eliptical chainring - want to try one?

[kendrick57]

Hi
What bike was the chainring to go on? It looks too big for an offroader maybe a road mainly hybrid MTB or a road bike?

kendrick

my brother asked me to knock up a 48 tooth elliptical chainring. I'll get this made (laser cut) in 2mm stainless

the major & minor radii are 107mm and 87mm. The ring of holes near the middle are 110mm PCD so the thing will bolt straight onto most 5hole crank spiders.
Weight will be 200 grams.
lotsa holes so you can play with angles and swapping right/left or rotating 180degrees both give a stack more options.
They will probably cost about £15 including postage, maybe less so if anyone wants to try one, leave a reply on here by tuesday lunchtime - that's when I'll be round at the laser place.
It's as easy for me to get 5 cut as one...... ;^)
You will have to chamfer the tooth sides (file or grind) and clean off any flash. There are none of the "easyglide" ramps and bumps to aid front deraillieur changing.

[bobc]

Road bike, my bro is working quite hard on his fitness right now & fancied a look at this. I'll get the ring tomorrow to fit it on saturday; I'll post a pic.

[Brucey]

I take my hat off to you chaps; 'tis clever stuff to get the program right for this kind of chainring.

Round ones are much easier!

BTW I harbour a lurking suspicion that sprockets (except for singlespeeds and IGHs) might be more difficult; certainly they seem far less tolerant of tiny amounts of wear, giving running issues that don't very often seem to afflict chainrings in the same way.

cheers

[GeoffApps]

I take my hat off to you chaps; 'tis clever stuff to get the program right for this kind of chainring.

Round ones are much easier!

BTW I harbour a lurking suspicion that sprockets (except for singlespeeds and IGHs) might be more difficult; certainly they seem far less tolerant of tiny amounts of wear, giving running issues that don't very often seem to afflict chainrings in the same way.

cheers

Fewer teeth engaged.
Splined sprockets easy to do.

[kendrick57]

Hi
To add to Geoff’s comment sprockets would be better made out of laser cut 2nn stainless steel with maybe a bit of milling on the teeth if it is for a 9 or10 speed drive train, the important bit would be custom width spacers would be needed, for that a milling machine would be required. It would work and can be done but the cost of the finished item may well be more than most want to pay.

Kendrick

[NATURAL ANKLING]

Hi,
Once the model's been constructed you can drive it through parrameters and link to an Excel sheet.
Out put to CAD CAM etc,
DONT look at the dimensions I knocked it up by eye to look proportional, the geometry's not clever either.

Cheers,

[DoctorRad]

That's pretty much what I'm aiming for, but with FreeCAD since I don't have a payware CAD licence to work with... unless anyone can recommend another decent free-to-use CAD package?

Either the FreeCAD script will read values from an Excel export, or I'll get Excel to write the basic script for me and copy it over.

[bobc]

Just got the ring from the laser cutters - looks nice. Best thing is that I finally DID get the spider bolt pattern right & that means there are 100 angle steps of 3.6degrees to choose from ;^)
BTW regarding the lead- in portion of the tooth notches; I'm sure having a straight section here will be fine on a big chainring, but it would be a disaster on a small sprocket, e.g. 8 tooth. I'd suggest putting a curve on here centred on or just inboard of the next roller position; I'll pop a couple of pictures on later. Has worked for me for years & is easy to do with CAD. Of course the design you make here doesn't stay like that for long ;^)

[RJC]

What grade of stainless was used? After all the effort a stronger/harder grade seems like a good idea.

[kendrick57]

Hi
I'm not sure what bobc used but the stainless steel that geoffs chainrings are made of is a high grade automotive type. i have had torque arms for electric bikes made by the same company and checked on the strength first.

Kendrick

[cycle tramp]

Blimey!! fifteen quid for a stainless steel chain ring! That's less than half the price of a surly stainless steel chain ring and they're round ( http://www.sjscycles.co.uk/surly-110-pc ... prod20828/ ). Sadly, i bought one for my bike before i saw this thread. Admittedly i'd have to ask if it was possible to produce a completely round chain ring as i use a hub gear without a chain tensioner, especially as the other attractive feature of the chain ring shown here was the number of crank spider bolt holes ~ which means with a completely 'round chain ring you can advance the chain ring everytime you clean the chain, thus neatly avoiding 'the teeth at 90 degrees of the crank wearing out first problem'. And you can advance that chain ring lots of times, too. Something that i can only do ten times with the surly chain ring (5 bolt holes, but i can turn the chain ring over). It also makes the current 'bought of the peg' chain ring trouser protector discs (that fit on the outside of a single chain ring transmission set up) look rather expensive, too.

Is it me or is there a gap in the market here? As a service to cyclists the CTC could offer the excel spreadsheet/ CAD Design package on their website, allowing cyclists to design their own chain rings or chain ring trouser guard; with any degree of elipticalness or non-elipticalness, as well as teeth shortening to aid any gear changes. Once the chainring has been designed and all measurements supplied, the cyclist can then down load or print off that data and send it to the engineering firm of their choice, who will then cut the chainring or guard. If the CTC wanted to, it could actually reach an argeement with an engineering firm, so that once the chain ring had been designed, the cyclist could pay for it over the website and then the engineering firm could lazer cut it.

No more hunting for your perfect chain ring. Just click onto the CTC website and get one made up to your specs. If anyone wants to give me a quote for two chain ring protectors with 'cycle tramp' etched into them (for theft prevention purposes) please let me know

[bobc]

I forget the stainless grade, to be honest pretty much any would be so much tougher than an ally chainring......
here's a picture of an 8 tooth sprocket design with tooth leadin centred on next sprocket roller position

and a picture of the chainring on the bike

It wasn't fitted properly & the front mech wasn't set up, but it was possible to pedal down the street. John thought it was quite weird & will give it a week or so to see if it agrees with him. I had a go & it felt just like a round one to me, but I'm not used to his bike. However, of one thing there is no doubt - it looked SO whacky & cool!
If there's a file repository on here I'll happily dump the dxf file in it, it may not be to everyone's taste but it's a start....??
I'm afraid I didn't make an automated XL/CAD thing - it's just too easy to do a custom one - I'll probably never make another.

actually, if Johnny boy likes it I might have to do a custom oval small ring for the same bike....... ;^)

BTW cycle tramp, plenty of folk use elliptical with no tensioner - the chain wraps 1/2 a circumfrence of the ring & that's always the same length....

OK I just tried to attatch a dxf file to this post but the system wouldn't let me :^(

[Brucey]

BTW cycle tramp, plenty of folk use elliptical with no tensioner - the chain wraps 1/2 a circumfrence of the ring & that's always the same length....

not exactly the same length, but close enough for most folk running a freewheel or an IGH, provided the ovality of the chainring isn't too great.

BTW the chainring looks suitably wacky!

cheers

[kendrick57]

Hi
A good guide to what is a suitable chainring on what bike is to check with Highpath's web site.
From what I read you can have a maximum of 15% ovality with hub gears without a chain tensioner.
Bobc's chainring would be no good it has an ovality of about 23% fine for what he is using it for but too much for a hub gear setup on its own.

Kendrick

[kendrick57]

It

OK I just tried to attatch a dxf file to this post but the system wouldn't let me :^(

Hi
From the look of the way you have the ring set up at the moment the angle between the major axis and the cranks is wrong with the chainring as it is in the picture reposition the crank to about 2 o'clock I'd say 2 or 3 holes.

As for loading up dxf files try compressing it into a zip file

Kendrick