Eiko

I'm trying to convert a 7 speed Suntour Ultra freewheel to an 8 speed per Sheldon Brown. Last section describing bolting on a sprocket to the innermost cog: sheldonbrown.com/suntour-freewheel.html

Dishing a sprocket seems more difficult requiring more skill and feel for the metal when heating to red hot. But I'm hitting a road block trying to drill holes. A cobalt bit in a drill press isn't making a scratch on the hardened steel cog. Next thought is to heat up only the drilling site with oxy/acet to remove the hardening and then drill.

I only have one 34t cog so I'd rather not destroy it. After a minimal forum search, I'm asking has anyone done something similar? Any tips for drilling and cutting hardened steel cogs?

Eiko

oh, Plan C is to just weld the 34t cog to the innermost cog. Usually I try to keep modifications reversable.

Lascauxcaveman 

Ambitious!

Eiko

I didn't think it was ambitious until I tried to drill that hardened steel cog.

jcb3

Seems to me it would be easier (and sure to work) to get a hub with a freehub, build a new wheel, and then get an 8 speed cassette, although I think you would be left with either needing to go with a 32 or 36 as largest cog..

I'm sure you wouldn't have any problem getting a reasonable condition hub/freehub from the members in the ISO (in search of) section for the cost of shipping (I'm pretty sure I have a few extras floating around that I'm wondering what I will do with them).

Wheel-building skills are transferable into the future. I doubt the market for franken-freewheels is all that large

seypat

+1.

Eiko

Freehub and 8 speed cassette: Yes it would be much easier. But what's the fun in that? I'm running Campy Nuovo Record freewheel hubs that would (quite illogically) pain me to give up.

Cyclone GT is not supposed to handle a 36. Although I haven't tried that.

Wheel building skills - that would be nice. I tried once and am traumatized. Market for franken-freewheel isn't a concern.

EDIT OF ORIGINAL POST: Oops. It should read "My cobalt bit isn't making a scratch".

Maybe I will buy a carbide drill bit.

GrainBrain

Stop it.

Buy a cheapie silver prebuilt freehub wheel for that price. I bet you could find a hub from Formula that is high flange.

Eiko

You're being overly logical and rational.

seypat

Bear in mind that the more gears you try to ride on that hub, the more likely it will fail. There is a reason the freehub/cassette replaced the freewheel system. So if you love those Campy hubs, quit trying to put 8 cogs on them.

dddd

Another ambitious possibility for greatly expanding the capability of the Nuovo Record freewheel hub might be to adapt a SRAM Powerdome cassette, so that perhaps as many as 10 gears could be fitted to a 126mm-spaced hub.
A threaded freewheel cog would likely need to be machined to interact with a shortened Dome, and the splined largest aluminum cog (which sustains all of the 1-piece steel cassette's torque) would also have to have it's hole enlarged and shaped to fit on the freewheel body.

jeirvine 

Just keep it a 7 speed, and swap in the 34t for whatever's there now. Easy peasy.

thook

being the enabler....

i got some dewalt hardened steel bits at lowe's. came in one of the cute yellow dewalt plastic fold out boxes. i've used them on some pretty hard steel the past several weeks and they worked well. for example, the square tubing my flat bed trailer is made of.

Kuromori

Square tubing usually is soft mild steel. Cogs are often some sort of hard heat-treatable possibly tool steel.

masi61

SunTour Winner Pro freewheels came in a 13/34 configuration for 7 speed. No need to drill or weld anything. Here is one:

https://rover.ebay.com/rover/0/0/0?m...2F153446217139

People here kind of respect Campy Nuovo Record hubs, you know? They are beautiful and classic and anything beyond 7 cogs is sounding mongrel and wrong.

Maybe you are a more resourceful home machinist than we know, but based on what you’ve shared so far it sounds like you’ve got some wild ideas for an 8 speed freewheel conversion presumably for the purpose of obtaining one more low climbing gear. I mean there you have it - a 7 speed freewheel that is the same brand and ultra and preserves the integrity of your Campy Record hub. The $220 price tag is prohibitive, yes but if you put your feelers out, these pop up for more reasonable prices from time to time.

Me personally, I love custom classic and vintage challenges. Things that sound cool that aren’t routinely done and just scream out for the right person to implement it in a build where it would be useful. SunTour gear is fantastic that way.

To take your concept out of the realm of fantasy we need to know exact rear dropout spacing, and what is your current axle length on the Campy Record hub. If you don’t already have a 137mm axle on there, you will need one in order to have good frame clearance for 7 speed. Wheels Manufacturing chromoly axles have a reputation for being stronger than the original Campy ones BTW.

If you could pull off this 8 speed SunTour freewheel then the axle would now need to be like 141 mm long in order to go wider, for 130 mm spacing. You should tell us what frame you are using. If it is already spaced 130 there are so many better stronger more modern and more affordable options which is why we’re scratching our heads and saying, huh?

There were 8 speed freewheels at the end of the freewheel era. Sachs/Aris made them and a few years a“go you could pick up NOS ones on eBay for like $30. I guess the prices have now shot up due to relative scarcity. They floundered along, unloved because of a (deserved) reputation of being a bad idea - flange width (freewheel hub) was too narrow and the lack of bearing support out to the edge of the smallest cog caused inherent weakness with potential for bent and broken axles.

Here’s a 12-28 one BTW:

https://rover.ebay.com/rover/0/0/0?m...2F192872156217

Do share more specifications of your proposed mongrel drivetrain. You might yet convince the grumpiest of us that your proposal has merit, but for now the prevailing wisdom is to use classic parts inside of their engineering tolerances.

top506

Old gunsmiths trick: spot anneal the hole site with a drop of solder.

