#219 drive sprocket - please check my drawing

egokart

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Hi everyone :)

I'm reusing as many parts as I can from my petrol powered kart, which I'm converting to 800w/36v for a 32kg boy.

So here's a drawing of a custom 12T #219 sprocket to fit a Double-D motor shaft.

Could any of you check the pitch and radius of the teeth for me? A friend did the drawing and he's not sure they are exact.

There's a list of specs attached as well.#219 chain data.jpeg

12T #219 sprocket tooth detail.jpeg

#219 sprocket 12T.PNG
 

itsid

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Wow that's a lot of numbers when creating a viable sprocket profile
is as easy as drawing a few circles ;)

For all I know (DID chain documents)
chain pitch is 7.774mm and while 7.78 isn't too far off, it sounds like asking for bindings
(not on a small sprocket like that but copying that over to a bigger sprocket and it'll likely start binding)

Same goes for the Roller diameter.. 2.23mm accepts no Rollers bigger than 4.44ish Rollers..
the Racekart chain is 219H chain however and that means
the Rollers are 4.59mm in diameter so that radius should be 2.3mm instead
(tiny amount of play)
219H chains have an inner width of 5mm.. I wouldn't use a 2.5mm wide sprocket I'd scale up to 4mm do reduce the wear that'd also fit the slightly narrower 219HTM (inner width 4.6mm)


'sid
 

egokart

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Cheers for that :) Detailed answers are much appreciated! I'll get the drawing updated and see who can fab it for me.
 

itsid

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Okay I used a much simpler approach forming the teeth...

simple_sprocket-219h-12T_do.jpg

A few parallel lines (half the chain pitch)
a few angles (360/<numberofteeth>)

and just five circles (you cannot see on the pic, since they've been cropped to form one tooth)

two at each crossing point,
one the roller diameter plus a bit (4.6mm in this case)
and another tangentially touching the the other side's 4.6mm circle

and a last purely cosmetical circle to cut the points off the teeth..
(well and the hub portion of course.. just for completeness..)

I'll check with my kart (it uses 219H chain) since I think I do have a 12T engine sprocket somewhere in here:
tony_engine_sprockets.jpg

to see how far I'm off, but in any case I'm fairly confident it'd be close.

Oh btw.. if you want that as a 3d file let me know..
I can export that to something usefull to you
(if for comparision)
just let me know what readable formats you software supports.

'sid
 

egokart

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Hi Itsid, thank you that would would be great! Can you send it in dxf or dwg please?
 

itsid

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Hi Itsid, thank you that would would be great! Can you send it in dxf or dwg please?

Hi, sorry for the delay.. yes sure (see below)

I struggled a bit tbh since last AutoCAD I actively used was R13,
which is quite some time ago, and I had to pick a segway converter
And then the much smaller dwg (129kb) wouldn't compress small enough to be attached here..
(results in 108kb compressed)
and it took me a while to try and compress the 1.06MB dxf instead..

mindboggling, I thought both use about the same amount of compressed space tbh...

Anyways.. it's a 2007 format I hope that's old enough for you to open,
else we'll try again with an older version ;)

'sid
 

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egokart

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Thank you Itsid, I've sent that to the machinist. Next is to sell the KT100 motor to pay for the conversion :)
 

itsid

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uh.. I'd keep the KT100 for a while tbh...
800W might not be very satisfying (coming from a KT100)

Sooo maybe you wnat the KT100 to pay for the next upgrade instead ;)
(or reuse it one fine trackday in the future :D)

'sid

PS Wait what you sent the file to the machinist?
it's almost unchecked (apart from it conforming to DID dimensional drawings)
I hope it works,
but the hub bore for example is a perfect ten to eight double flat;
and with zero clearance it unlikely fits your motor shaft :eek:
I hope he adds the necessary tolerances where necessary.
 

itsid

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Sooo..
since it's easier to do it here than via PM..

