puchfinnland

I have been thinking about this for some time and a fellow forumite said he could try it.

the objective is to take a new HG Shimano 7 speed freewheel
MF-HG37 13-15-17-19-21-24-28



and narrow it down to be 24mm thick 6 speed.
why???

I have 120mm spaced junior road bikes that are 5 speed- it would be great to built them to be 6 or possibly even 7.
yes I hear you -it sounds quite easy to respace to 126
or throw in an Ultra-6 suntour freewheel.

well I have tried it and the ultra 6 just does not work.
why?
a regina 5 freewheel is 25mm outside cog to outside cog,
the ultra-6 is 27mm
a junior road bike(JRB) has such a short distance between the bottom bracket and the rear axle that the chain just cant flex that much-
yes I hear you- I have tried a 7 speed, 9 speed and 11 speed chain.


I looked at an old 9 speed casette I had lying around and noticed that 6 cogs outside to outside are 24mm!
now the HG freewheel has the same thickness cogs
cogs are 1.8mm thick and spacers are 2.6
so a 6 speed with narrow cogs should be something like this-
1.8 x 6= 10.8
2.6 x 5 = 13.0
total is 23.8

HG body.



the 7 speed,6 speed and 5 speed HG bodies avail are all 31-33mm wide assembled

this wont do- 27 is the max I can go on this.-it just wont fit.

idea is to mount it up on the lathe and turn off the threads, and make new deeper threads,
and new shims at 2.6 and see how it goes.

any thoughts on this project are greatly appreciated.
and then again if it does work I hope we can make more- even a narrow 7 could be assembled with just shim swapping
mike

fietsbob

Quasi Ultra 6 of 7 with the lock ring wider, instead of the 13 top cog?
and just using the lock ring to secure all splined cogs?
say 15~28t


What's wrong with 5 speed freewheels? that 6th cog
is why the width went to 126.

Sram/Sachs made a 2 cog 3 speed hub hybrid hub as a supplier
to Brompton

those are closer to a 110 .. so narrow and still wide hub flanges for lateral strength..
then you get a 6 speed setup. a half stepped 3 speed.
standard: a 13,15t combo..

mrrabbit 

You are going about it all wrong, and are probably working with hubs that are not in spec...

Dimension A = Freewheel Stop to End of Drive Side Locknut
Dimension C = Outside Lock Nut to Outside Lock Nut

[Regular Spacing]

25mm 5-Speed A=29mm C=120mm to 122mm
31mm 6-Speed A=35mm C=120mm to 122mm OR 125mm to 127mm

[Narrow Spacing]

27mm 6-Speed A=31 C=125mm to 127mm
32mm 7-Speed A=36 C=125mm to 127mm
36.5mm 8-Speed A=40.5 C=130mm is usually the case


All you have to do is shift 2mm of spacer/locknut from the non-drive side to the drive side of the existing hubs - redish the wheel and you're all set for an Ultra-6 / Narrow-6 freewheel on a 120mm-122mm rear hub.

To go 7-speed, chances are you need to go 125mm-127mm OLD (Dimension C) simply to keep asymmetrical dish from getting too extreme...

=8-)

puchfinnland

its the distance between the cogs -that is the issue.
a narrow hub wont fix the problem, re shimming the hub wont fix the problem
this is a junior road bike w/ 24" tubulars
the distance between the BB and rear axle are much shorter increasing the chain twist

my thoughts are
the 5 speed is 25mm wide and works perfect.
the ultra 6 at 27mm did not work because the cogs were too thick(old fashioned) and the chain just did not like the flex at the smallest cog or the biggest cog.
modern chain did not help either

new HG teeth are narrow and if I could build a Ultra HG at 25mm running a modern chain it would be perfect.

dabac

Freewheel bodies are HARD, and don't take kindly to machining, let alone thread cutting. IMO, you'd have some serious heat treatments to go through before being able to pull that off.

