Go Back  Bike Forums > Bike Forums > Framebuilders
Reload this Page >

Simple carbon fork extension for scooter

Notices
Framebuilders Thinking about a custom frame? Lugged vs Fillet Brazed. Different Frame materials? Newvex or Pacenti Lugs? why get a custom Road, Mountain, or Track Frame? Got a question about framebuilding? Lets discuss framebuilding at it's finest.

Simple carbon fork extension for scooter

Old 04-05-22, 01:38 PM
  #1  
scottfsmith
I like bike
Thread Starter
 
scottfsmith's Avatar
 
Join Date: Feb 2021
Location: Merry Land USA
Posts: 662

Bikes: Roubaix Comp 2020

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 267 Post(s)
Liked 283 Times in 191 Posts
Simple carbon fork extension for scooter

Hey frame builders, I'm not one of you but I like doing home-brew projects and I am trying to adapt a scooter to run larger (12-16") bike wheels. The scooter now has 8" wheels and my plan is to get a sheet of durable 1/4"-thick carbon fiber and cut some forks out of it which I can tack on to the existing forks as extensions. I have limited tools but I do have a jigsaw and can cut the appropriate fork shapes out of the carbon fiber sheet. I am thinking this will be easier for me as I have no easy way to cut metal sheets, and as an added advantage it will keep the weight down.

I'm curious if this sounded doable, in particular if a 1/4" sheet of carbon fiber like this would be strong enough for a fork that will extend 4-6" from the existing fork. Also I'm not sure how wide to make each fork blade, I was thinking around 1" wide on average with thicker toward the base. I want to keep the weight down and the carbon sheet weighs around 7g per square inch. So 6" fork plus 3" overlap on existing fork to mount it x 4 forks = 36 inches = around 250g which seems OK.
scottfsmith is offline  
Old 04-05-22, 01:54 PM
  #2  
guy153
Senior Member
 
Join Date: Dec 2019
Posts: 950
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 321 Post(s)
Liked 261 Times in 212 Posts
Interesting project! It will probably be strong enough in theory but a tube or a box section is a more optimal shape. You might not have enough stiffness. If the fork bends in use then it's loaded in a different way and might break. So although stiffness is a different concept from strength it can contribute to the strength of the overall structure.

6" long you might get away with it though. A full length bicycle fork (probably 14" or so) would not be safe made out of 1/4 inch CF "plate" like that I think.

Metal is very easy to cut with an angle grinder and cutoff wheel (about $40). Plus a few more for eye and ear protection if you don't have any
guy153 is offline  
Likes For guy153:
Old 04-05-22, 01:59 PM
  #3  
zandoval 
Senior Member
 
zandoval's Avatar
 
Join Date: May 2010
Location: Bastrop Texas
Posts: 4,416

Bikes: Univega, Peu P6, Peu PR-10, Ted Williams, Peu UO-8, Peu UO-18 Mixte, Peu Dolomites

Mentioned: 13 Post(s)
Tagged: 0 Thread(s)
Quoted: 928 Post(s)
Liked 1,594 Times in 1,020 Posts
Man... This is a worthy project... I would probably start with using Aluminum first and get all the bugs out of the design before going to the Carbon...
__________________
No matter where you're at... There you are... Δf:=f(1/2)-f(-1/2)
zandoval is offline  
Likes For zandoval:
Old 04-05-22, 03:30 PM
  #4  
scottfsmith
I like bike
Thread Starter
 
scottfsmith's Avatar
 
Join Date: Feb 2021
Location: Merry Land USA
Posts: 662

Bikes: Roubaix Comp 2020

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 267 Post(s)
Liked 283 Times in 191 Posts
Thanks for the feedback! Mainly I'm glad you're not saying "this is nuts!" I had a similar feeling that because it was such a short extension the stresses would be much less than in a bicycle fork.

I should probably get an angle grinder, it is useful for a whole bunch of things. I have a mini version of it on my Dremel tool which I have found many uses for. It would be work to cut a metal sheet but looks doable.

