BMX forks

[tomknox]

Hello to all, this is my first post here. Lots of cool stuff being built in this section!

I need a set of forks built for my late 80's cyclecraft crusier and i had some question's that maybe someone could give me some pointer's on?? Here's the fork's that i need built....

(1)

(2)

(3)

Here's my current cruiser forks (same make) that i was gonna use for the measurements....

(a)

(b)

(c)

(d)

Here's some of my question's/concern's....

1) What type of tubing should i use, butted or straight gauge like the steerer tube is?

2) How do i go about finding rings or whatever to make the crown/race in picture (a)?

3) What plate should i use to make these simple drop outs in picture (c), any advice??

4) I found the tap to make the thread's but what about the slot that is machined in there (d), any advice there?

5) Is it me or did they just weld some washer's to end the tubing or what?? (3&b)

6) If i use straight gauge tube what thickness would you recommend?

7) As for the "crown" section in pic (a), notice it has a very thin piece above the welded on ring section, is this all one piece that is just welded from below? My fork has to have one of these 27.0 mm crown's:

I've got more question's but this is a loaded plate here, i'm a little prepared. Thank's to anyone who has the time to read all this and help me. Thanks, again!

Tyler

 

[CompoSimmonite]

How do you need them building compared to what you already have ? Longer or wider ?
I enquired about having a set of forks custom made wider so a rear wheel with electric motor I'd already got would fit and silly quote from specialists (around £300).
Whit the simple design of the BMX items personally I'd consider cutting and sleeving the originals rather than make from scratch.

Paul h

 

[pedrobedro]

You need a die to make those threads not a tap and it looks hard work to do accurately manually Round here we have a useful bike shop and if I need any parts I take them in and just ask if they have something that will do the job. For the slot you need someone with a milling machine to run it down after threading then run the die down it to clean it up again. The dropouts in the purple forks look like 5mm plate while the clean ones look like 3mm, either should be man enough for the job. Washers in the end of the tubing would be the obvious way to provide drainage and tidy them up. For a cycle I would not use anything heavier than 16g tube and if you can get the butted tube it will probably be stronger better grade steel than ordinary mild so you could go thinner.

 

[Master-of-none]

The slot has no purpose other than to align a hanger for a centre pull brake outer cable, see picture.
If you are using alternative brakes (or no brakes) then you don't need to cut the slot.

Modern forks use a different system, 'threadless' which is stronger (cutting a thread impacts the tube thickness) but involves new bearings, spacers and a clamp on stem. These parts are and ready made forks a easily available as the older style have gone out of fashion.

 

[tomknox]

CompoSimmonite: My raw forks are sized fine, the square forks aren't mine and they are for a standard 20'' bmx not 24'' cruiser. As for cutting and sleeving, i'm not even considering doing that, these are vintage 80's forks. I would get hung for doing that...


pedrobedro: Dye is the proper word, had a brain fart. My local bike shop is a hole in the wall, and not capable to do this kind of work. The dropouts on the purple fork's are two regular size dropouts welded together. I really don't care about the thick dropouts, the standard will be fine with me.


Master-of-none: You are correct the slot doesn't matter, i looked at some other bmx forks from that era that do not have the channel in them. I certainly understand that it's old sizing, it's from the 80's. That's why i'm having such a difficult time with the crown area. The threadless stuff didn't show up in bmx until the mid 90's, ten years difference in sizing here.


Thanks for the comment's, please keep them coming because this is helping!!

Thanks again,

Tyler

 

[pedrobedro]

The slot is used for a locking washer with a locating tab to stop the bearing from tightening or loosening when turning the steering, it is used on scooters and motorcycles as well.

 

[tomknox]

Pedro: You are correct, here is a pic of the locking washer that fits that groove. How important do you think it really is? The old bikes that i've been taking apart havn't had them in the headset but i certainly do remember them from back in the hay day. Could i get away without one??