If I were to try for your goal, I think I'd start with a freewheel that'd fit. Then I'd consider two different options:
1) outside help - find a guy with a water jet cutter, and a good stock of sheet metal. Have him cut new sprockets that'd fit the existing spline pattern out of a suitable thick plate. Then cut spacers on a lathe, assemble and ride. Bevelling the tips of the teeth is easily enough, but you'd have to do w/o the ramps.
2) the home shop approach - Pull the sprockets off a couple of scrapped freewheels. Disassemble a 9-speed cassette. Use a hole saw in a drill press to cut out the splined center of the sprockets from both cassette and freewheel. Might want to use a slightly smaller hole saw when you cut the centers out of the cassette sprockets to get a slimmer seam. Fit cutout freewheel centers to cassette outer sections. Weld/braze them together depending on seam width, available equipment/skill, and personal preference. Cut spacers on lathe, assemble and ride.

mrrabbit 

You are trying to take an Ultra-7 at 32mm and reduce it to a Ultra-4 at 24mm when what you'll really end up with is an Ultra-6 at 24mm THAT WON'T WORK BECAUSE AN Ultra-6 REQUIRES 27MM and a Regular-6 REQUIRES 31mm.

I'll say it one more time:

Your rear 120mm hubs are in all likelihood setup at Regular 5-Speed with a Freewheel Stop to Locknut distance of 29mm.

Move 2mm of spacer/locknut from the non-drive side to the drive side so that you have Freewheel Stop to Locknut distance of 31mm.

That way you will have a 120mm rear hub setup for Narrow 6-Speed. Correct the dish and you are set to go.

=8-)

puchfinnland

you fail to consider the factor of cost and time.

you cant find a narrow freewheel body that accepts narrow HG splined sprokets
they were never made

cutting with a holesaw and brazing the center to another cog would take forever,and impossible to get perfectly centered and flat.

waterjet cutting 1.8mm flat plate will not get you the same quality long wearing teeth as a manufactured cogs- plus its not free.

an entire HG freewheel new costs 11 bucks-
the body is case hardened- only need to redo the threads which are not very much under load.
the spacers need to be turned on a lathe.

so when the cogs wear out (the only wearing part) just buy new off the shelf cogs

mrrabbit 

1. Spacer and Locknut change. 5 minutes labor.
2. The exact same Shimano freewheel (Ultra-7) can be had as Ultra-6 - same for IRD. 5 minutes online shopping.
3. Modern day 6/7 speed Shimano compatible chain. 5 minutes online shopping.

DONE!!!

Reference: Sutherland's Fifth Edition, p. 10-5, Sutherland's Sixth Edition, p. 10-6

=8-)

puchfinnland

I respect your opinion.

as I said- I can get the ultra 6 in there just fine, it will kind of work, but the chain angle side to side is too extreme on both the smallest and the biggest cog.

all the respacing will only improve the high or the low but not both
this is a junior 24" tubular bike.
I bought the ultra 6 because it does fit in 120mm spacing- but the distance between the bb and axle is much shorter then 700 wheels.

mrrabbit 

https://www.modernbike.com/itemgroup....FcV7QgoddhgACQ

15.99

Chain is about 15.00-17.00

=8-)

mrrabbit 

1. Wrong - FACT! I provided the Sutherland's Reference for you already.
2. 29mm to 31mm - that's only 1mm more per each side of the rear chainline centerline.
3. Respacing to spec does BOTH - see #2.
4. The short stays will always be a problem - and you'll always make it worse irregardless anytime you try to increase gears. Going Ultra-6 is not too bad - just 2mm. Going Ultra-7 at +7mm will be awful.

Pick your poison on #4.

=8-)

mrrabbit 

I wouldn't be surprised if someone else jumps in suggesting an IGH 8-speed - assuming one is available in 120mm or 126mm spacing.

