RF25/30 Drill Mill CNC conversion FINISHED!

[rotec]

Hi All, thought I'd post some stuff about my Drill Mill conversion.
The machine turned out great and works as expected. Please feel free to ask me any questions about this machine as others were there to help along the way so I'm more than happy to reciprocate.

Some Specs:
Ball screws 16mm x 5mm pitch X and Y axis
Z axis has anti-backlash air ram with no springs. Works good.
Z axis 3:2 belt reduction
XY 2:1 belt reduction.
XYZ All DC servos from old robot.Sanyo Denki 75V
A axis closed loop stepper with 1000 PPR encoder
XYZ Drives are DGS4-8020 (DC servos)
A Axis leadshine (copy) closed loop stepper drive
NPN proximity switches on ALL 4 axis for limit and homing.
Power supply are 240VAC / 48 volt DC / 12 volt DC / 75 volt DC
Motion Control: Mach3 and USB Smooth Stepper
AUX: Coolant, Spindle control all via mach 2 control

See pics attached and also a short movie of the machine running on it first job.

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[80gus]

Top effort, nice workshop.

[Bubba]

Excellent job and really like the idea of an air cylinder to take up the backlash on the quill!!! Real neat idea.

[rotec]

I got the idea for the Z quill air spring from a forum member here, Tom Babcock. He was kind enough to share his idea with me. I then went about making my own air cylinder after having troubles find just the ram I wanted.

CLOSED LOOP STEPPER:
Interesting experiment in the shop yesterday, where I managed to successfully add an encoder to the back of a Nema 34 two phase stepper which now makes that motion closed loop! This will be used on the 4th axis rotary table which was previously driven by the same open loop stepper with Gecko drive. This same stepper with encoder now mounted is driven by a Leadshine type (copy) closed loop stepper drive. All I did was drill the rear of the stepper's armature and Loctite in a 1/4" stub shaft just long enogh to drive the rear mounted encoder.
This opens up all sorts of possibilities . It now means I can buy relatively cheap drives and convert my own regular open loop steppers to closed loop.
I'll post some pics when I’m done.

[Fastest1]

Hoss did this with a treadmill motor. Put an encoder on the top.

[rotec]

Yes but im pertty sure Hoss's treadmill was a DC motor with an encoder added, making it a servo? Or perhpas he was just using the encoder as a spindle tach.
What Im talking about here is expanding a regular stepper motor into a closed loop stepper. I personally would not use an open loop system again. When for just a few bucks more you can make a closed loop system than in my opinion is a proper set up.
You can buy any regular stepper 2 or 3 phase, easily addapt an ecoder on the rear AMT ecoders are like $15, then use a closed loop lead shine drive for about the same money as decent open loop stepper drive.

I'll post some pics shortly. Im almost finsihed the 4th axis. Still wiring.

[Fastest1]

Cant wait to see them. However there is no auto correction is there? Just a fault within Mach?

I would like to see more info about the backlash cylinder and how it works.

[Zenji]

Neat conversion rotec!

[rotec]

The Z back lash air ram is pretty simple, I litterally made it from junk I had laying about the shop. Its made of a stock aluminum tube. with a 22mm turned aluminum piston with two 3mm section o-rings used as piston rings. The shaft is just a length of polished 1/2" steel rod, tapped at each end to attach the piston and at the other end to attach to the quill, I attached the ram rod to the lug where that measuring ruler / stop used to be. There is just a regular 1/2" lip seal at the botton end, to seal the ram rod, and the other end of the ram, the top end, is open, vented The ram is not even mounted it just located on the quill lug and is presseing againt the underside of the spindle pulleys cover.. Its expanded in position and can go no where. The ram has a small 3mm air nipple near the base that feeds regullated air press to the under side of the piston and thus continuously pushes the cutter AWAY from the table (UP direction) this way all the Z motion drive train right up to the servo is loaded and there is no backlash. I run the ram at around 80 PSI and that gives me plenty of upwards force to stop the cutter from ever diving. The has cutter has never dived or pulled into the work piece yet.

[rotec]

Here are some pics of the 2 phase stepper motor i converted to closed loop by adding an encoder to the rear. The stepper in question did not have a rear protruding shaft, so I drilled the rear shaft and simply Loctite in short length of 1/4" stainless rod. The AMT102 encoder easily adapted to the rear and coupled with the shaft extension.
This motor is used to CNC convert my Vertex 10" rotary table. This is now a true forth axis. I also wired a proximity switch to the rotary table for referencing. Very pleased with how it works.

