hahahhahhahahaha, Yup, dorks
you are right a 1/4 2 flute would be almost equivalent to a 1/8 single flute.I'm confused, can you explain? I'd think the velocity of the cutting edge of a 1/4" bit would be double that of the 1/8" at the same RPM, because the cutting edge is farther from the center so it has farther to travel each revolution. I'd think the extra flute would further compound that and you'd get (very roughly speaking) 4x the cutting ability at the same RPM.
...already took the top tier goal though (lunch with me, he asked to bring his cat).If you observe the cat as alive, do the quantum end mills have 3 flutes? Maybe they're entangled!
Think of it this way, twice as fast (at the cutting edge), but also take twice the power (or twice the rigidity) to cut at that distance. A ten pound weight in your arm extended straight out, or a ten pound weight at the end of a broomstick at the end of your arm extended straight out.
It is the same with the Z axis half the extension is twice as rigid.
So yes, the more flutes the more cutting ability but also the more rigidity and/or more torque needed in the spindle (or system) to do it. To keep all those flutes fed you need to move faster, to move faster you need more rigidity (or spindle torque depending on the systems weak link). For most all cncās torque is far cheaper than rigidity so you will typically get chatter before a stall of any kind (spindle or stepper).
Check it out in a calc, keep all things equal and only vary the flutes and diameter.
I could be totally wrong, but I spent enough time in that rabbit hole for today. Tomorrow thoughā¦new day.
Yeah. Thatās true. Why did I think it was slower? If I got it right through some feeds/speeds/rigidity jujitsu, that was not intentional.
Now Iām also not sure the speed of the ātoothā makes much difference. If itās one flute, moving at 10mm/s and 100 rotations per second, the depth of cut will be about 0.1mm deep, no matter the radius or the outside speed of the flute.
I googled SuperPID, looks pretty nice but a bit priceyā¦ Does it work with Marlin firmware?
I am wondering if you can tell anything from the āchipsā produced during cutting, sort of like you know if your chainsaw chain is dull just from looking at the chips. Both times I have used the machine, it produced a fine powder like a coarsely milled flour. Somewhere between grits and AP flour, but closer to the flour. I have never produced such small āchipsā using a handheld router or on the router table.
I googled SuperPID, looks pretty nice but a bit priceyā¦ Does it work with Marlin firmware?The SuperPID is firmware-agnostic. It can run in two different modes, depending on your preference:
- With a dial pot, and no connection at all to your PC or microcontroller - just turn the dial to move the RPM up and down. I'd say 90% of people on the Shapeoko forums run it like this.
- Listening to a PWM or analog voltage signal from either your PC or your microcontroller.
I know that Marlin can output a PWM signal based on S commands, so yes, you could control it via Marlin if thatās what you wanted. I havenāt done this before, but in theory it should be very similar to configuring in GRBL. You do need both a PWM wire, and a RUN wire coming from your microcontroller (and a GND wire, but thatās easy). Depending on the board you have, this can be trivial, or it might require some soldering. I had to solder a couple of pins to available (but not populated) output holes on my motion board.
The only thing I dislike about the SuperPid, is that itās still just running a trim router or other AC motor, so at higher RPMs itās always going to be louder than a real spindle. If you donāt mind the volume of a trim router though, the SuperPid is a very nice device. I can cut all the way down to 5,000 RPM now and maintain torque.
I recently purchased an inexpensive Chinese 1.5kW spindle, which has the same functionality as a trim router with a SuperPid, but should be quieter (especially at higher RPMs). I wouldnāt put 1.5kW on the MPCNC (itās really heavy) but a smaller Chinese spindle might have the benefits of the SuperPid, plus be quieter, at about the same price as the SuperPid by itself. Of course, you have to play build-quality roulette, compared to a DeWalt and SuperPid that are always very well made and have good customer support.
I am wondering if you can tell anything from the āchipsā produced during cutting, sort of like you know if your chainsaw chain is dull just from looking at the chips.I believe that is true, but I'm not yet experienced enough to tell you what it *should* look like. I can say that I tend to get dust from my 1/8" bits, and actual chips from my 1/4" bits, using feeds and speeds for each that produce good results from each. I'm not sure if this is optimal or not, but dust (similar in composition as the dust from a circular saw) from an 1/8" bit is normal in my experience.
From @Jeffebe3:
Iām also not sure the speed of the ātoothā makes much difference.From @Ryan:
Check it out in a calc, keep all things equal and only vary the flutes and diameter.I understand and agree with everything both of you said... we're on the same page again. :)
What Iām wondering now, is how to quantify the extra lateral force a 1/4" 3-flute bit needs, compared to a 1/8" 1-flute bit. Anecdotally from hand-routing, moving from 1/8" to 1/4" doesnāt seem that different to me.
I tend to run 35 IPM at 21,000 RPM and 1/8" DOC with 1/8" 2-flute bits, and I tend to run 55 IPM at 17,000 RPM with a 1/4" 2-flute bits and 1/4" DOC. If 55 IPM at 1/4" DOC is too fast for the MPCNC, Iād just reduce the DOC, feedrate, and RPM to get back to a healthy chip load at a reduced torque requirement. I wonder if there exists a way to quantify the difference in required lateral force (stepper torque and rigidity) between a 1/8" and 1/4" bit at the same feed rate and DOC, with RPMs tuned for each.
