Help with frame alignment

[Tom Mancuso]

Framebuilders,
 
I need some advice on the quality of my frame alignment.  I presently have a head tube, down tube, seat tube assembly.
 
I have taken some measurements by using my table saw as a reference table.  If anyone is interested looking at my measurements and giving some advice, it would be greatly appreciated.  I have a pdf file with a picture and some data in it I can email out off list.
 
Is this frame close enough to put on the top tube?  Should I attemp to make adjustsments now?  Send me an email and I will send the file off list.
 
Thanks,
 
Tom

[Wissahickon Cyclery]

Tom,

This topic is usually a hard topic since many people either won't talk about it or speak unrealistically.  The truth is there is no way someone could effectively communicate with you without actually being there and watching the measurements being taken.  So many variables that could effect stuff.  If it is a table saw with a cast iron top then you do have a rather descent surface but that does not tell you if it is a good datum.  

I would trust your gut and eyes at this point.  Look at the frame from far away and observe the twist (or lack there of) and if it looks good put the top tube in.  The quality of the miters on the top tube will either change everything or keep it in phase.  

My best advice on this topic is if you don't know the answers to your questions then you are over thinking it.  All the data in the world is useless if you are not sure why or how to get the data and what to do with it.  

-Drew 

--
You received this message because you are subscribed to the Google
Groups "Framebuilders" group.

Searchable archives for this group can be found at http://groups.google.com/group/framebuilders (recent content) and http://search.bikelist.org (older content).

To post to this group, send email to frameb...@googlegroups.com
To unsubscribe from this group, send email to
framebuilder...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/framebuilders?hl=en

--
Drew Guldalian
Wissahickon Cyclery
7837 Germantown Ave Phila,PA 19118
www.wiss-cycles.com
www.engincycles.com

[jon norstog]

Tom, list:

This is a situation where a cheap torpedo level and some scrap steel
shims can do you some good. Shim up the frame so the seat tube and
down tube are both level. (two straight lines determine a plane).
Then check that the head tube is also level. If not, tweak it.
Unless it is grossly, visibly skewed.

This method will get your front triangle in-plane. It will not tell
you whether the BB shell is properly aligned with its axis
perpendicular to that plane. It will not tell you if the angles and
dimensions are right, either.

Good luck.

jn


"Thursday"

[Truls Erik Johnsen]

There's a pretty good thread on alignment over at Velocipede Salon. Well worth having a look at:  http://www.velocipedesalon.com/forum/f26/tell-all-no-holds-barred-alignment-thread-atmo-21294.html 

Truls

[Alex Wetmore]

It would be helpful to have more description of what you are seeing. Maybe you could send the PDF out to the list, or post it somewhere online and link to it?

I built my first front triangle in the same order that you are (and that I think Paterak recommends) and got geometrical issues that I couldn't fix nicely. On my frame the downtube and seat tube pulled together at the bottom bracket, making my STA steeper than I wanted. I've since switched to tacking the whole front triangle before brazing any of the joints (and changed my brazing order around the bottom bracket to avoid pulling those tubes together, plus my mitering is better).

alex

________________________________________
From: frameb...@googlegroups.com [frameb...@googlegroups.com] on behalf of Tom Mancuso [tom.m...@ymail.com]
Sent: Wednesday, May 30, 2012 7:25 PM
To: frameb...@googlegroups.com
Subject: [Frame] Help with frame alignment

Framebuilders,

Thanks,

Tom

--

[Alex Wetmore]

Tom sent me his PDF. His BB tower is made from a 1-2-3 block with 3/8" rod sticking up through the center of the BB, and a thick round steel bushing (about 1.75" in diameter) on the top of the BB, with a nut holding it all in place.

With the BB left side down his down tube drops 67thou, seat tube 50thou, and then the top of the head tube dropping 48 though from bottom to top.

With the BB right side down it is seat tube dropping 12 thou, head tube climbing 34 thou, head tube climing 27 thou.

1) Did you face the BB?
2) Do you believe in the flatness of your table saw?
3) Does your makeshift BB tower have anything to try and keep the BB shell perpendicular to the surface plate? Just clamping it between two flat surfaces isn't necessarily enough. Also, is your top fixing bushing faced flat, or could it be out of true? I'm also not sure that a 3/8" piece of all thread extended that long is necessary enough.

The numbers should be much closer to equal for both sides if you faced both sides of the BB.

You need to trust the alignment fixture and datum surfaces, and I'm not sure that I trust this one yet.

alex

________________________________________
From: frameb...@googlegroups.com [frameb...@googlegroups.com] on behalf of Alex Wetmore [al...@phred.org]
Sent: Thursday, May 31, 2012 9:09 AM
To: Tom Mancuso; frameb...@googlegroups.com
Subject: RE: [Frame] Help with frame alignment