Aluminum might be a good way to try it out, it looks like jigsaws can work on aluminum according to Google.
scottfsmith is offline  
Old 04-05-22, 03:43 PM
  #5  
guy153
Senior Member
 
Join Date: Dec 2019
Posts: 950
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 321 Post(s)
Liked 261 Times in 212 Posts
I do basically everything with a grinder. I know we're supposed to have a collection of files and hand-tools and things but really, for me, I can just do everything better with a grinder using mainly a cutoff wheel or a 120-grit flap disk. Birds-nest wheels also good for stripping paint. Like a Dremel only about 1000x faster. But with great power comes great responsibility so be careful
guy153 is offline  
Old 04-06-22, 03:56 AM
  #6  
dsaul
Senior Member
 
Join Date: Jan 2013
Location: South Jersey
Posts: 2,258
Mentioned: 18 Post(s)
Tagged: 0 Thread(s)
Quoted: 712 Post(s)
Liked 793 Times in 471 Posts
How do you plan to attach these extensions to the existing fork?
dsaul is offline  
Old 04-06-22, 07:27 AM
  #7  
scottfsmith
I like bike
Thread Starter
 
scottfsmith's Avatar
 
Join Date: Feb 2021
Location: Merry Land USA
Posts: 662

Bikes: Roubaix Comp 2020

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 267 Post(s)
Liked 283 Times in 191 Posts
Originally Posted by dsaul
How do you plan to attach these extensions to the existing fork?
The existing forks are cut from a flat sheet of ~2mm metal of some stiff sort. They extend around 4" from the main body and I was going to overlap the carbon for those 4" and bolt in several places. There are no curves like on a bike fork so it should be easy.. I hope.
scottfsmith is offline  
Old 04-06-22, 07:41 AM
  #8  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 17,998

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Stewart 650B ATB

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4171 Post(s)
Liked 3,789 Times in 2,269 Posts
I have followed this thread and I guess someone has to be the bad guy and say "this is nuts". When nearly every stressed carbon bike frame/fork uses a bonding joining method and ZERO (well there were the Alan frames from the 1980s that had the "lugs" and tube ends threaded AND bonded...don't see any company doing that any longer...) use a bolted only joining one might question why that is.

Bolt holes through a weaved material is not my first choice. Or second. Especially with a fork that will flex like a beam (that the blades are), even if you don't feel the flex. Foek failure is one of the ways to crash that can be pretty bad on your face. Perhaps a piece of that carbon sheet cut and bonded to your helmet like a football helmet face guard should be considered too Andy
__________________
AndrewRStewart
Andrew R Stewart is offline  
Old 04-06-22, 07:46 AM
  #9  
dsaul
Senior Member
 
Join Date: Jan 2013
Location: South Jersey
Posts: 2,258
Mentioned: 18 Post(s)
Tagged: 0 Thread(s)
Quoted: 712 Post(s)
Liked 793 Times in 471 Posts
Originally Posted by scottfsmith
The existing forks are cut from a flat sheet of ~2mm metal of some stiff sort. They extend around 4" from the main body and I was going to overlap the carbon for those 4" and bolt in several places. There are no curves like on a bike fork so it should be easy.. I hope.
I've found that bolting that sort of connection is prone to movement, unless the bolt hole tolerance is very tight. I would think about bonding with some sort of epoxy, in conjunction with the bolts. Perhaps a picture of the existing fork would help us to make suggestions for a better method of extending the fork.
dsaul is offline  
Old 04-06-22, 08:08 AM
  #10  
guy153
Senior Member
 
Join Date: Dec 2019
Posts: 950
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 321 Post(s)
Liked 261 Times in 212 Posts
Yes agree bolts are not good with carbon fibre. Most CF frames and forks I've seen also have glued in bits of aluminium for dropouts etc.

But it's easy to glue either with epoxy or MMA glue so long as you cover a decent area. A couple of small bolts as well perhaps but their purpose is more just to clamp it while the glue sets.
guy153 is offline  
Old 04-06-22, 08:09 AM
  #11  
scottfsmith
I like bike
Thread Starter
 
scottfsmith's Avatar
 
Join Date: Feb 2021
Location: Merry Land USA
Posts: 662

Bikes: Roubaix Comp 2020

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 267 Post(s)
Liked 283 Times in 191 Posts
Yes I was thinking of epoxying them if I thought the change was a keeper.

Here is a picture:




The cardboard cut-out is 12" and I plan to start with 12" wheels and see how that goes. I was going to bolt at the two existing spots plus one more in the middle .. or so was the vague plan.

