Question Setting reference positions

Hi,

What do you experienced CNC'ers use to set the reference position of your spindle?

On my mini mill I use a LED edge finder and DRO for X,Y and Z - this gives me better than 0.001" (25 microns) for all three axes. Bad news is that physically it is relatively huge, overall about 6" long, with a 20mm shank, so no real chance of adapting for the Proxxon spindle 1/8" collet!

As an alternative a wiggler is not bad on the mini mill - maybe 2 -3 thou and a spindle speed less than 200rpm, but the minimum spindle speed (5000rpm) of the Proxxon spindle probably rules that out. That is unless there is a clever way of slowing it right down.

Ideas gratefully received!

I'm still searching for a cheap alternative to manual methods too.
Seems that the "beepers" (the ones edmitting a sound when touching a surface) are not so bad. I would like to know if anyone has got some experience with tools like that.

For my purposes, a precision of half a tenth (i.e. 0,05 mm) would be more tha enough.

Until now I'm still using the cigarette paper to find even X and Y reference points. I just take care that the tip of the flute is pointing to the vertical surface so it can block the paper against the surface.

Then:

- I make the spindle closer and closer until the paper is blocked in position,
- then I go back of 0.02 mm,
- I slide away the piece of paper,
- I go forward again of 0.02 mm,
- I zero the axis X (or Y) axis

(Don't laugh, please! )

This is the method I have adopted when limited to 1/8" spindle.

Dry Erase Edge Finding

Hi,

I am using small laser pointer mounted on the bottom side of extrusion adaptor. It helps me a lot when I do something and need to remove machined part from the table and put it back to finish work (sometimes after few days and other projects). I don't need to worry about the same x/y position, just point the laser to start position, home x and y, adjust X and Y and job done.

Laser pointer:


3D printer housing:






Double side adhesive tape used to mount:


Attached to extrusion adapter:


It works but the laser point is quite big. Laser pointer has lens adjustment but did not help too much:


Very small "wheel" with the 0.2mm hole at the centre:

"Wheel" attached to housing.


Now the laser point is much smaller:


Measure difference in x/y between tool and laser pointer. It should be done each time extrusion adapter was reattached:
1) Home X/Y axes:


2) Drill small hole:


3) Move laser pointer to position where drilled hole is:


4) Note x/y values for future adjustments:

Hi

That's a neat idea to use a laser - but is the position relative to the spindle axis absolutely fixed? I believe that crossed polarisers are often used to reduce laser intensity to a more useful level (much more complicated though).

I am still waiting for my SC420/2 to be delivered, so in the meantime I am making a digitising probe using a Renishaw probe with a 2mm ruby ball. Fortunately I have a mini lathe and mini mill with DRO to allow me to get creative. If it works as intended then it should be sensitive to a few microns according to other DIY makers.

This will allow X an Y to be set up very accurately, but will not help much with Z, I think. Maybe there is a positive stop in the collet mount which might allow both tools and the digitiser to be accurately positioned in Z. It will still be a rather long winded operation though - and I guess I would want to double check before setting the machine running.

Nice work Sir, I like it a lot.

I wonder if we could take your idea and develop it further? Perhaps use two pointers, one either side of the spindle and angled at 45 deg to vertical...

With a jog up or down to make the spots align with each other we'd have our datum directly under the tool and have Z determined too. (Well enough for 2.5 axis work at least I'd imagine)

I'm sure I've seen this practice used once before but probably best not to delve into that on an English part of a German forum until I've introduced myself properly.

Regards,

Owen S.