Down Bits (Down Cut) And CNC Routers [What You Didn't Know] - Garrett Fromme

do you find yourself getting frustrated with  some of your cuts on your cnc router around   your lettering or cleanup surfaces where they're  uneven there's burrs and it just doesn't look good   and you don't know what's wrong well there's  a very specific reason this is happening   it's because of the down bit and the way it's  set up hi i'm garrett with idc woodcraft and i am   so glad you've come to this video because you are  going to learn the mechanics of the down bit for   cnc routers yes there is an engineering level that  once you get you're going to know what's going on   with your projects when they come out you're going  why is why are my surfaces uneven why did the the   lines around the letters show up why  am i getting so many witness marks   there's a science behind it and you're about to  learn it in fact when most people most cnc router   owners don't get this just because they don't  understand it at this level so you're going to   be like at the top 0.1 of knowledge where you  can pass this on to other cnc router owners   now the first half of this video is going to  discuss up bits versus down bits it's the second   half where you're going to start getting the big  aha moment so you want to stick with this video   all the way through and by the time you're done  you'll know exactly how to set up your projects   to avoid this problem in the first place so let's  just dive right on in and get you educated to that   like engineering level of cnc routing let's go  so let's start right off at the beginning what   is a down cut bit for all intents and purposes  on a cnc router a down cut bit is a side cutting   end mill designed to profile out  around items like this letter n and to clear out material as you can  see it's starting to do right now   there are two types of side cutters typically  that do this they're called end mills   one is an up bit and the other is a  down bit so let's look at the difference   this is a down bit when it rotates you can see  the spirals are going downward whereas an up bit   when it rotates the spirals are going upward   there's a distinct difference here the up bit  actually pulls the material upward and is making   a cut in the upward direction and that leaves  a burr on the side of the cut at the very top   whereas the down bit when it's cutting is  cutting in a down direction so at the top   of the cut it leaves it clean but there's one  other thing i want you to notice on the up bit at the very bottom there's a cutting blade right here and  right here the up bit is actually shaving   the bottom of the cut at the same time whereas  the down bit does not have a cutting edge on the   bottom in fact the bottom of the down bit is going  backwards so when it's rotating it's actually   trying to screw itself out of the material by  virtue of the forces here it wants to lift up and   the reverse spiral and the  reverse spiral on the flute   what that does is that actually  pulls the bit up out of the material   the down bit wants to pull it down a bit however  it's got the bottom cut and therefore won't do   that so much here's an example of the difference  this first cut is with a down bit and the next one   this one is an up bit now if you look at the cuts  up close the one on the right is with the down   bit you can see that the corners are very clean  and you don't have to sand them whereas with the   up bit the corners are rough you are going  to have to sand some wood away from that one now there is one other distinguishing  difference that i want you to take notice of   if you look at this slot on the right with the  down cut bit at the bottom and compare it to the   bottom of the slot on the left you're going  to see that there are two different heights   it's actually quite distinctive if we look  at it from the end it becomes very clear so we're gonna measure these two now this  board i actually cut another slot into before i   took it off but we are going to measure the left  the right one first the one with the down bit   and the depth is 0.24 inches now if we  measure the left one the one with the   up cut bit and just avoid the bur we have a depth of 0.285 inches very distinct  difference so basically what's going on is the   direction of the corkscrew of the cutting blades  or the flutes is actually mechanically pushing or   pulling the bit in one direction or the other so  an up cut bit is actually trying to draw itself   into the material whereas a down cut bit is trying  to push itself out of the material now how does   that translate more into the finish work of your  project well you've noticed on your projects that   some areas will be nice and smooth other areas  will have these little steps and they'll go down   and and you'll get the little burrs along there  well that's because of your tool offset or the   step over function that you're using when the  router bit is first making its cut it is cutting   100 percent diameter of the bit through the  slot like the example i showed you before   but if you have say a forty percent step over  that next cut it's only cutting forty percent   of the material and what's going to happen is it's  not going to pull itself down nearly as hard and   because of that you're going to  end up with a step just like that   so we're going to try to describe it this  way let's pretend that this is a job and we   are in my vectric software by the way and  this here is a slot being cut in the wood   this arrow is indicating the direction that the  router bit is moving the down cut now remember the   down cut wants to push itself upward well as it's  making its cut on the first pass it is literally   cutting the full 180 diameter of the router  bit so you have all that surface that's trying   to push the router bit up now when you come  into your step over passes let's say you have   a 50 step over half the diameter of the router  bit right here now we're only working with   90 degrees of the bit or a quarter of the bit and  because there's not nearly as much upward pressure   the router bit is going to relax down a bit  and what you're going to end up with is a line   right along here where this area is sitting higher than this area   now let's say the router bit comes back through  again with a 25 step over and now it's over here   that's less pressure there plus there's  much less material on the bottom   so this router bit is going to relax almost  down to its full depth so you're going to   show another step going on right here and this  area is going to be the deepest this will be   the second and this will be the shallowest right  here if you took it and looked at it on the side   but basically it's going to look like this in the  bottom of your cut where this