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

[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:

[Davek0974]

I left 0.1mm from the roughing pass.

The 2mm cutters are spec'd to 3mm DOC but I still have concerns where they hit the rads from the 5mm tool and also have to plough into the corners a bit to create the sharp internals. Maybe my option 2 above would work?

[Davek0974]

Looking at figures there is a fair difference between the finishing pass and the sharp corners -

Lets go for a 2.5mm DOC this time, just below the cutters limit and half the final depth...

Finishing the edge wants 23,000rpm and 670mm/min feed
Ploughing out the rads and creating the sharp corners - basically a slotting cut - wants 18,500rpm and 180mm/min feed

So quite a change, all other parameters being left fixed, sounds like a path rule in SheetCam might work there?

That would be a 25% speed reduction and setting feed to 28%.

[Davek0974]

The machine made it's first saleable parts today :)

I did sacrifice two 2mm cutters, here's how...

On the part in the OP, there is a little square notch, first from the left along the top edge, it's about 4mm square and as such was not roughed out by the 5mm tool on the first pass. I set the code for a 2.5mm deep cut on the finishing pass with the 2mm tool and added a reduction to feed with CAM rules, it worked nicely until the tool reached that notch when it died.

I then increased the before and after feed change in CAM so the rate slowed well before and after the notch - ping went another tool. I then reverted back to 0.6mm per pass and 450mm/min rate as before and it sailed through. Still got that slightly poor surface finish though.

So, it seems despite what HSM says, even on severely reduced settings, you cannot slot 2.5mm deep with a 2mm tool.

Now, in light of the slow finish passes and the fact that it did seem to handle the 5mm rads with a CAM rule and 2.5mm DOC, is it worth singling that feature out and running a pre-finish run on it like I did with the loops??

Apart from that, I'm not happy with the paraffin/oil mix, seems to be affecting my hands a bit, I have found a suitable retail item - MilliCut J40 from Cutwell, its a veg oil based product.

Has anyone got there mill in an enclosure? I'm finding the floor is covered in chips about a 4' radius around the little bugger from the roughing passes - the 2mm tool just makes dust.

[lucan07]

The machine made it's first saleable parts today :)

Next step get the processing nailed down and make them profitable too, let the bugger start earning its keep!

[Davek0974]

Yep, already on that ;)

I just revisited the original plans for the part with the notch in it and it appears it's non-critical so I have altered it from 4mm wide and square to 5.1mm wide and half-round so the roughing tool will rip out most of it and I can try the 2.5mm DOC on the finish pass again - the 0.6mm cuts were where most of the time was eaten.

While it was running today I was also making other stuff so the time taken is not critical to a tight degree, once I get going I can finish one set of parts while the next is running - there are holes to drill and tap etc. Demand is not massive for these but crucially it means I don't have to send them out for laser cutting anymore.

I can also move another part I make from the plasma cutter to the mill as the quality is higher and finishing/clean-up time would be far less as plasma leaves a very rough edge on aluminium.

Just need to sort out a better bucket for the cooling water, possibly some sort chip management, and some better cutting fluid.

I might also try some low-speed tests just to see how low she can go.