Upcut bits or downcut bits for a novice...?

Ok, this weekend I should do my first real attempt to cut foam and then plywood…need advice on what bits to go for, my idea is to cut a sort of chair and also try a new project I’ve had in mind for very long which will basically consist on making slots with a slight recessed area just touching the slot…

Any advice will be welcome…



Upcuts are the safest, simply because they actively clear the chips on their own. With a downcut bit, you have to be very aware of making sure you get those chips out. That means pretty much everything is a pocket so you can use an adaptive/trochoidal toolpath. You don’t want to cut straight bit-width slots or bit-sized holes with a downcut bit.

The downside to that is tearout. Upcut bits tend to leave you with a rougher surface edge. This can be mitigated with a sharp bit, a light sanding and/or finishing pass(es), but you’ll never get rid of it altogether. But many people prefer a light sanding to replacing the shop fire extinguisher…

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If you can, get a known good bit to start with. The ones in Ryan’s shop are great. The single flute upcut endmill is a workhorse. It is nice to not worry about the quality of the bit.


I bought these 2 bits just in case…but I’ll probably need an adapter…which one should I go for first ?

The short one works great. I haven’t used the long one, myself. I think the short one, and the v bit are what I would start with, and if you’re not planning on buying them from elsewhere too, I would get more than one. It’s not fun to have everything ready, and you break your last bit.

Thanks Jeff…pitty I didn’t get the collet adapter and more bits from Ryan…will do it next month…for now I’ll have to stick to something I can buy around here…delivery was very quick…just 10 days or so !!!

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I’m stuck, my graphics card went bollo**s on Sunday eve so waiting for a new one, unfortunately for me it just blew off when I was finishing a redesigned XZ support for adjustable belt tension…and guess what??? Didn’t have the time to save it :man_facepalming::face_with_symbols_over_mouth:
For now I can’t either get any fancy easy design to test try my LR2, so I’m a bit frustrated at the mo…but hey !!! Good things come to those who wait, isn’t !!!

Rant over…I really needed to let it out.

I’ve found OnShape’s Android app surprisingly useful and functional, given the smaller screen size. Certainly not the full-featured desktop app, but mostly all there. I’ve added a feature or two while on the couch in front of less than compelling TV. And while I don’t use it, Kiri:Moto can handle CAM for both FDM and CNC machines (even SLS and lasers).


Btw does anybody know where to get a collect adapter from 6mm to 1/8” ??? It’s for a KATSU, Makita rt0700c style machine which I want to give it a try before moving to something better…

I can’t seem to find anything and I have 2 bits from Ryan’s shop that are asking to be used :rofl:


That’s tricky. A lot of them add a huge amount of stick out and aren’t very rigid, and have runout. But some people swear by the er collets. The best is to find a collet made for your router and they aren’t always from the manufacturer.

I’ll keep searching then, I understand Ryan’s adapter won’t work on my cheap Makita version of the RT0700C…??? I’m a bit confused on size collet as in EU almost all are 6-8-10mm and in USA are as far as I’ve read people talk about 6,35mm etc…which are not an exact match when converted.

I have a set of ER11 collets and, they work in my Makita. The 3mm collect does the trick for 1/8" bits.

After operating a variety of CNC machines over the years I can say that you should start with Up it’s as they are way less likely to start a fire in most materials. Just remember that using an hour will pull up the hairs on your top layer but will leave a clean bottom layer.

Now with down it’s I wouldn’t use them with all materials. Specifically MDF. MDF is very prone to starting fires especially with added friction. So think about making holes in mdf with a 1/4in bit, there is no where for the chips to go but down and that is like you rubbing 2 mdf sticks together really fast. Poof fire that is now a pain to put out. This can also happen with plywood but it’s not as prone to lighting up like mdf is.

What I love about downcuts tho is that very nice surface finish that you get.

However, if you plan your cuts ahead of time and flip your A-side/B-side (if you have one) than it shouldn’t be a problem.

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Y-van what is ER11 ?

Thanks m8, very explanatory…we don’t want fire…and yes I’ve worked with plunge routers on mdf and it always at some point end up smelling as it’s going to light up the day :rofl:

I’ll stick to 1 flute and upcut bits then and see how it goes.

It’s a standardized collet size. Kind of like NEMA-17 is a standardized motor size, or M3 is a standardized connector size.

Thanks @kvcummins , I’ll do a search with that and see if I can source it local.


Ordered these to see if they’ll work…never seen or used anything like it before, so I’ll to check how to securely use them. At the end I’m interested on the 1/8 one so I can abuse Ryan’s bits too…
Will report back when I have them delivered…

Cheers and thanks,

3pcs ER11 CNC pinza de alta precisión para la máquina de grabado CNC Fresadora torno herramienta del titular 1/8 pulgada (3.175 mm) 4 mm 6 mm https://www.amazon.es/dp/B07DK8HF4B/ref=cm_sw_r_cp_api_i_irbuFbJ5GFTG0

I don’t think they were ever intended to fit, but they do… well. The taper matches up and there is no more runout than with the OEM collet.

Please let us know if you agree when you receive yours.

I would say though generally I only use single flute bits for cutting plastic I generally don’t use them for cutting wood generally only use two flutes for wood. However, i dont see any issue using them on wood