I think I'm ready for wood....

Mostly Printed CNC - MPCNC Advice
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Ryan - you’d be awful proud if you could see me now. Hahaha…

I think I’m ready to start trying to cut some wood here. I was watching a test run in foam and couldn’t help but wonder two things. First, does the awe of watching the MPCNC run ever go away? And second, more on point - is there a table or chart out in the webiverse somewhere that lists feed rates and plunge rates for given types of woods? Or is it too variable due to the wide range in bit diameters, spindle speeds etc? What’s the “cautious” approach on feed rates? Is it the “For the Impatient” in the Basic Info stuff?

Also - I was looking through the bits in the store and those on Amazon (I had to order a fresh set of ice carving endmills today…the season is coming up soon…so while I was doing that I popped over to Amazon and v1Eng to have a look at the wood CNC bits). There surely must be a semi precise way to facilitate tool changes without going to the dual end stops, no? I was thinking an adjustable pedestal that you can screw/unscrew to different heights such that you slide the bit into the collet, slide the pedestal under, let the point of the bit rest on the pedestal while you carefully tighten the bit in? When the time to change comes you just do the same with the next bit? Any reason why that wouldn’t work with some degree of accuracy?

Then lastly - to really convolute this thread…what sort of bit collection “should” I be building? Short, long, ball nose, flat,

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Wait…One thing. To this point I’ve been using the foam as my “CAM” testing because I don’t have a working CAM preview solution yet. When I open a code file in Repetier on the Mac sometimes I get a wireframe, sometimes not. In either case I can’t get a program cut preview anywhere (or I don’t know how). I do get the preview with Estlcam when I save the code off but that’s only partially intuitive to me. Any advice?

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I have an ESTLcam tool change script that will lock the x and y motors and let you move z to change the bit, and then press to start again, but you need an lcd to do it. If you search my posts Im pretty sure I've posted it in the past. With this method you will only have to make sure z is set correctly.

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Lowrider v1 with 4’x5’ cut area.

For an initial bit collection you would probably like to have a V-groove end mill (90 or 60 degree), upcut flat endmill, and a downcut endmill.

V-groove: Used for carving/engraving into your wood. Usually for sign making. The cuts are beveled or shaped like a “V”.

Upcut flat endmill: Used for cutting things out (i.e. cutting all the way through the wood). The upcut is needed to eject wood chips out of the top of the cut.

Downcut flat endmill: Used for inlays/engraving. Some people prefer their engraved cuts to look like a channel “|_|” rather than a “V”.

As for size, you have to get the shank size that fits your collet. Having both 1/8" or 1/4" collet come in handy. For flute size, I personally have better results with 2-flute endmills on wood and 1-flute on acrylic. I have the DW611 with adjustable (1-6) RPM setting in which I set relatively slow at ‘1-2’ for 2-flute and ‘3-4’ for 1-flute.

For sign making, I prefer:

Engraving - 1/4" collet with 1/4" shank 90 degree V-groove bit with 1/2" cut diameter (XY-15mm/s, Z-3mm/s, DOC-4mm).

Cutout - 1/8" collet, for my 1/8" shank and cut diameter upcut endmill to cut the profile out (XY-13mm/s, Z-3mm/s, DOC-4mm).

Caution, the speeds and depths of cut (DOC) vary from machine-to-machine. These setting work well for my Lowrider but there was trial and error before I was comfortable with the results.

Hopefully this makes sense to you but it really all depends on what your planning on making.

The sign size is roughly 14"x24".

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Can you tell me why or in what situation we’d want to use a downcut vs and uncut flat or the reverse? Could you not just use the uncut all the time for everything or is there a specific scenario where the downcut is used?

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Good question.

Lets start with the upcut. The upcut works great for cutting all the way through the workpiece. The reason for that is because it ejects the chips upwards and it could be messy but a dust collection (vacuum) can help with that. The cuts made by an upcut bit are usually the thickness of the bit itself and makes multiple passes over the same cut. Also, by ejecting the chips upwards you’re removing material from the actual cut which allows the bit to cool a bit better and not recut chips. The problem with an upcut bit is that since it cuts upwards, the surface of the workpiece won’t be smooth. You would have to clean up the surface by either sanding or using an exacto knife (tedious work).

Now for the downcut. The downcut mill bit sends the chips downward into the cut. I use the downcut mill bit to make shallow pockets that are wider than the mill bit being used and shallow cuts that only need 1 pass. You can do multiple passes on pockets because the chips that are sent downward have somewhere to go…the pocket. The problem really lies when you make single line cuts because the chips being sent downward have no where to go so it kind of gets packed down into the cut. This can cause the bit to heat up, steer off course, start a fire, and/or dull your bit. So why use the downcut? Well, since the downcut mill bit cuts downward, you would end up with a much cleaner/smoother surface when your job is complete. This can be helpful because you may have pre-painted your workpiece and sanding would just ruin it.

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Oh wow! What a difference. Could a person (assuming he/she knows and is good at tool changes do a first shallow cut with a downcut and then complete the rest of the mill operation with an upcut? Although I guess once the first shallow cuts are made the chips have place to go…

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I don’t see why that wouldn’t work.

I have gotten away with just using a downcut bit for both engraving and cutouts on 1/4" plywood, 1/8" downcut single flute mill bit, DOC 1mm, and a vacuum. You’re basically sucking out the chips/dust before it accumulates and gets packed down.

I’ve also heard of people putting masking tape down on the workpiece and using an upcut for engraving. The masking tpae is supposed to reduce splintering and fraying.

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Sure. I did that for a few jobs and then I just moved to a compression bit. Upcut and downcut in one bit.

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Oh my! Now that’s a perfect (and spendy) solution!

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It is, but when you cut stuff on a daily basis for work, time is money, and time saved is money made.

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