Note these things are in fact "Nordic Cross Skates", I lied a bit about the scooter as nobody here has probably heard of Nordic Cross Skates. Here is a picture of the full skate with potential 16" wheels (which sound like will be too long in back and bumping into each other - you use these like skate skiing on cross country skis):


scottfsmith is offline  
Old 04-06-22, 09:05 AM
  #12  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 17,998

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Stewart 650B ATB

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4171 Post(s)
Liked 3,789 Times in 2,269 Posts
Understandings usually are better with good descriptions and information. Photos also say a lot.

Given the new understanding I have less fear of an injury causing failure in general but still doubt the use of only bolts/rivets if a fibrous material is used. Carbon works best in tension, compression is generally avoided w/out some sort of reinforcement or sandwiching.

Were these skates mine I would use an Al plate, cut to fit and then bolted in place. A hacksaw will cut the plate well enough and are fairly inexpensive. As to the weight differences between Al and carbon- I see this as a non issue, after all these skates are for training purposes (I assume there are no race events that use them). I seriously doubt the weight differences would be more than a few oz.(far less then the added weight of the bigger wheels/tires). Andy

I'll add that the re engineering of the scrub brake will also take some thought and added material (although I ran my rollerblades, both 4 and 5 wheel ones, w/out any brakes so "do as I say, not as I do" ) Andy
__________________
AndrewRStewart
Andrew R Stewart is offline  
Old 04-06-22, 09:14 AM
  #13  
dsaul
Senior Member
 
Join Date: Jan 2013
Location: South Jersey
Posts: 2,258
Mentioned: 18 Post(s)
Tagged: 0 Thread(s)
Quoted: 712 Post(s)
Liked 793 Times in 471 Posts
Where are you located? Its hard to tell from the photo's, but are those side plates just bolted onto the deck or are they one piece and bent up on each side? I could cut new side plates on my CNC plasma table.
dsaul is offline  
Old 04-06-22, 09:27 AM
  #14  
scottfsmith
I like bike
Thread Starter
 
scottfsmith's Avatar
 
Join Date: Feb 2021
Location: Merry Land USA
Posts: 662

Bikes: Roubaix Comp 2020

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 267 Post(s)
Liked 283 Times in 191 Posts
Originally Posted by dsaul
Where are you located? Its hard to tell from the photo's, but are those side plates just bolted onto the deck or are they one piece and bent up on each side? I could cut new side plates on my CNC plasma table.
I'm in Baltimore. What you are describing is the "right way" to do it, if I had a full shop that would be the way to go. I have not taken the side plates off but am 98% sure they just screw off.

Re: the brakes, I will need to rig a new brake mechanism. I was going to wait to get the tire in place to see the options but the initial plan I had was to remove the existing brake, bend a 1/4" or so sheet of aluminum to a tire-like contour and then bolt to the back. The braking action will be more flat against the tire as opposed to down on it as with these smaller tires. I need the brakes, I'm going 25mph downhill on these and would be toast long ago without the brakes.
scottfsmith is offline  
Old 04-06-22, 09:45 AM
  #15  
dsaul
Senior Member
 
Join Date: Jan 2013
Location: South Jersey
Posts: 2,258
Mentioned: 18 Post(s)
Tagged: 0 Thread(s)
Quoted: 712 Post(s)
Liked 793 Times in 471 Posts
My daughter lived in Baltimore for a while and still has friends there, that she visits on a regular basis.

Do you have any CAD drawing experience? If you could give me a CAD drawing(DXF) of the side plate with the extended fork ends, I would cut them for you for the cost of the metal.
dsaul is offline  
Old 04-06-22, 10:03 AM
  #16  
scottfsmith
I like bike
Thread Starter
 
scottfsmith's Avatar
 
Join Date: Feb 2021
Location: Merry Land USA
Posts: 662

Bikes: Roubaix Comp 2020

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 267 Post(s)
Liked 283 Times in 191 Posts
Originally Posted by dsaul
Do you have any CAD drawing experience? If you could give me a CAD drawing(DXF) of the side plate with the extended fork ends, I would cut them for you for the cost of the metal.
Wow thanks I might just take you up on that. I have a bit of modeling experience, not much but enough to do such a simple thing.

