Machining Small Wood Items Without Sanding on the CNC

      Can a CNC router make small pieces out of solid wood that don't require sanding for a smooth finish? November 8, 2007

Question
I am not a CNC owner, but am considering a purchase. I'm still exploring the scope and limitations of the machines. Let's imagine for a minute that I just had my CNC router cut a bowl out of a solid piece of hardwood. The bowl is about 2 inches deep and 4 inches in diameter. It's just small enough and deep enough that I can't get an orbital sander in there to sand the inside. Let's also imagine that I make enough of these bowls that hand sanding is not a realistic option.

1: Are sanding operations usually necessary on routed parts or is the finish already that good?
2: Can CNC routers be fitted with sanding attachments somehow?
3: If not, are there any other tools out there for sanding small inside contours?

Forum Responses
(CNC Forum)
From contributor J:
If you use a small enough tool stepover, .02 or less, with a ball end mill, you should not have to bother sanding if the machine is mechanically sound.



From contributor R:
If you have a specific application like this in mind, you would be very wise to have a part like this cut on any machine that you are considering purchasing. There are ways to adjust step-over and vibration. Tool quality and wood species also have an influence, but my experience is that there is almost always some hand cleanup on these types of routed parts. Make someone show you a completely finished part that comes off the machine without further cleanup before you pay for a promise. Keep in mind that what you consider acceptable finish, as a woodworker, may not be the same to a machine salesperson or engineer.


From the original questioner:
Thanks for the input. I'm sure that there's a point where using a fine stepover with more machining time takes more work/time/money than using a rough stepover and hand sanding parts. I'll need to consider that.

I have actually been talking with a local guy that owns a CNC router. He has been helpful and I will definitely want to see some parts before I drop the money. Just for my own information, how about question #3? Any idea where I might look for something like that?



From contributor I:
I am certain that you will have to sand. No matter how fine the step-over. Ball end mills don't cut well at the apex. There are no rpms at the center. A 5 axis will let you machine on the side of the ball mill and get the best finish. Then there is the choice of which hardwood. Walnut will be good, red oak a mess.

I think hand sanding will be the only option. That's also a fair amount of material to remove. You will need roughing cuts and a finish pass. I'm sure a lathe will be faster.



From contributor G:
When you get tooling for your machine, make sure it's for wood. There are different angles vs. other types of materials.

Based on what you are machining, there are no sanding heads. Get the correct tool, use the correct feed speeds versus rpm's, and at best a slight sand may or may not be needed.



From the original questioner:
Well, it looks like some sanding will be necessary however I slice it. I will make sure to do some research and pick my tools carefully. So... there must be a few people out there that make something other than cabinets or signs or doors. How about wooden kids' toys? Those little train cars, dump trucks and such? In a situation like that, there would be high quantities of parts coming off the router and they would all need to be sanded. Does anyone have experience with automated bulk sanding processes? I have this picture in my mind of a machine that is similar to a rock polisher, but for wood. You would put your items in the machine, load in some sand or some other abrasive material, then hit go. You would do something else for 15 minutes, and bang... your parts are nicely sanded! Has such a magic machine ever existed?


From contributor B:
Have you looked at the Quickwood machines for sanding? As long as your parts are large enough to not jam and be securely in place while sanding, they should do the job you describe. If the parts are not large enough, you could leave them onion skinned together or leave multiple parts left joined together, and sand them as an assembly, as opposed to individual parts. This would not take care of all the sanding, but most of it. I have no affiliation with Quickwood, but I have customers who seem to get their sanding needs met by their equipment.

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