Metal Lathe Tutorial 21 : Speeds & Feeds

hello Internet my name is Quinn and this is blondie axe this is lathe skills a series of quick videos on getting started in machining this is episode 21 speeds and feeds yes the one everybody's been waiting for this is a meaty topic so let's go speeds and feeds is a very complicated topic and I think that's why you don't see a lot of really great videos or kind of quick summaries of this topic everybody always wants like a quick summary of speeds and feeds just tell me what to do right okay fine here's the numbers you should use got it no don't go back and try to freeze frame your YouTube player because I'm going to show you where those numbers come from and how to get those numbers for you you know Machinery's handbook devotes a hundred pages to this topic and there's a reason why there's a ton of nuance to it however there are some kind of rules of thumb and there are some shortcuts that I think hobbyists can take and I'm going to show you you know what happens when things go right yeah and we're gonna push things to fail you're on my little machine so that's gonna get exciting stay tuned for that the fundamental property that we're after here is surface speed in the Imperial machine shop we measure that in surface feet per minute but that's a really stupid unit the thing is though the unit's don't matter we're ultimately after a spindle RPM so it doesn't matter what we use to get there it could be centimeters per deck a second or King George's thumbs per fortnight doesn't matter if like most beginners you frantically googled around looking for some kind of guidance on speeds and feeds mostly what you'll find are these charts of surface speed that people have produced and you know they'll confidently state things like steel should be cut at 120 surface feet per minute it'll have a formula so you can convert your the diameter of your part or your cutter into surface feet per minute and that's all you need to know the problem is that these charts are all varying degrees of wrong they all have a set of unspoken assumptions about your cutting conditions so what I'm going to show you here is how to work forward from first principles to basically make your own chart for your particular machine now most of those homemade charts are getting their information from this section of Machinery's handbook and so there's a series of tables in here for different materials so here we're looking at 10:18 mild steel and do you know the Brinell hardness of your mild steel I bet you don't but most people are assuming you know somewhere in this range here ninety 220 surface feet per minute for high speed steel so you know this is where those numbers come from that you find in all those charts however what nobody ever seems to mention is that the tables in Machinery's handbook are calibrated for a hundred and twenty five thousand of cut and a twelve thousand feed rate now for the hobbyist those are extremely aggressive numbers those are very unlikely to be numbers that your average hobbyist machines can achieve remember Machinery's handbook is a professional tool for professionals who have big machines and are trying to maximize production so if you try and push your bench top hobbyist machine to 1/8 inch depth of cut that's a quarter of an inch off the diameter on a direct read hand wheel a quarter inch diameter reduction at 12,000 you're gonna blow that machine up so I hope you got the warranty I think I can summarize this in that there are two basic ways that you can calculate speeds and fees there's the correct way and then there's the way that everybody especially hobbyists tend to actually do it the correct way is a three step process step one is to select your depth of cut now this is generally dictated by three things it's dictated by the rigidity of your machine the rigidity of your setup and how much of a hurry that you're in if you've got two hundredths out of a move off a dimension obviously you want to do that as quickly as possible so you're not standing around all day for this exercise we'll assume that your setup is as rigid as it can be for your machine so you've got good tail support you've got a good grip with your Chuck you know all those sorts of things so from there it's really down to the material that you're cutting you know the most common hobbyist materials are going to be aluminum brass and steel for aluminum and brass they're very easy to cut so 60 70 80 thousand that cut all you know all within the realm of possibility now a steel we're much more in the four teeth out of cut range kind of at the upper limit I don't typically get that aggressive with steel and my little machines I tend to stick around you know 30,000 of cut or you know sixty sixty to eighty thousand wheel for a direct read hand wheel so step one establish your depth of cut step two is figuring out your feed rate now with larger machines with complicated transmission or electronic leadscrews or things like that you may have a lot of choices on feed rate however with hobbyist benchtop machines like this you're probably only going to have one two or three choices here so this is typical of these benchtop machines you're going to have change gears in here that are set up for specific feed rates so there's on this particular machine there are two sets of change gear options for power feeding so there's a course set and a fine set the course set is incredibly fast and I don't know why you would ever use them so you're going to start with the fine set and the fine set is what's installed on the machine in this case from the factory and so this tells you what your actual feed rates are for both turning and facing because this machine also has power cross feed now on these tables here for a given gear set there are three options C a and B and those correspond to the