twin plate crown material: 1018 or 4130?

[Alex Wetmore]

When people are building twin plate fork crowns do they typically use 1018 or 4130?  From the archives and photos it looks like 1/4" material is typical.

It's a lot easier to find 1018 cold roll in useful widths (like 1.375" or 1.5") than 4130, but the higher strength of 4130 seems like it could be beneficial.

I'm building a fork for a 26" wheeled adventure touring bike where the rear triangle fits 2.1" knobbies pretty nicely, but where the bike will normally be ridden with 1.75" tires.  I don't have the ideal 65-70mm wide fork crown for that on hand (the PBP crown that I do have is a bit narrow) but I do have a little CNC machine and thought I might play with making a twin plate crown for this project.  I need to buy material no matter what, all of my steel flat stock is 3/16" thick (what I use for making dropouts that work with the Keith Anderson TITO inserts).  Today I'm just making prototypes out of aluminum to see if I'm happy with the shape.

alex

[David Porter]

Alex,

 Preface/disclaimer: I’m not starting an argument.

 If you’re just looking for bragging rights then use 4130, otherwise common sewer pipe/cold roll stuff is more than adequate. It was used for years and probably never failed.. The structure is such that after it’s brazed up it is very strong.

IMHO of course.

dave

 

fro...@porterscustom.com

Porter Customs   2909 Arno NE
Albuquerque, NM USA 87107
505-352-1378
1954 BN2  1959 AN5
Porter Custom Bicycles

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GO HERE: http://porterbikes.com/  nice pictures-fun facts-my world

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[Thomas]

When I was looking at this style a few years ago, I seem to remember seeing (on web) a few made with 3/16ths 1018...    and you could always go for a triple    =)

   1/4 or 3/16 or....     up to a point, I imagine it would make a difference how much width you used... 

FWIW, For your stated use, I agree, I'd go with, 1018 @ 1/4 ...
   Thomas

 If you’re just looking for bragging rights then use 4130, otherwise common sewer pipe/cold roll stuff is more than adequate. It was used for years and probably never failed.. The structure is such that after it’s brazed up it is very strong.

IMHO of course.

dave

 

Subject: [Frame] twin plate crown material: 1018 or 4130?

When people are building twin plate fork crowns do they typically use 1018 or 4130?  From the archives and photos it looks like 1/4" material is typical.

 

I'm building a fork for a 26" wheeled adventure touring bike where the rear triangle fits 2.1" knobbies pretty nicely, but where the bike will normally be ridden with 1.75" tires...  I do have a little CNC machine and thought I might play with making a twin plate crown for this project. 

 

alex

[Clockwork]

Alex-

I have just the thing for you: http://www.flickr.com/photos/28879558@N04/6660957593/in/photostream

1/4" is way overkill. I talked with folks about this a while ago
before making these and 3/16" was the consensus.

These are laser-cut 4130 and are pretty easy to use. Just trace
around the edges with a sanding drum to get rid of the black shit and
any imperfections left by the laser. The holes are slightly under-
sized to compensate. 2.4" between blades.

-Joel

[michael giannico]

I had designed and built some twin plate forks using 3/16' 4130 chromoly. after recieving the test pieces from the cutter i determined that because of the amount of material i removed to lighten them up they just seemed inadequate for the mountain bike. i then chose to go with 1/4" and changed the reliefs slightly. once the forks were assembles and  thoroughly beta tested i can assure you that the 1/4" for this particular application was not at all overkill when taking the design into account.

with that being said if you are designing this fork to be similar to the ones in the previous post and for similar usage (road, touring, multi-use) I think you should be absolutely fine with 3/16" 4130 plates. I wouldn't personally use 1018 when 4130 is an option, it is just so much stronger. what i would recommend though is adding a gussett that tapers toward the bottom underneath the bottom crown to aleviate a stress riser where the leg and lower crown intersect. twin plate crowns have been know to crack the fork leg at this junction due to the high strain at this juncture. I know there arent any on the orange forks in the pic but the unpainted ones absolutely have them due to the style of riding this bike is doing (aggro east coast trail riding). the orange one will rarely have its front end on the ground (think trials).

you do however have to consider that as you mentioned you will be using a cnc mill to cut these and that factor alone is worth some consideration seeing as how 4130 is hell on tooling.  so if you want to do a few test crowns and are more interested in using and experimenting with your mill then by all means use 1018. I hope i didnt just talk myself into a circle.

These previous statements are only based on my limited experience and opinions. There are many more knowledgeable people on this forum and all of there insight is equally important.


fork crown pic 1

full mtb mockup with fork



ps I have a couple sets of these mountain crowns left and also the dropouts for 1-1/8 .058 tubing if your interested. I'm prepared to sell them for a loss just to have someone get some use out of them. the two plates and the dropouts will run $40.00 plus shipping. the total offset is 1.5" and believe me they will take a beating. keep in mind you will still have to make a crown race. and the gussets for under the crown if you choose to use that method. and also purchase some 1-1/8 .058 4130 for the legs and a steerer tube (also 1-1/8.) they are also quite a challenge to braze. i attached a pic of the exploded assembly.

I did not write this reply to sell fork crowns, I could care less if i sell them, they are just sitting here and i would rather they were used for something.



