Spreading a steel front fork - solution found

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JohnW
Posts: 6667
Joined: 6 Jan 2007, 9:12pm
Location: Yorkshire

Re: Spreading a steel front fork - wisdom sought.

Post by JohnW »

fastpedaller wrote:My thoughts (for what they're worth) are that it's best to keep the forks as they are - It's a lot easier to give the wheel some dish than it is to modify the forks. Secondly if the width of the hub is anything but (about) 100mm then the wheel won't fit other bikes. I'd space the hub so that it is 100mm, as near to equal distance for both flanges, and of course so that no parts clash with the forks. The rim is then centred to be between the locknuts on the axle. It may only be 1mm of difference in spoke length between the 2 sides, so will be of no consequence. The last sentence assumes the same spoke hole diameter on the hub flanges, which may not be the case!


I'm very much with fastpedaller on this. I've never sprung front forks open myself, and as far as I know I've never known anyone who has tried, but apart from stressing the blades by bending them out, what stress/damage would you be doing to the brazing of the blades into the fork-crown? And how would you re-align the dropouts to restore them to perfectly parallel? I've ridden alongside three people whose front forks have failed under them - one was slow-motion and resulted in grass stains, one was noticed before a disaster came about, but the other was normal speed on the road, and resulted in blood - the cause was failure of the braze of one of the fork-blades into the crown..........and it was horrible.

This is something that I personally would never, ever do. A decent framebuilder would build you some forks, bespoke for the job.
Cyril Haearn
Posts: 15215
Joined: 30 Nov 2013, 11:26am

Re: Spreading a steel front fork - wisdom sought.

Post by Cyril Haearn »

So some bikes are built with front wheel drive, what sort of forks do they have?
One knows how the forks buck if the headset is loose!
It is earnestly to be hoped that the drive starts and stops gently, even then the drive force has to be transmitted to the rest of the bike
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Geoff.D
Posts: 1982
Joined: 12 Mar 2010, 9:20pm

Re: Spreading a steel front fork - wisdom sought.

Post by Geoff.D »

JohnW wrote:.......... I've never sprung front forks open myself, and as far as I know I've never known anyone who has tried...............

This is something that I personally would never, ever do. A decent framebuilder would build you some forks, bespoke for the job.


I think you're right, JohnW. I've come to the decision not to solve my puzzle by widening the forks. I know it can be done, and there are YouTube clips showing it. But, as you say, there are too many unknowns as to what hidden damage may ensue.
As I mentioned, I do have a bespoke set of wide forks, for a tandem. But, I'd prefer to keep them paired with the tandem (even though I don't use it).
I realise now that the motor is made to fit forks 100mm wide, but with plane, 100mm wide, parallel inside surfaces to the forks for a significant distance above the drop outs. Having the traditional dropouts very close to the bulbous end of the fork leg is what is causing my restrictions.
Geoff.D
Posts: 1982
Joined: 12 Mar 2010, 9:20pm

Re: Spreading a steel front fork - wisdom sought.

Post by Geoff.D »

Cyril Haearn wrote:So some bikes are built with front wheel drive, what sort of forks do they have?
One knows how the forks buck if the headset is loose!
It is earnestly to be hoped that the drive starts and stops gently, even then the drive force has to be transmitted to the rest of the bike


I just don't know how the drive will initiate, Cyril Haearn. This is virgin territory for me. So far the questions have been engineering ones. When I get to the stage of a motor control system I may need to jump over to the "Electric Bikes" section for ideas and support.
Brucey
Posts: 44513
Joined: 4 Jan 2012, 6:25pm

Re: Spreading a steel front fork - wisdom sought.

Post by Brucey »

the hub sounds as if it has an IS disc mount on it. If so, it is meant to go into a modern fork that has the dropouts set to the inside of the fork blades, and does indeed remain nearly 100mm wide between the blades for some distance above the hub, mainly so that the disc will clear OK.[ If you are not using the disc mount, but the screws have a blanking function, grub screws and threadlock would work OK.]

Modern carrier bikes and bikes with disc brakes have forks that are usually strong enough to take a modest front hub motor. The problem is that most of these forks have a 1-1/8" steerer and such forks won't fit older frames very well.

If the motor is capable of significant torque, it is a very good idea to fit some kind of reaction arm between the hub axle and the fork, rather than rely upon the axle not spinning in the dropouts by virtue of the flats on the axle alone.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Geoff.D
Posts: 1982
Joined: 12 Mar 2010, 9:20pm

Re: Spreading a steel front fork - wisdom sought.

