Repair crack in Shape-rite crank link (was Opinions on how to repair) - Page 2
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  1. #21
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    I would fill the hole with braze too,and use a different retaining method,like a thru bolt in the pivot.......years ago I bought some extra agressive flux for cast iron,supposed to oxidize the graphite,anyway it works,but is used to wet the iron,after that use normal brazing flux................I will just mention this,but ive seen a lot of successful cast iron welds done with normal mig,but on a red hot workpiece....Strong enough to build up broken out tapped holes in mtorbike cylinder heads,and take full bolt torque....highly recommended by those doing it.

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    You say you don’t have a welder. What’s that thing in the background of the first picture?

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    Just hoses and regulators....maybe the OP only has LP gas /oxy....like me.plenty for brazing or cutting.

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    Quote Originally Posted by Flail View Post
    You say you don’t have a welder. What’s that thing in the background of the first picture?
    Let me rephrase, I dont have an electric welder, Mig, Tig, Stick. That is indeed a small oxy-acetylene torch.

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    Quote Originally Posted by Tenaya View Post
    Here's a link to his currently listed items:
    https://www.ebay.com/sch/kwktools/m....p2047675.l2562

    By the way, do you have the later "Model B", or, like mine, the earlier "HY DUTY". Both are 8" stroke.
    Thanks for this I did reach out to him. I do have the model B. in the process now of tearing it down and finding all these little problem areas. Has quite a few Battle scars and the ways do have a bit of scoring. I have hope it will be usable.

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    Once the weld repair is done, I would not drill and tap hole on that piece. Make a new shaft and put a Tru-Arc retaining ring on each end of the shaft and do away with the set screw, to retain the shaft. Ken

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    If you have room around the outside get a 1 1/2 dia. stainless steel washer drill and tap 6 or 8 10-32 holes around pin and attach with flat head screws. should keep it from cracking further. If you try to weld that yourself your asking for trouble

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    This part would be simple to make in mild steel, and would be many times as strong as the original.

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    Nobody mentioned it
    They all advise a unexperiened welder to go ahead
    I would drill a hole on my milling machine and tap it and put a bolt in it
    Even possible drilling by hand with the proper technique
    M6 will do I think
    Peter

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    I agree with Peter and some of the other contributors to this thread on several counts. When I saw the photos, I saw a very small set of oxygen & acetylene tanks. Way too small for the kind of heat and time a brazing job on this broken link would require. As noted, brazing or welding cast iron takes some skill, a sense of what the process used is about in terms of how the cast iron will behave, and obviously, equipment for the job.

    Without getting into the brazing vs welding discussion, from what I've seen of the broken part and thinking of the loading it sees in service, a "mechanical repair" would seem the best option. It would also maintain the center-to-center distance of the holes for the pivot pins, as well as parallel between the two holes.
    I'd go with some sort of "repair plate" in the form of a "washer" screwed to the face of the part if space permits. This washer, machined from plate steel, and screwed and dowelled to the face of the part would span the crack and hold things together. I'd drill & ream thru the repair plate and into the casting for some small fitted dowel pins aside from the screws. The face of the casting where the repair plate is to be secured has to be machined (or filed) flat so there is good bearing contact between the repair plate and the casting.

    Cast iron has a lower tensile strength than steel. I like to go with a mechanical repair on jobs like this one, using a positive connection and steel to span the break or crack. When I am faced with a casting where I have to span a crack or tie together a break on a curved or irregular surface, I have heated the steel and hot formed (forged) it roughly to shape on my anvil, then heated it and formed it to final shape on the actual casting. To insure good bearing contact on repairs of this sort, I have filed the casting to a reasonable surface and made a soft copper shim (flashing copper as used on roofing is what I have around the shop). The copper has enough ductility to be compressed by the repair plate so it conforms to both the casting and the repair plate surfaces, taking up any areas where there might be a localized lack of contact. It is a casting repair method I have seen used by old timers to repair cracked engine water jackets and similar damage. On parts having mechanical loading such as machinery parts, I feel a lot better about providing a mechanical connection, even when I am going to weld or braze the casting. In those types of repairs, I incorporate the steel repair plate, laying in weld or braze in the crack or break, then setting the plate and fastening it, and then welding or brazing around it to tie (or seal it, if a part which must contain fluid or steam) it in.

