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Boot
07-19-2012, 09:58 PM
I have a Cub Cadet with a 50" mower deck. I stripped a blade holding spindle. It's a 5/8-18 thrd. I want to weld over threads or turn it down and put on a threaded sleeve and weld that fast. The blade itself is located on a star shaped lock at the end of the thread. I think it's a forging made probably of 4140 type steel. I plan on maching the threads off before I weld. Don't get me wrong I will buy a new one ,but I would like to have this one as a spare. $19.95 for new one on Jim's Small Engine Supply + shipping. How would you repair this ? It slides out of the bearing housing. I cleaned it and I'm ready to procede.

wierdscience
07-19-2012, 10:16 PM
I would not even think about it after seeing the damage done by a flying lawnmower blade.Almost any mom & pop lawnmower shop will have that spindle for the same money through the Oregon brand replacement parts label.Chances are that CubCadet is an MTD or Murray in disguise.

becksmachine
07-19-2012, 10:17 PM
Have done just that many times, no failures that I know of.

Use 7018 if using stick, or E70 something if wire. I have never taken extraordinary measures to let it cool slowly, it will get red with the multiple passes. Let it cool on it's own.

Dave

danlb
07-19-2012, 10:23 PM
You should be able to build up the threaded area with MIG and ER70S-6 wire. That should be machinable Then it's a matter of getting a good, well centered thread on it (die or single point )

Dan

Tamper84
07-19-2012, 10:23 PM
I used to do alot of build up work when I worked for a strip mine outfit. When I built up something that had to be machined after, I would preheat until spit boiled off (technical I know but the way I was told to do it lol) and I started to weld. Didn't stop welding until the part was built up or the day was over. I was told if I didn't heat it up that much, the machinist would snap bits left and right. It's was all 7018 btw.

Hope that helps,
Chris

Fasttrack
07-19-2012, 10:30 PM
Well, I will say that rethreading a welded up area is not an easy task. You want to have the right rod or wire for the job and you want to make damn sure you keep everything clean as you build it up. Hitting a slag inclusion or a porous section while single point threading sucks. Also, watch your interpass temperature. You want it the whole part to get good and hot so it cools slowly.

I think a much easier repair is to weld on a threaded sleeve but I'm not convinced this is a safe thing to do. By the time you turn down the existing threads and bore a hole in a threaded sleeve, you don't have much area to weld. If it was a 5/8 - 30 or some really fine machine thread, then you might get away with hit.

Also, if it is 4140, you'll have to be careful how you weld it and what material you weld to it. When welding mild steel to 4140, I preheat to about 450* F before welding and I use a 309 SS rod. If welding 4140 to 4140, use low hydrogen rods (e.g. 7018) and remember to keep the rods in an oven before use. Keep the bead fairly narrow - not wider than 1/2". 4140 is supposed to be welded only after it has been annealed and should be stress relieved at about 1000*F, IIRC, after welding. Then, once you've done the stress relief, you can re-harden and temper it.

:Edit: Looks like other's beat me to the punch.

Dr Stan
07-19-2012, 10:34 PM
I've threaded welded shafts (my own & others) and the key is making sure it is soft enough to thread. However, as Weird pointed out the potential hazard of having a mower blade flying off is more than offset by a $20 part. There are some things I just will not work on such as trailer hitches,
w a y to much potential liability.

However, if you're dead set on making the repair I'd consider completely cutting off the mangled threaded diameter and drilling & tapping the shaft for a 5/8-11 stud made from a grade 8 bolt. Of course this is only possible if there is enough material in the shaft. I'd also Loc-tite and cross pin the stud.

Just my $0.02

Boostinjdm
07-20-2012, 12:03 AM
For $20 I wouldn't phuk with it, but if you want to fix it....
Cut the threads off flush with the star, drill and tap 1/2" 20 and use a bolt. That's how most of the decks I've seen are anyway (john deer, grasshopper, etc.).

