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Framebuilders Thinking about a custom frame? Lugged vs Fillet Brazed. Different Frame materials? Newvex or Pacenti Lugs? why get a custom Road, Mountain, or Track Frame? Got a question about framebuilding? Lets discuss framebuilding at it's finest.

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Old 08-06-13, 09:37 PM   #1
seankanary
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Alignment table procedure

Hi guys, I was wondering if you could shed some light on the steps you take while checking the frame's alignment on a table. The past few frames I have done have been loosely checked by sight and string. While everything has been ok, I'd really like to get things much closer. I don't have the money for a legitimate surface plate, but from what I've been reading, a lot of hobbyist use a piece of thick counter top granite and the tolerances are pretty decent. I often see pictures like this:



I guess I'm trying to understand what the different steps in checking alignment are and what all the different tools are used for. I would appreciate any insight as to your process.
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Old 08-07-13, 07:49 AM   #2
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I have a mill table with a BB post and I use it to check that the BB axis is perpendicular to the frame. I also have a piece of granite countertop (it's very flat from what I can tell) and I use it to check HT twist: I insert a rod w/ cones in the HT and support the frame with v-blocks.

For the fork and rear triangle I use wheels and straight edges.
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Old 08-07-13, 08:08 AM   #3
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If you support the frame with v blocks while locked in the bb post, doesn't that give a false reading? Or, does that just prevent sag from the weight of the frame?
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Old 08-07-13, 08:46 AM   #4
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I usually check the twist separately on its own, no v-blocks when using the BB post. If I check for twist on the post I'll use a jack to support the frame before inserting the HT rod.
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Old 08-07-13, 10:31 AM   #5
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I assume the jack is the little white thing at the top of the seat tube?
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Old 08-07-13, 11:40 AM   #6
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[FONT=Times]What you see in the picture is Bringheli's tools for checking and correcting frame alignment. There is a post that inserts into the seat tube that is held by a U shaped piece. Under the bottom side of the top of the seat tube is a jack that has a white nylon top that can be screwed up and down to insure the tube is level with the table top. These pieces stabilize the seat tube while the head tube is bent to be in the same plane. If the seat tube wasn't being held still, it would rise or fall in phase with the head tube when it is twisted. The axle in the rear dropouts has a center line. The height gauge is set to the center of the seat tube and then moved to the axle to see if its centerline is in the same place.

What isn't shown is what everyone needs for an alignment table and that is a surface gauge. Its pointer is adjusted so it barely scratches against the lower part of the seat tube. Then it is moved to top part of the tube to see if it agrees. If not, the tube is bent up or down until it does. Next the point of the surface gauge is adjusted to the bottom of the down tube and checked at the top. More bending occurs. When all 4 or those points are in agreement the pointer is set to the bottom of the head tube and checked against the top. When you get a clean 6 point check without bending your alignment for the front triangle is finished. It is easier to bend tubes if they are supported by jacks and seat tube inserts. [/FONT]
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Old 08-07-13, 11:43 AM   #7
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There are some valuable tips in THIS THREAD from some of the most talented framebuilders in the world.

He can correct me if I'm wrong, but I believe this is the type of surface gauge Doug is describing.

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Old 08-07-13, 03:13 PM   #8
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AKA height gauge
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Old 08-07-13, 06:46 PM   #9
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AKA height gauge
Yep.

