Tips and tricks for shallow milling/ engraving ?

[Gasgasbones]

Hi Fellas

As well as deeper 2D milling I will also be engraving small metal buckles. As Im not going deep if the work piece is not 100% spot on level then Ill get spots that are missed if its down at one end say.

What tips and tricks do you use for getting your work piece 100% level ?

My buckles are around 24x30mm and at the moment im dropping them into a pocket I machined from aluminium plate. Trouble is, just a tiny missed bit of swarf between the table and Jig or pocket and buckle can be enough to throw it off a smidgen.

I could skim over them before engraving but I pre 'grain' the top prior to engraving.

HHHmm, any thoughts ? :friendly_wink:

Thank you

Carl

[JAZZCNC]

Spring loaded engraver bit is needed if surface isn't flat. Like this http://www.2linc.com/engraving.htm

[Gasgasbones]

Great idea !! I made one today :-)
Works a treat

http://i956.photobucket.com/albums/ae44/ggbones/GGB_5837.jpg (http://s956.photobucket.com/user/ggbones/media/GGB_5837.jpg.html)

http://i956.photobucket.com/albums/ae44/ggbones/GGB_5838.jpg (http://s956.photobucket.com/user/ggbones/media/GGB_5838.jpg.html)

http://i956.photobucket.com/albums/ae44/ggbones/GGB_5840.jpg (http://s956.photobucket.com/user/ggbones/media/GGB_5840.jpg.html)
http://i956.photobucket.com/albums/ae44/ggbones/GGB_5850.jpg (http://s956.photobucket.com/user/ggbones/media/GGB_5850.jpg.html)

[totts]

Im a little confused at how this works, so whats stopping it from engraving too deep on the high spots? As gradually the spring pressure will engrave deeper? Or am i looking at this totally wrong?

[Gasgasbones]

It will engrave deeper at the high spots but not significantly so, not for me anyway :-)
Im not sure of the difference in hight from high to low spots on my plates Im engraving but its hardly anything, probably a nats chuff :-)
Mostly I get them dead flat but this seems to have solved it if they are off a smidg as I had no missed bits on this batch of buckles.

Im not sure how a commercially available one would work any different?

[totts]

So when you set the z datum do you just set it a bit lower so it touches in the low spot, so are we saying that the spring acts as a damper in the high spots to stop the tip from chipping/breaking?

[Gasgasbones]

So when you set the z datum do you just set it a bit lower so it touches in the low spot, so are we saying that the spring acts as a damper in the high spots to stop the tip from chipping/breaking?

I set the Z offset of the tool exactly the same way as I would if a normal tool was in there. I then set the depth in the program as usual.

I was having tips break but with the spring taking up the initial impact it's been so far so good. I'm cutting stainless steel so it's a big ask for the tiny cutter, especially as I'm a noob and still learning. The high and low spots are littraly a nats chuff so with a solid tip and a shallow cut it was missing some.

Ive also used a diamond drag tip in it too and seems to work well too !

[totts]

Yeh i can see how the drag engraver would work well, i had a variation of about .2mm so i may make one for the next time i have difficulty and see how it goes :) will pinch your idea haha

Cheers

[JAZZCNC]

Im a little confused at how this works, so whats stopping it from engraving too deep on the high spots? As gradually the spring pressure will engrave deeper? Or am i looking at this totally wrong?

How deep is controlled partly by feed rate and spring pressure. Go slow and with stronger spring and it will cut deeper.
There is some trial and error to using them but when dialed in they work good. I made my own as well and it took a few goes before dialed in.

[gavztheouch]

Nice solution. How does that grub screw effect the balance of the spindle you must be spinning quite fast with that tiny cutter?

[magicniner]

You can use an engraving spindle which takes a Gravograph nose and allows cutting depth to be set by the amount of cutter protrusion, a nose with a pivoting ball with through hole for the cutter allows engraving over 10 degrees either way around a 20mm cylinder with a 2D engraving job

http://www.gravograph.us/engraving-products/Engraving_Nose_Cones.php

[GEOFFREY]

[QUOTE=magicniner;65341]You can use an engraving spindle which takes a Gravograph nose and allows cutting depth to be set by the amount of cutter protrusion, a nose with a pivoting ball with through hole for the cutter allows engraving over 10 degrees either way around a 20mm cylinder with a 2D engraving.

That only works fine for 2D engraving if everything is to be engraved at the same depth. G.

[magicniner]

http://www.gravograph.us/engraving-products/Engraving_Nose_Cones.php

By mounting a spindle with this type of nose on a vertical sprung slide (to mimic the original use where hand pressure on a manual pantograph kept it at it's set depth) one can engrave on convex, concave, rippled and non-level surfaces.
The text on this 20mm radius curved Titanium sheet part is about 3mm high -

http://i135.photobucket.com/albums/q158/magicniner/45ACPCover800x600_zpscf33e62c.jpg

It's possible to engrave 3 or 4 lines of text on these 20mm radius parts without noticeable depth/width variation.

Geoffrey,
If you want 3D engraving you just set flat parts perfectly level, anything else you model the surface for and then set up your part in exactly the orientation in which it was modelled,
Regards,
Nick

[GEOFFREY]

Thanks Nick, I am aware of what you are saying, I was merely making the point that whilst a fixed projection from a spring loaded toolholder will follow the existing surface and ensure a steady depth below that surface, it will not allow engraving at different depths. I do have a card/vynal cutter that uses exactly that system. G.

[magicniner]

Does a spring loaded cutter with no depth guide allow accurate variable depth engraving over an uneven surface?
Or will changes in surface height change the pre-load on the spring and vary depth?

[GEOFFREY]

When I referred to a fixed projection, I did of course mean a fixed projection from a nosing that touches the surface. G.

[magicniner]

.... not allow engraving at different depths.

So what will?
The OP referred to parts that are not flat, I was responding to the OP with ideas that might help achieve fixed depth on curvy surfaces

[EddyCurrent]

Here's another spring loaded tool
http://www.mrrace.com/SpringTool/index.htm