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  1. #1
    shifty
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    Tig tack, weld length and sequence questions

    I've been messing around a good bit with an inverter tig and gotten to the point that I'd like to start some more 'realistic' practice welds. I've had a hard time getting my mind around how long of a continuous stitch to put together when doing practice welds on mitered tubes. At some point, it just gets awkward as I rotate around.

    General questions:

    - You tack on the center-line of the frame? what constitutes a good tack? one 'dime' of puddle and filler? Pictures would be lovely.
    - How many 'segments' of welds do you do when going around a mitered tube? sequence?
    - Do you clean between segments of welds? i.e. wire brush off any discoloration?

    Obligatory pic of practice weld. I'm still in the mode of trying to get the hands coordinated. Very humbling stuff.

    Thanks much,

    Bernie
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  2. #2
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    weldingtipsandtricks.com Lots of TIG advice and videos

  3. #3
    shifty
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    Quote Originally Posted by RidingMyTrail View Post
    weldingtipsandtricks.com Lots of TIG advice and videos
    I've spent a ton of time on that site... lots of good info there!

    I guess what I'm looking for is a little more guidance as to the specifics and steps for a bike tube miter weld. Don does a good overview here in the third paragraph....

    RE: [Frame] tig sequence..

    I think I'm to the point with my practice that I'm sorta banging my head against the wall with making that 'next step'. Trying to teach myself, I don't want to reinvent the wheel... or teach myself the wrong thing. I suppose I would benefit greatly from spending just a little time watching someone that knows what they are doing.

    -Bernie

  4. #4
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    Weld sequence is all about alignment and tube stress.

    Step 1a: Tack Seat tube / Bottom Bracket Joint
    Tack weld in the front than the back. The tack welds should be short but not tiny welds and cover about 10% of the joint. The first tack should be moving right to left and the second tack should move left to right. After tacking, the welds you should check the joint outside of the jig. When you check the joint you will notice that it leans to one side or the other. In particular it is likely to lean in the side where your first tack started.

    Step 1b: Progress on ST/BB joint
    Based on alignment after the tack move on to the right hand side or the left hand side of the joint first followed by the other side. Leave a 5% in the middle on each side unwelded at this point because it will allow you to fine tune the final alignment.

    Step 1c: complete ST/BB joint
    Perform some additional alignment checks and then move on to weld the final 10% with the order and pace for each side based on the alignment you found in step (1b).

    Step 2a: Front triangle
    Tack the Top tube, head tube, down tube such that the tacks are in effect pulling inline with the triangle. Each tack covers about 10% of the respective joint and after tacking in the jig the frame should be in fairly good alignment.

    Step 2b: Progress on front triangle
    Progress welding is similar to the first joint leaving 5% unwelded on each joint.

    Step 2c: Complete the front triangle
    Check alignment after step 2b and then complete each weld with your order and pace based on your measurements. At this point the alignment should be close. If you have a minor problem another TIG pass on a joint can correct the alignment without very much tube stress. When the frame is +/- 2mm you are in good shape.

    Step 3: Chain stays
    Chain stays are tacked and welded similar to the front triangle.

    Step 4: Seat stays
    Seat stays are tacked and welded similar to the other joints. You will notice that they do not impact overall alignment very much but you should still be careful to balance the stresses as you make the welds.

    When everything is done perform the final alignment checks and if needed touch up a joint or two with a TIG wash.

    Cleaning with a wire brush between weld segments is fine but does not seem to be needed in most cases.
    Last edited by febikes; 10-17-2012 at 09:46 PM. Reason: Clean up advice about tacking
    Mark Farnsworth
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  5. #5
    shifty
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    Awesome. Thanks!

    I think that my next effort will involve tacking/welding to a tube to simulate the BB shell seat tube weld and checking 'alignment' between tacks and welds to get a sense of how things move.

    -b

  6. #6
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    Tacking

    First, Don's description is very good. That is the same general procedure that I follow (which he told me to do, which saved me a lot of time wasted on redundant alignment work).

    Second, everyone's sequence is different, because everyone welds each joint a little differently, has different standards and techniques for alignment, etc. The only way to figure out *your* sequence is to experiment. Obviously you'll want to swap sides frequently (ie, don't weld one entire side of the frame, then flip it over and do the other side).

    Finally, on tacking, do whatever you want with the following goals in mind:
    The tack should:
    1: Hold things together well enough that it won't break when you're welding the other side of the joint (so it can't be *too* flimsy).
    2: Not create a problem for you when welding over it (so not too big of a blob of metal or massive undercut either).
    3: Be removable if you realize you screwed up and need to take things back apart. That's the last priority but it's a good reason to make the tacks as small as you can get away with and still satisfy requirements 1 and 2. IMO 20% of the joint is WAY too much. I'd say my tacks are about 3mm long, each, with 4 of them evenly spaced around every joint. I don't tack on the frame centerline, instead at 10:30/1:30/4:30/7:30 (approximately)

    Hopefully that helps. If you live in UT you're welcome to stop by and watch me tack as much stuff as you want!

    -Walt
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  7. #7
    The dirty knacker
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    I follow a similar sequence to what Don posted and would agree with everything Walt added. The only bit of advice I would add to these is to consider the whole tack and weld sequence as a whole. With the piece contracting and moving as you work you should aspire for a symmetry, much like tensioning a wheel.
    Rosko Cycles Inc.
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  8. #8
    Nemophilist
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    Hey;

    How about adding a little discovery to this? I'm always better when I can see and feel it. Set up some sort of rig where you can track the movement of your tubes. Maybe throw together a practice ST/BB joint "incorrectly" with tacks at front & back of the BB housing instead of at four corners. Square that joint up, add a side tack, measure, and leave it alone. Flip it and tack the opposite side. Try as hard as you can to keep the duration of arc and size of your tacks equal. Measure and see how far back against the first side tack your opposite tack brought things. You should be able to derive some feel for how things will move and then how you can make them move where and when you want.

    I should try it myself!
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  9. #9
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    Are you guys adding filler to your temporary tacks? (or doing them autogenous style..) I'm thinking without filler would certainly make it easier to weld over the tacks later without issue.. but that's just an opinion. What do you guys do?

    many thanks,

    --zip

  10. #10
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    Add filler to tacks on thinner steel. You won't have enough base material to fuse them, without filler, generally. You're more likely to get a hole, than a tack.

    It takes skill to adjust your filler when welding over tacks, but it will come with time.
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