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Wild custom fillet brazed trials frame


31511_1442861986
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On 2/2/2022 at 4:41 PM, PLIW said:

That disc mount won’t last! Fillet brazing is an art. Making it nice and smooth like that isn’t always best. Any more info on it. 

The builder is called Dave Bohm. Found it on the framebuilders facebook thread. Apparently he wanted a bike to start doing trials with. So he built one himself. Thats all I know. Regarding the smooth fillets the way brazing works is by having a root pass done in which the silicone bronze flow inside of the tube mitter and create a inner fillet. This gives it the strenght, the big outter fillet is pretty much overkill, you would need 2 to 3 times the thickness of the wall tubing in the fillet to make it really sound. From the picture it looks like way much more than that. Id say the tubes buckle way before the weld. I say this from doing test runs on fillet tube. The problem with smooth fillet is actually undercutting the tubing while one smooths it out. That can create problems.

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3 hours ago, 31511_1442861986 said:

The builder is called Dave Bohm. Found it on the framebuilders facebook thread. Apparently he wanted a bike to start doing trials with. So he built one himself. Thats all I know. Regarding the smooth fillets the way brazing works is by having a root pass done in which the silicone bronze flow inside of the tube mitter and create a inner fillet. This gives it the strenght, the big outter fillet is pretty much overkill, you would need 2 to 3 times the thickness of the wall tubing in the fillet to make it really sound. From the picture it looks like way much more than that. Id say the tubes buckle way before the weld. I say this from doing test runs on fillet tube. The problem with smooth fillet is actually undercutting the tubing while one smooths it out. That can create problems.

I’m a frame builder by trade dude. I use to work at Argos Racing Cycles in Bristol and also Bike Workshop frame building before going on my own. Fillet brazing is just an art and flare, showing off.  A brazed joint is fine. Look at Chris and Leeson for example. 
 

The mount is unsupported and has very small surface contact for support. It’ll flex and twist off very quickly. 

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13 minutes ago, PLIW said:

I’m a frame builder by trade dude. I use to work at Argos Racing Cycles in Bristol and also Bike Workshop frame building before going on my own. Fillet brazing is just an art and flare, showing off.  A brazed joint is fine. Look at Chris and Leeson for example. 
 

The mount is unsupported and has very small surface contact for support. It’ll flex and twist off very quickly. 

Thats cool, good to know you're building frames too. Thought you were giving you opinion on fillets in general and not on that specific part of the build. 

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Interesting and weird at the same time.

The yoke of the chainstays is just incredible... it seems to be CNC'd. Don't want to know the cost of it (steel is really expensive to machine)

Some of the tube shapes is unconventional, I don't think you can order this kind of shapes, so it will be interesting to know how he got those.

Also the frame has a direct mount disc brake. This is typically used on gravel and road bikes. Not sure what calipers are available in this standard and how much power or modulation you can expect from them.

And I agree about the fork brake mount.

 

Really nice project though and I love the look of it.

 

I owned an Explozif Zon'up. It was a perimetric brazed steel frame. It broke twice!

 

The material of the frame has not the major influence on the frame behavior. The specific modulus from steel, aluminium or titanium is almost the same. That is why the design of the frame is much more important.

But one has to take in consideration that huge diameter steel tubes will be very easy to dent (to maintain a good weight you have to reduce the wall thickness ), so it is difficult to build a stiff frame (due to the second moment of area, when the radius of a tube doubles, it gets 16x stiffer) with this material.

Now if you compare the chainstays and seatstays of a Crewkerz to the ones of this frame, you can imagine that either this frame shall be pretty heavy to get the same stiffness or it won't be as stiff as a Crewkerz (which has much wider chain- and seatstays)

 

Edited by La Bourde
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That yolk is two cnced halves which you then sandwich together, you can buy them in steel or titanium, they’re really cool!

 

I’m curious about the flat mount brakes, I’d thought about using this style of I got a frame made…it’s way more compact and removes the weak “tabs” a normal caliper has. Only issue is no DH powered brakes have this design however Magura do make an MT6 version and that is a pretty powerful brake so should be a decent option. 

FB68DF2D-2BEA-4788-82F7-3DA9F3DD8711.jpeg

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1 hour ago, Ali C said:

That yolk is two cnced halves which you then sandwich together, you can buy them in steel or titanium, they’re really cool!

 

I’m curious about the flat mount brakes, I’d thought about using this style of I got a frame made…it’s way more compact and removes the weak “tabs” a normal caliper has. Only issue is no DH powered brakes have this design however Magura do make an MT6 version and that is a pretty powerful brake so should be a decent option. 

FB68DF2D-2BEA-4788-82F7-3DA9F3DD8711.jpeg

Nice!

Small concern: I think it makes the frame alignment more difficult due to the length of the weld.

 

On some dirt bikes (YT, Norco, DMR, Eastern), there also a yoke with a similar form. But it is not CNC, it is one piece hydroformed piece of steel that goes to the rear end of the frame!

eastern-nighttrain-frame_Matte_Black-59_

 

eastern-nighttrain-frame_Matte_Black-57_

 

Regarding the brake mount: thx, I did not know that the MT6 was available in direct mount.

On one hand, I love when someone tries something different

On the other hand, as an engineer, having only one solution available on the market is a bit dangerous -that is why I tried to buy bikes without special solutions/standards.

 

 

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