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

[Davek0974]

If this is a regular job I cannot see why you do not create a jig waste board to hold material in a recess with appropriate hold downs permenantly in place so 4 nuts or so to lock jig onto bed, material in recess and locking tabs clamps (cheap chinese 120kg hold downs or similar you could have a couple to swing in after finishing pass goes by if needed and cut clean threough each time) to hold material off you go, no more biting into the bed, cutting through not going to matter occasionally one out quick vacuum next one one in, seems to me a lot of wheels being reinvented.

Ok, but if the part is finished all round that would mean diving in to fix clamps while the finish pass is running ? Or pressing feed-hold mid-cut? Neither sound good to me personally. I'm not deliberately trying to reinvent wheels, I just do what makes sense to me at the time i need to do it. The plate is fixed with the three bolts down the centre, these go through the scrap part, the outside clamps don't really do too much.

I just can't 'see' a way to clamp the parts as they are being cut.

As for spoil board then yes, if the bed was not already damaged I would fit one, this one sacrificed itself in the name of education;)

[Davek0974]

On my website, there are some modified macros that will zero the Z axis for all of the G54-G59 offsets at once, regardless of which one you are currently in.

As for material thickness, there's another option in the 2010 Screenset called "Material Offset". When checked, you zero the Z axis to the table, and Z zero is set at the material thickness value above the table. It's works basically the same as setting Z zero to the bottom of your material. If you are doing pockets, note that this will affect the pocket depth if the material thickness varies.

Thanks Gerry,
downloaded the macro's, seems like a better system to me.

I'll keep the ref method as it is at present and try other ways of sorting it out, the bed zero method looks useful but I can see ways it would land me in trouble sometimes ;)

I am fairly certain the issue is the variable thickness of the metal, surprised me how bad it is but it does explain why the part fails sometimes.

[CharlieRam]

I just can't 'see' a way to clamp the parts as they are being cut.

Use a M00 at a convenient point, then press cycle start to continue, spindle stop might also be good at this point :)

[Davek0974]

Use a M00 at a convenient point, then press cycle start to continue, spindle stop might also be good at this point :)

Yes but the finish cut is one continuous cut, you don't want an M00 in the middle of a continuous cut because you will not get another lead-out and lead-in so a tool mark is going to show, let alone stopping and starting the tool mid-cut will probably break it.

Fitting clamps will mean working in the short space of time while the cutter is up the other end of the job, these parts are small so time is short and this is therefore dangerous. The Z axis mount is wider than the job so all clamps have to be low-profile <=10mm high or it means using a longer stick-out on the tool which again is not good on a 2mm cutter.

These are difficult parts to make well but that does not mean they cannot be made ;)

[routercnc]

Hi Dave,

I tend to use the tab method but this does leave a small witness mark (although the parts are just for me so that's ok). For customer parts I can understand why you are trying not to.

So I think if I were to try the onion skin method I would skim the bed first then zero the end of the tool to the BED. Then MDI jog the Z axis up to 5.1mm (if the part is nominally 4.9-5.1 say) and then ZERO the DRO again.

In your CAM you would than ask for a depth of 5.0mm. This would leave exactly 0.1mm of onion skin. This method is independent of the variation of part thickness.

[Davek0974]

Thanks, that sounds a very similar method to Gerry's - using his "material height" DRO. I might have a go at skimming the bed and try that out.

[lucan07]

When I use the M00 I simply extend cut into scrap section past end of cut or put in a small loop and restart on a corner with change of direction and no signs of me doing so. think about it like cutting it on your manual mill overshoot on external long straightish edge to fascilitate later clamping, pause in scrap material on overshoot, add clamps to suit which could be pre mounted to swing over and clamp and carry on.

[CharlieRam]

Looking at your part, there are quite a few holes to screw into a spoil board so I would have the M00 after the holes were drilled to insert some screws to clamp the piece down, then just cycle start for the profile

[Davek0974]

Hi

yes there are some 3mm holes on one part and a couple of useful apertures but nothing at all on the second part, on the right in the picture, I can't add any holes either :(

[CharlieRam]

OK then, complete the outer profile, m00, remove waste outer profile, clamp right component leaving room for profile cut, cycle start and finish profile cut to separate parts. Easy :-)