I couldn't find the sprocket generator,
what I did find however was the DIN standards to form roller chain sprockets.

and that's essentially only a few more lines
219h-12T-construction.jpg

All denoted dimensions within DIN specification
rd: roller diameter (4.59mm)
p: pitch (7.774mm)
z: toothcount (12)
d: pitchdiameter ( p / sin(180/z) = ~30.036mm)

OD of the sprocket 35.15mm
(min: d + (1-1,6/z)*p - rd & max: d + 1.25p - rd)

Roller clearance radius 2.32mm (shown as 4.64mm diameter)
(min: 0.505*rd & max: 0.505*rd + 0.069*rd^(1/3))

even tooth flank radius is within spec (of course) 5.454mm shown as 10.908mm diameter
(min: 0.06*rd*(z + 2) & max: 0.004*rd*(z² + 180) )

the roller seat angle was added (the 66.25° angles denote half of that angle [since the two sides do add up of course])
(min: 120° - 90°/z & max: 140° - 90°/z )

That roller seat angle's perpendicular is then used to cut a section of the tooth flank
219h-12T-detail.jpg
to allow for additional roller clearance

and form the final tooth shape:
219h-12T-final_tooth.jpg

which is then rotated about the center point 12 times @30°

to form the sprocket
219h-12T-DIN.jpg

Tooth-chamfer was set to a 30° angle
(2mm cut on the side, 1mm cut on the tooth tip)
and the hub is a 10 to 8 again without any clearances (should be h7 IIRC)

all purely decorative chamfers are left out to reduce filesize.
(zip of dxf attached)

if you are okay to maybe file the hub bore a bit for a good fit, that dxf should create a good working sprocket if CNC'ed
(at your own risk though ;) I can't see any mistakes, but I cannot guarantee that there are none ;))

'sid
 

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egokart

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That's super detailed, Itsid. I bought this kit from Alfawheels in the USA and it ships with a sprocket for #25 chain. I guess there will be others like me who want to use as much as they can of their existing kart, so the drawing you've done will be very helpful.
 

egokart

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H
Sooo..
since it's easier to do it here than via PM..

I couldn't find the sprocket generator,
what I did find however was the DIN standards to form roller chain sprockets.

and that's essentially only a few more lines
View attachment 122139

All denoted dimensions within DIN specification
rd: roller diameter (4.59mm)
p: pitch (7.774mm)
z: toothcount (12)
d: pitchdiameter ( p / sin(180/z) = ~30.036mm)

OD of the sprocket 35.15mm
(min: d + (1-1,6/z)*p - rd & max: d + 1.25p - rd)

Roller clearance radius 2.32mm (shown as 4.64mm diameter)
(min: 0.505*rd & max: 0.505*rd + 0.069*rd^(1/3))

even tooth flank radius is within spec (of course) 5.454mm shown as 10.908mm diameter
(min: 0.06*rd*(z + 2) & max: 0.004*rd*(z² + 180) )

the roller seat angle was added (the 66.25° angles denote half of that angle [since the two sides do add up of course])
(min: 120° - 90°/z & max: 140° - 90°/z )

That roller seat angle's perpendicular is then used to cut a section of the tooth flank
View attachment 122140
to allow for additional roller clearance

and form the final tooth shape:
View attachment 122141

which is then rotated about the center point 12 times @30°

to form the sprocket
View attachment 122142

Tooth-chamfer was set to a 30° angle
(2mm cut on the side, 1mm cut on the tooth tip)
and the hub is a 10 to 8 again without any clearances (should be h7 IIRC)

all purely decorative chamfers are left out to reduce filesize.
(zip of dxf attached)

if you are okay to maybe file the hub bore a bit for a good fit, that dxf should create a good working sprocket if CNC'ed
(at your own risk though ;) I can't see any mistakes, but I cannot guarantee that there are none ;))

'sid
Hi Itsid. The machinist is asking for drawings like this, with front view,side view, top view all with details as od, thk , pitch, teeth type marked. I have already sent him all the files you have uploaded here. Have you got time to export another batch as requested by the machinist please?
 

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itsid

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Sorry, but no...
a machinist that isn't able to read and measure a dxf file shouldn't be called that any longer IMHO.
A mindless tooling chimp is not going to cut it (excuse the pun ;))

yes, it takes a minute or two, true,
but most effort is actually dependend on what material is being used as a blank and what machine is being used
(heat during machining and related shrinkage after cooling, machining tolerances etc...)
things I have zero influence of.
All critical measurements are given (you can even read them in the other images above)
regarding the tooth form, no tolerances have been added (and I will not even try ;))
min/max values are given in terms of math equations you can drop in pitch roller diameter and toothcount
(a sensible way to dial in proper tolerances for the machinist)