area was the first   slot and this would have been from the step over  and this would have been where there was almost no   resistance at the bottom or on the side so this  is why you're getting all kinds of weird cuts   on your projects particularly around letters when  you're doing offset and it's tracing the letters   okay well i just want to stop for a second and ask  you if you feel like the information i'm giving   you is giving you some aha moments as to maybe  why your projects aren't turning out quite the   way you want maybe give me a thumbs up that tells  me that i am giving you the right information   to make you a little bit better actually this is  intended to make you a lot better and if you're   brand new to this kind of stuff still trying to  figure it all out well subscribe to the channel   and if you're really stuck you can always set up  an appointment with me we will do a one-on-one   get you like out of that stuck place and move you  further along also when it comes to router bits   i got tired of dealing with the big boys and the  real expensive bits and the cheap ones off amazon   so i source my own now and if you're interested in  a nice set that's built for like the cnc beginner   it's got everything there's a link down below and  individual bits as well so yeah check it out huh   you are getting some deep dive information  here i mean this is engineering level stuff   and almost no cnc out there gets this and this  doesn't register just because they don't know   but now you do you can pass on that information  as well anyway we got to get back into this so   you can get on your next project and make it  nice and clean all right let's go so let's   talk about how to stop that i'm going to show you  in the software here this is vectric particularly   vcarve your software will in some way shape or  form have this where you have a finish pass so   what we're going to do is go over our tool  path function and i'm going to close that   and so let's just pretend we'll just pick  this item right there it doesn't matter and   what we're going to do is do a pocket  so i've got to stop and tell you this   this happens when you are doing surfaces where  you're making multiple passes over a surface   so if you're doing a surfacing cut or any kind  of pocket cut this is where this happens at   and you'll see that from now on it's always  happening in pockets around letters uh curves   anything where you're doing multiple passes over  the same like area where the tools just gone past   so all right let's get back to this so in this  pocket we are set up for a depth of 0.1 inches   using a quarter inch end mill and this is a a down  cut now it says here we have one pass and what   it's going to do it's going to pocket out this  entire project right here if it was all one vector   but it's you're not going to see it in this  example it only shows up in the actual project   but we're just going to pretend that this  is the project and we're going to pocket out   this area here so it's going to make one  pass it's going to go down it's going to   do all its cuts and you're going to see  different elevations at the bottom of this   job and there's gonna be rough  areas there's gonna be okay areas the way that you fix this is go into your tool  path in this case we're going to go to edit   i'm sorry we are going to  go to the edit the passes   and we are going to set a last pass thickness so we're going to set that thickness actually  quite thin we're going to go to a .007 so you   want to set it to maybe a point zero zero five  to a point zero one and what that'll do is when i   apply you'll see here in the software it actually  created a second tool path so it's telling me what   the depth of the first cut is the final depth  and you see that final depth is a very thin cut   the reason what this will do is it's going to  shave off all the extra material there's going to   have no resistance from the side cutting action  and therefore it will be able to make a nice   smooth cut along the bottom now some people may  not like doing that because it doubles the time   but this is the way to stop this from happening  now you can do other things too like adjust   your step overs make them a little bit smaller  but you're not going to get this effect if you   adjust the step over in your single roughing or  single tool path if you want to do it in one shot   because at some point around your project  you're going to have less pressure and it's   going to go down so if you were to go  in to try to do that i would probably s   set up your step over to 80 percent or 90 percent  but that's not going to work because you're going   to leave some other tool marks called witness  marks you want to do a second pass always and   make that second pass thin and you will have a  much better finish at the bottom of your projects   and that's what we're doing on this sign here we  are cleaning up with a very shallow cut this is   a .07 you can see it's just taking out a little  bit of material but the key is there's no side   pressure on the tool so all pressures equal at  the bottom of the router bit and so we get a   nice clean surface all the way around we have a  little bit of witness mark from the router bit but overall it's very clean a  little bit going on inside of   the seat that's because of the tool  path so you may want to raster it we're looking quite good very happy with this  okay well do me a favor leave a comment of the   big aha moment that you just got out of this and  i'm really curious and also of course like it if   you felt like this was useful and router bits i  got them and one on one if you really just want   to get some one-on-one training to take you to  the next level you don't have to be stuck you   just want to get there faster it's like drinking  hard liquor versus drinking uh light beer you know   we'll do some one-on-one you can set  that up down below and um yeah that's   it all right go make a cool project and  give me a comment and give me a like and   have an awesome day doing this amazing  creative cnc stuff i love doing this and   i love teaching you all right this is  Garrett and i'll talk to you next time

Channel: CNC Routers, Beginners & Beyond - Garrett Fromme

Views: 33,194

Keywords: down bit, what is a down bit, what is a downcut bit, what is a down cut bit, down cut bits, bits for cnc router, down bits for cnc routers, down bits, downbits, cnc router bits, bits for cnc routers, down bits for cnc router, downcut router bit, down cutting bits for cnc routers, cnc router down bits, what are down bits, cnc router down bit, cnc down bit, cnc router, cnc machine, cnc woodworking, cnc bits, end mill, upcut bit, router bits, garrett fromme

Id: tykj6Nn-ysM

Length: 15min 51sec (951 seconds)

Published: Tue Mar 16 2021