Note I did think a bit about that approach but was not sure the metal would be strong enough without making it too thick (and heavy - I don't want to add much weight as they are already pretty heavy). The metal of the existing side panels seems something hard and light but not sure what it is.
scottfsmith is offline  
Old 04-06-22, 11:07 AM
  #17  
dsaul
Senior Member
 
Join Date: Jan 2013
Location: South Jersey
Posts: 2,258
Mentioned: 18 Post(s)
Tagged: 0 Thread(s)
Quoted: 712 Post(s)
Liked 793 Times in 471 Posts
Originally Posted by scottfsmith
Wow thanks I might just take you up on that. I have a bit of modeling experience, not much but enough to do such a simple thing.

Note I did think a bit about that approach but was not sure the metal would be strong enough without making it too thick (and heavy - I don't want to add much weight as they are already pretty heavy). The metal of the existing side panels seems something hard and light but not sure what it is.
It is probably aluminum. I can get 3/16" 5052 aluminum in a 2' x 4' size that should be enough to cut the parts you need.
dsaul is offline  
Old 04-06-22, 11:48 AM
  #18  
guy153
Senior Member
 
Join Date: Dec 2019
Posts: 950
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 321 Post(s)
Liked 261 Times in 212 Posts
I think you need to use tubing (or something similar). With the forks longer than 6" as they will be they will bend quite easily if you get your foot sideways or something, especially if made of aluminium, although 3/16" thick might be enough I guess (and if CF they might break). I guess if you aren't welding could just bolt some box section to the outside of the proposed aluminium plates.

Another option that might work and also look cool and industrial is to use checker plate (or diamond plate it's sometimes called). I think it's a bit stiffer than flat plate but not much.​​​​​
guy153 is offline  
Old 04-06-22, 01:09 PM
  #19  
Darth Lefty 
Disco Infiltrator
 
Darth Lefty's Avatar
 
Join Date: May 2013
Location: Folsom CA
Posts: 13,775

Bikes: Stormchaser, Paramount, Tilt, Samba tandem

Mentioned: 72 Post(s)
Tagged: 0 Thread(s)
Quoted: 3126 Post(s)
Liked 2,102 Times in 1,366 Posts
Pursuant to what Andrew said. In my work we do sometimes have a metal/carbon interface for bolts. We usually either...

Bond a metal piece to the carbon and put the bolt holes in that. There may be a taper between the thickness of the materials that is conceptually similar to a bike frame lug point.

Or, we make a thicker carbon section and put a lot of very small bolts through it, in one or two rows arranged so that the second row is cutting different tows than the first
__________________
Genesis 49:16-17

Last edited by Darth Lefty; 04-06-22 at 01:24 PM.
Darth Lefty is offline  
Old 04-06-22, 01:42 PM
  #20  
Darth Lefty 
Disco Infiltrator
 
Darth Lefty's Avatar
 
Join Date: May 2013
Location: Folsom CA
Posts: 13,775

Bikes: Stormchaser, Paramount, Tilt, Samba tandem

Mentioned: 72 Post(s)
Tagged: 0 Thread(s)
Quoted: 3126 Post(s)
Liked 2,102 Times in 1,366 Posts
Curious, how do those steer? There's nothing like skateboard trucks or ski & snowboard side cuts or indeed a bike fork to make caster. I had an idea which may be wrong that rollerblades did it with flex in the truck

Edit- clearly wheels want to turn when leaned over, that's obvious. I'm just not seeing how they don't cancel out torque with multiple wheels. They do turn, so this is a conceptual difficulty on my part to work through and not a problem with skates! Different from skateboard / 4 wheel skates because those don't lean the wheels over and must definitely be steered
__________________
Genesis 49:16-17

Last edited by Darth Lefty; 04-06-22 at 01:55 PM.
Darth Lefty is offline  
Old 04-06-22, 02:37 PM
  #21  
scottfsmith
I like bike
Thread Starter
 
scottfsmith's Avatar
 
Join Date: Feb 2021
Location: Merry Land USA
Posts: 662

Bikes: Roubaix Comp 2020

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 267 Post(s)
Liked 283 Times in 191 Posts
Originally Posted by Darth Lefty
Curious, how do those steer?
They are not like a skateboard. They can do very broad turns (as in, following a curvy road) just by side pressure, but if you want the turn radius less than about 30' you will need to pick up the front wheels. Cross country skiers do this, it works better than it might sound. It would be nice if there was a way they could turn more like bike wheels do; one idea I had was a spring on the back which would allow the back wheel to "rudder" like a boat rudder if there was side force on the skate. The spring would be strong enough to hold the wheels straight normally, and side force could allow them to rudder. It would require some skill as you don't want to apply side forces if you don't want to turn... not sure at all if it would work.

