2D pocket toolpath not following max stepover value

[tomsaubi]

I'm using a 3018 hobby CNC machine, using a 6mm bit with a 3mm stepover on a 2D pocket toolpath. However, rather than doing a helix plunge at the beginning of the toolpath and working out from there, the tool makes a long carve the full width of the tool. The machine seems to struggle with it - is there any way to prevent this from happening and have a 'kinder' start to the pocket?

(I would like to do adaptive clearing instead, but don't think my machine can handle it...)

The setup is the Wood setup in the file.

[JimHeaney]

I'd really suggest doing an adaptive strategy for this. I've always had similar problems with pocketing, and usually, I have to brute-force it with a series of sketches. 

If this is in wood, you do an adaptive at 15-30% engagement, then step down 2-4x the tool diameter and get the part done faster and with less tool load. 

[tomsaubi]

Thank you - I'll have a look into that. Being able to pocket faster with less tool load would be incredible.

What kind of machine are you using? I very briefly looked into this before right when I first got my machine, and at a glance it looked like it was too much for my machine, which I think was backed up by someone else with my machine. I think it's because of that larger stepdown that you mentioned - I found the max stepdown on my machine to be 0.5mm. Does adaptive clearing somehow negate the difficulties of using a larger stepdown?

[JimHeaney]

I use a few different machines, mot of them bigger than yours but one of them is close.

Adaptive relieves tool pressure by only engaging a portion of the tool, no matter the geometry. In traditional strategies, the tool may get to a corner and shoot up to 75% engagement, then back down to whatever it is supposed to do. 

Adaptive is generally easier on the tool and allows you to use more depth at once, reducing overall machining time. I've done 1" depth of cut with a 1/4" tool using adaptive before, it helps to wear the flutes evenly. 

The only limitation I've run into with adaptive is that it generally needs a smaller tool, and some machines can't keep up at the speeds they want to be at. 

[daniel_lyall]

That's a very lightweight machine, For the wood setup in your toolpath you have a maximum stepover of 3mm and a minimum stepover of .3mm(this gives it a range to work too)  change this to 3mm if you do not want a tinny step over.

The step down is .5mm are you sure you want A step-down of .5mm, If it was me with the size of your spindle I would do a max of 1mm in wood, foam can be way more as it is soft.

[tomsaubi]

I see. I think it's those 75% engagement points where I get loads of chatter and subsequently have to reduce the speed on the whole toolpath.

A new 6mm roughing bit should be arriving tomorrow so I'll wait until then and do some experiments.

When you say adaptive needs a smaller tool - would you recommend going smaller than 6mm, then?

Was that 1 inch depth on your smaller machine? The idea of using more of the bit sounds good - so far I've only been using the bottom mm or so, on wood. Really doesn't help with heat buildup and bit wear!

[tomsaubi]

Anything over the 0.5 and my machine makes horrible noises. Although I'm figuring out how to increase spindle speed limits so I can maybe go deeper as you say.

[JimHeaney · Accepted solution]

The smaller tool is a general rule. It sounds like you are already at a small tool, if anything I'd try to go larger. The smaller tool comes into effect when you have a part designed for a 1/2" endmill, but need to use a 3/8" or something along those lines.

That DOC was on a larger machine. For smaller tools on smaller machines, You can't go as far down, but 0.5mm is what I'd do brass or aluminum on that sized machines, not wood. I usually keep around 2x tool diameter for stepdown in wood with small tools, but you're more familiar with your tools and material than I am so stick with what seems best to you. A part that takes a long time to complete is better than a part with a tool broken in it! 

[daniel_lyall · Accepted solution]

[tomsaubi]

2x a 6mm bit smells like trouble (yes that photo above is very similar to my machine) but I'll give a much deeper cut a shot.

For now I'll play with my new 6mm roughing bit, next time I'll go up to 8mm! Thanks for the advice guys, feels like I've got my foot in the door of a new part of the toolpath world...