How To Speed Control Your Miter Saw For Cutting Steel #080

I got myself a new miter saw and by new I mean old beat-up piece of junk that somebody else didn't want while fixing this guy up I started to wonder can I make this guy into both a miter saw as well as a cold cuts off each manufacturer makes there's a little bit different for example here I've got a belt drive my old Harbor Freight saw which is the one that this guy's replacing was closer to a direct drive there's a gear reduction in there but there's one thing that is consistent amongst all miter saws that I've seen they use a universal motor a universal motor is a good choice for a miter saw they're really fast super-powerful and dirt cheap for their size the problem is they're terrible at speed control and that's why they don't speed controllers don't come standard on miter saws like this however we're going to try a couple of things like that before we do more adjusting modifications the first one I want to try is controlling the voltage I don't think that's gonna work but if I don't show you that then I'm gonna have a thousand comments from people telling me why didn't I just turn down the voltage so let's try it and see what happens first let's collect some data the label says that the blade spins at 3600 rpm that's pretty typical this guy has a lot of commutator damage though which is part of one of the things that I'm repairing I'm basically replacing the motor but with that in mind I want to go ahead and double check while I'm here that the blade is still spinning at 3600 rpm with this set up before we replace anything and also see what the motor speed is and we'll log all that down before we start changing anything alright I call it at 3600 and now we're checking motor speed turns out that the edge of this pulley here is a little bit too reflective giving me all those weird numbers so I've added some painters tape and put the reflective strip on top okay we're gonna call that 17900 okay piece of wood cut with no modifications not bad original blade I don't know how old this blade is this is the blade that was on it when I bought it all right let's look at the transformer okay first up is the auto transformer some of you might know it as a very act but that's a brand name for my quick search online it says that coal Kassala generally run between 22 and 88 RPM so that's the goal we got 125 volts approximately coming from the wall I've Dow that down to 48 volts all right it's down to about 1100 rpm which is still way too fast all right we've down to voltage down to about 20 volts right okay as you can see approximately 20 volts we don't even have enough power to rotate the blade and now you can start to see the problem we're trying to use voltage control to reduce the speed of a universal motor the powerful any motor is a combination of its torque times its speed for universal motors most of that is speed and a very little bit of it is torque when you turn down the voltage you are basically turning down a total power which is reducing both the torque which you don't have much to begin with and also the speed in our case we had to turn the voltage down so much that we didn't even have enough torque to rotate the blade we're certainly not gonna cut any steel let alone even cut a piece of wood we can't get the blade to rotate we're not totally out of options though the universal motor will run on both AC and DC and I happen to have a shop build leg that I'm controlling with a DC speed controller this is my motor and speed controller which I have so gracefully gutted from my lathe we're gonna use this Dow to adjust the speed and we'll see here in a moment if we can use this kb electronics speed controller to control my miter saw all right test one turn it all the way up you should have full power and speed all right so that's about a hundred rpm slower I'd say the performance is the same then turn that to 50% and it was 3200 rpm turn that down to about 20% about 500 rpm all right that's the lowest speed I can set it to which with this combination is still over 200 rpm basically we've got two options if we're going to keep this motor we can try to change the pulley ratio but we need something like I don't know seventy to one if we're going from 3,600 down to fifty rpm it'll be close to that that's not realistic I don't think are getting pulleys that different in size to fit in this setup related to that would be the same thing with gears if you could somehow get a gear in there a gear reduction worm drive or something that will give you seventy to one but again I don't think that's practical in this application the second option will be to change the motor entirely if we take this motor off and put a three-phase induction motor on which I have several options available and control the speed with a VFD now I can get the full torque of the motor at any speed that I want and that my friends is how you're able to cut steel even at just 22 rpm so now we get to the fun part tearing this guy apart so that we can mount our induction motor on okay I think I have a plan at first I thought this might be as simple as making an adapter plate and then putting the new motor in the same spot as the original but after making a sketch in SolidWorks and putting the two hole patterns on top of each other you can see that the one horsepower motor that I want to put area is considerably