=8-)

puchfinnland

I tried to put in the falcon body-its 31mm and it touches the stays and I cant fix that.
shimano is slightly thicker.

regina5 -- ultra 6 --falcon-- shimano


I was after only 6 cogs not 7 in a 120mm space

the ultra 6 at 27 was as far as possible with the short stays.

I have considered reshaping the big and small teeth on the ultra6 but it will never be the same as a modern hg cog set

i found a freewheel for 11 on th enet-its not worth arguing who has it for the cheapest price-
ok 11-15 bucks

mrrabbit 

You are confusing freewheel thickness with freewheel stop to end of lock nut dimensions.

27mm thick Ultra-6 / Narrow-6 freewheel on a re-spaced hub such that freewheel stop to lock nut = 31mm

PAY ATTENTION!!! Re-read the chart I initially posted for you...straight out of Sutherland's.

=8-)

(night)

puchfinnland

OK I got the wheel in my hand..

Dimension A = Freewheel Stop to End of Drive Side Locknut
Dimension C = Outside Lock Nut to Outside Lock Nut


25mm 5-Speed
A=30.4mm C=120.4mm

campagnolo GS hubs.

-mike
(off to work)

dabac

I wouldn't say failed, I've just not done it.
How am I supposed to know what it's worth to you to get this done? Bike riding is a hobby, a deliberate choice. There's no specifiable "worth" to it.

Now, if you'd started your post with "I need to get this done in under one hour", or "I can't pay more than XX EUR/USD/GBP for parts" or something like that, then I'd left this thread alone.

We see it all the time. People build their own frames, wheels, bike lights, racks, have old generic frames sand blasted and repainted etc etc. Dead stupid things to do if you were to try to fit a price tag to them.

You're missing the point: take/keep the freewheel that'll fit the spacing, either custom make sprockets that'll fit the splines of said freewheel from sheet metal, or graft splined part from thick sprockets onto thin sprockets. Trim sprocket pitch to desired value by adjusting the thickness of the spacers.

Again: How am I supposed to know what it's worth to you to get this done?

Although several steps, this is readily doable, w/o fancy shop equipment.

Forever - I don't think so. I'd need 3 jigs to hold the sprocket(s) - one hour to build those. Align-clamp-cut - I'd have the 1st set done in 30 minutes tops.
Brazing is slower, so I'd weld this. That's a 30 sec operation for each sprocket. Hardly worth counting, under the circumstances.

Including building the jigs, but excluding cutting the spacers, I reckon I could make one set in about two hours. For a batch build, time would drop dramatically.
But you don't need "perfectly centered and flat". Ever looked at a cassette/freewheel wobble on its axis as the wheel is spinning? Getting it "good enough" seems well within reach.

So? Ever heard of something called a compromise?

But sure, if you prefer holding out for a perfect solution while ignoring possible workarounds, be my guest.
Wasn't this for a junior racer anyhow? Can't see wear rate being a critical feature there.

So?
Any attempt at solving this that doesn't rely on moving washers and/or redishing the wheel will have a definite cost associated to it anyhow. The amount is what should be important, not where it goes.

Water jetting is fast, once you've gotten the pattern worked out.
Doing one set of sprockets is probably scary expensive if you have to pay shop prices for it. But for a batch production, the cost-per-unit would drop right down.

.. which you'd need to get rid of before cutting the threads, then back in to keep the serrated area where the pawls engage from getting chewed up. Good luck with that.

True. Aluminium bodies tend to do OK.

So?
How were you planning to cut the threads? By hand? I see your whole scheme as relying on having access to a lathe anyhow, so cutting spacers is no bid deal.

puchfinnland

"How were you planning to cut the threads? By hand? I see your whole scheme as relying on having access to a lathe anyhow, so cutting spacers is no bid deal."