quick change gearbox so for a given set of change gears you've got three feed speeds and this chart tells you precisely what those feed rates are now these units here are in thousandths of an inch per rotation of the spindle which is a very logical way to measure feed rate and here's why we measure feed rate in distance traveled per rotation of the spindle because as you recall from the surface finish video the lathe is always cutting a helix and like I said at the top of the show ultimately what we care about here is the surface speed of the cutting tool over the material however you know people think of rpm as being the only thing that contributes to surface speed that in diameter but in fact the feed rate also contributes to that and as you remember from your junior high math classes you know we've got two vectors to get the final velocity you add them together so in this case we've got one vector here coming from the spindle rpm that's you know contributing to our velocity and then you've got a second vector here that's coming from your power feed rate contributing to your velocity and so this the sum of these two vectors is ultimately going to be your service feet per minute and this is what we care about so part of the reason that we start with power feed rate and in this calculation is because we have less control over that rpm we have lots and lots of choices but power feed rate is much more limited but we do have a couple of choices you know on this machine that I'm Dennis straining we have three choices for power feed rate so how do we choose between them well there are three things that go into our decision for feed rate first is once again how big a hurry we're in if we have a lot of material to remove we want to be feeding as fast as possible to is the power of the machine the the feed rate is limited by the horsepower of the machine and how aggressively you know it can pull that cutter through the material and the third main factor is surface finish now recall from the surface finish video that one of the main contributors to surface finish is the radius on the nose of your cutting tool what I said in that video is that the affect of the nose radius is basically to smear the thread cutting lines that would otherwise exist if the tool was sharp nosed again since the lathe is cutting helix a nose radius kind of blurs the lines well now that we're trying to choose feed rate it's time to get technical about this or best possible surface finish the rule of thumb is that you want your feed rate to be less than half the radius on the nose of your tool and that ensures that each lap around that helix some portion of this curve is gonna be there to smear out the the tool marks from the previous pass so guesstimating this guy with the calipers this particular tool has a nose radius between 10 and 15 thou so I'd be looking for a feed rate somewhere like 500 bucks mmm surface finish so if I'm setting up to do a finishing pass with that tool I just showed we know that we want a power feed rate somewhere 5,000 feet gear range on this machine because I'm not insane and so on the turnin section here and I've got three options I've got 10,000 or five or two and a half thousand the a or C range five or two and a half though but for finishing I'm always going to go with the C range because that's gonna ensure that each lap around that material is going to be within my nose radius once again grounding tools by hand it can be tricky you know exactly what your nose radius is so just go as fine as you can for finishing but once again for this exercise we're trying to determine the upper bounds how aggressive we can be with all the variables for speeds and speeds so we're going to resume our calculations using this 10,000 will use steel so I've established my depth of cut the maximum that I can do is 40,000 most I'm comfortable with and my feed rate the maximum on that machine is going to be 10,000 so I go to my materials chart here and Machinery's handbook and let's take this 120 surface feet-per-minute number as my baseline and then I multiply that base speed by this scaling factor for my feed rate which is 10,000 tells me that I can increase that speed by 1.08 and this reflects the difference between the 12,000 the tenth our eight that I'm going to be using and then we look up my depth of cut and we find it there's an additional scale factor of 1.15 because this 47th out depth of cut is going to be quite a bit less than the 125 that the original table was calibrated for so with our depth of cut and our feed rate established the final step is convert that surface speed that we derived into a spindle rpm and this is done based on the diameter using this chart here so I like to do this for a one-inch diameter so that's going to be the diameter of the stock for the lathe or the cutter for the mill and one-inch is kind of a nice average of things you're going to be working with in a hobby shop and then you can mentally fudge these numbers up or down for smaller or larger stock or cutters so for steel for example we're typically going to end up in this surface speed range so we're gonna end up somewhere between like 450 and 800 rpm so a great exercise is to calibrate your lathe based on this data so starting with the surface feet-per-minute baselines on those other charts which again are for an eighth inch depth of cut and a twelfth AO feed rate and then modify those numbers using this chart for you know the maximum depth of cut that your lathe can handle you need to those materials and then modify it again for whatever your fastest feed rate is that you're going to use and that's going to give you the upper bounds of RPM and feed rate for each of your materials and then you can kind of go down from there now that's a lot of fooling around so I've done that math for you for a typical