Questions on using a moving gantry style mini-mill...

[lucan07]

Now you tell me good job I like apples just brought a 2.2kw HY VFD and spindle but at £146 delivered from UK with the eBay codes yesterday i don't think I would have got near the Scheider

[Davek0974]

£146 for spindle AND drive?? thats pretty darn cheap!

The Schneider was £148 delivered BTW

[lucan07]

Yeah saw the 20% discount for everything on eBay so had to go for it only ran from 4-10pm found a HY chinese supplier with warehouse in UK near me in Leicester so did the deal can resell on ebay for that money and still not lose so gotta be worth a shot.

[JAZZCNC]

Now you tell me good job I like apples just brought a 2.2kw HY VFD and spindle but at £146 delivered from UK with the eBay codes yesterday i don't think I would have got near the Scheider

Don't threat I fit these all the time and think Dave had VFD which wasn't setup correctly or possibly faulty. Normally they work very well above 6000rpm.

Yes the Huanyang won't match Vector drives for torque, esp at low rpm but it's more than good enough for cutting wood an aluminium between 8000-24000rpm with smaller cutters which is where you'll mostly run it.

[Davek0974]

I agree, I have a strong suspicion it was a duff drive - setting it up wrong would not give the odd fact that I could not get a voltage reading on the 0-10v inputs when running - that is extremely suspicious.

[Davek0974]

Ok, getting somewhere now :)

I checked the Z axis calibration, microscopic tweak to steps-per but nothing major.

It turns out the reason my previous onion-skinning and tabbing failed was because of operator error - garbage in, garbage out! The metal i ordered was 5mm thick, I set that in CAM and tried to leave a 0.1mm skin or a 0.3mm tab.

In real life however the sheet was only 4.85mm thick - there was the missing skin and tab, I was telling it to go deeper than it really was - lesson learnt - don't ever trust what you order is what you get :)

Another possible source of error in the sub millimetre range was the probe touch-plate, it miked up at anything from 1.42mm to 1.51mm depending on where you place the micrometer. I have fixed this by scribing an area on the surface of the plate where it measures exactly 1.5mm - always using that spot should sort it out.

So, on to cutting stuff, I threw in my sacrificial 5mm 3-flute HSS cutter and set a lump of my 4.85mm ally on the bed.

In CAM i made a straight line 40mm long, 4mm deep, slot width, plunge in, 1mm DOC, speed at 8000rpm(where it bogged down before) and feeds ranging at 600, 800, 1000, 1200mm/min.

Result was perfect in all settings, no speed drop at all, perfect cuts.

Next test was the same job but this time 1.5mm DOC per pass, same speed ranges.

Result was 100% perfect, it didn't even know it was cutting!

A video of a 1.5mm DOC 1200mm/min, 4mm deep slot cut...
https://youtu.be/cL3Om6xMfK8

So, I am now going to risk a tool and try my job again, onion skin at 0.15mm to start with, I am expecting a failure as I don't think the sheets are really big enough for the job but who knows :)

[Davek0974]

Made it's first full-job :)

Yes, I know it's a failed part - i lost a cutter due to it hitting a hold-down bolt caused by my messing with the CAM so much I forgot which file was which I didn't want to add wasted metal to a wasted cutter so i reset the file and cut the next run over the first one.



Onion-skin was perfect, too thick and hard to remove at 0.15mm but i did manage to take the job right through all the post-finish drilling, counter-sinking and fettling just to prove the process.

OK, education time...

Poor quality on the finish passes, 2mm single-flute cutter, 0.6mm DOC, 450mm/min cut, 23,000rpm - chatter I think.



How to improve?? It looked better on the roughing cut ;)

Videos...

Roughing cut...
https://youtu.be/oSgf-0C5PHM

Pre-finishing the fiddly loops, 2mm tool...
https://youtu.be/nD4If43P3c0

Job took 43 minutes including tool-change, mostly the delicate finish cuts, I will look at these a bit more as something is off a little there I think.

Any pointers?

On the next run I'm going to take the skin down by 0.05mm and also put a sheet of paper or card under so I take the fine detail - holes and slots, down to 100% depth.

[Boyan Silyavski]

The pointers: i said it many times, and most disagreed. For perfect aluminum finish if the machine is normal, that combo gives me the best finish. I don't care about 12k rpm or 30 krpm. That combo for 3mm bits gives me best finish. On the yellow machine i could cut at 12krpm and 2500mm min at 1mm deep with 1/4 bit. But best perfect finish is around 600mm min/ hence 25 ipm/

[Davek0974]

Those settings are not far off where i was, I was a little slower feed and faster rpm, that may make a difference, don't forget there is a fair bit difference between a 1/8" and 2mm tool.

Thoughts over dinner...

1 - Make the final pass on the main parts with the 5mm cutter then isolate the small features and machine only those bits with the 2mm tool?

2 - Try the final pass with the 2mm at full depth but add a slow-down in the corners where it's biting the rads from the 5mm tool?

3 - something else?

[routercnc]

On the finish pass question - I don't often use small cutters so don't know what the problem is. But 0.6mm DOC seems small for the finish pass ?

I generally use 6mm cutters and for finishing I leave 0.1mm roughing on the part - how much are you leaving?. Then I cut at 3mm DOC as this works well but I could probably do anything up to 10mm DOC as you're hardly removing any material on the finish.

Here is the finish on a 10mm part using this method: