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.
Printable View
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.
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 :)
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.
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.
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)
I've pulled the existing handwheel / leadscrew combination apart. It uses two helical/screw gears crossing at 90 degrees to transmit the handwheel rotation to the leadscrew.
The gears are metric, mod 3 with 11 teeth, giving a pitch diameter of 33mm. The teeth are 16mm long. The leadscrew gear is keyed to the shaft and secured with a washer/lock nut. The handwheel gear is pinned through a hub to its shaft.
There won't be very many that have converted your machine F3 Mill, getting the machine parts done will be the hardest part, the electronics should be quite straight forward
Any type of gears will have backlash, if you can change them for PowerGrip GT2 or PowerGrip GT3 Pulleys 5mm pitch you would be a lot better off
Thanks for the help. I was coming to that conclusion when researching more info on gears and how to remove the backlash - not an easy task or one that I think I could achieve.
So back to an earlier plan to mount the fixed end in a pair of back to back bearings in the existing housing in the mill chassis, and drive the screw from the supported end via a belt/pulley arrangement.
I got to spend a few hours over the weekend and turned down the supported end of the ballscrew (THK BIF 2004 ground ballscrew travel 257mm) as it was 30mm too long. I first attached the ballnut with tape to ensure it would not move and no chips/dust could get in, and then used the bench grinder to remove the hardened layer so I could turn it with a carbide insert. Luckily the screw had originally been turned between centres so it was an easy job to get it centred in the lathe and relatively straight forward to turn a 15mm diameter for mounting the ball bearing.
So there are a few mechanical parts to make to connect the ballscrew to the sliding head, and to support the far end of the ballscrew/motor.
The connection between the nut and the sliding head, looks like this in CAD
Attachment 401786
and after a bit of work at the mill like this (cut out of 12mm CRS,faced with a fly cutter on the side that contacts the ballnut flange an
Attachment 401788
So a little bit of downtime as I have other commitments that need to be fulfilled. In the interim I am starting prelim work on the power supply design. The machine is powered by a 3 phase 400V AC supply. I need something in the range of 60-70V DC for the motors and a lower voltage supply for the electronics.
I'm currently investigating a design using a 3 phase step down transformer along with a 3 phase bridge rectifier to supply the required power rails.
You could take ( 1 ) leg and neutral and Ground and use a single phase Transformer to get your 70V DC a much easier way to do it
Have a look at this company for a 70v DC supply you may have something similar in NZ AnTek Products Corp
Thanks for the link. I'm still just at the research stage for this part of the project.
The 3 phase power is supplied via a 3wire plus earth cable - no neutral is available in the machine so the easy way of tapping one line and neutral is not available.
I did find this prebuilt power supply though on the local Farnell/Element14 site. - will deliver 48V which might do in a pinch.
https://nz.element14.com/xp-power/dn...48v/dp/1634807
In the interim I will see if I can get a 3 phase step down transformer locally - and compare costs.
More chip making today :)
I designed a backplate which will attach the ballscrew support frame to the back of the mill.
From this on the computer
Attachment 402056
To this (fabricated from 12mm CRS)
Attachment 402058
I found some more time this weekend to progress with making the mechanical components required.
First off I remade the backplate as the hole for the shaft was misaligned by 1mm and I also decreased the clearance between the sliding head and the plate, to increase the mount of material left.
I also made a small 10mm thick spacer plate to fit between the sliding head and the ballnut bracket.
Next job was finishing the design of the ballscrew endplate and the motor mounting plate.
The endplate holds the support bearing for the ballscrew and looks like this in QCAD ...
Attachment 402678
The motor mounting plate will be mounted approx 20mm behind the end plate and the space between contains the drive pulleys and belt, and is attached to the end plate with spacers and M8 bolts. In QCAD it looks like this ...
Attachment 402680
These two parts are made from 12mm CRS. First step is to cut to rough size on the saw and then mill to 10mm thickness, before milling the edges to the final size and then drilling / boring the required holes (Would be a bit faster on a CNC mill - oh the irony :)
The end plate and motor plates now looks like this ...
Attachment 402682
(Spot the mistake on the end plate)
At this point we are finally ready for a trial fit on the machine.
Attachment 402684
Attachment 402686
This also allowed measurement, cutting and test fitting of the 40x40x3 equal angle steel that will connect the backplate and the endplate together.
Attachment 402688
I've run out of time this weekend. Looking forward, my next task is to remove all the parts, grind off any scale and rust and then reassemble and clamp in place so it can be TIG tacked before removing again for welding.