Top

dddd

I can't see a drop of solder raising the temperature of the steel even close to the annealing temperature of steel, even before accounting for the degree of heat-sinking that would be considerable.

The OP's idea seems interesting because of how today's largest cassettes are being offset toward the leaning driveside spokes, which creates room for more cogs without widening the cassette toward the drive side.

thook

right. but, the bits were/are for hardened steel. maybe i should try them on some actual hardened steel

Eiko

That was irritating. Didn’t know about the 5 post and the 24 hr restrictions. I know – spammers.

?? Could you explain the physics behind that? I don't understand why having more gears will cause it to fail faster. I do understand the physics behind the superiority of freehubs over freewheels.

Very interesting out of the box idea. A reason I asked you guys. I don't however understand the current tech, however.

I have a 32t in that spot right now. 34t is not going to change my low gear much. I seem to be in between gears constantly. Going from 7 to 8 cogs seems to significantly improve the jumps between gears.

I figured most on C&V are enablers. Thank you. Hardest Home Depot bits are cobalt at about $1/bit. Next possibility I'm thinking is carbide at about $10-20/bit (Amazon or HD online).

These particular cogs are absolutely heat treated/hardened steel. I was surprised the cobalt bits didn't scratch it.

I'd agree with @dddd. I can't imagine solder is going to do enough heat transfer. Carbide or your idea with oxy/acet is what I'm currently thinking. I've never used carbide or used oxy/acet in this manner. I was looking for "old tricks" like yours.

Eiko

I didn't know about the 13/34. Thanks. It doesn't address my main issue; decrease the spacing between the gear ratios. I'm already running 32t for the low gear.

haha. yeah, I know what you mean. But I'm not touching the Campy hub. That would be psychologically difficult for me too. And the freewheel internals are not modified, only the largest cog. This mod shouldn’t be visually that obvious. I think.

Neat! Thanks for teaching me something. I stopped riding just before the 8 speed freewheel so completely missed those. Didn't even know Sachs were still in the market. And Aris is new to me.

I tinker but I’m not a home machinist. A friend is a capable machinist - a last resort. I’m not looking for an extra climbing gear. I’m at the Cyclone GT’s 34 or 32 limit. The purpose is to decrease the jumps between gears. I seem to be in between gears too often.

I'm getting the sense you think I'm doing major re-machining of the hub and axle. I'm not. No changes to the hub, axle, or freewheel. I'm merely bolting on (or trying to) an 8th cog to the innermost cog. This 8th cog will overhang the inner flange of the freewheel but since the wheel is dished, the cog should clear the spokes if the cog is large enough.

But since you ask, my rear dropouts are 126 mm. My rear axle is 138 mm. Those specs are not being touched. The frame is a Raleigh Competition GS with all Reynolds 531. My other road bike is a Seven Odonata with Campy Record 52/42 and 11-28. I could change out the crank to Campy's Record microdrive and I'd have 10 cogs in the back instead of 7 or 8, but I kinda like the Raleigh better. Cost isn't really a factor in all of this.

Again, the goal isn't the low gear but to improve the spacing between gears.

My current setup in rear cogs / gear inches for the front 39t chainring:
13-14-15-18-22-26-32 / 81-75-70-59-48-41-33

My proposed setup in rear cogs / gear inches for the front 39t chainring:
13-14-15-17-19-22-26-34 / 81-75-70-62-55-48-41-31

The only benefit is decreased gaps between the 3rd through 5th cogs. But that's where I always seem to be in between gears on 4 hour climbs at a 3% grade.

Eiko

Update: A few seconds with the oxy/acet completely removed the heat treatment and I could drill the cog like it was mild steel. Now I'm trying to decide whether to go with oxy/acet method, drill the holes, and leave it at that? The torch time was brief enough I don't think it affected the hardened teeth. But I'm wondering if I need to re-heat treat the cog (that would be a new skill for me).

Or should I go ahead and buy a $10 carbide bit and not have to worry about removing the heat treatment.

EDIT: oh, I have to remove the heat treatment anyway in order to cut out the splines and enlarge the center hole of the cog so that it will fit over the inner freewheel flange. So I may as well go ahead with the torch prior to drilling instead of a carbide bit.

Another thought. I may be able to slide the current innermost cog onto the freewheel and then bolt the new 8th cog to the inside of the 7th cog. Without enlarging the center to slide it over the freewheel's inner flange. And not have the 8th cog interfere with the hub or spokes?

lasauge 

Even if you succeed in attaching the extra inboard cog in this case, will you be able to shift to that gear without putting your derailer into the spokes?

Eiko

No idea. I'll find out. As you can see, I find out if something will work empirically. I have friends who will measure first, do calculations with complicated formulas before doing the thing. I'm not that smart.

pastorbobnlnh 

Which model of Suntour freewheel body are you using?

FWIIW, I'm 99.9% certain the Sachs Aris 8 speed is designed for a 130mm rear spacing and won't work on 126mm spacing. The 8 speed bodies are wider/deeper than a 7 speed body.

A very rare item, is a modified set of threaded Suntour sprockets which Moulton had made for their 20" wheeled bikes (they also made a Regina version). The Suntour went from being 7 speed Ultra to an 8 speed. But this was all designed to gain a higher gear and to work on a Moulton hub and spacing. I write a little about this and pictures of a Regina 6 to 7 speed on my website here https://www.freewheelspa.com/pictures.html. IIRC, this increased the spacing on the freewheel, which you can't afford to do.

Velo Mule

This is an interesting project. Please post pictures. That is, if you don't get the Sachs 8 speed freewheel. I like Suntour and tinkering so I would be interesting in how this works out.

If the cog fits without interfering with with the spokes, shifting the derailleur should be no problem.