Frame alignment

In an ideal world, nobody would need an alignment table. Many builders probably don’t have one and just are *that* good, or assume they’re that good and that nobody will even notice the frame is out of alignment.  Perhaps.  But unless you have absolutely spot-on miters and are a perfect welder that can use the frame fixture as your only alignment device…i think it’s pretty important to know how on or off you are, especially in the beginning stages.  So, I bought myself a Bringheli alignment table – the small version – a few months ago and have been using it a LOT to figure out along the way in which my welds pull the frame to what directions and to see how much my non-perfect miters actually throw the frame off.

So far, what I’ve learned is that it’s MUCH more difficult to cold-set a frame back into alignment. I mean…it takes some serious pulling to get the seat tube back straight if it’s off by even a few millimeters. After finishing my last frame (Rivbomb) I didn’t want to do a second pass on the BB so I tried to pull it back to straight. The Bringheli table (it’s really just a 6″ wide by 48″ long steel C-channel) comes with a rather large steel bar that fits nicely into a 27.2mm seat tube with fittings that slide onto the bar for larger diameter tubes. I gave the seat tube a few pretty light tugs thinking i only needed to bend (i mean, cold-set) it back to straight..yeah, right.  I was soon standing up on the table with one foot on either side of the steel bar doing a dead-lift, trying to get as much torque on the bar as I could.  It’s scary how much I had to pull to get it into alignment.  I eventually did get it straight(er) but in the process realized why builders try their hardest to avoid cold-setting a frame back into alignment.  It just can’t be good for the tubes.

So on the frame I’m currently building I decided to try and NOT cold-set it back into alignment.  It’ll get enough torque on it as it is, being a singlespeed and all. So after I welded up the front triangle and the chainstays to the BB, I faced the bottom bracket (some warpage occurs while welding even with a heat sink).  Then, I put up the frame on the alignment table to see how it looked.  This was the first time I put it on the alignment table after welding as much as I could in the frame fixture, and the rest out of the fixture.  I just did the BB joints out of the fixture since my heatsink won’t fit over the BB-post that comes with the frame fixture. These BB joints are just easier to weld outside of the fixture for me.  By the way, the Access65 is great for welding in the fixture (nice access, duh) but it is a beast of a thing to rotate around to get the right angle to weld. I’m not sure any other fixture is easier but I think the Anvil ‘balance point’ is better and it’s also on wheels so is likely easier to move around.

Anyways, how I figure out alignment is to first use the cool frame/fork alignment gauge seen below clamped to my height gauge and put the v-notch as close to the bottom bracket on the seat tube as I can (this is where it’d be nice to have a full, or at least wider, alignment table).  This gives the frame centerline – the center of the BB and seat tube is at the point of the v-notch.  Then I swing the frame a little to see how the TOP of the seat tube looks.  That’s what is seen in the below pic.

top of the seat tube in the alignment gauge

EDIT: A better and more accurate way of doing this is by using a universal height gauge or scratch gauge like Alex commented below.  You first set the height of the gauge to scratch the top of the seat tube close to the bottom bracket, then move the gauge to the top of the seat tube (or below the external butt if you are using such a seat tube) and see how far it’s off or if the scratch on the tube sounds the same as the 1st. Pics below:

Seat tube alignment step 1

Seat tube alignment, step 2

The table showed that it was about 3mm out of alignment – the seat tube was pulled to the driveside.  I then rotated the frame on the table so I could check the head tube.  It was similarly off to the driveside.  I looked at the BB welds and saw that my non-driveside BB/ST weld was a bit smaller and less hot than my driveside weld and so I went back to the torch, installed the heatsink, and laid a second pass on the non-driveside of the BB/ST joint and took it back to the alignment table.  What you see above is the result…back in alignment – perfectly! Beginner’s luck, i swear. It was sweet…i didn’t have to crank on it at all.

The head tube (above) also was back in alignment with the centerline of the frame.

After checking the front triangle, I checked the rear dropouts.  This tool is cool cause you can see if the spacing if off immediately.  If the gauge slides inside the dropouts to the right ‘level’ you’re good to go.  If it won’t fit in the right spot (135mm for this case), you need to do some work.  The driveside dropout was pulled inwards by a couple mm’s and the non-driveside was pulled outwards only about 1mm. The chainstays are super easy to cold-set so i just bent them quickly into place (Above photo = before, below photo = after).

The alignment table comes with a nice rear dummy axle with the middle marked with a clear etched line.  The alignment gauge pretty much does the same thing in a different way, but I wanted to make sure it was all centered before adding the seat stays.

I did this by the method below – using a universal height gauge and just eye’ing the center of the v-notch in the alignment gauge and then measuring how that height compared to the dummy axle’s centerline. Yeah, not super exact but pretty good.

Spot on!

An alignment table is definitely not needed, but it is very nice for figuring out what is not obvious to you at the start of your framebuilding ‘career’.  It makes sense when you think about it but here are some simple general tips that I learned over my 1st three frames:
  • Welding pulls the tubes to the side you are welding.  So, if you are welding the seat tube to the BB, the top of the seat tube will be pulled to the driveside.  This is why welders do each joint in 1/4 sections like i said in the last post, so to not overly pull it to one side and maybe not be able to pull it equally to the other side and equal it out.
  • Related to the first point, welding at the bottom bracket will pull the head tube one way or another as well.  If the HT is pulling right, another tack or a 2nd pass on the left side will pull the HT over to the left.
  • Welding on either side of the head tube will not pull it out of the centerline of the frame as much as it will twist the headtube one way or another. So if you have a HT twist, try a second pass in a strategic location to pull it that way.  Usually, you can get it in alignment before welding – when it’s all tacked up – but if not, a second pass is an ok solution as far as I can tell.  Obviously, you want to put as little heat into the tubes as you can, but i think it’s better to do a 2nd pass than crank on the frame to get it straight.
  • EDIT1: The frame/fork alignment gauge seen above is made by Alex Wetmore and can be bought from this link.
  • EDIT2:Before getting the above gauge, I used either a universal height gauge or a digital height gauge both seen above, to see how far exactly each tube was off from center.  For the time being, I will stop finding out if my frame is 0.05cm or 2cm off the centerline.  The gauge gets the bike to an acceptable level of alignment when doing what I did above.  However, I do use one of the other gauges to check heat tube twist to see if I need to do a second pass on one side or another of the HT to get it straight.  The Wetmore gauge can show if your HT has a twist, but not as fast for me to tell.  The reason – you’re measuring frame and tube centerline with his gauge and it’s super quick to do that with the v-notch.  But twist is easier to measure when placing a height gauge on the top of the tube since the tube is of consistent diameter (unless you’re using a new-fangled tapered HT obviously).  You could also do this just for the seat tube but when you compare that height of the ST off the table to the height of the HT you’ll need to figure out how much higher the HT is supposed to be and that involves more math that in really necessary.

One Response

  1. Thanks for linking back to my store.

    I like to use a scratch gauge (like the one in your last photo) to see if the head and seat tubes are perpendicular to the bottom bracket. You can adjust it to just barely scratch the seat tube at the bottom bracket, then sweep it across the seat tube near the seat cluster to see how far out it is. I find that a bit easier than using the V-notch on my alignment gauge. You can do the same thing with the head tube.

    A scratch gauge is nice because when it is properly adjusted it makes a very easy to hear sound from just grazing the top of the tube. If you get the same sound anywhere along the tube then you are golden.

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