Tips for head/seat tube centering cones & bottom bracket fixtures

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Elijah B

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Feb 4, 2014, 12:23:45 PM2/4/14
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Hello Framebuilders!

I have finally taken the first steps to start building frames.  I have a nice little Oxy propane setup, slapped 
together a simple jig out of aluminum extrusion and have been practicing mitering/coping and brazing 
(filet/sweating) different tube diameters and angles.  I still have some work to do on getting the right flame 
size and heat control, but not doing terrible everything considered.

In any case, the last few pieces I am missing for my jig are the dummy axle, bb fixtures, and centering cones.
I need some advice as to how to slap together a cheap solution or what to tell a machinist to put together.

For example: would it be sufficient to say I need a piece of aluminum machined to a cone 50mm on the large side,
29mm on the small with a 50mm height centered on a M8 threaded 25mm long hole on the large side?  
Or is there more to it?

Any advice would be appreciated!

-Elijah

Alex Wetmore

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Feb 4, 2014, 12:36:57 PM2/4/14
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Just buy the Anvil dummy axles.  They are great and easy to incorporate into custom fixtures.


Centering cones for the head tube and top of the seat tube can be almost anything.  A 45 degree angle going from 2" down to 7/8" works well and covers all tubing sizes.  I would go smaller than 29mm if you ever want to build a frame with a 1" steerer or 27.2 seatpost.  Have a center hole drilled for a mounting bolt and bob is your uncle.


A nicely stepped flange for the bottom bracket works better than a cone in my experience.  It makes it easier to precisely locate the bottom bracket, which is important for alignment.


These photos show how my dummy bottom bracket was made.  Note that I no longer use the cones and use a stepped flange, as shown in later photos.  The critical part is that adjustable width shaft clamp, it lets me fine tune the BB position and came from McMaster Carr:

http://alexandchristine.smugmug.com/Bicycles/Fixtures/Frame-Fixture/i-z8KTSMt

http://alexandchristine.smugmug.com/Bicycles/Fixtures/Frame-Fixture/i-62V2Njj

http://alexandchristine.smugmug.com/Bicycles/Fixtures/Frame-Fixture/i-74tvmcx

http://alexandchristine.smugmug.com/Bicycles/Fixtures/Arctos-Clone-Frame-Fixture/i-D2nBTh9

http://alexandchristine.smugmug.com/Bicycles/Fixtures/Arctos-Clone-Frame-Fixture/i-SW7NdJF


This is Alistair's take on the flanged bits:

http://www.flickr.com/photos/duncancycles/6650023473/in/set-72157629275211943


and his version of the same BB fixture:

http://www.flickr.com/photos/duncancycles/6932445274/in/set-72157629275211943


He is currently changing the design to something that allows for easy backpurging since he has interest in TIG welding.  My approach is very simple and works well for brazing.  His fixture standoff distance is also much greater than mine, but our jigs are otherwise close cousins (we made them at the same time and shared drawings with each other).


alex



From: frameb...@googlegroups.com <frameb...@googlegroups.com> on behalf of Elijah B <ebn...@gmail.com>
Sent: Tuesday, February 4, 2014 9:23 AM
To: frameb...@googlegroups.com
Subject: [Frame] Tips for head/seat tube centering cones & bottom bracket fixtures
 
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TomTheBuilder

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Feb 4, 2014, 12:55:51 PM2/4/14
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For a cheap set of centering cones I use the cones from a motorcycle wheel balancer. You can get a wheel balancer from Harbor Freight for around $30 with a coupon when they are on sale.

David Bohm

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Feb 4, 2014, 4:41:48 PM2/4/14
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Sent: Tuesday, February 04, 2014 10:56 AM
To: frameb...@googlegroups.com

Subject: [Frame] Re: Tips for head/seat tube centering cones & bottom bracket fixtures

For a cheap set of centering cones I use the cones from a motorcycle wheel balancer. You can get a wheel balancer from Harbor Freight for around $30 with a coupon when they are on sale.

 

http://www.harborfreight.com/motorcycle-wheel-balancing-stand-98488.html

On Tuesday, February 4, 2014 9:23:45 AM UTC-8, Elijah B wrote:

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