I have friends with access to cnc machines, this would be a moonlight job.

older freewheels have each cog threaded on.
the hg freewheel type they are splined, just like casettes

of all the choices on how to do this -narrowing the body,
by cutting new threads for the locking washer
and making some spacers
is the most simple and repeatable method of doing this
all the wearing parts are replacable and off the shelf then.

puchfinnland

"How were you planning to cut the threads? By hand? I see your whole scheme as relying on having access to a lathe anyhow, so cutting spacers is no bid deal."

I have friends with access to cnc machines, this would be a moonlight job.

older freewheels have each cog threaded on.
the hg freewheel type they are splined, just like casettes

of all the choices on how to do this
-narrowing the body,
by cutting new threads for the locking washer
and making some spacers
is the most simple,reliable and repeatable method of doing this
all the wearing parts are replacable and off the shelf then.

mrrabbit 

For Ultra/Narrow 6-Speed you need:

27mm Ultra/Narrow 6-Speed
A=31mm minimum, C=120-122mm OR 125mm-127mm (your call on OLD)

Narrow 6/7/8 speed chain required and re-dishing required....


=8-)

puchfinnland

so you are telling me by moving one shim it will improve the chain/cog contact on both the high and the low??

mrrabbit 

OP

You really should grab a copy of Sutherland's Fifth or Sixth Edition...

On the pages I noted earlier, 10-5 / 10-6 under the "Hubs" section, the specs for the various freewheel widths are clearly spelled out. Furthermore, the specs for the freewheel stop to locknut on the hubs are clearly noted. You will also see that when the specs are followed - it in general establishes the centerline for the cogset - typically being the middle. A graphic is used on the noted pages to illustrate.

=8-)

Booger1

Looks like you need to narrow it about 1/8 inch or so.......no thread cutting involved.After the gears get narrowed,an 1/8" or so of the spline will be showing correct?

You could surface grind about .020 thou off each gear to narrow it.Remove the theaded part and add a clip instead of threads to hold the gear pack together.Using the spines to our advantage,machine the spines for a clip,then using a belleville washer retained by a clip will easily hold the gear pack together.If you machine the clip in the correct place,you can set the side clearance tight using a belleville washer and it won't rattle.

You can always shim it if you don't like belleville washers.

It doesn't HAVE to be threaded,clips work in car and power transmissions,it should work on a bicycle trans also.

puchfinnland

thanks booger- I think you understand the situation,

I believe making spacers to 2.6mm will narrow the cluster down fine,
then its the same distances as a 9 speed so I should be able to use a 9 speed chain with it.

the housing is too fat and is wider then the axle nut so thats why I need to cut it down.

a clip- sounds like a good concept to investigate.
with a 13t it get pretty thin at the nutted end.
the falcon has the last cog 13t threaded on so that would be a good locker.

these freewheels are cheap so if I muck one up Im not going to cry

miamijim

Puch,

Why not space a 126mm HG hub down to 120mm and use 5 or 6 cogs with thin 8 speed spacers. Doing it this way will aloow you to place spacers on either side of the group of cogs to set your chainline.

Booger1

I think he's having trouble fitting the inner body in 120,...he needs to narrow the whole body.Then respace the gears and spacers,then run a 9 or 10 speed chain.

I never tried,but I think you could respace down to 120 but you move the hub to the left 4-5 mm......not the best direction as far as wheel strenght goes and it's not helping your chainline any.You could shim the gears back out to help with the chainline after you narrow them,but then your back to threading the body again,and the wheel strenght still suffers some.

I guess you could run 9 or 10 speed gears also to give you some more room between gears,if you wanted to try and run 8 speed chains,but they are not so cheap....I don't own any 9-10 speeds......I think the gears are a little thinner but the splines are the same.

You also might want to look at the splines themselves from underneath.Are they solid or hollow.If hollow,your going to have an open slot when you machine them for threads or a clip.......not so good for bad weather....

You may have to sleeve the right side of the hub if the splines are hollow,so that you have some strenght,to block the weather and to support a clip or threads......it's starting to get complicated........spreading the stays is starting looking better all the time........