Boot
07-20-2012, 11:25 AM
Thanks for all the good advise. I'm out the door to buy the new spindle this morning. I think I will try welding and single pointing new threads on it. I like the idea of using
7018 rods on it. I'll let you know how it turns out and I'll post pictures. It may take me a while to do this so be patient. Thanks again , Boot

wierdscience
07-20-2012, 04:06 PM
With all due respect,reconsider the situation.The welding process will affect the heat treat condition of the base metal.The original threads are rolled threads which are 30-40% stronger than cut threads and the machine is spinning a 3-4 lb mass at 3,000 rpm which is known to occasionally strike objects.

After 20+ years as a machinist what you are considering is something I would not do for myself.Just because it can be built up and rethreaded doesn't mean it should be.Not harping on you,it's just not a good idea IMHO.

Dr Stan
07-20-2012, 06:25 PM
With all due respect,reconsider the situation.The welding process will affect the heat treat condition of the base metal.The original threads are rolled threads which are 30-40% stronger than cut threads and the machine is spinning a 3-4 lb mass at 3,000 rpm which is known to occasionally strike objects.

After 20+ years as a machinist what you are considering is something I would not do for myself.Just because it can be built up and rethreaded doesn't mean it should be.Not harping on you,it's just not a good idea IMHO.

Weird is absolutely correct about this. Throw that piece in your junk pile to be taken to the scrapper on your next trip.

CCWKen
07-20-2012, 07:15 PM
I've got a bunch of those spindle shafts protruding from my Kazoo but none, that I recall, with the star mount. (I'd have to look again.) If I had it, you could have it for postage. I bought the inventory from a mower service center at auction a few years ago and still haven't gone through all the stuff. I know there's complete spindles and a load of shafts but don't recall seeing the star type. :(

Bill736
07-20-2012, 10:42 PM
I agree that a lawn mower blade shaft is not a good place to experiment. Besides, I think there have been enough replies that I can now tell my " related" story without highjacking the thread ! Many years ago, I " fixed" the thermostatic engine fan on my '62 Oldsmobile by welding it solid. I used three or four short pieces of angle iron, and had them welded in by a welding shop. The arrangement worked for a few hundred miles. Then, one day out on the turnpike, there was a violent vibration from the engine, followed by terrible noises, and steam and coolant spewing everywhere. I opened the hood, and found that the cast iron water pump housing was broken in two, and the now unattached fan had flown around and eaten up lots of things in the engine compartment ( radiator, hoses, wires, etc.) What apparently happened is that one of the welds holding down one of the angle iron pieces had broken, caused an imbalance in the fan and pulley assembly, and that shook the water pump casting apart. I've been a little reluctant to weld parts that rotate at high speeds and loads ever since.

mike4
07-21-2012, 05:08 AM
Some "fixes" should not be done , like the one above , however I have repaired my trailers , and manufactured a coupling or two for rotating machinery , if you are not confident or competant then by all means dont do anything . However many people are imtimidated into not attempting to repair a machine part by the growing "what if " group which is popping up everywhere. I for one will not be intimidated because I would not be able to earn an income .
Michael

oldtiffie
07-21-2012, 08:46 AM
A lot here may have had their confidence boosted to a "of course I can do that" level by reading John Stevenson's many posts on just this sort of work.

If you can't control your ego just leave it alone.

John has a huge store and knowledge of and about such things as well as a vast skill and ability doing it and may make it look easiet than it might be for others less skilled.

I certainly would not try it and I certainly would not "farm it out" to some self-proclaimed expert either.

If I could not get a replacement part - preferably new - or in very good "used" condition - I'd probably scrap the mower and begin again with a new(er) and perhaps better one.

J Tiers
07-21-2012, 09:39 AM
if you re=read the OPs posts, you will find that in the last one he said he was going to try doing the weld-up and repair.

Many of you pounced on that and cried "WOLF" yet again......

I believe you MISSED THE PART where he said he was out the door to get a new part....... He will do the weld-up as a practice which he said "may take some time".... at least partly because hehas to put the NEW part on and get some mowing done before he fools with the weld-up.



If I could not get a replacement part - preferably new - or in very good "used" condition - I'd probably scrap the mower and begin again with a new(er) and perhaps better one.

BIN IT!

The whole half ton thing in the scrap for a 150 gram part..........

Another alternative is to manufacture a new part out of 4140PH..... Should be as good as the old one.

