Intro to CNC - Part 5: Feeds & Speeds

[Music] hello guys Winston here one of the most mysterious subjects for people just starting out with CNC is feeds and speeds getting that perfect combination of travel speed and spindle RPM plays a big role in determining whether or not your CNC project ends in success or failure many of us myself included started out by having this information spoon fed to us looking up cutting parameters in a chart is easy and safe but the information you get from sources like carbide 3ds suggested feeds and speeds table is just that a suggestion those were determined empirically using one type of end mill on a finite set of materials with one objective to achieve a nice usable surface finish on the first try if you want to use an end mill with a different geometry or a different coating or on different materials or you're trying to remove large amounts of material fast then you're going to have to step away from the safety blanket of predetermined feeds and speeds what I want to do in this video is give you a high-level crash course in calculating and applying feeds and speeds knowledge I'm primarily looking to give you guys some insight and intuition into the physical process of machining so that you're better prepared to receive knowledge from people who are smarter than I am I'm just barely going to touch on the formulas and calculations you'll need to note because sources like transponders and applied science and CNC cookbook all do better jobs than I ever could on this subject that and I don't want to sit here and speak at you guys for 25 minutes so let's cut to a new camera angle and start laying out the basics this is a crude representation of the cross section of an end mill I realize this looks like a fidget spinner just bear with me here the shaded section here represents material to be removed as the cutter traverses from left to right two of the most important variables in the calculation of feeds and speeds are sfm surface fee per minute and IP T inches per tooth here's what those values represent sfm details how fast the edge of your cutter is moving how many feet does the cutting edge travel in one minute that's basically the circumference of the end mil times the number of revolutions per min inch per tooth is how far into the material your cutter has advanced each time a tooth comes around this is also the thickness of a chip that you can measure if you're cutting a material that shaves off cleanly IPT is sometimes referred to with other names or units like chip load or inches per revolution when you bind and mill the vendor will usually have a table of recommended sfm and/or IPT what they don't tell you is RPM and feed rate this is your sign that you've left the little leagues and are now entering machinist territory your job is to derive a feed rate given the constraints of your machine for example let's say I have a three Flute uncoated carbide end mill that I want to use an aluminum altar into an online calculator like this one to get a ballpark estimate for a feed rate to start with I'll plug in my end mill information into the calculator and look up a suitable trip load for a plane and carbide end mill this vendor recommends a trip load of between one to two thousandths of an inch you're not going to break any high speed machining records with a shape OCO so just accept that you'll be working near the lower bound of that range sfm is a parameter that should be considered more a guideline than anything else especially since the recommended sfm for aluminum dictates an impossible rpm to achieve on the shape OCO so I'm just going to put my foot down here and say we're gonna use 10,000 rpm this leaves us with a recommended feed rate of 30 inches per minute feed rate of course isn't the only cutting parameter we need to know for that you can try and match the horsepower of your spindle with material removal rates but honestly you'll run out of machine rigidity long before you reach that theoretical limit JPL richard has a good rule of thumb I like to use which is 0.25 inch end mill can cut 25 thousandths of an inch deep that lines up pretty well with carbide 3ds recommendations except for rpm which I find to be way too high I took the recommendation of my feeds and speeds calculator and I started at 30 inches per minute on this pocketing operation however during my tests I was finding some weird vibration issues traveling in the positive y-direction and this wasn't chatter it was a quirk of the shape pocos rigidity and modes of vibration people generally recommend feeding faster to overcome chatter that didn't help in my case what I had to do instead was slow down my feed rates and engage less material at a time that is use a smaller step over recommended feed rates are not firm you need to use your intuition and apply correction factors to them based on the capabilities of your machine you may want to back down by 10 20 even 50 percent depending on the rigidity of your machine and how well calibrated it is I backed off by 17 percent to 25 inches per minute and found that my CNC became very well mannered and trustworthy enough to let run indefinitely without problems but in this example you shouldn't go any slower than 50 percent of the recommended feed rate that would make your chip load dangerously low to explain why that matters let's go back to the desk cam every cutter has a finite sharpness represented by the blunted edge on my spinner represented by the blunted edge of my end mill model if the amount your end mill advances isn't enough for the next tooth to properly bite into the material then it just ends up smearing or pushing the material away this isn't cutting it's burnishing and it's not healthy for your end mill it creates friction and heat and it dulls your cutter there's also an effect called chip thinning as your end mill reaches the root of the chip it's actually cutting thinner than your feeds and speeds calculator predicts because of geometry at this point assuming your end mill is even cutting more than it is rubbing you're ripping out smaller chips that have a smaller capacity to carry away excess heat that's generated by the violent shearing action of machining this all contributes to the downward spiral of your end mills as a rule of thumb never accept a nominal chip load of less than half a foul this all of course is essential if you're cutting aluminum or other metals but honestly in wood I'll often wing it in cut by ear I'll ramp up my router speed if it sounds like it's struggling or not cutting cleanly I'll increase my feed rates if it sounds like I'm leaving performance untapped you have a lot more wiggle room with wood so don't let a lack of feeds and speeds knowledge stop you from milling the easy stuff seriously do you think people who use routers manually have calibrated for arms that push material across the cutter at a calculated speed no so just go out there and make something now for plastics Thermal considerations are a bigger so choosing a spindle rpm is a no-brainer for me as low as possible the feed rate will fall out from their different cutter geometries will also affect your cutting parameters I'll usually back off on my depth of cut by about 40% when using down cutting end mills since they don't do a good job of clearing chips conversely special coatings and lubrication will generally allow you to be a little more aggressive with choosing your cutting parameters and that basically covers what I wanted to talk about today there's no magical cutting recipe that will work for all of your needs there are guidelines that will get you close and then you need to exercise your judgement to dial in the best settings for your setup hopefully you'll now be able to look at documentation from end mill vendors and figure out where to start for a variety of materials if this subject interests you I invite you to stare at literally hours of discussions of feeds and speeds calculations on the internet I'll have links to some of my favorites in the description box down below if this subject does not interest you then I hope I saved you time by helping you discover your inner apathy in a much shorter video that's all I have for this week I want to thank you all very much for watching and if you'll excuse me I have some cleansing to do [Music] [Music] you

Channel: Winston Moy

Views: 126,238

Rating: 4.9616437 out of 5

Keywords: Shapeoko, CNC, Workshop, DIY, Maker, Carbide Motion, Carbide 3D, Milling, Projects, How To, Do It Yourself (Hobby), Woodworking, Sign, Carbide Create, Fusion360, Shapeoko 3, CAM, CAD, Tutorial, Workflow, 3D, Nomad 883, Nomad CNC, Feeds and Speeds, Chip Thinning, getting started, introduction

Id: S9bceJxpqG0

Length: 7min 41sec (461 seconds)

Published: Wed Oct 18 2017