larger I'd like to be able to put the original motor back in place so we're gonna leave this side unmodified I'll make an adapter plate that fits here with an additional hole pattern that allows me to move my new motor on the opposite side and then it's pretty easy to reverse by just taking the boats out and putting the old motor back in before I cut out any steel and when it makes sense to do so always make a template like this and just double-check that the hole is actually line up the way I think I did you know I took good measurements and I don't have any interference in there places where I didn't expect I wasn't thinking about this little foot that sticks out on the other side for putting tension on the belt it's interfering so I'm gonna have to put an additional hole here for that just things like that that you didn't and for so I need to go modify my sketch a little bit and then we can go cut some steel before our grandness I thought I'd take a second to show you how much dross is left on the part this is an indication that I'm getting much better at getting the speed and power correct before it was a lot more material tripping over the side or I didn't cut all the way through and so we're starting to get that doubt in [Music] there's a few features I need to add to make this thing totally awesome number one I'm gonna cover out the belt because that's just what you're supposed to do regard those moving parts and I'm going to add a potentiometer right here in front so that would be a little 3d printed mouth that'll be right there that'll allow me to adjust the speed and then reach out grab the handle and pull the trigger to start the VFD and the VFD or be in an enclosure to keep metal dust and stuff from getting inside of it okay change of plans I thought I was gonna have to make a custom piece but this contour actually has enough of a cavity that that would allow me to put my potentiometer in this original piece as you can see I painted it black one time I'm just gonna paint it blue now and match everything else so I just need to trim this out to fit this contour and I think I'll just put the original piece right back in there I'm liking that [Music] [Music] so close just a tiny bit too much there but hey I can work with that the motor we're using is a one horsepower three-phase motor so I'm going to be using this BFD in order to control the speed this is the smallest one I have that I still do the job it's pretty beat up but it does work so I'm gonna wire it up real quick while those pieces are while the paint's drying on those pieces and then I'll have to rewire all this once I make the enclosure and everything I clip the wires inside of this guy to make everything a little bit neater and just let the wires that are connected to the switch I've got two coming out of this side and two coming out of this side and it turns out that these two are normally closed here that when you pull the trigger the circuit opens so I'm guessing this side was meant to be connected to the potential laser add-on for this song I don't know anyway i want the normally open side there we go my VFD will let me wire an external switch to turn it on and off so that's what I'm going to use these two for [Music] [Applause] there's one more question I want to answer before I change this blade out and start cutting steel that is can I get enough speed range with this motor setup in order to cut both wood and steel by just turning the dial now I need to give you some perspective normally a miter saw runs at about 3,500 3,600 rpm and the current pulley setup that I have now gives me 800 rpm at 60 Hertz which is what the motors designed for however my VFD will let me adjust the settings from 0 all the way up to 400 Hertz so what I've done is I've set it to go from zero to two hundred and twenty Hertz which will give me about 3000 rpm you might be wondering with Jeremy why not go all the way to 3,600 here's a problem after you pass 60 Hertz the motor is not going to put out any more horsepower than it already has so the VFD is gonna have to compensate by lowering the torque in order to get the speed up so that you have the same total power output so once we go past 800 rpm the torque is gonna steadily go down as we keep going up in speed that's why I want to stop at about 3000 rpm I feel like that's close enough to the typical speed without sacrificing all I want to torque the blade I have on this saw now only has a few cuts on it it's got 32 teeth speech turned up to 3000 rpm let's give it a shot Oh helps a turn power up well that's promising with most VFDs all the parameters are adjustable so right now I've got like a five-second deceleration time that's also adjust the block and make it stop faster if I want just so you know why I'm waiting so long you try go a little faster alright alright I've got a couple pieces of plywood I'm gonna go a little bit slower because I think that's what you would normally do and let's see how it goes well that's not bad so in terms of cutting wood I would say that if your primary goal is to cut steel you just want to be able to cut a 2x4 occasionally this will get you by but you definitely have to need more power if you looking for production level cuts I could take this to two horsepower in fact I've got a C phase two horsepower motor with this same boat pattern right behind me so I could just change it