CNC 2.0 - Knee mill

[Bob Willson]

Hi Andrew.

What size steppers have you used?

[andrew_mx83]

Bob the motors are NEMA34 1700oz/12nm units, except for the quill which is slightly smaller but still 34 frame.

Progress pics
Bought a nice Schneider E Stop button but didnt like the enclosures that were available so i made my own to mount the switch on the back of the Z axis motor.





Mini junction box for quill motor conndctor and probing indicator led. Billet, of course )



Control enclosure. Everything is entirely self contained in the machine. Just needs 240v and USB to run. Still need to add fans/ventilation and get the door back on. The middle section where the large bundles of cables run is sealed off from the top and bottom sections by the door so no issues wigh ingress of lube or chips.
Hiding in here is the KFlop controller with Kstep amp behind it, a 5v power supply for each, a 24v power supply for the limit switches, a 12v power supply for relays and fans, 48v power supply for motors, 2x40a solid state relays for the spindle motor and a 30a relay for coolant. I also made up an alloy cable tray to keep the wires neat.

[andrew_mx83]

First cut -long and not too exciting video
https://www.youtube.com/watch?v=Bc_N...e_gdata_player


Second cut, getting braver
https://www.youtube.com/watch?v=5PCf...e_gdata_player

Third cut
https://www.youtube.com/watch?v=XBwW...e_gdata_player

Surface finish using a hss facing type cutter



Very happy so far. I had to face off a through-hardened steel part today which it ate through at 1.5mm DOC with no fuss at all.


Now i just need to get the bloody software sorted out...

[Hornetb]

Beautiful work.

I just got my first mill last week (BF20L). A mere baby compared to your monster. Mine will end up CNC'd also but I should actually use it to make some stuff first before i throw more money into it. No chips made yet, still waiting on tooling and currently desiging/building a decent bench for it.

But again, your machining and execution is just excellent.

[andrew_mx83]

Thanks mate. Tooling up is usually the expensive bit! I only have a small selection of bigger end mills, so i need to buy some of those and either buy or make some indexable milling cutters, a decent surfacing cutter, a 200mm flycutter, the list goes on!

I managed to close the feedback loop today and do some positional accuracy testing and am very happy with the result. There is no backlash correction in mach3 but the kflop is working quite hard to catch the last few microsteps.
I can move back and forward in 0.01mm steps perfectly
0.005mm steps are pretty good but it does hunt for the last couple of microns
0.002mm steps generally come out on the mark but it hunts a fair bit when changing direction. Stepping in the same direction it is pretty much bang on.

Video of 0.005mm steps
https://www.youtube.com/watch?v=T05y...e_gdata_player

Some maths for those interested
1.8deg steppers with 16x microstepping = 3200ms/rev
4mm pitch screws gives 0.02mm per full step and 0.00125mm per microstep, however you dont get full holding torque on the smaller microsteps.
0.003mm internal clearance in ballnuts and negative clearance in preloaded AC bearings means 0.005 is about as accurate as this setup would get.

Given all that, my goal for the machine was 0.005mm, but i didnt really expect to get it that good. So im a pretty happy chappy at this stage )

[Hornetb]

Got to love it when a plan comes together.

Glad you are happy with the outcome, it looks to me like you really did some great work to get it there.

I fully agree with the tooling. The $$ keep going out, but as yet not too much has arrived yet. Hopefully over the next few days/weeks. But this mill will make me a few $$, not likely a great deal but enough to help offset at least some of the costs. But it will certainly keep me occupied for a while

[Bob Willson]

There is no backlash correction in mach3

Hi Andrew

Yes there is backlash correction. I don't use it myself, but I have seen reference to it often.

[andrew_mx83]

Yep that's correct Mach does have backlash compensation but it is fairly crude. What i meant to say is that i have it disabled on this machine (well for the x and y axis' anyway, no scales on my Z's so still doing it the old fashioned way on those)
In this case the Kflop is reading back absolute position from my linear encoders, comparing it to the commanded position in Gcode or MDI and then changing the output signal to correct any discrepancies. If you watch the DTI needle closely you can see this happening- if it lands not quite on the mark it will make another very small move to catch upto the commanded position. I still have some tuning to do, gotta find the sweet spot of micron accuracy vs hunting but it is very cool to watch it do its thing. Of course this is a pretty severe test and in real cutting situations i am not going to be going back and forward in these 0.005 steps so i think i will end up with pretty accurate finished parts either way. We will find out soon enough!!


The plan is coming together nicely so far. There is still work to do but i may even run a big batch of parts on it next week, at least for roughing rather than hogging a ~40mm bore out on the lathe 100 times. Im thinking i will load 3 pieces of bar in the vice, hit em with the 32mm drill then pocket the rest in a separate operation using a 1" slot drill. Then back in the lathe for finish cuts and threading.

[BaronJ]

That is one mean metal chomping machine.
Brilliant work ! I'm most envious.

[andrew_mx83]

Thanks baron. Here's a vid of it chomping through some steel. Cutting 10mm deep and 12mm wide )
https://www.youtube.com/watch?v=4J6S...e_gdata_player

Surface finish:



You can also see in the video that ive got the coolant working. I use a neat cutting oil (ie no water) which i find is pretty effective, you dont need much of it and it doesnt rust up your machine. I use a mach3 brain to fire the injector for 0.005 seconds every X seconds depending which coolant mode is active. I usually run every 3 sec for flood and every 10 for 'mist', depending on the material and how hard it's working. I had to crank it upto 1.5 sec for these deep cuts in steel, although there is lots of smoke the cutter didnt get particularly hot and still looked like new when i finished the job (6 of these big cuts, each 300mm long)

[BaronJ]

Hi Andrew,

I've just watched the video, very impressive indeed. I like the idea of quick squirts of neat cutting oil. Did you use a pressurised tank with a solenoid valve at the nozzle end to control the ejection of fluid, or was it just pump pressure ? The stop button is neat, posh even.