For those who STILL say that a spinning blade is no place to do such a risky thing...... I'd point out that the OLD one has had the blade hit innumerable rocks and old hidden stumps. For all you know it is even now cracked over halfway through, the crack is propagating, and currently is only 20% stronger than it must be to handle the force of grass-cutting.... The next piece of rock or old stump may send it spinning off and right through the side of a passing school bus (worst case scenario #2).

Your liability is in actual fact the same either way.... you "knew or should have known" that the part was degraded/unsuitable material/poorly made/etc.....................

vpt
07-21-2012, 12:05 PM
As far as the blade flying off. When it comes to safety type deals similar to this I will normally test a bolt in the new threaded hole past its recommended torque value to make sure it is going to hold up. If you've turned enough bolts in your life you should know by feel if the (bolt, hole, threads) are "right" and will hold. Blue loctite when assembling and all should be fine.

But the bolt has to be able to be torqued past tight. If it doesn't feel right or if it starts to pull threads right at or just past its torque value then it isn't good enough.

May not be considered safe enough to some of you. It hasn't failed me yet.

Fasttrack
07-21-2012, 06:47 PM
Some "fixes" should not be done , like the one above , however I have repaired my trailers , and manufactured a coupling or two for rotating machinery , if you are not confident or competant then by all means dont do anything . However many people are imtimidated into not attempting to repair a machine part by the growing "what if " group which is popping up everywhere. I for one will not be intimidated because I would not be able to earn an income .
Michael

Excellent post. I was going to add a similar commentary but decided to stay out of it. Machines are made by people. There is nothing magical or mystical about them. If you don't have the tools, materials or skills to repair or fabricate a replacement part, then so be it. If, however, you have those three things, don't let unwarranted fear hold you back.

As I understand it, the threads and corresponding nut just hold the blade on the "star", which does the driving. Why not do away with the threads entirely and install a washer and cotter pin or roll pin?

Just like to point out that my "home made" trailer hitch has survived for 5 years of extreme abuse. It's gone over 1000 miles with 17000 lbs behind it (which is a lot for a bumper pull). I've locked up the wheels with a loaded trailer, used it to tow a bunch of piggy backed anhydrous tanks across a field, etc. I give it a close inspection before I hook a trailer to it, but I do that with any hitch. No signs of stress or strain on the hitch and I can say with absolute confidence that there is no factory or commercially available after market hitch that is built as strong as mine. I'm not saying everyone should go out and build their own, just saying that there is nothing "magical" or inherently special about parts that come from a factory.

Dr Stan
07-21-2012, 07:39 PM
Just like to point out that my "home made" trailer hitch has survived for 5 years of extreme abuse. I give it a close inspection before I hook a trailer to it, but I do that with any hitch. No signs of stress or strain on the hitch and I can say with absolute confidence that there is no factory or commercially available after market hitch that is built as strong as mine. I'm not saying everyone should go out and build their own, just saying that there is nothing "magical" or inherently special about parts that come from a factory.

You apparently built an excellent hitch. In my earlier post I should have stated I will not work on a hitch for someone else. I've seen numerous signs at welding and automotive shops also stating they will not weld on hitches. I base my refusal on an incident in Bradenton FL about 35 years ago when a shop made hitch failed. The "Eisenstein" driving the tow vehicle neglected to attach the safety chains so the trailer went into oncoming traffic hitting another vehicle head-on. Yes the idiot should have been held 100% liable, but the plaintiff's attorney also went after the welding shop. Needless to say it went out of business due to the monetary damages.

You just never know what someone else will do and their level of safety awareness and practices.

oldtiffie
07-22-2012, 01:17 AM
I have a Cub Cadet with a 50" mower deck. I stripped a blade holding spindle. It's a 5/8-18 thrd. I want to weld over threads or turn it down and put on a threaded sleeve and weld that fast. The blade itself is located on a star shaped lock at the end of the thread. I think it's a forging made probably of 4140 type steel. I plan on maching the threads off before I weld. Don't get me wrong I will buy a new one ,but I would like to have this one as a spare. $19.95 for new one on Jim's Small Engine Supply + shipping. How would you repair this ? It slides out of the bearing housing. I cleaned it and I'm ready to procede.

