How about starting a Bits Thread?

Hi there,

I’m new to CNC and overwhelmed, make that OVERWHELMED by everything related to bits. Also feed, plunge, hell, all the dress neckline rates. Sorry, Dad CNC joke.

I’ve seen a few good videos (Mitz on speeding up via Max Jerk rates, which was good) and also the Cyber Reef Guru on bits.

- YouTube.

Here’s my question. It seems like down bits are the clear winner for cleanest cut…and up down bits as well. But with the up down or compression bit, it seems like you have to get the whole bit in there for it to work as advertised.

That seems really aggressive to me. I need to cut either 1/2 plywood for templates, or my dream would be to cut 1" mahogony for final.

I have no idea how to go about this in a way that won’t take 3 hours per cut. (Okay, some writers embellishment there)

Finally, while I have learned more about the various types of spiral bits, I have no idea what diameter I should be using. My first efforts have been using 1/8th" upcut bits from Amana, but it’s only good for 1/2" depth.

Would a 1/4" bit (I’ve got a Makita, so all shanks are .25") be the best way to go?

It’s it nuts to rout final cuts in mahogany, vs. just cutting plywood templates? This whole CNC experiment started becuase I wasn’t excited at the mediocre quality of my Rockler pattern bit, 1/2" diameter, which tears the hell out of everything, unless I trim the wood to about 1/32nd proud of what I need, which is pretty damn hard with a bandsaw.

Sorry for the FAQ. But I couldn’t really find what I was looking for.

And what do people think of a Bits section on the forum?

Thanks. I really am impressed with the responses I have seen here. Great community.

Not exactly. The downcut will make a smoother cut on the top surface but a rougher cut (tearout) on the bottom surface of your material. Downcut bits have a problem ejecting chips so they’re only good for shallow cuts - it’s possible to pack the chips in a cut channel to the point they catch on fire. At the very least they tend to trap heat which is bad for the bit.

A compression bit has a small portion that is an upcut geometry (usually no more than 1/4 - 1/3 of the overall length). To get the clean cut through on the bottom you don’t need to go full bit depth, just the bottom portion needs to go through the lower surface. These bits are good for plywood & melamine so the surfaces are good but the downcut problems of packing chips into the hole or cut channel remain. Also, you want to ramp these into the material so the upcut portion gets below the top surface.

Depends on the material. I usually use 1/4" as my go-to. A qtr inch has less deflection potential than the 1/8" bit. For 1/8" bits you can use either 1/4" shanked bits that are tapered down to 1/8" or straight 1/8" bits with a 1/8" shaft - you’ll just need a 1/8" collet. You can get good ones from Elaire. A 1/8" bit typically has a longer cut depth than a 1/8" tapered from a 1/4" shaft. You probably want to get a 1/8" collet so that you can get smaller bits like 1/16 or 1/32 which are good for 3D projects.

Nope. You may find a speed advantage to using a template but that’s typically because we tend to overdrive the pass depths when we’re routing by hand. Also, consider that when the CNC is cutting the final piece, it’s essentially a robot assistant and you can do something else. I tend not to make templates unless I need depth that I can’t get with the CNC and I’ll use the bandsaw to do the pattern cut followed up with lots of sanding, etc.


Jim, you rule. Thank you. Super helpful.

To recap: for 1" mahogany (my final material, on this modern Adirondack project), you would use 1/4" compression bits? Or 1/4" upcut bit?

I bought a few 1" x 1/8th upcut bits, 1/4 shank…and was just going to go slow.

But taking 1 hour, to cut a 30 x 10" pattern is sloooooowwww.

Was about to increase max jerk, which may not do too much, since, it’s just an outline cut.

Again, thanks for the info!

The only thing I might add to Jim’s post is that feeds and speeds are not absolutes. I try to look for chip load (saw dust bad, chips good) and adjust feeds/speeds/plunges from there.

I haven’t cut 1" mahogany yet but have 1-1/4" walnut and sepele (sp?) with a 1/4 upcut and not experienced any trouble. Cut direction might be a concern due to mahogany’s fine grain though.