Someday I may do a semi-scientific comparison, cutting circle-diamond-square tests and measure precision and speedā¦ but probably thatās a pipe dreamā¦ I donāt really have time. 
Yup. So many things I want to try but it cuts within my needs so this never comes about. After a few cuts your ear should know if you are close. For me test cuts get ran in every material anyway so I havenāt had the need to dial in my settings with the utmost precision. Once it works I hit run.
In wood it is pretty easy to understand what is wrong. Burning means too high of RPM (or moving too slow), broken or wandering bit means you are moving too fast (or your RPM is too slow). Once you understand wood then you can cut some other stuff which is not so easy to diagnose, plastic and metal.
I cut two more tool holders today at 3.5mm depth of cut and speed dial set to 5. I am happy to report that it sounded like a router cutting and no longer like a banshee.
On the second one, I tried climb milling instead of conventional, which made no appreciable difference in the amount of fuzz on top. Curiously, there were small dimples cut into the part above all the tabs. I donāt know if thatās related to climb milling or not. The only other difference was where on the bed the part was cut from. Iāll keep an eye on it and report back if I can determine the cause of the dimples.
Thanks to everybody for your help figuring out how to use the machine. I am pretty excited about how it performs.
1 Like
Iām not sure I helped.
I can say that a downcut but works great for fuzz in plywood. You just canāt plunge straight down (or drill).
Does the down cut have the same problem as the up cut, just on the other side? The bottom (which I have been using as the top) looks perfect with the up cut bit. I am not too concerned about the finish, itās just tool holders for the shop I am making, after all.
I have never used a compression bit, but maybe thatās just the thing to use to have both sides come out nice. What I donāt really understand with down cut or compression bits is where the chips are supposed to go. The up cut bit I am using already has some trouble getting the chips out on the deepest pass and that is in 12mm (~1/2") material. Maybe a vacuum or compressed air would help with that.
The down side isnāt as bad, because it has the spoil board as a backer, but it does still get some fuzz.
Iāve never tried a compression bit, but it seems like there would be a lot less flexibility, because you need to have the crossover point in the material.
The chips have a lot of speed, and they get everywhere, but there are still a lot in the cut. I sometimes follow it around with the shop vac, but itās not a huge deal. Maybe Iām not pushing my machine hard enough.
I made two more tool holders yesterday, one for pliers and one for a Japanese saw. For the pliers, I cut two Baltic birch brackets on the CNC and inserted a ~30cm piece of 8mm stainless rod between them. I really like the way this one turned out. I made a similar one by hand some time ago which looked quite a bit cruder in comparison. I think this is the only CNC project so far where I would say I saved time vs building by hand. The design on the computer was quick, it took less than five minutes to cut the two brackets and there was minimal sanding required.
[attachment file=52823]
For the saw, I cut pockets into a piece of plywood for the blade and the spine. There is a small magnet behind the blade. This one I am not 100% happy with. There is a little too much space on the right side and I had all kinds of problems with splintering. I was able to fix most of it with CA glue. It holds the saw fine, though, so Iāll call it a success.
[attachment file=52824]
Hubert, what are you using for software? The only thing I can quickly design is a circle or a square. 
Nice work too. I will have to borrow some of our ideas if I ever get around to getting things more organized.
I used inkscape. It is quick and easy if you know how to do it, but it is not really obvious if you donāt. It took me a while to get used to inkscape. For the pliers bracket, I started with a circle, then converted to a path, added extra nodes and moved those to make the part of the bracket that attaches to the wall. I also had to convert the node type on the corner nodes and move the tangent handles on a few nodes to obtain a decent looking curve.
For the saw holder, I scanned the cardboard blade guard that came with the saw and conveniently had an illustration of the blade itself printed on it. I imported that into inkscape and drew Bezier curves on top.
Ā
I just canāt understand Inkscape. I really want to. Someone I know who uses Inkscape and some other cad programs said Inkscape is for form and cad is for functionality. I do use it to convert images to SVG, but thatās it so far. I just get frustrated when I want something to be exactly spaced for something.
I like that pliers holder. I have a stack of pliers I need to attach to my tool wall. I think Iāll use your idea.
If you want exact in inkscape, turn off stroke and use only fill. That way, the size reported is the actual size and does not include the width of the stroke. You can also set your grid to whatever your spacing needs to be or make guide lines and the software will snap control points to the right spot. If that doesnāt work, you can manually enter the location of the control points. I donāt really have any experience with CAD software, we still had to hand draw everything when I went to engineering school. I started using inkscape for illustrations after years of using xfig, maybe that explains why I like it.
If you decide to make a pliers holder similar to mine, donāt make the hole for the rod too tight. It is easy to break the outer ply when you hammer in the rod if the hole is too tight. Let me know if you want the SVG file for the brackets.
Iāll have to find some inkscape tutorials. What you describe is the sort of drawing I once did in Freehand. I understand the concepts but havenāt figured that program out enough. I have Illustrator via subscription but it doesnāt make sense either. 