I think you are doing the right thing all round by fitting a new shaft.

I dont know what type of blade mounting you have - one of mine (USA-made "Simplicity") had three - with a welded-on mounting plate with two (I think) 5/16 high tension bolts for the blades. They were not a problem as the bolts on the blades and the vee-belt drives (3) looked after most stuff.

The other two (USA-made "Toro" and my current "Husquana" (sp?))had a single bar with an integral formed blade at each end. I was surprised at how hard it was to undo the centre drive nut which kept the blade on the drivve spindle. As I recall it was about a 9/16- UNF-18 (or perhaps finer) as it was friction drive. As I recall the torque required at replacement or new blade/s was very high - and I've seen no sign of the blade slipping on the spindle. But I am very careful and my wife and I walk the whole area to be cut before starting - its amazing what we've found!!

Boostinjdm
07-22-2012, 02:29 AM
Thrown mower blades are no joke. I've got a mower with a nice blade shaped hole through the side of the deck. It broke two factory blade adapters before I figured out the crank was bent and a very slight vibration was doing it in. It's been parked now for several years while I decide whether to fix or toss it.

J Tiers
07-22-2012, 11:23 PM
Some stuff is dumb to fix, best to replace.

That said......

If the best toolroom machinist in the company comes home and makes a part to print in his basement shop with his like-new mill and re-built to spec Monarch lathe, the part is "homemade", and would be labeled as such in the newspaper report.

If the two worst drunkards on the factory floor make that same part in production on a clapped-out Bridgeport and the old Springfield in the welding department, while hung over on Monday afternoon plus having had a tall can for lunch, it was "professionally made", despite being at (or over) the tolerance limit on every dimension. The newspaper would be silent about it.

Fasttrack
07-22-2012, 11:32 PM
Some stuff is dumb to fix, best to replace.

That said......

If the best toolroom machinist in the company comes home and makes a part to print in his basement shop with his like-new mill and re-built to spec Monarch lathe, the part is "homemade", and would be labeled as such in the newspaper report.

If the two worst drunkards on the factory floor make that same part in production on a clapped-out Bridgeport and the old Springfield in the welding department, while hung over on Monday afternoon plus having had a tall can for lunch, it was "professionally made", despite being at (or over) the tolerance limit on every dimension. The newspaper would be silent about it.

Agreed on all points. :)

mike4
07-23-2012, 03:19 AM
I would still make the part if it was not readily available at the local suppliers.
Wouldnt be home made as I would be making it at work, not all of us are under insured when it comes to the people who want to sue you because of their stupidity implied or otherwise.
I have to carry a minimum of $20 million for normal work and a minimum of $10 million for design and professional indemnity just to have the doors open .
As for those who try to blame others for their shortcomings or position on the stupidity tree they are becoming very common and I have to deal with them almost daily .
Some customers still have common sense and wouldnt even try to do some of the dangerous things that the dimwits perform .
Michael

lazlo
07-23-2012, 12:59 PM
The original threads are rolled threads which are 30-40% stronger than cut threads

That's only true if the threads were rolled after heat treat. The vast majority of consumer-grade fasteners are rolled before heat treat, which eliminates any cold rolling advantages.
As Carroll Smith points out, aircraft fasteners are rolled after heat treatment, but even ASTM grade 8 bolts are rolled before heat treat.

http://youtu.be/EiN6SOqdt9k?t=2m34s

...then:

http://youtu.be/EiN6SOqdt9k?t=4m0s

wierdscience
07-23-2012, 03:01 PM
In terms of pullout resistance(shearing at the thread base)they are stronger either way.

lazlo
07-23-2012, 03:21 PM
In terms of pullout resistance(shearing at the thread base)they are stronger either way.

If the thread is cold forged, definitely, but once you heat the bolt to critical (as they're doing in the How It's Made video), you've reset the grain structure. It's functionally identical to cut threading, if you heat treat afterwards.

It's like the fuller on a sword: if you forge in the fuller, you've compressed the grain structure and have made the sword stronger. But if you then heat treat the sword, you've lost any value in forging the fuller -- you might as well have milled the fuller.