I recently cut 3/4" MDF to make internal ribs for a large curved TV lift cabinet. (used bendy plywood so there are no angles on the body) All of the nested cuts couldn’t have taken more than 20mins to cut. I don’t know if that description is clear enough to give you an idea as to how playing with tool settings can really speed the process up though. Suffice it to say that I didn’t adhere to prescribed tool settings.

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Thanks for this, Phil.

Would love to see a photo of the TV cabinet. That sounds pretty cool.



I’d use the 1/4" upcut myself with a n inch of ramp.

For a super anal-retentive approach I might do a single pass using a 1/4" downcut to make the cleanest surface cut & then switch to the upcut for the rest of the passes.

Compression bits are good for composites like plywood or melamine, they don’t offer a lot of benefit for solid hardwoods.

The other but I use a lot is a chip-breaker. Instead of smooth cutting flutes the length of the cutting length, the flutes have horizontal cuts in them to really aggressively cut through and eject chips. But that usually requires a bit more edge sanding afterwards.

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It is finished in rosewood veneer while the top is curly sapele mahogany. (it took two days to cut and apply the veneer pieces…many had to be edge finished with a shooting board)

Picture is a bit dark because it is overcast today.
I call it the Big Bang cabinet. LOL


That Sir is absolutely beautiful!
I hope to see more of your upcoming projects on here.


Okay, that is nuts. Which is to say, amazing. Holy shit, Phil. My brain can’t even process half of the steps to build that. Hard to see, but did you inlay the veneer in a geometric pattern using cnc to carve? On a convex and concave curve?

If you made a video on the construction of that, or say, hypothetically, building one for your new biggest fan, you’d get 500k subscribers, pronto!

Super impressive.

Ha ha. Nah, though the build was 100% from scratch, the veneer was probably the hardest part being hand cut and applied. It didn’t like being applied to curved surface at all and took about 48sq ft. in total.

You have wicked skills

Not sure where the best place to post this is, but I wanted to let everyone know about a source for bits that I’ve been using and have been very happy with.

I discovered CarbideToolsSource a few months ago and have been using the 1/4" upcut bits with good success. They make their bits in their own shop in Oregon and shipping is free and quick. They’re in Southern Oregon and I’m in Portland and have received the bits the next day.

Their website is a little confusing to navigate. There is a page for woodworking-specific bits where they have a selection of up, down, compression, and V bits in several sizes. However, the bits I use aren’t on that page and can be found here . Five bits for $34.75 or less than $7 each. I’ve found them comparable to the whiteside bits but would be interested in hearing what others think.


Nice! The prices aren’t bad, either and, for those looking to scrutinize whether these are legitimately US-made tools, here’s the confirmation.

I like the notion of supporting small businesses, too, so thank you very much for posting this.

Their bits work awesome. I have been using them since I bought my Onefinity 2 years ago. I have used sizes 1/32nd up to 1/4 inch. I have used both the upcut and the downcut. Ordering is easy and turn around is fast. I have never had a problem with their bits.

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I would like to piggy back on this thread a bit to ask a few newbie questions on downcut/upcut when it pertains to specialty bits like keyhole, roundover, and spoilboard surfacing bits.

I am using Easel software and I am inputting all my bit info, and they are asking for: upcut, downcut, straight, v-cut options. So you have to select which option for each bit. While 90% of my bits are clearly marked as either upcut or downcut. I am unsure on some as they are not listed anywhere I could find.

I specifically need help with these 3 bits:

  1. Whiteside 6210 CNC Spoilboard Surfacing Router Bit, 1/4" Shank
  2. Amana 56125 Solid Carbide Point Cutting Roundover 1/8 Radius, 1/4" Shank
  3. Meihejia Keyhole Bit 3/8", 1/4" Shank

So are the above neither up-cut or down-cut and considered “Straight-Cut” instead. I am not sure. Thanks for your help!

Up-cut and down-cut are properties of spiral bits. The bits you mention are straight-cut.

These links are both to the same video, but I have selected specific times which show slow motion what is happening in each case.


@Matticustard Gotcha - that makes sense. I kinda figured that to be the case, but didn’t want to assume anything as I am just starting out my CNC journey. Thanks for the help!