    In my opinion, one very good suggestion which I would go with above all of the others is to make a new link out of carbon steel. I am a bit spoiled having welding equipment and experience with welding and brazing. I have replaced cast machine parts that were either missing or busted into pieces with parts made by welding steel together and then machining. Something like the link in this thread could be made by cutting two link plates from carbon steel, and welding a spacer block between them. This lets a person get away with making the part out of lighter steel, much less machining, and makes a very strong part. I stress relieve parts like this by my backwoods method: heat them in the firebox of my home heating boiler (if during the heating season), or in an outdoor forge or wood fire (depending on size), then slow cooling in a bucket of dry ashes. This "relaxes" the steel after the cutting and welding, and relieves "locked in stresses" from rolling the steel at the mill aside from the welding and cutting operations. After this stress relieving ( I get the part to a red heat and hold in the fire for one hour per inch of thickness, watching carefully so as not to let the steel get burned), with a slow cooling and cleaning using wire wheels, the part machines nicely and has good dimensional stability after machining.

    Hogging the part out of solid steel is always an option if a person does not have any welding capability. It means getting hold of a substantial block of steel, and roughing out by use of a bandsaw if possible.

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    Joe, could a new piece be made without welding the spacer?

    I see three rectangular pieces, 2 holes drilled and reamed, and 4 holes drilled and tapped (if stacked or done as an assembly). Ugly but effective. Round the ends to make it pretty.

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  17. #32
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    Frank R
    You hit another nail squarely on the head with your idea. The original cast part is simple enough to allow making a built-up assembly as a complete replacement. You are correct: if the part were made using socket-head screws in counterbored holes and some through-dowels, there is no reason it would not work.

    I'd make the two "link plates", and depending on the size of the pivot pins and what the OP has for machine tools, that would determine how the job progressed. One method is to make the two link plates and fasten/dowel them to the center block, then line bore the pivot holes in the completed assembly. Another method, if the pin size is small enough, is to make the two link plates as a pair, line drilling and reaming for the pivot pins. Then, assemble as a pair with the pivot pins to jig things in place for "sandwiching" onto the center block and drilling/tapping and dowelling.

    It's a solid repair and a good fix that will work, and eliminates the need for welding, brazing, or attempting to pull the broken casting together. If a person were strapped for machine tools, making the two link plates by boring them as a pair in a lathe would work (no milling machine to run a boring head on hand). I'd try to make the dowel pins sized for a shrink or drive fit into the parts to be sure things stayed solidly together. Some Loctite 603 on the dowel pins and some permanent grade Loctite on the screws would insure things did not work loose in service.

    Year ago, before I had a Bridgeport in my home shop, a neighbor was restoring a hit-and-miss engine he'd found in a collapsed building. The bearing block for the exhaust valve rocker arm shaft was destroyed. It was a fairly complex casting. Realizing the loading it saw in service and how thin some of the sections of that casting were (it had a "pocket" which a cylinder head stud went into, and the nut for that stud was in that pocket), I decided to make a weldment. I built up the part out of A-36 hot rolled steel using stick welding. I did a lot of the shaping with an angle grinder and finished with filing. I blended the welds with an air die grinder since I wanted to get the look of the casting as much as possible. I think there were about six separate small pieces that made up the part. I drilled and reamed for the rocker shaft in a drill press. I made the new rocker shaft from a chunk of automobile transmission main shaft (i had a Southbend Heavy 10" lathe). The part worked fine, and with a coat of paint, was not really noticeable. As far as I know, that part is still in place on the engine and the engine runs fine when needed.

