October 13, 2019 at 8:47 am #117720
I am brand new to CNCing. My MPCNC works great, it passed the “crown test”, and I’ve even done some successful engraving of acrylic. Today I decided to make a sign for our BBQ team for a competition next weekend, and admittedly, I’m using really cheap plywood…. but the edges of where the bit travels leave a lot of “hair” (see picture). I’ve tried reducing feed speed from 8mm/sec to 4mm/sec and that did not help. Cranking the spindle to max speed helped some. It seems to be worse when the X-axis is traveling toward the left. I am using a 1/4″ carbide square end mill.
Does anyone have any advice for a more clean cut in this material ?
Attachments:October 13, 2019 at 9:16 am #117728
That’s normal for an upcut bit, just sand it off afterwards. You can minimize it with a downcut bit instead, but you run the risk of compaction while pushing the sawdust down and that can lead to other problems. If you are working shallowly you can use a downcut, if you are cutting deep use the upcut, a small finishing pass and plan on sanding a bit at the end.October 13, 2019 at 10:27 am #117734
Agreed, a downcut bit is the solution. You run into problems for very deep cuts if the sawdust isn’t naturally blown out of the cut, but for your task it will be fine.
Maybe you could put another board on top of your workpiece and cut through both? It’s wasteful but perhaps the top board will hold down the hairs so they are sheared off instead of lifted. I’m guessing, I’ve never seen this done.October 13, 2019 at 2:51 pm #117758
The same trick does it when you drill holes in wood. Countering the lower surface where the drill comes out with another piece of scrap wood rewards you with a clean edge.
Another option is to use a straight endmill bit for wood without any twist in it.
You just have to make sure you remove the debris (blow and vac!)
And applying toroidal milling leads also to very clean cuts. Also ideal for the MPCNC since the forces acting upon the bit remain small.
And yes, clamp the bit as short as possible. Just leave the absolutely necessary part hang out of the chuck.October 14, 2019 at 5:15 am #117827
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