I bought four of them from Grizzly Industrial. Part Number H2712.
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Old 08-07-13, 07:01 PM   #10
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Quote:
Originally Posted by Scooper View Post
There are some valuable tips in THIS THREAD from some of the most talented framebuilders in the world.
Great thread, and informative too atmo.
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Old 08-07-13, 07:49 PM   #11
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OP, that thread is totally inclusive, but if you have no table for reference, which is what I believe you are saying, keep in mind that a 4x8 sheet of mdf cut into thirds and glued together will be far flatter than you are able to build to until you've go a bunch of frames behind you. So if you get a post and start there it may be the least expensive way to getting better. After all, if you are asking a question such as this you are not likely to go out and buy a surface plate quite yet. As said above, get a height gauge, vernier is fine.
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Old 08-07-13, 09:03 PM   #12
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Thanks for the info guys. The bit from Doug was exactly what I was looking for. I have been reading that thread on VS (3 times now) and now I can connect the dots knowing the correct verbiage.
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Old 08-07-13, 09:28 PM   #13
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My third frame was a MTB I built in 1985, so far I had been using a metal yard stick, string and calipers to align with. A couple years later having ridden the bike thousands of happy miles, I tore it down to have it repainted by a friend who was working for a local bike factory. I take it over and he says "hey Rich lets check the alignment!" So he sets it up on their alignment table and we start measuring. Well it turns out there is about 12mm of twist in the frame measured along the 30" bar running through the head tube. I leave the frame with him to paint, I built it back up the following week and it rode like sheot. Same frame, same componets, Problem was that I now knew the frame wasn't perfect. I couldn't stand to ride it, so I cut it up with a hacksaw. I soon had a machinist grind me a plate from an old table saw top and I built a new frame working from that. I never let anyone since put my frames on an alignment table. Ignorance is truly bliss.
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Old 08-07-13, 10:38 PM   #14
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I think a surface gauge (like the Grizzly one Scooper posted a picture of) is just the right tool to use with a flat table. Bicycle tubing is inaccurate enough that putting a dial indicator on a post with .001" graduations is just a recipe for driving yourself nuts. A tube just isn't accurate enough for such fine gradations. Listening to the sound of the tick of a point scratching the top of a tube has the right amount of accuracy for not-perfectly-straight tubes.

If I was to start out again, I would buy a flat table first before I got any other complicated piece of equipment (and I've acquired a lot of equipment over the years). 2' X 3' if I was space and financially challenged and just under 3' X 4' if I could swing it. That way I would not be dependent on a fixture for alignment accuracy. However I held the tubes to match my design, I would use the table to get a straight frame.

Just as a point of reference, all my framebuilding class students can get a frame within a mm (or greater) accuracy on their very first one. If you are taught the right sequences of tacking, aligning and brazing, and you choreograph your brazing patterns correctly, they will end up to be straight. If your 3rd frame is crooked you either weren't taught right or you didn't learn right or you were sloppy.
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Old 08-08-13, 06:59 AM   #15
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I'm still riding on my first frame. Have probably 1500+ miles on it and it feels just fine. Very comfortable. I know it is not as strait as it should be...I'd be mortified to see how bad on any type of inspection surface... I'll leave it alone until I build myself another one. That surface gauge listed above will be next on the list of things to pick up. Fortunately I haven't invested all that much money into this adventure. The only real money has been put towards a decent O/A setup that is also useful in other parts of my life. My inner nerd of course wants heavy machines but realistically is not all that necessary...I wouldn't even know how to use such tools. A hacksaw and files still does the job just fine. Thanks again for the tips and suggestions.
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Old 08-08-13, 07:18 AM   #16
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Doug, The first two frames(C 1980) I built were Proteus frame kits (book included). Came with all the tubes mitered. Pretty easy to build since the hard work was done and I had access to good tools. When I built the MTB I used a tube notcher from work. The notcher's holesaw was not well suited for thin wall tubing and tended to pull to one side of the tube. I forget who made the stamped lugs but they were really sloppy and didn't offer much of a reference point. I no longer had access to a head tube facer and reamer so I used a flat file and Dremel. All that coupled with my lack of knowledge, That 12mm of twist could have been worse.

Once I had a plate to reference from,I got some practical advice on procedure and paid more attention to details on the next MTB frame . 25 years later I still ride it most everyday.

My plate is 25"x 34", 45"+ long would be better so I could more easily/accurately check the alignment of an assembled frame and fork. For a surface gauge I use a dial indicator on a magnetic base. Since I only make a frame every 3-6 years my surface plate spends the majority of it's time as a jig for gluing up cabinet doors.
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