    The reason for remembering this little job is that a person can do a lot with simple and basic tools in the way of making parts and repairs. I know there are people who would have said the way to build the part was TIG welding, and the way to locate the holes and establish and machine the critical surfaces was on a milling machine. For what that part has to do, it worked fine. If the OP built up a replacement part for his shaper using capscrews and dowel pins to tie the pieces together, he could do it with fairly basic means and have a solid repair that would never bother him again. Sometimes, simple and basic means provide a quick and sure repair.

  18. #33
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    Thanks Joe.

    Is it always good practice to use alignment pins when constructing a piece like this? I am guessing you install the pins before drilling and tapping for screws to pull the assembly together.

    Could you just clamp the pieces together in place and drill/tap in place without using alignment pins?

  19. #34
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    Frank R

    I learned a kid in first grade, when the teacher kept twisting my hand around to hold a pencil her approved way, that there is no single right (write) way to do anything.

    Dowels are about the only real way, short of welding the individual parts together, or using some sort of machined/interlocking fit, to keep an assembly like this one in alignment. Without dowels or something equally solid, the two links would likely tend to slew relative to each other under the load when the shaper was taking cuts.

    There are a couple of ways to approach making this part:

    1. Make the links, drilling or boring the holes undersized by perhaps 1/32" in diameter.

    2. make a pair of alignment pins out of some scrap steel so they just slip into the holes in the links with a little hand pressure and twisting or wringing.

    3. Layout the holes and drill the holes for the capscrews using the tap-drill size.

    4. Clamp the links to the center block with the alignment pins thru the bored pivot holes.

    5. Spot drill the holes for the capscrews into the center block. Make sure to match-mark the links relative to the center block (punch marks or letter or number punches are used for this)

    6. Drill the holes in the center block with the tap drill, then tap each hole for the cap screws.

    7. Open the holes in the links to the body diameter for the capscrews & counterbore for the socket head screws.

    9. Reassemble the two links and center block using the alignment pins and pulling the assembly together with the socket head screws.

    10. Layout and drill thru the links and into the center block for two (2) dowel pins per side. OK to thru drill if you do not hit the tappings coming in from the
    opposite side.

    11. Line ream the holes for dowel pins.

    12. Make the dowel pins from something like O-1 drill rod if you are using thru dowels. Or, you can use stock sized hardened and ground dowel pins, coming in from either side. Two pins per side.

    13. Apply Loctite 603 to the holes and pins before driving the dowel pins.

    14. Remove the screws and re-set using permanent grade Loctite.

    15. Line ream or line bore the pivot pin hole to final diameter.

    Again, tapped holes and capscrews are NOT going to take the place of dowel pins. Unless you make body-bound bolts or studs to take the place of the dowels, some relative motion between the link plates is going to occur if you rely solely on capscrews. Capscrews are not designed to be shear connections. They clamp the pieces together and rely on what is known as "bearing" between the mating surfaces to prevent motion. Under the kinds of loads and cycling that the part would see in service in the shaper, there is no way capscrews would hold things in perfect alignment. Dowels in reamed holes with a light interference fit are what it takes, and those are what will take the shear loads.

    I know this sounds like the old timer who wore a belt and suspenders (braces to our UK brethren) to hold up his pants. I've seen some interesting things over the past 50 years I have been around this kind of work, both as a mechanical engineer as well as machinist. I learned a lot along the way that was never taught in engineering school, and was fortunate to be able to do a lot of design work on actual machinery and equipment and see it happen in actuality. Needless to say, getting the job done right so it does not give any failure mechanism a chance to get started is what I try to do when I think a job like this through. My own 'druthers would be to make the part as a weldment, since welded construction, properly done, is not going to allow relative motion between the two link plates and the center block. Since the OP has no welding capability, the built-up construction using capscrews and dowel pins is as good a method.

  20. #35
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    Thanks Joe, good info!


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