Let's Make Our Own Chain Sprocket!

friends patrons countrymen lend me your views today I thought we could take the opportunity to turn a little problem into a much bigger problem check this out the technical term for what you're looking at is rocket wobble if you couldn't tell by the ridiculously clean chain I've already taken this thing apart the front sprocket the drive sprocket is all wonky at first I was worried it was the actual motor what happens is that chain goes from extremely taut to super loose to taut again I'd like to get this sorted before it kills the motor bends the shaft kills the bearings in there before this becomes much more expensive a fix than it currently is there's a permanent magnet DC motor in this thing and the natural cogging that it does like between poles I think has hidden that problem from me since we got this though frankly it's my fault for not having a closer look let's get this chain off breaks my heart to see things like that no don't try to adjust your picture you see in this right we moved to electric well the boy did anyway don't tell child services but we often use him as a bit of a canary he outgrew the little 50 cc pretty darn fast and there really wasn't any other option for him to safely move to long story short we drove a million miles to a dealership traded in the gasser for this thing I'll admit ever since Edison invented it I've never quite trusted electricity but this thing is turning out to be quite the Firecracker the boy absolutely loves it with one very expensive caveat this absolutely moronic lead acid battery from the little I could find online which is essentially what the factory and dealers will tell you is that these batteries should be good for two hours I don't know how they measure that maybe they've got some really expensive scientists and smart lab equipment but I've come to the conclusion they must mean if you don't use the bike these batteries are an absolute joke in an otherwise pretty okayish bike it took me a couple of weeks to suck it up and drop a few more hundred dollars on a lithium battery pack it's on the charger now this is just here for demonstration purposes it's turning the wheel while I sort the sprocket thing technically I'm keeping this as a backup but this is the first time it's been in the bike since we started doing lithium my boy weighs about 50 pounds when he's soaking wet these LED batteries brand-new and fully charged got him about 15 20 minutes of fun time maybe 10 decent wheelies and the day was over they still technically moved the bike but after about 15 minutes it was a slow descent into tears and madness the lithium batteries on the other hand get him two plus hours of real riding doing what these things were meant to do none of that puting around the backyard riding over 2x4 is kind of stuff I'm talking uphill climbs both ways wide open throttle jumping rocks ditches the neighbors cars you name it two real hours and when they lose their spunk they still have another good hour of just riding around time basically enough to get us home or wind the day down put that in perspective both of us are usually absolutely exhausted after about an hour an hour and a half of good riding all right so as you guys were yapping away about batteries or whatever on the clock I might add I went ahead and removed the sprocket turns out I got a whole truckload of problems here the biggest one ironically is not being able to identify this chain I have no idea what it is you probably didn't notice but I was gone for two days trying to hunt the answer to this thing down I expected this to be a number 25 it is not it's also not an eight-millimeter metric chain it's not a 2:19 the numbers I'm taking off of this match nothing I've been able to find online the parts manual for the bike says absolutely nothing just lists chain and the two sprockets dealership couldn't help they didn't know either they say they just sell the chains or the sprockets or the whole kit and it's a real head-scratcher my plan was to make my own one of these that's hard to do if I don't know what size chain I'm dealing with also the chain is shot chains should not bend this way not this much at any rate a long story short I ordered all new parts the new stuff I'll be getting is all 219 sighs okay sorry I skipped a step chains come in all sorts of sizes and flavors the your sprocket on the bike is still good it looks good anyway if I knew what size that was I could just get a new chain and a drive sprocket since I can't seem to figure it out and nobody wants to tell me I'm just gonna change all three unfortunately lead time for the drive sprocket that I need is impossibly long it's all in order but they can't seem to tell me when I can expect it so back to plan a let's try to make a new sprocket the drive sprocket has one of these D shaped poles in the middle in my case this probably means CNC router or a broach or both well I am gonna have to route it I don't have cutters for sprocket tooth shapes I don't even have that many for gear teeth let alone sprockets but if I had a cutter and I could do this on the mill like on a dividing head I'd probably just make that a round hole