a bit of a challenge but I won't have to take it back apart to do what I am thinking about doing. It will be the last part of the conversion. I'll play with little items for months even after it is so called "finished".

Right now I'm on hold waiting for some small pieces to complete the control cabinet. Once I have that done I can start by breaking in the spindle and then on to the conversion. I'll actually get the X and Y axis working and run the quill by hand to make some parts that need arcs on them.

Coffee time!

Dave C.

Re: G0678 CNC Conversion Build Log

Posted: Wed Dec 13, 2017 3:49 pm
by BClemens
Dave,
Check the spindle housing front slot. There's an antirotation 'key block' bolted to the spindle riding in that slot. I found that the slot was not axial with the spindle nor did key fit the slot so the spindle could also 'dance' around in that slot - any cutter chatter could have set it off....I set up the housing on the mill and enlarged the slot to align it with the spindle then made a new key piece. That may not concern you but I did a lot of work on the headstock and wanted it correct. I'll dig out the headstock photos just to let you see how an old fart did it back a number of years (about 2008)....((and it has worked OK. bragging is quick death to a project so stand back)) I used that key piece to fasten the ball nut for Z axis. - So the reason for finding the slot misalignment was sort of by accident while machining the Z ball screw bearing block mounting pads.

You're right; these projects go on for as long as you can see a better way....

The white painted machines are grand looking - until you get more interested in machine work than the wipe downs. My big lathe and a mill are Jet white.... or used to be.... Heaven forbid ever dropping some dainty little part down into the lathe chip pan...I thought about enclosing the mill table in a plexiglass box with a big funnel at the bottom for a coolant anti-mess container - never did it.

Martini time!

Bill C.

Re: G0678 CNC Conversion Build Log

Posted: Wed Dec 13, 2017 6:14 pm
by Dave_C
Bill,

We are on the same page! I've already seen the slot problem and I plan on solving it just like you did. The anti rotation block has to come out and I will remake a new one to hold the ball nut for the quill.

The head will go to the other mill table and get the "ears" milled down so that the front is flat. Then there will be a mounting base plate with some parts to hold the Z axis motor and limit switches. Much like the design of the Route 66 compu-cut system except I don't plan on having a disconnect screw like the Route 66 system.

Same idea though to drive the quill up and down with the ball screw.

Just needs a little TLC and some planning! Thanks for your input and feedback.

Dave C.

Re: G0678 CNC Conversion Build Log

Posted: Fri Dec 22, 2017 10:13 am
by Dave_C
Progress:

My Adorn board arrived yesterday afternoon! I laid it all out, got familiar with it and this morning I downloaded the software from the web site to my PC (laptop actually) and ran the bench test.

The MPU updated (re-booted) and all sample programs ran as expected!

I watched the centroid setup video twice just to be sure of what to expect, no surprises there and it was very easy to do.

I don't plan on running the Mill on this PC but it is more than capable, it has two Ethernet connections (one wireless and one wired) 16 Gigs of memory plus touch screen. (quad core processor)

So today if my dual voltage power supply comes in from Jameco, I'll get the rest of the wiring done and put the control panel in the control box on the wall.

THEN I can start to make parts for the ball screw mounts. I like having my electronics all done and tested before I start hooking up motors to a machine. I like to be able to install, test, move and so on before I go on to the next step.

So far, so good! it will be awhile before I get any more done!

Dave C.