[RossMosh]

I have a project to cut 60 crosses out of hardwood. This is a little out of my comfort zone. I normally machine plastics for signs primarily but I figured why not take a shot at it.

I tried cutting the design out of 3 hardwoods: poplar, cherry, and hard maple. I used the same feed/speed for all three of 120ipm and 16000 rpm. DOC: .25" and climb direction. I'll admit, the 1/4" upcut bit I used has been around the block so I ordered a 1/4" Whiteside downcut which should come in tomorrow.

My issue is the edge quality I'm getting needs sanding. A good bit of sanding. The straight sections need minimal sanding but around the curves and contours, it needs quite a bit of sanding. It either shows the machining lines or has minor tear. There isn't a huge difference in quality of cut between the three woods. Hard maple machined the best with Cherry and Polar essentially tied for 2nd.

When I get the new bit tomorrow I plan on doing the following: Oversize the part cutting in the climb direction. Then do a cleanup pass, full depth conventional pass.

I also have new rack gears coming in this week as I noticed the machine had a bit more backlash than it should. Hopefully that will help get a better product as well.

Any other recommendations?

[ger21]

How thick is it? And how big are they?

I would not climb cut the roughing passes. Conventional cut everything, and leave about .015" for the finish pass. You might want to try shallower roughing passes, it might come out a little cleaner.

The sharper the bit, the better.

[RossMosh]

The part is roughly 13"x8.5"x.75". Wood is supplied by a mill that does molding in house so the quality is better than what you'd get at a big box.

[jueston]

having a new high quality sharp bit will do a lot and a clean up pass will help, but i sand every stick of wood that comes off my mill.

do other people feel they have pieces ready to finish directly off the mill?

[aarggh]

having a new high quality sharp bit will do a lot and a clean up pass will help, but i sand every stick of wood that comes off my mill.

do other people feel they have pieces ready to finish directly off the mill?

I cnc machine many different types of woods and I also sand everything that is done. I've never had a machine finish I would consider good enough that it didn't need at least a lick or two of sandpaper, but I am pretty fussy which doesn't help.

cheers, Ian

[scedward]

I cnc machine many different types of woods and I also sand everything that is done. I've never had a machine finish I would consider good enough that it didn't need at least a lick or two of sandpaper, but I am pretty fussy which doesn't help.

cheers, Ian

I've had really good luck with 0-Flute bits....

Try this one: CMT 198.008.11 Solid Carbide Spiral Bit, 1/4-Inch Diameter, 1/4-Inch Shank - Spiral Router Bits - Amazon.com

-Scott

[CNCSammy]

The spiral up bit will pull the wood fiber up so this is why you have tearout.

A spiral down will be better but pushes the saw dust into the wood and causes over heating since the bit has to rechew the wood dust in addition to eat the material to be removed.

The best is a strait bit and take passes that are no more than 1/8 in. deep.


Sent from my iPad

[aarggh]

I've had really good luck with 0-Flute bits....

Try this one: CMT 198.008.11 Solid Carbide Spiral Bit, 1/4-Inch Diameter, 1/4-Inch Shank - Spiral Router Bits - Amazon.com

-Scott

Most of my finish work is with a small ball nose cutter, and in Aust hardwoods, so it's almost impossible to avoid any required sanding, no matter how minimal. Plus, I'm pretty finicky and apply many coats of oil, so I like to get a mirror smooth finish on most stuff.

cheers, Ian

[louieatienza]

Likely, if you experience roughness around curves, you either

1) have backlash in one of both axes
2) have flex in your machine, motor mount
3) need to fix your part down better

Generally, you would need some sanding work after cutting. The idea is to minimize that work. You can try running your finish pass at a lower speed, maybe 75% your federate, to see if that helps. I've never had much trouble with climb cutting, even finish passes, on wood since it's really soft enough for most any router to cut. But maybe you're pushing the boundaries of rigidity and accuracy of your machine. Hopefully you have a dust shoe that's connected to enough vacuum power to keep the kerf relatively clean during the cut/finish pass.

If you want clean edges on top and bottom, and you have a powerful enough spindle to do this in one pass, then a single edge mortise compression spiral may be what you need, run at a higher spindle speed and slightly lower federate. Another option is a 3-flute low helix finisher; the 3 flutes can sometimes "break up" the vibration that can sometimes be caused by 2-flute, and the low helix angle will make shorter chips (less edge engagement) than the normal helix on the 2-flute.

But even the cleanest of cuts can "glaze" the cut edge of the wood, regardless. It should be sanded. CNC machines are not replacements for such work.

[Jon.N.CNC]

I can't say I suffer these issues with 2 flute downcut, I get a very good finish. 16000 rpm is quite fast. I run 120ipm @ around 13000. However I do use an onsrud 5mm upcut compression for profile contours which keeps underside edges clean. And you can make multiple passes over 5.5mm just makes sure to use leads. Though the deeper the cut I find the better the finish. I use between 7 and 10mm, using feed optimisation on outer corners helps reduce tear out. Using a finishing pass with a small 0.3-.5mm stepover is a must. Depth of part permitting I finish only at full depth and repeat finishing pass.

Don't get me wrong you need to optimise the tool path as mentioned I'd likely get similar results of i didnt. 120ipm constant velocity if you have outer corners in the profile it's going to be pretty rough. Slowing the machines acceleration is a good idea. And as mentioned fixing solid is key, if your parts have holes in them, stick a screw in it, makes a huge difference.

You do also need a good bit of torque for hardwood, my 1.5kw spindle isn't up to the job imo but the 2kw on other machine is ideal.