and then weld or braze in that little D shape but since it's a CNC project anyway I can cut any shape I want I just won't get those sharp internal corners but we'll burn that bridge when we cross it we're in my leave I've made a little D shaft that's 12 millimeters fits the sprocket I just want to see what my reference is here that's better than I expected it's just some cold rolled steel i milled the flat on it's a good fit that's brockett's at about 25 on the hub I'm sure that only gets worse up where the chain runs the face is about 10,000 from the top no sense in beating around the bush we need to get this machine to make us this part I'm no CNC expert but I'm almost positive one of those letters stands for computer my money is on the end before we can do anything here everyone take off your shoes and meet me inside the living room computer like I do every morning when I wake up let me restate my goals we need to design a chain sprocket something like this to fit my chain which looks something like this spacing between rollers looks to be seven point seven seven millimeters roll diameter about four and a half inside width about that same size these are sort of my best guess averages and as far as band-aids go this one's a real doozy I'm sitting in CAD about the design a chain sprocket around a worn out chain anyway let's get to work although there are some subtleties we're going to ignore here designing a chain profile is usually easier than designing a gear tooth form I'm gonna lob this one to you going through a lot of extra steps that aren't strictly necessary but hopefully this makes it easier to follow here is my chain link my original sprocket is 11 teeth since I'm making my own I'd like try 10 tooth that should knock the edge off the top speed and give the kid a smidge more torque 10 tooth saw pattern this set of 2 5 times I'll set the distance from pin to pin to be the same as the 7.7 millimeter dimension a little bit of tidying and there it is 5 links properly spaced in a circle I picked a circle as I found the round sprockets usually work better than square ones for clarity's sake I'll exit the sketch and start a new one on top of it let's pick up the link from before as this chain rolls around the sprocket the links will roll into and out of the gullets so let's do another circular pattern like before but this time roll the link around one of its pins that represents the link sort of rolling into or out of the sprocket I'll do that again but this time around the opposite pin on a new sketch granted that looks quite the mess but can you see our sprocket tooth profile in there we didn't really need to do all that we only really needed to know the pitch minus half the roller diameter but I didn't want to scare anyone off with math again new sketch now let's just pick up what we need to chain roller diameters and now we'll drop in a circular arc that is tangent to the rotating link and coincident with sort of the start point we're just drawing an arc sort of kissing off on the circles that that circular pattern made when the link rolls up or down we could mirror this arc but let's just do it again manually this time we'll make the arc concentric and there it is same result like I said we could have just dimension the arcs since we already know the numbers but maybe this paints a better picture of what's going on I'll trim out what I don't need throw in some construction lines that can cut the roller circle where we need it hide all the other sketches and there we have it our 10 tooth give me just a moment to knock that sharp point off nobody likes sharp points then just pattern that tooth around the center and bingo was his name-o next we need a 12 millimeter D bore and since I'm seeing some blue points in my sketch which means they could move on us when we're not looking I'll throw in a construction circle just to tie them all together extrude the thickness add a hub and we're done well almost since we're here and I want to give my router a fighting chance at actually pulling this off I'm going to make a dummy body that will represent my rough stock like the blank that I'll be starting with I'll make a revolve with just a smidge more material that I need and we'll turn that shape on the lathe and here's that sprocket blank that will be the sprocket at the top this is just material to hold on to I added extra material in the sketch or you know didn't take off all of the material while I was turning it just to leave me some wiggle room here in the router I'm under no illusion that I'll be able to pick this Center up perfectly on this machine so I left the blank a little bit larger and the router will just cut it in place the better I could Center this the less work the router would have to do but it's not a perfect world and the last thing I want is another wobbly sprocket I already have one of those [Music] [Music] I've got an indicator in the spindle I'm just sweeping around the part adjusting the spindle position until I'm zeroed out [Music] [Music] and here's the almost finished part doesn't look all that bad does it come on don't be shy come in for a closer leads a little bit of deburring small file maybe