Reeves drive sheave hub bore repair

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BadDog
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Re: Reeves drive sheave hub bore repair

Post by BadDog »

Ok, thanks for the correction. I've welded 4140 tube before with good success, but never solid, or in this application. I was under the misimpression that it was low enough in carbon (or to rephrase, barely enough to harden) that it would not be a problem for welding in this application. I will revise and either use the hot rolled or drop buy the local steel supplier for something more suitable. I generally use common hot roll for most of my projects specifically because they often involve welding, I was just trying to use "better stuff" here, which it turns out was wrong thinking. But that's why I posted up my plans in hopes to correct whatever mistakes I might otherwise make. Thanks again!
Russ
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redneckalbertan
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Re: Reeves drive sheave hub bore repair

Post by redneckalbertan »

I wouldn't shy away from using 4140 because of the welding aspect, but in my opinion would not be my first choice, as well my first choice would not be a stick weld, although if using stick I would almost certainly use 7018.

I have had good luck welding a premachined fitting of 4140 to an unknown steel. Most likely a mild steel it was coil tubing from a coil tubing drill rig. The tubing was about 1 1/4" diameter with a thin wall, a guess would be about .090" the fittings were a tapered design from about the same wall thickness as the tubing to about 3/16" at the thickest part of the body then either a male thread or female thread. I TIG welded the fittings on with a high amperage setting and very quickly around with ER-70S2 wire although ER-70S6 should be fine as well. I can't remember how many of them I did, several batches totalling somewhere around 300 fittings welded. I was never told about cracking on any welds. They were all, as far as I was told, xrayed for QC. A crack would have failed the weld so I'm sure I would have heard something. I did the weld in two passes, the procedure I developed kept the interpass temperature right around or below 450*f. This was measured on the body of the fitting, and left to cool down to about 200*f before the next pass.

A few things we must consider when welding a shaft with complete penetration, what you do to one side you just do to the other, think of it as the golden rule of welding! If not the shaft will have a much greater tendency to pull and cause alignment headaches. Since you aren't going for full penetration and you will have a pilot section on the shaft which would all but eliminate this. I would TIG weld the shaft on for two reasons, the first being cleaner starts and stops - no porosity. The second you can get full penetration from the beginning of the weld. If you go with TIG or stick I would, after wrapping the armature as you describe, preheat the shaft near where you are welding and your entire extensions its a torch to about 200*f and weld in 2 short beads across from each other on the shaft, maybe 1/4 of the shaft per pass. Check the temp with a templestick make sure you are below 450*f. If using TIG, assuming you use appropiate pre and post flow, you should have no porosity wait till you are back to 200*f and then continue the welding, think of welding the shaft like you would tighten lug nuts on a 4, 6, or 8 bolt rim. Skipping around to minimize the risk of warping or pulling. If using stick I would use a 3/32" rod and grind out the start and stop making sure to clean any porosity or slag inclusion out of the weld, let cool and see my previous comments about skipping around. This will take more welds because you will be grinding some of your weld out each time.

When starting welds with the 7018 rod they are prone to porosity when you pull a long arc and the developing atmosphere around the weld is drawn out too far thus resulting in being polluted with oxygen and porosity forming. To help alieveiate this always use a new rod... Since this is not always practical/economical I will take my thumb and forefinger and crush the cup of flux at the end of the rod shortly after the arc is extinguished. Too soon and you burn your fingers, too late and the coating is more fragile and more likely to chip past the end of the core increasing the likelihood of porosity. Removing the length of flux that sticks past the core of the rod will aid in ease or starting reducing porosity. Another option is to save the once used rods for later when porosity is less of an issue and grab a new rod everytime.
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Harold_V
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Re: Reeves drive sheave hub bore repair

Post by Harold_V »

BadDog wrote:Ok, thanks for the correction. I've welded 4140 tube before with good success, but never solid, or in this application. I was under the misimpression that it was low enough in carbon (or to rephrase, barely enough to harden) that it would not be a problem for welding in this application.
4140 contains enough carbon (.4%) that it can be heat treated up to 50Rc hardness, which is the reason why it's not the best choice for welding. 4130 is low enough in carbon to permit welding with greater success. Also, don't make Stressproof or Fatigue-Proof a choice, as each of them also contain too much carbon for successful welding.

Harold
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BadDog
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Re: Reeves drive sheave hub bore repair

Post by BadDog »

Thanks for the information and advice.

I'm a bit leery of preheat given that I don't know what temps the vanish and other potential materials involved may have. My general welding plan was to use MIG just for convenience. And as I tried to describe earlier, alternating short stitches on opposing sides was always in my mind. I can switch to TIG or stick easily enough, but MIG using 75/25 and ER70S wire is more convenient. And I'll definitely avoid the funky alloys, leaded or otherwise, I've seen what happens when people try to weld them. This is all why I machine "mild steel" the vast majority of the time. "KISS" is my motto...
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redneckalbertan
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Re: Reeves drive sheave hub bore repair

Post by redneckalbertan »

TIG would still be my first choice, but should be doable with the wire feed setup you mentioned. Keep in mind with GMAW (it's not really MIG because the gas is not inert in this case) your starts are cold and you do not get any/good penetration at your start. So I would grind out the starts and stops.

I wouldn't be too concerned with preheating the shaft with a torch (just a small flame cutting tip or large brazing tip would be fine definitely no rosebuds or tigger torches), and I would be more inclined to preheat with GMAW than other methods. If you wrap it in wet rags the armature won't be any hotter than 212*f, as long as the rags are wet. You are going to get higher temps., and more thermal input from the welding.

