[fastbike]

I have an Emco F3 mill which I am planning to convert to CNS.

Does anybody have any links or experience in how hard this will be to do. I am a CNC newbie, although learning fast, and have OK hobbiest machining skills.

[fastbike]

I've just seen another thread, which looks like a similar project.

My first job is to replace the Y axis leadscrew with a ballscrew and stepper, and control this via a jogger switch and driver.

To progress this, I've removed all the bolted on panels etc on the gearbox, and removed the quill assembly and motor.

My next job will be to remove the gearbox from the machine to access the Y axis handwheel assembly so I can remove the Y axis leadscrew/handwheel pinion.

To attach the ballscrew to the chassis I will need to fabricate a bracket that attaches the thrust end of the ballscrew to where the current leadscrew/pinion is located, and then drive the ballscrew from the other end. So, I can't disassemble too much at this stage as I need the mill working to fabricate these brackets

[fastbike]

I've been out to the workshop again and measured the offsets between the existing leadscrew centre, and the 4 bolt holes in the gearhead assembly. This is where the leadscrew nut attached and gives the layout for the new ballnut bracket that will need to be fabricated.

The existing acme leadscrew, which is 20mm diam, rotates and is located with a thrust bearing set into the mill chassis. This is retained with a threaded collar with 4 small holes - I unthreaded this with a punch (although a pin spanner would be more appropriate). The bearing is 42mm diam x 26mm deep. Internal diam matches the shaft of the leadscrew.

[fastbike]

A bit more progress today. I can source a 20mm x 4mm ground ballscrew from ebay. I have found an really useful spreadsheet to help on motor sizing so that is the next task: figure out motor, belt drive and stepper driver.

Then I can fabricate brackets to mount all of this. I have two mounting plans I working around with:
- the first uses the existing bearing housing in the chassis to mount the fixed end of the ballscrew, with the ball nut attached to the gearhead assembly. The disadvantage is that the ballscrew will need to be driven from the other (supported) end which is outboard of the chassis so a substantial bracket will be required to support the motor / resists torque etc
- the second idea is to mount the ball nut to the chassis and the screw fixed end support to the gearhead. This will require a bit of rework on the chassis although provides easier / closer mounting of the motor.
Time for some sketches / pictures tomorrow.

[fastbike]

Progress. I've figured out the performance and loads the motor will see and have ordered 4.5NM Nema34 closed loop stepper motor and driver today from StepperOnline.

I'm still investigating the various ways of mounting. I've come up with a third method which is to use the existing machined bearing housing in the chassis to mount the fixed end of the ballscrew, the other end being unsupported.. The ballnut will be attached to the sliding gearhead with an alloy bracket. I will need to fabricate and attach an extension shaft to the fixed end of the ballscrew and drive the ballscrew via the extension.

[fastbike]

Progress. I've figured out the performance and loads the motor will see and have ordered 4.5NM Nema34 closed loop stepper motor and driver today from StepperOnline.

I'm still investigating the various ways of mounting. I've come up with a third method which is to use the existing machined bearing housing in the chassis to mount the fixed end of the ballscrew, the other end being unsupported.. The ballnut will be attached to the sliding gearhead with an alloy bracket. I will need to fabricate and attach an extension shaft to the fixed end of the ballscrew and drive the ballscrew via the extension.

Unfortunately this method is not available as there is insufficient clearance for the shaft pulley inside the chassis.

An alternative would be to use a mitre gear on the end of the ballscrew shaft. This would need to be sized and positioned to engage with the mitre gear on the existing hand-wheel axle. Obviously the hand-wheel will be removed
So more investigation is required - in particular finding the correct size of the mitre gear and ensuring any backlash is acceptable. (NB mitre gear is a specialised form of as bevel gear with a 1:1 ratio)

[fastbike]

There is approx 1.5mm clearance between the endplate and the pulley. The pulley surface itself is 20mm wide for the 15mm wide belt so there should be no problem with the belt rubbing on the end plate.

Attachment 402828

[fastbike]

The 25 tooth motor pulley arrived from SDP/SI today I'll see how I get on cutting a 5mm keyway this weekend. I plan to use the Lathe to cut the keyway

[fastbike]

I enlarged the bore in the pulley yesterday, by mounting the pulley in the lathe in a 4 jaw chuck and dialling it in to get it centred. I then drilled it out - first to 13mm - and used an undersize 14mm drill, followed by a 14mm reamer to get it to be a friction fit onto the motor shaft.

