Hi,
I'm trying to make the bed of my MPCNC but I encounter issues and I don't really want to burn my house down :
I tried to level the bed of my mpcnc by milling 2mm deep into the plywood surface but the some areas are burned like if the RPM or feedrate are too high, sometime the milling machine slow down, like if it was moving too fast, the lines are not straight and sometime, the milling machine is going too far, bumping into the limits (I think that for this part, I'll just remove 5cm in X and Y, it's no big deal, this MPCNC is already huge). [EDIT:the .SVG files where not on scale for some reason, I changed to .DXF and this bumping issue is over.]
So far I know the RPM that my milling machine can achieve with it 6 speeds:
13000 RPM
17000 RPM
22000 RPM
29000 RPM
31000 RPM
33000 RPM
I think that my flat endmills are in "HSS TiAlN" (it seem to be an old stuff that is used to cut trough metal), that they have 4 teeth each and this:
diameter 2mm (0,078"), 13mm (0.512") high cutting zone
diameter 6mm (0,236"), 7mm (0.276") high cutting zone
it's written like this on their boxes:
4 teeth 2x6x7x51 HSS-AI (for the 2mm)
4 teeth 6x6x13x57 HSS-AI (for the 6mm)
To summarizes all of this, I need your expertise to tell me if I'm doing something wrong/very wrong/incredibly stupid
You'll find an image of what I managed to write for my 2 endmills in Estlcam.
Thanks a lot for reading trough this, and thanks in advance for your precious help!
at 30,000 RPM you should have a single flute endmill, a 4 flute is basically spinning more than 4 times too fast, trying to start a fire, not actually cutting anything.
30k rpm in poplar plywood with a 2 flute upcut end mill will do 20mm/s easily, with a 4mm DOC, and 15mm/s with a downcut one
downcut kinda needs vacuuming or something that blows chips out of the way, because it tends to pack them into the groove; before I built a vacuum attachment, my makita router did this itself because it is air cooled and blows the air down with the force (and noise) of a shop vac; the downside was, of course, that dust and chips went everywhere
4 flutes is too much for wood, there is no room for evacuating chips so you need to go slow and adjust RPM accordingly, unless you want to start a fire; even 2 flute bits made for metal have the same issue (no space for chips)
Â
get some 1 or 2 flutes compression or downcut bits, they give the cleanest results (straight 1-flute bits work as well, but youâll have to sand a bit and I donât think they make them in small diameters)
also, see this for a visual comparison of different cutter types in plywood: https://invidio.us/watch?v=2FjXsZKrobQ (I remember seeing one that did the same kind of comparison, but included acrylic and possibly other plastics a long time ago, but I canât find it now)
Thank you very much guys!
Based on your answers, I think I need to find these end mills and to set them up like this:
Ă1mm Compression (up-down) end mill with 2 flutes [feed-rate 20mm/s, 29k RPM, 2mm depth/pass] (but maybe I should aim at something pointy instead, I really don't know..)
Ă2mm Compression (up-down) end mill with 2 flutes [feed-rate 20mm/s, 29k RPM, 5mm depth/pass]
Ă6mm Compression (up-down) end mill with 2 flutes [feed-rate 10mm/s, 29k RPM, 5mm depth/pass]
Do you think it will do?
I'm having a hard time searching for these 3 tools online (especially if I want to keep them the same total length, because my MPCNC can't get really high).
Also, I really can't find something smaller than Ă2mm. Is that because it would be too weak?
Can you recommend me a website that will sell that?
I found quite nice results with around 17000 but evrything its depends on machine, material, speed that you are truying to cut and how dep. You need to find sweet spot.
Thank you, thatâs really helpful!
The material is going to be plywood or MDF (medium density wood).
The speed is probably going to be between 10mm/s and 20mm/s, depending on the diameter of the end mills (I intend to use Ă1mm, Ă2mm and Ă6mm).
For the depth, m0n5t3r kindly showed me a picture where we can see a 5mm deep cut in one pass but I should probably try something more shallow at first, like 2 or 3mm deep.
(I really hope that you understand me, my English is far from good)
Thank you, I will have to do full depth cuts, so I have to use compression bits.
Youâre right, they are quite expensive, but I donât mind spending 50$/⏠for two end mills if the counterpart is getting clean results at the bottom and the top (and not burning my house down)
But now that I know what I need I canât find it anywhereâŚ
2 flutes flat compression end mill Ă1mm, 2mm and 6mm seem to be some kind of unicorn end millsâŚ
I think Iâll just switch the Ă1mm for a spherical end but I just canât get the two other ones.
Gosh I feel helplessly ignorant about all of that. Itâs really frustrating.
Never-mind, Iâll go with the flat ones.
30k RPM is what the typical palm router will do (I used a makita 3709 before switching to a water cooled spindle), itâs not that unusual;
please mind the endmill diameter, 2mm will do 20mm/s at 30k RPM, but I wouldnât try this with 1mm ones: the cutting edgeâs speed will be half of a 2mm endmill at the same RPM, and then you also have to look up acceptable chip loads for the thing, and halve them just to be sure
Â
I havenât seen compression cutters smaller than 1/8 inch / 3.175mm or straight cutters smaller than 4mm at the usual suspects (aliexpress); 6mm ones are pretty easy to find and hard to break, but they wonât work for small features due to their size (edit: search for âup down cutâ, because reasonsâŚ).
Here in Australia I use âAdamâs Bitsâ great qulaity & price. I purhased several Compression bits (profile cutting ) on my Makita router. ALso bought a few tapered round nose bits.