--
Mike.
Nicola Cycles
200 Grove st.
New Milford CT. 06776
nicolacycles.blogspot.com
NicolaHandmademusic.blogspot.com
heatherandmikesraku.blogspot.com

[Darren Larkin]

I've gone with 1/8" 4130 for a twin plate project.  Its pretty wide, long axle-crown distance, and pretty real rigid legs.  Its made it through some long off road sections loaded with the food and beer and whatnot for 2 days.  Thinking back I went with 1/8" after using 3/16" 1018 on a track fork and it being a total hassle to braze with the mismatched thicknesses.  Felt ok after looking at a sloping crown i have the gets ridden pretty hard and how small that little section is between the steerer and blade.

Darren

--

[Mark Bulgier]

Plenty of old French tandems have plates about 3 mm (1/8”) and have survived tandem touring use for decades. 

 

It helps that their plates are curved, not flat – the curved shape adds strength as well as looking nicer.  A flat plate is much easier to twist.

 

In the early 80s the shop I worked at brought in a bunch of Follis tandems to paint and decal as house-brand, something we could sell cheaper and quicker than our own custom frames which had a 3 year waiting list at times.  As cheap as they were, I really doubt they used alloy steel for the crowns.

 

Mark Bulgier

Seattle

[Alex Wetmore]

There are some photos and description of what I played with today here:

http://www.flickr.com/photos/88336152@N00/

I made prototypes out of 1/4" and 3/16" aluminum just to see what they look like and get a feel for them in my hands.  3/16" does seem okay.

Curving the plates is a good idea and something that I'd been considering.  I don't like the look of a completely flat plate, but the curved plates that Pereira uses look good to me.  I'll have to make a form of some sort for doing this.

http://www.flickr.com/photos/pereiracycles/3100771715/

Thanks to the offers from Nicola and Joel for selling me some of your twin plate crowns.  I'm going to stick with making my own, part of the attraction of trying this experiment is knowing that I can make semi-custom crowns for myself whenever I want them.

alex

---

From: Mark Bulgier [Ma...@bulgier.net]
Sent: Sunday, January 08, 2012 1:50 PM

To: Alex Wetmore
Cc: Framebuilders

Subject: RE: [Frame] twin plate crown material: 1018 or 4130?

[Mark Bulgier]

The old French two-plate crowns were usually like the Pereira in that the lower plate did not wrap around the outside of the blade.  Barra plate crowns were that way too, and in aluminum!

 

The top plate usually did not overhang beyond the outside of the blade as much as the Pereira picture – that could be trimmed closer with no loss of strength.

 

Check this out this early 70s René Herse for inspiration:

http://www.classicrendezvous.com/France/bicycles/Herse/c_andrews_tandem/photos/photo19.html

http://www.classicrendezvous.com/France/bicycles/Herse/c_andrews_tandem/photos/photo20.html

 

This bike also has a tapered steerer, 28 mm bottom, 25 mm top.  OS headset for the bottom race, normal race and normal sized stem on top – brilliant.

 

Made about 40 years ago – not many builders today can equal it, in many ways.

 

Mark Bulgier

Seattle

[michael giannico]

quote"

Thanks to the offers from Nicola and Joel for selling me some of your twin plate crowns.  I'm going to stick with making my own, part of the attraction of trying this experiment is knowing that I can make semi-custom crowns for myself whenever I want them."

Of course isn't that the fun part.

 regarding all of the posts stating that 1/8" -3/16" will suffice. history has proven this to be true. I tend to overbuild....probably has something to do with my history of beating the s**t out of everything I ride. nose wheelying  and bunny hopping the horribly maintained potholed streets and hopping curbs tends to take its toll on front ends. grrrrr. I feel manly just writing that. LOL

[Fred Parr]

Guys I could comment for the Guinness book but Nah !

Every kind of cast and plate types of those came in with random orders from Kitching way back in the 60's, I thought about making a Collection out them many times.

Since those were all soft as butter ? Dah?

I sure like "Mikies" "Macho Sturdy" one! But 1018 is still a improved steel compared to yesteryear.

 

When I made one once for a custom tandem build, I sleeved through on the steerer all  the way to allow myself to sleep on it being fully secure?

 

I always liked the look of those and still do, you don't see all that many anymore, like Mark mentioned some of the better bikes had curved plates back a zillion years ago.

 

Pretty cool project ATFO

 

 

[Michael Catano]

Hi all,

Just wanted to bring this back for a second...

I received a few of Joel's crowns a few days ago and used one today on
a rando fork:
http://farm8.staticflickr.com/7141/6722790835_56be71668d_b.jpg

Given the price he's asking, these are a great option. They need a
good deal of prep work, but nothing outrageous. Thumbs up to Joel for
getting these made - more choices=more awesome.

best
Michael
chi il

[Fred Parr]

Well here is a new topic cycle design is doa what do you think about that?

[omar-...@cox.net]

That looks great Michael. I cannot tell from the pic, but what are you
doing for the fork crown race? Inquiring minds want to know. :)
Omar Khiel
Oasis Custom Cycles LLC.

--------------------------------------------------
From: "Michael Catano" <shuffl...@gmail.com>
Sent: Wednesday, January 18, 2012 8:42 PM
To: "Clockwork" <jo...@clockworkbikes.com>
Cc: "Framebuilders" <frameb...@googlegroups.com>; <al...@phred.org>
Subject: Re: [Frame] Re: twin plate crown material: 1018 or 4130?

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[Michael Catano]

Hi Omar,

I need to file down the little piece of 4130 sleeve that's sticking up
above the top plate and then I plan on brazing a race ring on w/
silver.

Thanks again,
Michael