[fastbike]

Today I cut a keyway in the pulley to fit the 5mm key on the motor shaft. I started using the lathe method and finished in the vise.
Attachment 403178
The keyway is a little deep at the end of the pulley but the key is a nice firm fit, and the pulley is located onto the shaft with two grub screws.

Next job is to buy some M8 bolts tomorrow and cut the spacers between the motor plate and the ballscrew endplate. I will use 20mm hex bar and bore the centres through to fit the M8 bolts.

[fastbike]

I'm waiting for some steel and bolts to arrive to finish the mechanical part of the Y axis. So in the meantime I will install Arduino for Linux on my laptop. Prior to full CNC, I plan to control the Y axis manually using two buttons (forward and back) and a potentiometer to control speed. This will send pulse and dir commands to the stepper driver.

Example 5 from the this page shows the Arduino sketch required. I will need to add limit switches as well.

[fastbike]

The 20mm dia rod that I need to make the stand offs between the ball-screw end plate and the motor mount plate arrived on Friday. I've made 4x stand offs and fitted the drive belt. Photos to follow tomorrow.

[fastbike]

I purchased the bolts I needed to finish the Y Axis conversion. This included longer M8 bolts to replace those holding the ballnut to the moving carriage, and stainless mushroom style socket screws that hold the sheet metal panels, and M6 bolts to secure the motor to the motor mounting plate.

Yesterday I cut 4 spacers from 20mm round bar, on the lathe. I centre drilled them to 8mm so the fastening bolts pass through.

Here is a photo of the motor with the belt installed - you can see the belt running over the 50T ballscrew pulley.
Attachment 404456

Here is a photo showing the mill from the back with the motor installed.

[fastbike]

The motor is from Steppers Online and is a closed loop stepper with 4.5Nm torque in a Nema34 frame. This came as a kit with a matching driver.

[fastbike]

So I got busy with a soldering iron yesterday. I mounted 5 switches and a potentiometer into a plastic case and soldered on flying leads for the arduino. There are two sets of switches: one for fwd/reverse for the Y Axis (and one for fwd/reverse for a future X Axis control) and a stop button laid out in a "+" formation. The potentiometer is the speed controller.

Tonight I will program the Arduino and mount it in the box and connect to the stepper driver. There are 4 signal wires (2x GND plus direction and pulse) to connect between the arduino/switchbox and the driver.
In addition, there are 4 motor winding wires and 6 motor feedback wires to connect between the motor and the driver. I will use my 60V 5A bench power supply to provide a temporary power supply for the stepper/driver.

Fingers crossed I might have some motion in the Y Axis tonight

[fastbike]

So I connected the motor feedback wires to the driver last night. This cable from the motor was terminated in a 3 row DB15 male connector, much like an old style VGA connector. As the cable is way too short (approx 300mm), I cut off the VGA connector and directly terminated the wires into the 6 way phoenix style connector. I'll need to source some 6 core shielded cable for a longer permanent connection but this works at the moment.

:banana: Anyway it was successful. I can now drive the Y Axis backwards and forwards and control the speed.:banana:

Next up is making mounts for the limit switches and fitting these to the mill and the associated mods to the software.

[fastbike]

And a small video - if the link works
https://photos.app.goo.gl/Zd4qtr3n6CbXQztF6

[fastbike]

So a little more diagnostic and exploratory work tonight.
With the power supply set to 60VDC I measured 800mA current for traversal of the mill head at 900mm/min. That is when it is not cutting, so more measurements over the weekend to see the current draw when cutting.

Also the driver unit is marked for setting the 4 DIP switches to set the step resolution.
Attachment 404624

However the documentation supplied with the driver is different
Attachment 404626

It looks like somebody forgot about zeroes when writing up the doc.

Also the default setting is not 200 steps per revolution, from the time I measured for traversing 200mm it seemed closer to 400 steps/rev.

The formula for steps per second is:
speed (mm/min) / leadscrew pitch (mm) * steps per revolution / seconds per minute

In this case I have chosen 800 steps per revolution so this becomes
900 (mm/min) / 4(mm) * 800 (steps/rev) / 60 (secs/min) *2(gearing ratio)
= 6,000 steps per second

The Arduino Uno CPU is not capable of driving much above this speed.

[fastbike]

So I made a limit switch cam and mounted it on the ballscrew adapter today. I also mounted the two limit switches onto the frame. The limit switches are snap action NC micro switches - part #854-1966 from RS Components.
Still to do is the wiring up of the limit switches to the Arduino and altering the sketch code to ensure the stepper stops when the limit switch opens. Two digital inputs will be required so the motor can still reverse.
More photos tomorrow.

[fastbike]

Photo of limit switches and cam