Re: the fork bending issue, I might just try it out with the aluminum plates and see how it works and add extra support if needed. But it still needs some thought. I have plenty of time as the wheels are being shipped by boat from China and I have a month before they are here. I don't want to finalize any design until I actually have the wheels with tires mounted and inflated, to see the clearances. They are 12" carbon wheels so will be the same weight as my existing 8" wheels more or less.
scottfsmith is offline  
Old 04-07-22, 07:22 AM
  #22  
scottfsmith
I like bike
Thread Starter
 
scottfsmith's Avatar
 
Join Date: Feb 2021
Location: Merry Land USA
Posts: 662

Bikes: Roubaix Comp 2020

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 267 Post(s)
Liked 283 Times in 191 Posts
OK I have decided to go with the replacing the side panels approach.. If you watch GCN or are British, that is a "hack" approach and my bolting on of carbon was a "bodge". If the strength is not enough I can always add another layer to the fork part with bolts and/or epoxy.

My main question now is what kind of metal to use. In looking it up, without paying nose bleed for titanium it seems like it is aluminum. Then the question is 5052 vs 6061 vs 7075. I was thinking 7075?? It is much stiffer according to some webpage I found, the yield strength is 572MPa whereas 6061 is 276 and 5052 is 193. The cost of a sheet of 7075 is ~2x the others but is not going to break the bank.. I already spent $200 on four carbon wheels. Another thing is the current side panels appear to be a different alloy than the main aluminum body, so I think they are already using something stiffer there. Note the current side panels are 4.15mm thick which is .163"; if I got 3/16" that would be .1875" which is a bit thicker for a bit more durability as well.

I know almost nothing about all of these stiffness etc numbers (which I got from here and here) so would appreciate any feedback.
scottfsmith is offline  
Old 04-07-22, 07:47 AM
  #23  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 17,998

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Stewart 650B ATB

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4171 Post(s)
Liked 3,789 Times in 2,269 Posts
Often materials are chosen for their ability to fabricate more than their end strength being more than with another alloy. As an example if welded 6061 really should be heat treated after. 7000 series alloys have an "aging" that happens at room temps and takes longer but with no expensive ovens or controls. I have also been told that the 7000 series can become too brittle if given enough time.

As to the stiffness needed don't forget that your "forks" will be a box like structure with the wheel axle closing the open end. So the flex (to whatever degree it does) that the material has is not the only controlling factor as to how stiff the in use structure has. Andy
__________________
AndrewRStewart
Andrew R Stewart is offline  
Old 04-08-22, 06:30 AM
  #24  
scottfsmith
I like bike
Thread Starter
 
scottfsmith's Avatar
 
Join Date: Feb 2021
Location: Merry Land USA
Posts: 662

Bikes: Roubaix Comp 2020

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 267 Post(s)
Liked 283 Times in 191 Posts
Well I decided to do carbon fiber after all, but replacing the whole side panels. The site sendcutsend.com will cut out my design and ship it for $80 total.. cheaper than a sheet of aluminum! I think they pack many designs into sheets and since this design is long and thin it doesn't "cost" them a lot of material so they can to it for cheap. It would be only $20 in 5052 aluminum, including shipping.. impressively cheap!

I plan on putting some fender washers on the bolts to help distribute the load as carbon is more prone to failure at attachments. The carbon will be 4mm thick. The price is double because they don't do very thick sheets so I will need to do two 2mm sheets and epoxy them to each other. They do have 3.2mm but that just looks too thin to me.. I think 3.2mm would be OK if just replacing the existing side panels, but not for the longer forks I need.
scottfsmith is offline  
Likes For scottfsmith:
Old 04-08-22, 08:02 AM
  #25  
guy153
Senior Member
 
Join Date: Dec 2019
Posts: 950
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 321 Post(s)
Liked 261 Times in 212 Posts
Good luck! You could glue a bit of aluminium plate on top where the bolts need to go and then just drill through the whole lot.

When I made a hybrid CF frame with tubes glued into metal lugs the carbon fibre supplier recommended MMA glue rather than epoxy. It's not quite as strong but more flexible I think.
guy153 is offline  
Likes For guy153:

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.