Post by Geoff.D »

Brucey wrote:the hub sounds as if it has an IS disc mount on it. If so, it is meant to go into a modern fork that has the dropouts set to the inside of the fork blades, and does indeed remain nearly 100mm wide between the blades for some distance above the hub, mainly so that the disc will clear OK.[ If you are not using the disc mount, but the screws have a blanking function, grub screws and threadlock would work OK.]

Modern carrier bikes and bikes with disc brakes have forks that are usually strong enough to take a modest front hub motor. The problem is that most of these forks have a 1-1/8" steerer and such forks won't fit older frames very well.

If the motor is capable of significant torque, it is a very good idea to fit some kind of reaction arm between the hub axle and the fork, rather than rely upon the axle not spinning in the dropouts by virtue of the flats on the axle alone.

cheers


Points taken, Brucey.
The motor is 36v 240 watts. But I don't have any specs to say what the torque is, or whether it is "significant". I've seen (You Tube again !! :D :D ) set ups with an additional torque arm, so as not to depend solely on the flats and tab washer bearing on the drop-out inner surfaces (which would create quite a force on those surfaces, and they'll never be a perfect fit anyway).
I suspect this is a rather modest motor - it was cheap enough.
Brucey
Posts: 44513
Joined: 4 Jan 2012, 6:25pm

Re: Spreading a steel front fork - wisdom sought.

Post by Brucey »

IIRC it is legally not allowed to be rated more than 250W or ~15mph else you have a motorcycle on your hands. However the motor may or may not make much more torque at low motor speeds, depending on how it is designed and controlled.

Some motors that are rated at 250W are actually capable of ~1kW (for a short period until they overheat), and are electronically throttled. They will (briefly) make full torque from a standstill though, which might be four or five times the torque that is required/allowed when you are doing 15mph... and that torque has to be reacted somehow.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
fastpedaller
Posts: 3435
Joined: 10 Jul 2014, 1:12pm
Location: Norfolk

Re: Spreading a steel front fork - wisdom sought.

Post by fastpedaller »

The 'jump' ie torque from standstill to moving is often more than during any other part of the load cycle - one could say it was infinite change (using maths, as we are starting from zero!). I recall many years ago whilst working as part of a team on an 'infinitely variable gearing' project for a car, that I had the opportunity of driving the beast.... The driveplate sheared right off when I was driving it. On returning to base I was accused of abusing it, but fortunately I had a passenger at the time who corroborated my story that I had left the site security gate from a standstill and used minimal acceleration!
Geoff.D
Posts: 1982
Joined: 12 Mar 2010, 9:20pm

Re: Spreading a steel front fork - wisdom sought.

Post by Geoff.D »

Brucey wrote:..............
Some motors that are rated at 250W are actually capable of ~1kW (for a short period until they overheat), and are electronically throttled. They will (briefly) make full torque from a standstill though, which might be four or five times the torque that is required/allowed when you are doing 15mph... and that torque has to be reacted somehow.

cheers


My understanding is that "pedelec" control has the advantage of requiring the pedals to be moving in order for the motor to kick in. Additionally, I read that there is a lag from standstill, which ensures that the bike is both moving at the time the motor engages and that there is also an input from the rider.

And I'm not altogether au fait with understanding the way in which the manual throttle works. I have assumed that at small throttle openings there's a smaller current to the motor, and therefore a smaller torque. I don't envisage starting from standstill with full throttle, and no pedalling (which would be the extreme situation). I would expect to feed it in gradually, in conjunction with pedalling.

As I get further into this project I think I'm going to need the "brains" from the Electric Bike section, especially regarding control and battery management.


fastpedaller wrote:The 'jump' ie torque from standstill to moving is often more than during any other part of the load cycle - one could say it was infinite change (using maths, as we are starting from zero!)..........


Hence the need for friction clutch plates in cars, etc, fastpedaller. But, you knew that anyway, didn't you?
catsnapper
Posts: 62
Joined: 19 Sep 2010, 8:29am

Re: Spreading a steel front fork - wisdom sought.

Post by catsnapper »

'Voilamart' is an Australian company (also in UK and Germany) supplying a range of goods including badged e-bike hubs and kits from 250W upwards. Judging by the weight you mentioned it's the 250W.

I agree with the several commenters suggesting caution - you're doing a few firsts, along with many other e-bikers :) There's a lot of knowledge in the UK forum http://www.pedelecs.co.uk/forum/ and the international forum https://endless-sphere.com/forums/viewf ... d385f984a8. There are skilled members willing to help first timers to avoid the pitfalls.

