Acrylic chips not clearing well & general cutting wisdom?

[TDA (John Torrez)]

@LiamN

That’s great John, I always have to read your posts at least twice to spot the things I didn’t know, then the ones I didn’t know that I didn’t know

Not quite sure if that’s a failure or success on my part but I’ll file it in the Pro side for now.

@LiamN

I’d be interested in what the downsides are on the compression cutters if you have time. I can guess that shoving chips together to the middle of the material is probably not optimal but is this bad when you have an open side cut as opposed to slotting?

Thx

Short version is that there’s rarely times that I find it’s necessary with proper feeds and speeds. Although, if those can’t be reached or maintained that would be a good reason to use one as a clean up where needed.

You’re right though that most of the problems are related to slotting (which is what they seem to mostly be used for). If you have an open side than most of the down sides are cutting force and geometry. They also tend to be more easy to break at the transition both from the meeting of the 2 cut directions and that most of the time more core has to be removed from the tool where they meet. The other option is to have an overlapping flute which is going to mess with chipload at that point. Add on cost and variations possibly needed for the transition point and it starts to leave a bad taste in my mouth.

@ProfessorEcks

Thank you John, i very much appreciate your detailed answer. Much of what you said, admittedly, is over my head right now… but between yours, and liam’s responses I look forward to coming back to this thread in the future when I have a better frame of reference for the concepts that you’ve shared with me.

No problem. Hopefully it’s useful either now or later. I might need to work more on the understandable part though…

@ProfessorEcks

For the UHG Gizir board, I’m not 100% confident about the composition of the PVC specifically, but they call it a PVC/PET sheet on MDF. It’s definitely not foil or melamine. They do have other products in this line that have Mel or foil but this is the UHG in black.

PVC/PET mix should be a bit easier to cut in combination as it shouldn’t require quite as high of a chipload than straight PVC.

@ProfessorEcks

Eyeballing the board, it’s about 1/32 thickness of whatever the blend of PVC/PET is that they use, on an MDF core. I wasn’t real excited about using a compression bit on MDF… I was originally gonna try for the whole thing with a single upcut, but then I’m thinking I’d just cut through the top layer with a straight bit, and then just take the rest of the MDF and the bottom layer with an upcut. I’d like to avoid an extra tool change for a third cut at the bottom. The good news is that only one side is the appearance face for my project, so I should be able to plan my cuts so If one of the faces isn’t quite as nice, I should be able to face it towards the inside.

Assuming you are willing to deal with the multiple steps for the coding you could use just a single tool and modify you chipload and cutting depth per material.

I wouldn’t use a straight flute unless I had to as it’s the highest cutting force of pretty much and geometry. The issue is that unlike a upcut or downcut you are engaging the entire flute at the same time. This causes a very high sharp load to the machine and tool.

@ProfessorEcks

You mention more aggressive tooling to balance the differences in material - can you give me a specific example of that recommendation? Is there a certain type of bit that I should be looking at? If you’re not comfortable with an open recommendation due to perceived bias, please feel free to direct message me. Thanks!

I’ll shoot you some specifics tomorrow. For everyone else though the basic things to look for are a higher rake, thinner edge and depending on the weakest material potentially a higher/lower helix. You also want a cutter the has relief and drop to keep only smallest part of the leading edge involved with the material. That last one does cost strength and potentially tool life though. If it’s someone you trust dealing with these kinds of cutters will usually be label for that specific material use. e.g. “soft media cutter”, “plastic cutter”, etc. Not listed as can cut it but that it’s designed for that material.

I did post some on geometry with some examples here Best practice for tiny endmills - #15 by TDA. Might help to understanding some of it. Although it’s in a completely different context. If I can get some time in the next couple days I’ll try to layout the basics in something more approaching english.