bench top you know hobbyist lathe and the nine or ten inch swing range and if you have larger machines these numbers will still work they'll be you know more conservative than you need or steel your base speed is 120 for a roughing pass of four teeth out of cut and 10500 RPM a finishing pass of 10th our less that's a two and a half thousand rate 800 RPM for aluminum your base speed is 500 for a roughing pass of 60,000 cut that's a ten thousand two thousand rpm finishing pass of tenth our lists you want a two and a half thousand as much RPM as you can muster for brass your base speed is 350 for a roughing pass of sixty thousand of cut and a ten thousand hundred RPM for a finishing pass of tenth our less you want a two and a half thousand as much RPM as you can muster okay so let's see what those numbers actually look like on the machine so this is the roughing pass that I just calculated for you in steel and this is definitely what I would consider the most aggressive cut that I would ever do on this machine and steel it looks pretty calm on video but in real life there's a lot of noise a lot of smoke and overall quite a lot of drama you can see when I wind the cutter back how it drags a fair bit on the surface and that spring pass tells you how much load there was on that cutter because it sprung back quite a bit once that cutting force was removed and here you can see that the chip action there is okay it's not breaking as soon as it should the grind on my tool might not be perfect might need honing but it goes to show why I don't typically run the machine this hard now let's see if we can clean up that finish using the finishing pass numbers that I just showed you and that's pretty good but I think we can do better so just to show you the affected speeds and feeds have on your surface finish here's a little higher rpm and a finer cut this is a 5000 cut and that's a very fine finish indeed for mild steel anyway and here's a roughing pass with those brass numbers now you can tell when you're really pushing brass because it's wheels like a banshee now let's see what happens if we push it too hard so this is that same tenth outfit but I've put some aluminum shims in there so the Chuck doesn't have as good a grip you can see that the force of the feed rate is actually pushing the part into the Chuck and has caused it to lose its tail support and well everything's gone pear-shaped quite literally you can see in addition to the dreadful finish that there's a taper in there that's been introduced because the part got pushed out of the tail stock just to show you how much wiggle room there can be in these numbers here's that same 60,000 if cut very rigid set up sharp nose tool mind you but a very fine feed the fineness this machine will do and look at how nice that finishes that's actually quite a good final finish for this part so as you can see play with the numbers and you'll find that there's maybe more possibilities than you thought quick sidebar note that that wasn't actually 1,400 rpm as I said in the numbers that was actually a thousand rpm because I'm my lathe that's as high as I can go without moving the drive belts so it just goes to show that there's a fair amount of wiggle room in these numbers especially at the higher rpm ranges now let's look at the other extreme here's a tool with a huge nose radius and I'm doing a very light pass extremely fine feed an extremely high rpm and that finish is like a mirror this is probably the best finish that you're going to get right off the machine without any kind of polishing so play with the extremes of the numbers just to see what's possible you might be surprised just to drive this point home let's take a look at these parts under the macro lens so here's the roughing pass that we did on the brass and you can really see the tool marks there very clearly from that sharp nose tool and the aggressive feed is also going to make this effect much worse but now let's look at that finishing pass that we did with the exaggerated round nose tool and this finish is so good that the camera the macro lens on the camera actually has trouble focusing it can't quite resolve the surface on it now over here on the steel this is the finishing pass and it's definitely good for mild steel but it's not gonna win any mirror Awards pop quiz what do you think is the biggest contributor to tool where is a depth of cut no it is surface speed this is an extremely important topic in a production CNC shop so much so that the big book devotes an entire section to calculating it full of lots of more tables the hobby shop that doesn't matter a whole lot but be aware that the tables in the big book are calibrated for 15 minutes of tool life so if you want your tools to last longer than that yeah things down a bit so that's the complete process of determining speeds and feeds for your particular cutting setup from first principles now why doesn't anybody actually do it that way at least not on YouTube well first of all it's a lot of fooling around it's a lot of math it's a lot of looking up tables in this very expensive book so people have shortcuts the most common shortcut that you'll see is this one you take your surface feet-per-minute for the material from the big book here or from a chart that was most likely copied from the big book and you just simply take that speed multiply it by 4 divide it by the diameter of your stock or your cutter and this mostly works and it's mostly fine why does that mostly work because it's obfuscating all of these very important cutting conditions that we talked about like depth of cut and feed rate and surface finish and so on well because people are taking those numbers from these charts and Machinery's handbook again which are calibrated for 1/8 inch depth of cut and 1/12 our revolution feed rate but ignoring that calibration