I've built quite a few e-bikes, from BMX to tandems, and built (and repaired!) many more e-wheels. Adding a motor increases all the stresses on a bike. Rims, spokes and the forks all need to be up to the job - before you start considering the frame!

Many forks may be OK, but I've only used tandem, trials or similar forks - maybe overkill, but a faceplant or worse is not pretty....
Yes, a retention system is worthwhile, Chinese axles and nuts can be a poor fit, and it's easy to forget to retighten a loose nut.

Current updated laws for pedelecs in the UK ban the use of separate 'throttles', DIY pedelec systems can vary from unusable to good.
Using supplied 'cut off' brake levers instead of the originals may use plastic or low grade metal that can break, use good quality ones or use the current alternative systems.
Controllers supplied with a kit are usually basic, but there are many more sophisticated ones available.

E-biking is increasingly popular all over Europe, due to an aging (and maybe lazier!) population. Most authorities are more aware of e-bike regulations - don't get caught out :wink:

Catsnapper
Geoff.D
Posts: 1982
Joined: 12 Mar 2010, 9:20pm

Re: Spreading a steel front fork - wisdom sought.

Post by Geoff.D »

catsnapper wrote:'Voilamart' is an Australian company (also in UK and Germany) supplying a range of goods including badged e-bike hubs and kits from 250W upwards. Judging by the weight you mentioned it's the 250W.

I agree with the several commenters suggesting caution..........

.................. Most authorities are more aware of e-bike regulations - don't get caught out :wink:


Thanks for all this useful and concise information, catsnapper. And the links. From being a blank sheet of paper only 5 days ago, I'm beginning to feel that some of the lines have been filled in, giving me thoughts as to further enquiry.
I'm of a mind that experience suits me best on a learning curve. But, others' input into the decision making, especially at this early stage, is a real boost (if you'll pardon the electric motor pun :D ).
fastpedaller
Posts: 3435
Joined: 10 Jul 2014, 1:12pm
Location: Norfolk

Re: Spreading a steel front fork - wisdom sought.

Post by fastpedaller »

Geoff.D wrote:
Brucey wrote:..............
Some motors that are rated at 250W are actually capable of ~1kW (for a short period until they overheat), and are electronically throttled. They will (briefly) make full torque from a standstill though, which might be four or five times the torque that is required/allowed when you are doing 15mph... and that torque has to be reacted somehow.

cheers


My understanding is that "pedelec" control has the advantage of requiring the pedals to be moving in order for the motor to kick in. Additionally, I read that there is a lag from standstill, which ensures that the bike is both moving at the time the motor engages and that there is also an input from the rider.

And I'm not altogether au fait with understanding the way in which the manual throttle works. I have assumed that at small throttle openings there's a smaller current to the motor, and therefore a smaller torque. I don't envisage starting from standstill with full throttle, and no pedalling (which would be the extreme situation). I would expect to feed it in gradually, in conjunction with pedalling.

As I get further into this project I think I'm going to need the "brains" from the Electric Bike section, especially regarding control and battery management.


fastpedaller wrote:The 'jump' ie torque from standstill to moving is often more than during any other part of the load cycle - one could say it was infinite change (using maths, as we are starting from zero!)..........


Hence the need for friction clutch plates in cars, etc, fastpedaller. But, you knew that anyway, didn't you?


Yes indeed, but the company developing the product hadn't made provision for the torque!
Geoff.D
Posts: 1982
Joined: 12 Mar 2010, 9:20pm

Re: Spreading a steel front fork - solution found

Post by Geoff.D »

Taking into account all the view expressed, I decided -
1. to go down the avenue which would cause least deformation to the forks
2. to use a different donor frame with new(ish), heavy gauge steel forks
3. to have an asymmetrical arrangement of washers on the axle in order to centralise the hub (so the rim will be undished)

Despite having seen many fwd electric bike conversions in London, on a recent trip just before Xmas, I was still mindful f the advice here that questioned the overall strength of a fork/steerer assembly not made specifically for the job. Chatting to my neighbour, who is an engineer for a nearby F1 team, he identified the weakest part being the hole in the fork crown. He also restores vintage motorcycles and has made parts as needed, including fuel tanks from scratch. He took my fork and shaped a sheath around the front of the crown, and underneath (welding it in place as he shaped it hot). He did the same at the back (incorporating a stud for the mudguard). The outcome was a total sheath around the crown. Attached are photos of his workmanship.



Fork 1.jpg
Attachments
Fork 2.jpg
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