And forgive me, but I do not care too much about if you need a slightly bigger shaft collar to install a grub screw,
or if your motor shaft is ever so slightly oversized so that you might need a bigger tolerance bore,
it's not important if the sprocket is 4mm or just 3.8.. etc etc..
So apart from the actual teeth everything's just winged.
(I think I took the hub 1:1 from your initial drawing so you'll find the numbers there)

if I now provide you with a fully measured technical drawing instead,
it WILL be lacking tolerances at the very least,
and the machinist will likely hand you a non functional part because of that.
And he'll truthfully tell you it's the fault of my drawing

Nope, I'm not going to waste your money that way I'm afraid.

If you want a truely impossible to falsely interpret /misread technical drawing,
with all proper tolerances and such,
you will need to find an engineer that'll draw it for you.
(will likely be more expensive than the machining itself [for good reason ;)])

Again, I'm sorry.. but I won't

'sid
 

egokart

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Sorry, but no...
a machinist that isn't able to read and measure a dxf file shouldn't be called that any longer IMHO.
A mindless tooling chimp is not going to cut it (excuse the pun ;))

yes, it takes a minute or two, true,
but most effort is actually dependend on what material is being used as a blank and what machine is being used
(heat during machining and related shrinkage after cooling, machining tolerances etc...)
things I have zero influence of.
All critical measurements are given (you can even read them in the other images above)
regarding the tooth form, no tolerances have been added (and I will not even try ;))
min/max values are given in terms of math equations you can drop in pitch roller diameter and toothcount
(a sensible way to dial in proper tolerances for the machinist)

And forgive me, but I do not care too much about if you need a slightly bigger shaft collar to install a grub screw,
or if your motor shaft is ever so slightly oversized so that you might need a bigger tolerance bore,
it's not important if the sprocket is 4mm or just 3.8.. etc etc..
So apart from the actual teeth everything's just winged.
(I think I took the hub 1:1 from your initial drawing so you'll find the numbers there)

if I now provide you with a fully measured technical drawing instead,
it WILL be lacking tolerances at the very least,
and the machinist will likely hand you a non functional part because of that.
And he'll truthfully tell you it's the fault of my drawing

Nope, I'm not going to waste your money that way I'm afraid.

If you want a truely impossible to falsely interpret /misread technical drawing,
with all proper tolerances and such,
you will need to find an engineer that'll draw it for you.
(will likely be more expensive than the machining itself [for good reason ;)])

Again, I'm sorry.. but I won't

'sid
Ok, thank you for the advice. I'm not having much luck finding machinists so I might just need to change the axle sprocket to fit #25 chain and the OEM motor sprocket. This guy was going to charge me USD40 to make it in stainless steel, probably with a lathe, around the price I would have paid to ship one in, of course the shaft wouldn't fit though. The cheaper guy was only charging USD4, that was basically a 2D laser cut out of sheet.
 

itsid

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frankly I'd buy a 12T sprocket for an OK engine (six splined shaft)
and have the machinist make me an adapter for it.
handing him the sprocket (so he can testfit the splines) and the double D is know, right?
(maybe it even fits splined stock.. https://www.a2zmetric.com/spline-shafts IDK)

that way you can easily swap sprockets at any time (10 to 12, back to eleven... as you like)
without having to machine each and every sprocket individually,
buying off the shelf sprockets and having just an adapter made is faaaar easier, no,
especially since the adapter is unlikely to wear out over time.


'sid

PS hang on 2d cut from sheet for four bucks?
that's not as bad as it sounds...
get a few of those then.
you can gently file the tolerance and tooth chamfere in as you need to.
ask him to also cut some collars for the double D shaft that you can later weld on the sprocket..

that way a sprocket costs no more than maybe 6 bucks... hard to beat.
 
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egokart

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Hi 'sid, here's a shout out to you, much appreciate your help with the project. My son is cheerfully burning up the parking lot, max speed looks like around 23kmh on flat smooth concrete. Driving at average speed of 15kmh or so for 300m caused resting voltage to drop from 38.7 to 38.1, so the range isn't huge but I have found a friendly machinist, so any improvements will be easier.
 

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itsid

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yeah sounds like range leaves room for improvement,
but I'm glad you found someone that was able to cut you a sprocket.
:thumbsup:

'sid
 
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