just a shot on the wire wheel I got one more step to do but full disclosure this was my third try the first two didn't go so well rookie mistake on the first one I used an end mill that was too close to my finished size I was getting too much cutter engagement and my router can't handle loads like that let me show you what that looked like I don't know if I mentioned this but it's trying its darndest to cut 4140 steel that's chromoly it's tough stuff and every time it tucks into one of those gullets the machine gets yanked left or right front back and it loses steps the computer no longer knows where the part is but it don't care it just keeps cutting real trouper my router is here it's trying to clean up the hub look how far off it's gotten it's probably taken sixty foul off that right side and nothing on the left this part is scrap it's more than that it's a dishonor to the old Tony family name but I let it keep running I mean at this point I might as well learn as much as I could from the part here it is boring the D hub and you know what I learned by router ain't cutting no D hub I spent an hour on the second one trying to tune the fit only to discover the router was cutting a taper material is just too hard I have too much tools stick out and a small diameter end mill so on the third one I just use the router to profile the sprocket I did it sprocket face up so I'm not trying to reach past the hub surface finish was a lot better and the note taper none that I can measure anyway then I moved to the lathe and just drilled and reamed a twelve millimeter bore it fits the chain well but I did have to finesse the tooth profile just a bit I have the teeth on the sprocket rolling over just a smidge more than what we saw on the CAD base circle and roller diameters is still the same but that sweep out at the end of the tooth has an additional 10,000 it that and i--i rounded the corners I shouldn't have had to do that but I probably still lost a step or two in this and the Sharps on one side felt a little tight on the chain so I just rounded them all over but that's all behind us now let's not dwell on the past at a sprocket with no keying feature to turn this round bore into a similar D bore I've milled a small insert and I plan to braise it in place that'll fit in there like that and turned it into an uppercase D here I must apologize batteries in my microphone went belly-up on me but just so you know braising with an oxy torch sounds something like this I wasn't quite sure how to hold the key in place anything I'd put in there risks being braised to my part in the end I opted for to internal snap rings you can't see it in this shot but I have my fingers crossed hoping these rings won't give up the ghost before the silver wets out I cleaned and flux the mating surfaces of course and I'm trying to keep a hawk eye on what that filler is doing and where it's gone if the scale hasn't come across on video this thing's about an inch and a quarter in metric that's thirty millimeters and after a bit of cleanup here's how it looks I did have to scrape the inside a bit got hard flux in there and some solder of course but it looks like it went out well I gave this a wire brushing in some scotch braiding but best I can tell it sweated out all the way around the perimeter of the key hopefully that means I got a good fill inside the fit is a little snug I think I got just a little bit more cleaning to do in the sharp corners I guess the Bray's left a little bit of a Filat you clean this up just a little bit more much they are probably one or two people wandering this old Tony well that breeze be able to withstand the torque could that key just shear out well great question let's try to figure it out if we take the motor power 750 watts and divide that by the shaft diameter which is 12 millimeter divide that again by the number of teeth 10 in my case and multiply that result by the tensile strength of silver solder we play it safe let's call it 18,000 psi and don't worry it doesn't matter if we're mixing our units because we're going to be taking the square root of that and everybody knows square roots are dimensionless and there we have it we should be totally fine [Music] changes back on their feels a lot better than before there's no really tight spots it's all the same tension all the way around now because I went from an 11 2010 tooth I did have to cut one roller out of the chain all right that's been bugging me ever since I first saw it I feel so much better now at peace with the world sure it took me a little longer than expected but my back was to the wall I didn't have a lot of pardon me sorry about this I'll take it out in editing oh I may have finally gotten the top-end parts for the other bike can't tell you how long I've been waiting for these I can finally get that put together and get this place cleaned up thanks for watching

Channel: This Old Tony

Views: 925,050

Rating: 4.9639034 out of 5

Keywords: sprocket, cnc router, chain sprocket, trials motorcycle, trials bike, brazing, D bore sprocket, D hole sprocket, CAD, CAM, Solidworks, Fusion 360

Id: 6mzTLPv636o

Length: 17min 48sec (1068 seconds)

Published: Sat Apr 18 2020