 

[hotrodder]

Threadless steerers were as much about saving weight (the quill, long bolt and expander wedge) as anything else- the quill reinforced the threaded section of steerer

Trying to die threads from scratch onto a steerer tube ain't likely to end well. Threaded steerer tubes can still be bought from places like Ceeway (framebuilding suppliers), dunno if they'll have anything BMX sized. Can also cut up another pair of forks (something not rare/valuable) for the steerer and crown

The collar for the crown race... also available to buy from frame building suppliers and yes the thin section is part of the 'steerer collar'. It's available as a longer piece as used in pic a, as a simple collar and as part of the fork crown (lugged and brazed forks). They're supplied fractionally oversize and machined to final dimensions (lots of different 'standards')* after the forks have been fabricated. Also simple to make for anyone with access to a lathe

As said 16swg is more than adequate, personally i'd steer clear of seamed tubing though... either DOM/CEW (seamed tube that's then mechanically Drawn Over a Mandrel) or CDS. Butted tube will make the forks feel a little more alive/comfortable, as said likely to be a better/posher grade. Pretty much your only source for butted tubing will be from a frame building supplier. Dropouts can made be from any convenient chunk of plate. Personally i'd use 4mm or thicker

* From memory BMXs used the same size crown race as the 'standard' standard 1" headset (26.4mm). The French and Italians did something ever so slightly different alongside the 27.0mm JIS standard

 

[Angusdog]

Is it worth pointing out that this requires a high-performing weld? I'm just conscious that there have been some pretty shocking examples of beginners' welding on here and the welds we're talking about here are integral to the safety of the bike.

My intention is not to undermine you or put you off in any way, but it's one thing to offer the above advice when someone's going to go off and try to stick weld it or 'have a crack' with an underpowered MIG. Personally I wouldn't attempt that with my skill set without doing some destruction testing and probably posting some examples here for feedback.

Meant in the nicest way, in lieu of knowing your ability with a welder

 

[tomknox]

Hotrod Wow, a bunch of info packed in there!! Thank's for you're input, thats the stuff i'm looking to hear right there! Major thanks!

Angus I certainly hear you, and take no disrespect what so ever. These puppies are gonna need some good weld's and i'm not qualified to do that. That's why i'm trying to get some good info before i have some ****** in a shop try to take advantage of me, and thus risk my well-being or anyone else's for that matter. I'm sure you guy's have plenty of newbs around here that post ridiculous stuff. I'm 200 pound's so i'm definately wanting to take that into consideration. Thank you Angus for bringing these points up, safety is first and foremost. I'd rather they weigh a ton then break, i'm 30 years young but i don't plan on jumping thing's. This will be a bike that i'd like to just cruise with my son.

 

[bod]

The locking washers make adjusting them easier when you're fitting it and sort of helps keep the headset from undoing. If you won't use the bike that often then I wouldn't bother with one, they don't work brilliantly and milling it will be a pain to do.
My mate's got a Skyway TA and the welds on it are awful, seems funny they're worth so much now.
Looks like a fun project, enjoy!

 

[tomknox]

Bod: I won't be riding it everyday, just when the boy want's to ride. I plan on adding a headset lock so i dont see how it could move after that??

As for the weld's, most of the vintage bmx bike's do have crappy weld's. This cyclecraft welds are one of the better that own out of Hutch, CW, and Elf. Those Skyway's fetch big buck's, if you can find a crusier then you're sitting on a gold mine!

 

[citizen kane]

As others have said, all the parts you require can be obtained from Ceeway. One thing to note, once the crown is welded on you need to get the crown race seat trued and OD correct. Normally the steerer tube is mounted in a lathe to do this. I would go with cromo at least 60 thou wall thickness and Tig

 

[ChrisJohnsSculpture]

Yeah chrome moly tubing would be the best thing, much lighter than mild for equivalent stiffness. It is tricky to weld though as it tends to crack, really needs tig or gas, as suggested.

 

[hotrodder]

Chromoly is not stiffer than mild steel, it's yield strength is significantly higher than mild (so it feels stiffer when permantly bending it) but within the elastic range there's next to no difference between different flavours of steel [/pedantic]

 

[Burf86]

Hi Tom, those are some cool looking forks you got there! Why is it you need some new ones made?
I saw that you said you only want them for cruising, and that you won't be doing any jumps or anything? If this is the case I would just use some mild steel tubing! I'll put my cock on the block and say, those ones you got there are made from mild steel.

I made a frame a few months ago now out of mild. It's a 'geometry tester' for this Enduro frame I'm making (I should be setting the jig for the real thing now!). I entered it into a race and did jumps on it, the lot, and it's still going. In fact we are racing it and this new one next weekend up in Scotland! All I'm sayin is mild steel will be fine with some good welds!

If you want I can help you out with the fabrication of the forks, hit me up at btrfabrications(at)gmail.com. I can help you with tube selection and the like if you want to do it properly too.
(Mods, is this allowed?)

Cheers,
Burf