and using lower depths of cut and lower feed rates in general at least in the hobby shop and the end result is that if you use that shortcut formula you're running slower than necessary and that's mostly fine you know running slower to a point is always okay and can be more pleasant for the hobby shop you know it's sort of less dramatic there's less heat less smoke less you know noise from the machine less wear and tear on the machine so you know running slower is okay and these formulas work for most people because of that because they are under estimating the ultimate speeds and feeds that you know you can use on your particular cutting setup so feel free to use those shortcuts but I think it's helpful to understand where they come from and I do think it's a useful exercise to go through this calibration that I described for your particular machine and kind of know what that upper bound is and kind of work down from there to wherever you feel comfortable on speed and feed for your particular machines we've been focusing mainly on the lathe here because it's easier to understand but speeds and speeds on the mill has a lot more nuance in modern milling operations the unit that we use to measure speeds and feeds is a little different here we talked about inches per two inches per tooth refers to the amount of material that's scooped out by each tooth as it comes around and goes through the work and this is a combination of three variables first of all the power feed rate how fast the stock is being pushed through the cutter by the power feed and then it's also a function of the RPM which is controlling how quickly these teeth are coming around relative to that table feed and this is also affected by the number of flutes on the cutter because of course the more teeth you have coming around the less each tooth gets to take for a given table feed and RPM interest per tooth is a very valuable and important metric on modern CNC machining where you can tightly control all these variables for optimum performance on the manual mill and especially the hobbyist manual mill don't really have the luxury of all that data because while we can control a lot of these variables like depth of cut and number of flutes and rpm the table feed rate is a lot more tricky because either you're feeding manually in which case your feed rate is you know however good your arm is feeling that day or you're using some sort of power feed now on some larger mills if the power feed is driven via transmission you might have known gearing and there may be markings on your power feed controls that tell you you know say an inch per minute rate for feed but on a lot of mills you've got an electric power feed like this almost certainly and it's got these utterly decorative numbers on the dial here that don't mean anything so how you calculate feed speed so this process is simply a matter of zeroing out your hand wheel make sure you take out the backlash in that guy as well zero that guy out and then you need to know how many thousands are on one full revolution so this particular mill has a hundredth out on one revolution and you're just simply gonna run your power feed for a fixed amount of time say 10 seconds and just see how far it went so for the current setting on that power feed knob it went 380,000 10 seconds which is two and a quarter inches per minute to give or take so now you can kind of map that speed to this knob so I don't know let's say the 4 is up so you might call for 2 and a quarter inches and you know that you know smaller numbers are gonna be less than that and larger numbers are gonna be more than that but you don't know that the scale is linear it may not be and there's no kind of markings or anything on here so yeah honestly this whole exercise is a little fruitless on these crappy hobby power feeds so what I would suggest is just set it low however the good news is you can pretty much gloss over that nuance for the most part and use the same rules of thumb same formulas same numbers just using the diameter of your cutter instead of the diameter of the stock however it is worth being aware of some of this nuance so that you can fudge the numbers up and down a little bit as needed for example if you're face milling it's clearly going to make a difference if your n mill is fully engaged or you know is only engaged on a little bit of the material you know all this is going to affect to a pressure and thus you know how hard you can push your surface speed and it matters if you're a climb milling or conventional milling but I'll be covering some of those details in the mill skills series but then if you're doing things like slot cutting it gets even more complicated because you've got one side conventional milling on one side climb milling so the differential forces on the cutter complicate all these variables and if you really want to get into it Machinery's handbook does have tables for all of this including you know adjustment factors to feeds and speeds based on slot cutting or different levels of engagement of the face mill but you really don't need to do that for Hobby work so I hope you found this useful please do like subscribe comment etc and consider supporting me on patreon and we'll see you next time you

Channel: Blondihacks

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Keywords: blondihacks, machining, machinist, abom79, this old tony, vintage machinery, steam, electronics, making, maker, hacking, hacker, lathe, mill, woodworking, workshop, shop, model engineering, engineer, engineering, live steam, machine shop, metal lathe, vertical mill, metalworking, metal shop, jewlery making, diy, home improvement, resin casting, how to, do it yourself, do it yourself (hobby), ASMR, mini mill, mini lathe

Id: NrcDr2WO6Ho

Length: 21min 19sec (1279 seconds)

Published: Sat Oct 05 2019