The motor pulley arrives this week, so upcoming tasks will be to mount the pulleys to the motor and ballscrew shafts, cut the frame spacers, paint the frame and then a final assemble before tackling the electronics.
Got the frame welded, and aligned, tonight. There are no photos but the ballscrew with the sliding head attached moves freely all the way along its travel (which is now 225mm compared to 200 on the original Y axis).
Hopefully I can get more work done at the end of the week - with the next job being to attach the pulleys to the shafts.
The motor pulley is 25T with a 12 mm bore which will need boring out to 14mm and a keyway cut to fit the motor shaft.
The ballscrew pulley is 50T with a 12mm bore. Either I need to turn the end of the ballscrew shaft down to fit or bore the pulley to fit the 15mm shaft. Either way I'm still figuring out whether to use the two grub screws, or whether to cut a keyway in the shaft and pulley to attach and transmit the torque.
Grabbed a quick photo this morning. Welds are functional rather than pretty.
Attachment 402756
After a bit of measuring and figuring out how to mount the pulley, I decided to turn the shaft down to 12mm to match the pulley. This provides a shoulder between the 12mm pulley diameter and the 15mm bearing diameter so provides lateral location for the pulley. The pulley will be secured with the 2 grub screws onto flats on the shaft along with a 3mm cap screw.
The ballscrew pulley is from SDP/SI, part number A 6A55M050NF1512, and is a GT2 5mm pitch, 15mm wide 50 tooth aluminium no-flange pulley.
I removed the ballscrew from the mill and mounted it between centres in my lathe to turn the end of the shaft. This was sized to provide an interference fit to the pulley.
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
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
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.
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.
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.
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.
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.
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.
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 :)
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.
And a small video - if the link works
https://photos.app.goo.gl/Zd4qtr3n6CbXQztF6
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.
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.
Photo of limit switches and cam
Attachment 404814
Very interesting, thanks for sharing!
Just bringing this thread back to life ... I will remake the ball screw / motor bracket using slightly larger angle (50x50x5mm) and simplify the transmission by coupling the motor directly to the floating end of the ballscrew with an oldham coupler.
But not quite yet :)
So, I've been rethinking this part of the design and how to simplify/improve it.
I've got another idea in mind, partly inspired by this photo of a dismantled F3 CNC mill.
Attachment 475012
In the picture, the large rectangular casting at the top is the moving Y carriage, containing the 4 speed gearbox, spindle, and the spindle motor (attached where the drive belt comes out the side), and showing the acme screw nut in a casting bolted to the rear of the carriage.
The casting underneath is the main Z axis column of the machine (moving knee design), the fixed end of the acme screw is retained in a recess by back to back 7302B bearings retained by a large flat 42mm diameter nut. The recess also contains a bevel gear that meshes with the Y axis handwheel (that will no longer be required).
My revised design would replace the acme nut on the carriage with a plate holding the fixed bearing end of a ball screw, and attach the stepper in line via 4 stand offs and couple the shafts with an oldham coupler.
The ballnut would attach to to the main column via a new attachment plate, and drill out the closed end of the recess to allow the 20mm ballscrew to travel into the recess in the column. Cast iron and a 25mm hole saw ?
The mounting of the ballnut would need to be spaced off the chassis so the length of the free end of the ballscrew can be accommodated i.e the allowable Y axis travel (~220mm) needs to fit into the column. The current ballnut is 40mm long behind it's flange, so allowing a for a little clearance, that requires ~270mm of free space between the mounting bracket and the inside front face of the column.
The advantages are that the stepper motor is no longer cantilevered out at the end of the machine's travel and shielding should be easier to fabricate.
Downsides would be the end of the screw is unsupported, although it is a short screw so unlikely to have issues with whiplash. Also the limit switches will need to be mounted elsewhere than in the current design.
Anyway that's enough musing - just good to capture the thinking here, which I'll revisit after I've got the other parts of the project working.
So a rough sketch to check that this is even physically possible i.e. will the ballscrew fit in the hollow casting that is the main column ?
Initial measurements show this has a top thickness of approx 35mm, and the centre of the acme screw is about 50mm from the top. Retaining the existing centre line would mean there is 5mm clearance between the ball screw and the inner surface of the top part of the casting.
The length of the recess is approx 240mm, so this will fit the amount of the ballscrew travel (220mm) plus a small extension (5mm)
Here's the sketch, as a vertical section front-to-back, showing the clearances and initial layouts of the various components.
Attachment 475032