out the reason I didn't do that though is because that motor is heavier than this one and this is already a bit heavy for this setup I wouldn't want to risk going any heavier than what I've done now I don't even know how long this is gonna last it's mostly an experiment at this point oh yeah what couldn't talk about it and I try it she might be a bit too much at some point you're gonna notice there now - mitre saws behind me that's because over the last several months while I've been sort of filming this in between other projects I knocked this guy off of my workbench and broke the back of it I tried epoxy in it back on and it didn't stay so I went ahead and bought another miter saw fast forward a little bit more and I realized that the epoxy I had was going bad so I tried it again and now this one seems to be holding up pretty well so for the moment I have to mitre saws incidentally that allows me to also go back and test a few things that I didn't check to first go around but we'll talk more about that in a little bit ladies and gentlemen we're now at two horsepower 225 Hertz which equates to about 3,000 rpm let's cut some wood [Music] that's what I'm talking about all right now that is good performance I like that in fact we're not even gonna cut any more wood let's switch the blade cut some steel earlier I told you Colette saws operate below 100 rpm but after doing some more research I realized that there are several that also operate at 1500 rpm and that seems to be the variety that we're interested in mimicking their performance so we're going to set the saw to 1500 rpm and that also means I need to redo my test earlier with the universal motor but fortunately I have a brand new saw so that removes all the other variables and I can Dow down a speed to try to get 1500 rpm and see if there's enough power to actually cut steel so that'll be at the very end of the video a tube is three inch by three inch by 3/16 thickness [Music] it's not even warm actually and the blade feels about like it did before I don't feel any noticeable increase in heat I have a brand new saw blade unused and a relatively new saw maybe a couple months old we're going to rerun the test from earlier to try to get the original motor down to 1500 RPM and let's see if we can cut steel 60-point Able's is what we have coming into the saw i've also noticed that it takes a little bit longer for it to get up to speed after I pull the trigger so I'm going to wait a few seconds and then push it down [Music] [Applause] [Music] [Applause] all right I don't I would prefer not to ruin this blade by trying to force this into the material as you can see it's really blogging yeah it's just not able to do the job now just for the sake of being thorough we're also going to set it up with my DC speed controller and give that a shot as well you saw this guy earlier but this is my DC speed controller made by Kitty electronics as I mentioned earlier universal motifs will run on DC so this would be our final test let's see if this speed controller can give us enough torque to cut some steel [Applause] [Applause] I don't want to disappoint you but I was really having to push hard down there at the end alright let's see if we can finish that guy [Music] you can tell this struggling it's warming up but it's not hot it's definitely warm the materials a little bit warmer than the blade man I was pretty surprised I thought it was gonna cut through for a second I don't think it's cutting anymore all right I have to admit that was definitely a surprising result I didn't think that their controller will be able to cut this far through the steel so you might actually be able to argue that perhaps I dealt the blade a little bit on this first cut and then it wasn't able to cut through on the second cut I don't know but at this point I really don't want to use up any more steel cutting blades testing this I've already gone through quite a few with a whole bunch of other tests that I've run but it would have made the video too long so I just cut all that stuff out I still don't think that this is the best option but I'm definitely willing to admit that that was better than I expected I didn't want to close this video without giving you one more option which is a cut off wheel like this these guys are readily available in big-box store but when you use one of these the parts gonna be really hot in the edge it's gonna be pretty rough anyway the controller kind of surprised me there at the end so I would love to continue to conversation in the comments section what do you guys think about the viability of using a DC speed controller because that guy is designed to try to compensate for torque as the speed goes down by increasing the current so anyway that's a different topic I don't want to dig in the weeds here at the end of the video hopefully you've enjoyed this project perhaps you'll make some upgrades of your own the last thing I want to say before I go is thank you to my patrons I burned through a whole bunch of saw blades both steel and wood cutting blades as well as some steel trying to get this project together for you so a big thank you to the patrons and also thanks for watching

Channel: Jeremy Fielding

Views: 870,940

Rating: 4.9205298 out of 5

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Id: gMVIdDKgG5A

Length: 22min 8sec (1328 seconds)

Published: Tue Apr 21 2020