[andrew_mx83]

Hi baron the 'nozzle' is an automotive fuel injector from the mighty Toyota 7m-ge (i have lots of them) but it is just a solenoid valve i suppose.

The oil is pumped to around 35psi to allow the injector to actually squirt the oil rather than just dribble it. I have had lots of problems on my little CNC with pumping it upto pressure reliably. I bought a couple of small electric pumps which were no good, best bet has been fuel pumps from the same engine but they only last a few months. They also generate a lot of heat, so i had an oil cooler plumbed up, pressure regulators etc, it was all quite messy. Then there is the 20+ amps of 12v they draw..

This time, i am using air pressure to pump the oil which seems to work well and better yet it's SIMPLE. I am using an old BBQ gas bottle as the reservoir/pressure vessel, with 1 fitting in for air and another at the bottom for oil outlet. Set the air reg to desired pressure and voila, pressurized oil with no heat and no power consumption. Because the volume of oil used is so low, the air requirement is virtually nil once the chamber is pressurized.



Yeah i am quite proud of the stop button, i wanted to do something a bit fancy for it from the start... seems a bit silly to go to all this effort and then use a crappy plastic enclosure in such a prominent place. I may still change the actual switch over, even after spending $70 the switch mechanism just doesnt feel as nice as the one on my small machine (was over $100, ouch). The el-cheapo switches are just awful and not confidence inspiring at all for an emergency stop....

[BaronJ]

Hi baron the 'nozzle' is an automotive fuel injector from the mighty Toyota 7m-ge (i have lots of them) but it is just a solenoid valve i suppose.

The oil is pumped to around 35psi to allow the injector to actually squirt the oil rather than just dribble it. I have had lots of problems on my little CNC with pumping it upto pressure reliably. I bought a couple of small electric pumps which were no good, best bet has been fuel pumps from the same engine but they only last a few months. They also generate a lot of heat, so i had an oil cooler plumbed up, pressure regulators etc, it was all quite messy. Then there is the 20+ amps of 12v they draw..

This time, i am using air pressure to pump the oil which seems to work well and better yet it's SIMPLE. I am using an old BBQ gas bottle as the reservoir/pressure vessel, with 1 fitting in for air and another at the bottom for oil outlet. Set the air reg to desired pressure and voila, pressurized oil with no heat and no power consumption. Because the volume of oil used is so low, the air requirement is virtually nil once the chamber is pressurized.



Yeah i am quite proud of the stop button, i wanted to do something a bit fancy for it from the start... seems a bit silly to go to all this effort and then use a crappy plastic enclosure in such a prominent place. I may still change the actual switch over, even after spending $70 the switch mechanism just doesnt feel as nice as the one on my small machine (was over $100, ouch). The el-cheapo switches are just awful and not confidence inspiring at all for an emergency stop....

Hi Andrew,
I like that idea, a fuel injector, diesel I assume. I don't know the Toyota but I bet the local scrappy does When you say 20+ Amps I hope the injector doesn't require that much current, though I have a couple of computer PSU that will supply around that at 12 volts. I have an old five gallon plastic lined water fire extinguisher that is looking for re-purposing and a suitable pressure gauge. I don't have a compressor but do have a very good ex-military stirrup pump that will do 60 or 70 Psi. A truck tyre valve...

I feel a project coming on !

Sorry to hear that the feel of the Estop isn't right. $100+ is a lot of money for one. I bet that the button mechanism could be massaged to improve the feel. The one on my mini mill feels rough to operate. I suspect that a little lubrication in the right place may help.

[andrew_mx83]

If you are going to use a pump instead of compressed air, the reservoir doesn't really need to be a pressure vessel. On my small CNC i just cut a hole in the 20lt drum the oil comes in and dropped my pump & plumbing in. Let me know if you want some photos of the setup.
The injector itself draws around 8amps @ 100% duty cycle, it is the pump that requires another 20 or so ( in my application)
It is just a petrol injector, no diesel. My cutting oil is extremely thin and seems to squirt out just fine once you get the pressure right. Too much pressure and it atomises into a mist....
I would happily send you an injector as i have heaps, but i dare say for the price of postage to the UK you could easily grab one from the junkyard and it would work out cheaper.

[andrew_mx83]

Anyhow ive been doing lots of stuff on the mill this week. Had a bunch of big threads to cut, and got bored of doing that in the lathe pretty quickly. So i knocked up a quick threadmilling tool, wrote some code then sat back and drank bourbon while CNC did all the hard work )
It cuts a 3mm pitch in 1 pass, followed by a quick cleanup/deburr pass (which still needs to deburr a bit more)
(Excuse crappy phone picture)



Also got some cermet inserts for my facing cutter, and took a cut over some steel, very very pleased with the result. You could quite literally shave in your reflection off the work. Cant wait to see what kind of DOC and feedrates i can push with this now, cermet generally finishes better and better the harder you work it. Note it is still running with 2 of its 6 teeth missing as i have to buy/make new bits for it. also note that the injector is just there for the photo, coolant was not used for the cut (cermet needs heat to cut properly)




Touch probing and workholding systems are almost complete, no pics yet though and maybe not til the new year as i forgot to order material before everything shut today...