Metal Lathe Tutorial 5 Turning

hello Internet my name is Quinn and this is blondie hacks this is lathe skills number 5 turning this is a series of quick videos on getting started in machining if you like my content please do subscribe on patreon where I post exclusive project videos ok let's dive in turning is reducing the diameter of stock in the lathe now the first question is why do we do that well first and foremost obviously because the stock is too big we need a you know a part that's smaller than that you know stock comes in standard sizes it comes in you know quarter inch half inch or you know three centimeter five centimeter whatever even if the shaft you're making let's say is exactly a quarter of an inch you can't use quarter-inch stock because from the mill it it might look pretty straight and pretty round but it's it's not it's going to be you know maybe ten thousand and it's going to have a lousy surface finish on it and it might have a bend in it somewhere so you have to buy stock that's larger and then turn it down to the proper diameter the second reason that we turn is to achieve a nice surface finish and that's not just for looks although machinists are very passionate about making things pretty you know any stock that you buy is going to have some kind of undesirable finish on it you know this is hot rolled steel which has mill scale on it this is a byproduct of the hot rolling process so you don't want that on any part of your machine and even cold rolled material such as this has this kind of corrosion inhibitor on it and you know it's it's not gonna it's not going to work if you have to press this shaft into a bearing or you use it in some other precision application the third reason that we turn is to achieve concentricity in our part you know you can spin this in the three draw Chuck and it looks like it's centered and it looks like everything's round but if you put an indicator on this you'll see that you know there's that this isn't actually concentric even the best chucks have a little bit of run-out in them so what we have to do is get down below the run-out in our system and that's a bit of a hard concept to explain but it's a very easy concept to visualize so let me show you what that looks like here's a piece of stock that I've chucked up with exaggerated run out so you can see what that looks like so you can see that part is is really far off center now watch what happens when I turned down that part aways this is really the magic of the lathe you can see that even though that part was incredibly out off-center when we started just by turning it down enough this section here is now spinning perfectly true you can see where the original Center was here on the face you can see it wobbling all over there but this surface right here is perfectly true even though nothing else in this chuck system is and you know that's that's what lathes are all about no matter how much run-out you have in your truck or your bearings or any other part of this system if you turn it down enough there's always a pure true concentric Center in the middle of it all so concentricity can be achieved by turning down the surface now before you put the tool to the material you need to understand backlash every machine has backlash doesn't matter how high quality it is it's just a property of mechanical systems so this is what that looks like see I'm showing it in the carriage here because it's the most exaggerated in larger gearing systems and you can see how much movement there is here and I'm turning this wheel back and forth you know 30 40 thousandths but the carriage isn't moving that's backlash now if I move back a little bit and then come in so now I've taken up that backlash now if I move 30 thousandths the carriage moves 30,000 s with it so whenever you're making a cut on any hand wheel you always have to make sure that you're coming at it from past where you need to be so that you've taken up that backlash so I wind out and then I come back I've taken up the backlash and now from this point on I can trust that reading on the dial and you also need to know what kind of cross-slide hand wheel you have these come in two types direct read and indirect read so of course there's markings on here in this case each tick is mm but what is that actually telling you on a direct read hand wheel it's telling you the reduction in diameter of the part so if I turn this in mm the part is going to be reduced in diameter by mm in an indirect hand wheel this is telling you the depth of cut on one side so in this case if it's mm that means I'm cutting in mm but the part is spinning so that same mm is getting from the far side so my reduction in diameter is double that for thousands so to be absolutely certain which you have you should just take some cuts on the machine and measure after each pass and determine from there what type of hand wheel you have okay let's actually make some chips now with any machining operation we don't know where that surface is yet so we have to find it the the numbers on the hand we also give you relative coordinates but we don't know where zero is so you got to find our surface first and we do that by touching off so we've taken up our backlash and now are coming in nice and slow until we just touch off on that surface there we go now we can come out here now I can set my hand wheel to zero and then I can dial in let's say 20 thousands and our goal here is just to clean up the surface and I recommend feeding by hand when you're first learning just to get the feel of it and the goal like I showed what the concentricity demo is to get inside any run out okay so now wind this out here and stop the lathe and you can see that we haven't yet cleaned up all the way around there's a part there that's not machined so what we're going to do is go in another 20,000 and take another pass [Music] okay so now without touching the cross light hand wheel we know two very important things first we know the surface is round and concentric and second we know exactly where this surface is because now I can look at my hand wheel and whatever number is there doesn't actually matter I know I can go in twenty thousands from that number and know that the surface will get twenty thousand smaller this is the first time that we can actually say that now we can start thinking about hitting our dimensions so we took that initial measurement which in this case was 969 and let's say our drawing calls for this diameter to be 900 so we've got 69 to come off of there now you don't want to do that all at once because you might overshoot it and overshooting is the cardinal sin in machining you only get one shot at that so what you want to do is often want machinists calls sneaking up on the dimension you break it up into passes that are smaller as you get closer and closer to the dimension and especially when starting out I recommend checking your dimension after every single pass just to make sure that the amount that came off is the amount that you think should have come off and by doing that you'll catch all the little mistakes that you're going to make you know miss reading the hand wheel and you know maybe you forgot to take out backlash one time so make all those little mistakes as you go along and by taking smaller passes as you get closer you'll eliminate those errors so in this case with 69 to go I might take two passes of 30,000 then a final pass of 9,000 that is turning in a nutshell hitting dimensions takes practice so don't be discouraged just grab some scrap and start spinning it and practice so I hope you found this useful please do subscribe both here on YouTube and on patreon there are links in the description for all of that and we will see you next time thanks for watching you