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

[routercnc]

I use 6mm 2f carbide 45deg alum carbide bits at 12000 rpm 900 mm/ min 1.0mm DOC. Any more DOC and the motor sounds loaded and risk of gumming up is pretty high.

I also drop the feedrate manually when deep into a profile cut as the chips are harder to clear.

I often manually drop the feedrate on the first cut as the surface seems to be harder than the core. Also my ramps in and pretty slow.
I've seen others post more aggressive rates but it does not work for my machine.

My tabs are about 3mm as you are not just holding the part but stopping it vibrate on the finish pass to get the best surface finish. Means you need to cut them out with a pad saw not just push them out .

[Davek0974]

3mm wide tabs? But how thick?

I set 2mm wide x 0.4mm thick but due to my z running low for some as yet unknown reason, they came out at 0.15 mm thick.

Sawing these parts out is going to bugger the finish, is there another way?

If not then I might have to revert to sending them out for laser cutting again but i really, really do not want to have to do that.

[routercnc]

Sorry typo
3mm high and ~12mm long
Careful filing and sanding then scouring pad gives a reasonable finish. If you want a mirror finish with no sign of tabs then you are back to fixing the part down in the middle using any holes that are available instead of using tabs.

On occasion I've also put the raw tabbed part in a vice edge up and used the machine to skim it down 0.05mm at a time and remove the last but if the tab. You can get a very good finish but you ideally need a parallel edge on the lower side to reference to sitting in the vice. But this takes time and is best for simple shapes.

[Davek0974]

Wow! 3x12mm thats a serious tab, really doubt it would go on these parts IMHO.

One idea I just had was to split the job into two overlapping parts and use solid clamps with a pause in the job to allow two new clamps to be set over the cut part and the other clamps to be removed. It would mean double the tooling changes but might work?

There are no holes for fixings internally.

I was using 1300mm/min and 2.5DOC for the 5mm single-flute tool.

[lucan07]

Is it not possible to leave 2 or 3 decent tabs 12mm x 3mm on straight edges and remove tabs as final cut after clamping the parts?

[Davek0974]

Possibly, I'm working on it now in CAD and will post when i've got to sheet cam to see if i'm barking up the wrong tree.

[Davek0974]

Ok, lets run this up the flagpole...

This is the job - two parts. Outer line is the base metal - 5mm Aluminium, the three point down the centre are M6 screws for fixing to the bed.

Looking at it now I can pretty much see why it failed - once the last pass of the roughing cut is made down the centres there is bugger all holding the two parts to the central stub - just the centre holding tabs which were way too thin to stand up to the cut.

This is my next plan - place some full-depth tabs maybe 10mm wide where the red dots are, make all the cuts, including the finish passes, then using the 2mm finish tool add some cuts to nibble away at the tabs after maybe fixing a couple of clamps - as suggested.


Doomed to failure or possible plan ?

[JAZZCNC]

Onion Skin will work better has it holds all round and can be lot thinner.

To be honest Dave and no disrepect meant here and I know you have some experience with milling but think your kind of trying run before can walk with this.? By that I mean you haven't had much time using this machine so don't know it's capabiltys and your part isn't exactly new user friendly with those smaller cutters.

You may be better stepping back a little and work upto this part.

Also the Water cooled spindles above 12000rpm do have resonable amount of torque and shouldn't struggle with 5mm carbide tool while ramping only 0.5mm so are you sure you have the VFD parmaeters set correctly.?

[A_Camera]

Sorry typo
3mm high and ~12mm long
Careful filing and sanding then scouring pad gives a reasonable finish. If you want a mirror finish with no sign of tabs then you are back to fixing the part down in the middle using any holes that are available instead of using tabs.

On occasion I've also put the raw tabbed part in a vice edge up and used the machine to skim it down 0.05mm at a time and remove the last but if the tab. You can get a very good finish but you ideally need a parallel edge on the lower side to reference to sitting in the vice. But this takes time and is best for simple shapes.

Why not using the "onion skin" method Jazz mentioned earlier? I think that a 0.1mm onion skin would give the same holding strength (probably even better) as a 3 x 12mm would, assuming you have 4 tabs with that size, converting that to onion skin, you can have a total circumference of 1440mm if you have a skin of 0.1mm. In my opinion it is easier to clean off the edges if only 0.1mm must be cleaned than if 4 times 3 x 12mm must be cleaned.

[Davek0974]

As some may have read, I am converting my Bridgeport mill to CNC, the idea is to attache the high speed spindle to it to make a dual purpose machine.

Seems I have a couple of options here - mount the spindle motor to the main mill quill or make a new Z axis complete and mount that to the head of the Bridgeport.

Mounting the spindle to the quill is easiest - a simple clamp block would do it...

The larger circle is the mill quill or Z axis (around 100mm dia), smaller is the 24k spindle (80mm dia), looking down from above. The distance between the two is 50mm and the clamp could be machined from 30-40mm thick aluminium or similar.

Would it work though??
Your thoughts...

Second option is far more involved and needs a mounting bracket and complete Z axis making to take the 24k spindle, this assembly would mount on the rear of the swivel ram (at the back in this picture)...


Would be harder to make but still do-able but if the first idea worked the much time and cash will be saved ;)

Thoughts??