Need help with speeds / bit choice, problems with rough edges

[Robert Lambie]

We don’t have much call for this, but when we do, we normally cut the ACM first, then apply the graphic using our vinyl mounting table. But not in any great volume as such.

I assume you have a machine with an onboard camera to detect registration marks?
The thing is, the only real successful ways to do this, that I have seen, is flatbed printed graphics, which will not lift or create a rough finish as the vinyl does when it is router cut. but can chip!

or, if your machine has a tangental cutting head option, it will do this with a blade and give a nice clean cut but obviously, not all hard materials will work.

[David Stevenson]

We haven’t a camera but have been printing a thin line around around the borders of our artwork and using this to line the cutting head up to. It was a pile of small signs for an outdoor pursuits company and it seemed ideal rather than putting each graphic on individually after cutting the dibond to get the cnc to cut them. Was hoping for a lazy, sorry automated way of doing jobs like this to get a perfect finish. We find it difficult to get a nice edge on dibond when cut manually. I know you can snap it quite easily but it always seems to have a slight bend in it afterwards which drives my ocd crazy lol. Thinking about possibly swapping to acrylic for some jobs and cutting them on the laser but this is a massive increase of cost for acrylic v dibond. It’s fitted with an oscillating head but I dont think the blade would be capable of cutting dibond 🙁

[Robert Lambie]

If you find that you are managing to get an accurate contour cut using your method of alignment, you could contour cut the print in your cutter, “leaving the line mark” that you use as your guide, when weeding. mount to the board as you are doing now, and leave a 2mm space around the perimeter when cnc contour cutting?

This is common, even on flatbed printed contour cuts and the like.

[Simon Worrall]

David if you want to cut through acm with vinyl on it use a downcut spiral bit. That will push the vinyl edge down onto the material rather than pulling it away from the ACM as with an upcut bit, which is whats causing your ragged edges.

Downcuts do generate a lot of heat, so you have to use shallower passes than otherwise.
They also help the small parts to not jump off the table by pushing downwards, so there is a bit of a bonus.

[David Stevenson]

Food for thought guys. Would like to get this perfect if possible. The cnc has endless possibilities it seems. Looking forward to whats to come 🙂

[NeilRoss]

Create two toolpaths on the same profile line.

First one using a V bit set to (say) 1mm deep ON the line.

Second one using a straight mill bit (up cutting should be OK) and set it to cut OUTSIDE the line to the required depth of your material (plus 1mm if you have a spoil board).

This should give you a clean edge with a chamfered edge.

You’ll need to carry out trials to determine the best speeds for the materials you’re milling. Try on a test panel around 10mm sec travel at perhaps 18,000 RPM cutter and adjust as required until you get the best result.

[David Stevenson]

Had a go Neil using your techinque and have to say we’re delighterd with the results 🙂 Perfectly smooth edge, finished product looks great. We’ve also ordered a downward spiral bit as recommended by Simon. The V bit creates a very thin black border which doesn’t bother us but will no doubt upset some awkward customer. Slowly getting the hang of this cnc , only broke 1 £70 bit and 2 £25 oscillating blade so far!!! We’ll get there in the end lol