The idea behind the preheat is to eliminate the stress and increased likelihood of cracks due to a rapid quench of the weld. The thicker/heavier the members are being welded or the smaller the size of weld/ thermal input, the more important this becomes. 4140 is more prone to this type of cracking and that is the reason behind my suggestion for preheat.

GMAW deposits a more brittle weld than other methods, if memory serves me, this is due to a more crystalline weld structure forming. If the shaft is preheated, the cool down period for the weld will be longer and will decrease the crystallization of the HAZ (heat affected zone) of the weld. The preheat, I think, will help more than post heat, unless post heat is, I can't remember off the top of my head but HOT, and then holding this temperature and slowly cooling it down... Which I know is not an option for you, I was just throwing that out there as general knowledge. (If one can do a proper post heat it is by far the best option for controlling stress induced cracking.) Wrapping the shaft in insulation after you are all done welding is another option that may help slightly, but again in this case not as much as a quick preheat.
spro
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Re: Reeves drive sheave hub bore repair

Post by spro »

Dear redneckalbertan, you are like my uncle. He welded all his working life. I stay back in awe of you guys. I asked him about working the pipelines long ago and he looked right through me. I was talking about welding so far below his grade, he didn't know what to say.
He had a lot to say and we were too young. The ravages of the work he did consumed him later. All he wanted to do is go fishing with his nephews. I couldn't make it for that. Job, another priority about whatever clearing property, ...........
Well, we should be better, having lost a bunch good people, while being busy.
My Uncle was before you and used different connections with different equipment. The spirit remains and if it is a thousand miles away, the music of the weld was played in rhapsodies which remain in
the evidence they remain.
redneckalbertan
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Re: Reeves drive sheave hub bore repair

Post by redneckalbertan »

Thank you Spro.
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BadDog
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Re: Reeves drive sheave hub bore repair

Post by BadDog »

Thanks for the great suggestions, I'm sold. GTAW it is. Still nervous about managing the pre-heat without damaging the rotor, but I'll take your advice, you clearly know much more about it than I do. Give me a nice simple isolated structural weldment any day, almost "zen" at times, but this tedious risky stuff is for the birds. ;)
Russ
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redneckalbertan
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Re: Reeves drive sheave hub bore repair

Post by redneckalbertan »

Keep the rags wet and tightly wrapped around the shaft and on the armature and you will keep your temps low. You may have to swap out the rags or rewet them during the processas but If you are worried about the temps climbing during welding let it cool right off and continue the job the next day.

I've never worked on a motor, but have worked on several hydraulic cylinders of smaller size where the Rod could not be extended and I had to weld the end back onto the rod right beside the seals. Wrapped it up with wet rags and it worked like a charm.
redneckalbertan
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Re: Reeves drive sheave hub bore repair

Post by redneckalbertan »

I've been wondering if you had time to work on this project and how you made out.
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BadDog
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Re: Reeves drive sheave hub bore repair

Post by BadDog »

It got side lined at the point where it was disassembled and I was going to turn the stub and make the extension, then weld it on. I sold an unrelated machine and had to get it ready, we had some perfect weather for getting some outside house/property work done, and so on. Still got some paint/finish work here, and my mother wants me to paint her house. It never ends. But the motor now sits parts gathered up in a "task box" at the front of the line when I get back into the shop.
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BadDog
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Re: Reeves drive sheave hub bore repair

Post by BadDog »

Well, I did finally manage to allocate the time to finish this project this past weekend. I added 3" to the motor shaft roughly the following process (high points).

1) Turned a 3" stub at 0.905" dia to provide for finish turning to size to allow for potential warp. Joint end was deeply chamfered and bored 0.500. Well, that was the plan, but made a mistake and wound up with 0.503. I'm a bit ashamed of that, I was hitting the numbers dead on for the previous 2 cuts, then went over by 3. <sigh> Oh well, luckily the shaft wasn't turned yet.

2) Attempted to mount the motor shaft between centers, and realized the drive side center was pretty damaged. So mounted it in a 4 jaw and trued the center hole using a boring bar. Then mounted the shaft between centers and turned the 0.503- stub. Shoulder was also deeply chamfered for welding.

3) The resulting fit was a light press fit, so I used a small reground bit to act as a graver to cut a groove for air escape when heated (learned that one the hard way some years back). Assembled and all appeared to be a go. Rigged up a simple rotary positioner using the rear bearing (insulated) and a v-block vise jaw. I forgot the temple sticks I meant to pick up (as I have consistently forgotten for the last 10 years or so), so wrapped in almost wet hand towels (tied in place with cord) and then heated (from the new stub end) just until a sharpie mark mostly disappeared and started getting some oxides on the motor shaft. Then welded alternating side stitch. Turned out real nice.

4) After cooling, back in the 4 jaw to produce a new center on the stub true to all original reference surfaces. Warp is limited to the stub and appears to have been no more than about ~0.004 @ 3", so plenty easy to cleanup. Shaft was then mounted between centers and finish turned stub shaft plus weld to size. After a light polish, other than a truncated keyway, you really can't tell it was done.

5) Extend keyway across stub and assemble.

Of course it was a bit more involved than that, but that's the gist. I got it up and running Sunday night before calling it a day. But other than final button-up with covers and shields in place, a Powermatic 20" has rejoined the ranks of operational shop tools today.

Of course it wouldn't be one of my projects is there were not something to dampen my spirits a bit. There is also an odd electrical gremlin I'll post in another thread. And I'll likely dig back in someday (I think I have an opening in late 2032) to investigate a bit of rattly noise at max speed from the driven variable pulley (I think it's just the floating finger pad).
Russ
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