Build Thread - Chevalier 2040 CNC Bed Mill

[Coolidge62]

Pressed pause on the mill this week to rewire the whole shop. Since I had to run several new circuits for the mill and RPC it was easier to just rip out the old stuff and start over. 9 new circuits total, new shop lights, 110vac outlets the works and no more cords across the floor!

In mill news the rather LARGE breaking resistor arrived today. The Maxi Torque Rite power drawbar also showed up this week.

[Coolidge62]

Major progress made here are some build details...

I paused on the mill to deal with power and decided to just redo the whole shop to address some other shortcomings. Installed 6 new LED shop lights at 20k lumens each now I can see to infinity! For the mill I'm running a 40amp 220vac to for the spindle motor VFD and the entire 3ph output of the 15hp American Rotary. Given the 6awg wire I decided to back up and go 1 inch trade conduit vs trying to cram it through 3/4 inch and a much larger box so that's still in progress. I also ran a dedicated 20 amp 110vac out to the mill for the Acorn stuff, computer, monitor, etc. While I was at it I ran a 20 amp 220vac all the way across to the lathe so no more cords on the floors.

[Coolidge62]

The 5hp Maraton Motors Black Max inverter is now installed with the direct drive 8P 30mm timing pulleys and belt (Gates GT4). I also got the Z Clearpath 2.5hp AC servo motor installed. The Maxi Torque-Rite power drawbar, the new head side vents and quill arm.

[Coolidge62]

Build details...

Here's the B&B Mfg taper lock pulley installed on the spindle. Fortunately in the Chevalier parts manual for this mill they also had a parts view of the direct drive inverter version of the mill, it looks exactly like this including the brake drum.

Here's the underside of the spindle motor adapter plate. I had to center up the head casting on the small mill and machine some clearance for the bolt heads. These feed up through the adapter plate into the motor. As you can probably guess working upside down, in tight quarters with my large man hands was NOT fun. Getting these bolts started (ditto for the Z servo only more so) took 3 hours when this whole job should have taken about 30 minutes. But it's done!

Here's the adapter plate for the Z servo. These Clearpath AC servos are much larger in diameter than the original SEM's so designing an adapter was a bit of a head scratcher.

This is the spacer for the Z servo, required to clear the rather large, thick and heavily radiused brim on the face of the servo so the servo motor sits flat on the adapter plate. This will have to be delt with on X and Y also.

Here's the servo installed.

The large NMTB #40 taper quill emerges, seeing no PREY to feed on it went back into it's quill cave.

[Coolidge62]

Powered up the small mill and made spindle drive dogs from some hardened 4140 bar stock. I would have preferred to just buy them but nobody seems to sell them.

[richardb15]

Looking great, have you sorted out what to do about mounting the spindle encoder?

[Coolidge62]

Looking great, have you sorted out what to do about mounting the spindle encoder?

It's looking like that won't be required. Acorn confirmed their software/board accommodates the 2nd reduced low speed range. The Marathon Black Max spindle motor has a reduced diameter rear shaft for an encoder and I'm running a 1 to 1 timing pulley between the motor and spindle so motor rpm = spindle rpm. But I have not looked into it further than this.

Someone else familiar with this specific motor was saying the other day I would likely not need the low speed range for tapping except in an extreme case so I looked up the motor torque, it's like 74 ft-lbs before RPM falls off.

On a side note I did a rough calculation based on the top RPM of each range for this mill, it looks like the reduction is 8.333 to 1.

[Muzzer]

On a side note I did a rough calculation based on the top RPM of each range for this mill, it looks like the reduction is 8.333 to 1.

You should be able to do an exact calculation now that you have toothed belt primary drive and a fixed backgear ratio. However, you still have the question of how to generate an index pulse for each revolution of the spindle if you are in low ratio, if 1:1 doesn't provide enough torque. The canned tapping cycle will wait until it sees the index pulse before it starts the move. Without it, the cycle will never start and the tap will sit spinning above the hole for eternity.

An induction motor generates torque proportional to the slip speed ie it spins at close to synchronous speed under zero torque (1800 rpm for a 60Hz, 4 pole machine), falling to ~1750rpm at rated torque. That's around 3% drop in speed between no load and full load. Equally, the inverter will need to be generating a rotating field (slip speed) of around 50rpm to generate rated torque at 0rpm. Some inverters can compensate for that characteristic to some extent but it's another factor to bear in mind when comparing induction motors and servo motors. I'm not suggesting this would be a problem but hopefully helps in understanding how they differ.

[cncsnw]

Tapping in low range will work, as long as you do not attempt to use peck tapping or otherwise re-tap the same hole.

Each tapping cycle will begin feeding when a motor encoder index pulse comes around. In high range, that will be once per spindle turn. In low range, that will be approximately every 43 degrees of spindle rotation (effectively random).

[cnckeith]

super nice to see the quality rebuilding and upgrading going on here in this thread.

we threadmill everything down to 3/8" anymore.