[rotec]

For those interested here is a short movie of my 4th axis with closed loop stepper and proximity homing switch operating.

[embraced]

Interesting.

Do you know what benefit closing the loop on something like that is?

And what is that horrible noise that occurs in the first few seconds of homing it?


Otherwise, pretty cool conversion.

[rotec]

The "horrible" noise you so delicately describe is nothing more than the other 3 DC servos ie ZYX axis homing first then the 4th axis homes last. Its just the normal sound of the servos.

Im running DC servos on XYZ and a stepper on the 4th axis. I had these three servos so I built around them.

The benefits of closed loop are great. The stepper motor much like a servo, now has an encoder mounted which gives the drive positioning feedback. Unlike an open loop stepper which if stalled or over loaded it will drop steps and then continue the rest of its movements with a positioning error, basically put it gets lost. A disaster!
But with closed loop system the motor will never lose position, even if partially slowed or stalled, due to an overload, once free it will quickly catch up and find its exact rightful position. This is why most if not all production CNC machines are closed loop.
The 4th axis you see here was originally open loop and if I loaded the table it would easily miss steps. Now it cant.
If the closed loop detects a gross positioning error due to sustained stall or crash It will alarm and relieve the drive.
The stepper with encoder running on the bench I could take the shaft with a wrench (shifter to us Aussies) and force it say 20 degrees off position. It would fight me to put the shaft back to exactly where it was before I forced it. An open loop stepper motor will just stay out position.

[embraced]

Sorry for my brash description.

Does the stepper run quieter than an open-loop counterpart?
I have a 4.5N.m. closed loop NEMA 34 stepper with the same drive (I believe - a 2HSS86H) and it is audibly quieter. Much lower heat too - I can leave it on for hours and the temperature will only marginally increase over ambient.

[rotec]

Yes, I noticed the stepper motor now runs smoother, quieter and faster than it did before on the Gecko drive with open loop.
You purchased a closed loop stepper system with the same features I describe? Did you buy it not knowing the advantages of your purchase?

[embraced]

I was aware of the features before purchasing.

The reason I asked was to compare your conversion to my factory model. It seems that you've achieved the same performance as mine.

[Raf-1200]

Well done ROTEC. Just saw this on YouTube and it bought me back here. What motors would you recommend in hindsight..?

The reason I ask is I'm doing the exact same conversion at the moment so any information on screw lengths, servo types etc would be very much appreciated. I have a 900x600 router which I have used for the last couple of years but naturally I have to do slow passes on it when doing aluminium.

What sort of speed and depth are you getting out of yours?

[Eskerinola]

Hi there;
Great job!. I wonder how easy it would be to go back to manual in case you have to do simple jobs.

[rotec]

Hi there;
Great job!. I wonder how easy it would be to go back to manual in case you have to do simple jobs.

Very easy! You can see I have the handle wheels still in place on each axis, so when I just want to use in manual mode I leave the power to the servos OFF and just crank the handles as a manual machine. SO I can be in CNC mode of not.

The quill rack can even be used by simple udoing the clucth and then use like a drill press.

Its a good set up, Im happy with it.

Gear reduction all all axis is 2:1 using tooth belts. I think the Z axis maybe 1.75:1 . It has plenty of grunt

[rotec]

I just grabbed a couple of 16 x 5mm pich Chinese ball screws with nuts, made sure they were longer than I needed and just cut them with a 1mm grinding disc, the rolled type they are fine. No turned ends. I made adapters to attach to the ball screws itself. This is where I got the idea from, I basically made my own version of this Flash cut conversion kit . Or search Flash cut CNC "Universal Retrofit Kit"

I just chose stock belts and pulley that gave me enough center distance to make sure I could still swing the manual crank handles. I can take good cuts in steel, the servos are not the limit. The light weight machine is. But 2mm depth in steel seems ok.

I started with mach3 thats was ok. But mach 4 now is much better only it has a few bugs . But I have it good enough now, Im sure mach4 is even better as they were fixing bugs regularly then.

I has some small DC servos, but the closed loop stepper on the Z axis is plenty good enough. I would NOT use open loop. Just my advice. Closed loop is better plain and simple. And not much more money these days.

X and Y are 2:1 reduction and the Z is 1.75 :1 I only made the Z different so I could fit the motor how I wanted. It had nothing to do with power. it has plenty

The air RAM (air spring really) I made keeps the quill loaded against the worm and rack, works well. The RF25 coil spring has been deleted. The RAM Works better, can be set to any force and is linear.
.