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View Full Version : M12x1.75 Left Hand Bolt



japcas
07-16-2009, 08:00 AM
I'm trying to help a friend find a bolt for his machinery. He had it checked by a friend of his who is a good machinist and determined that it is an M12x1.75 left handed thread. He can't seem to find it any where and he has checked out all of the usual places such as Fastenal. It needs to have a hex head and be about 40 millimeters long. Any one of you guys know where we might find such a bolt. He even went back to the machinery dealer and they told him to get it at fastenal but they didn't have it. The left hand thread seems to break the deal every time. I checked Mcmaster Carr but couldn't find it either.

And before anyone mentions it he really doesn't want to have to make one for safety reasons. Thanks for any information.

GKman
07-16-2009, 08:15 AM
And before anyone mentions it he really doesn't want to have to make one for safety reasons.

And where do you suppose the store-bought ones (if there were any) would come from, a mine in South Africa where they were formed by nature ten million years ago?

Start with an M12 that is too long and single point the LH threads and part off.

wierdscience
07-16-2009, 08:21 AM
It's on a finish mower isn't it?Bolt that holds the blade on right?I've removed a bushel basket of them,that's why it seems familiar.

If so dealer is full of it,they can get it,they just don't want to.Maybe find another dealer?

Another option is call McMaster-Carr and ask them if they can supply it.There is a lot more they can supply that isn't in the catalog.

Third option my local farm supply had them,if they still do I can send you however many they have.

J Tiers
07-16-2009, 09:03 AM
And before anyone mentions it he really doesn't want to have to make one for safety reasons.

So he'd rather have the OEM "made-in-china almost to spec and never baked after plating" version?

obviously I don't KNOW it would be that, but it seems reasonable, given the way things are now.....

airsmith282
07-16-2009, 09:45 AM
making what you need will likely be cheaper then buying one , left hand threaded nuts are hard to find i found only a few of them at my local home hardware store ,, any how thats my idea

gnm109
07-16-2009, 11:06 AM
My local ACE Hardware store had left-handed metric nuts but I haven't checked to see if they have any that coarse. If I needed a bolt badly I'd make on but I'd need either a die or a nut to check progress.

tony ennis
07-16-2009, 12:17 PM
It's on a finish mower isn't it?

That was my first thought too. Shoot an email to the manufacturer.

japcas
07-16-2009, 04:56 PM
Yes it is on some kind of mower. Good guess Weirdscience. These aren't for me and the guy that needs them doesn't have a home shop and I don't want to make any kind of bolt that holds a blade of any type on to a piece of equipment that is spinning it!

Usually you get the freakin internet police around here telling about all of the liability involved with making something like that. If I wanted to make them I'd use the cnc lathe and whip out any size needed, but like I stated I don't want to be responsible for making that kind of bolt.

Thanks Weirdscience, I'll tell him to go back and hound the dealer or call the manufacturer. Thanks for your help.

cuemaker
07-16-2009, 05:14 PM
kinda funny how the internet police have disappeared lately... might have something to do with the economy and people needing work and or having to making do.....

tattoomike68
07-16-2009, 05:55 PM
Yea dont make it, let a 9 year old girl in china make it. :rolleyes:

Its not that rare, you can find it . A good mower shop can order it from china.:D

japcas
07-16-2009, 08:11 PM
Yea dont make it, let a 9 year old girl in china make it. :rolleyes:

Its not that rare, you can find it . A good mower shop can order it from china.:D


If it's not that rare give me a part number and a place to order it then. It's easy to say it's not rare when you haven't looked for one. It's not my part either so it's up to him to find it, not for me to make it as everybody suggests. I just thought somebody on here might have a useful suggestion like Weirdscience did about where to find it. Not give smartass answers about some chinese kid making one.:rolleyes:

juergenwt
07-16-2009, 08:28 PM
Japcas - go here:http://mdmetric.com/

tattoomike68
07-16-2009, 09:05 PM
If it's not that rare give me a part number and a place to order it then. It's easy to say it's not rare when you haven't looked for one. It's not my part either so it's up to him to find it, not for me to make it as everybody suggests. I just thought somebody on here might have a useful suggestion like Weirdscience did about where to find it. Not give smartass answers about some chinese kid making one.:rolleyes:


I can make it in 5 minutes, sorry you are slow and lazy, cant help you there.

If you cant make a bolt by you should take up knitting.

madman
07-16-2009, 09:16 PM
I need some nice warm size 13 socks PLEASE winters coming.

japcas
07-16-2009, 09:21 PM
I can make it in 5 minutes, sorry you are slow and lazy, cant help you there.

If you cant make a bolt by you should take up knitting.


Mike, if you can't write up a helpful comment then shut the hell up and quit wasting my time. Go talk bull**** in another thread. I have more than enough machining to do then to be making bolts.

oldtiffie
07-16-2009, 09:39 PM
Japcas.

Stick with it - I admire your staying focused and not being distracted.

Its the owner's call after all, and as you say, you are only making inquiries on his behalf.

I'd imagine that "Grade" of the bolt is very important.

Only or best option seems to be a replacement part from an authorised dealer selling manufacturer's spares.

Around that area of my mowers I only use "original" spares from the local authorised Dealer - nothing else. The rest of the mower/s are usually a matter of using the highest tensile bolts and nuts I can get - just in case. I prefer not to have to "chance" it so always err on the side of safety and caution. If in doubt, I ask the Dealer who has an excellent reputation and work-shops.

I would not want to be responsible if a part that I suspect is as vital as the part under discussion "let go" for a whole lot of reasons - money and time being the least of those concerns.

"Macho" and safety rarely go well together - particularly if the macho bit tales precedence.

tony ennis
07-16-2009, 09:43 PM
deleted....

tattoomike68
07-16-2009, 10:22 PM
Mike, if you can't write up a helpful comment then shut the hell up and quit wasting my time. Go talk bull**** in another thread. I have more than enough machining to do then to be making bolts.


Well thats something, poor machinist wont take on the massive complexities of a bolt on a lawnmower. :rolleyes:

So some guy dont want YOU to make a bolt for his lawnmower, thats a huge laugh.

Whatever you do machine I just hope it dont go down the road or fly in the sky.

You made yourself look bad when you made this thread, clearly the guy wont trust you to make a bolt for a lawnmower. LOL LOL LOL this thread is the best LOL

J Tiers
07-16-2009, 11:45 PM
Well, I'm the smartass who first said it would be a brittle chinese bolt from teh OEM.

Actually, the best path IS to get it from the OEM, and neither make it NOR choose anotehr bolt from MDmetrics etc.

Either of those is "re-engineering" the part, and using "substitute parts"..... Even if the part is better, it is a "substitute", and I could make you look like a monkey in court, for using a "cheap substitute", whether it's true or not.

The OEM part may be a POS, but it is the RIGHT POS, and not some "make-shift substitute". if you install it, and torque it to spec, you'll still get jawboned if something fails, but your liability is likely to be minimal, to some extent you are a "co-victim".

When a jackass can win a case when he picked up a running mower and got his fingers cut off, you have no chance if you do anything at all unusual in a repair.

wierdscience
07-17-2009, 12:51 AM
Geez guys,lay off.None of you know the situation so I'll explain.

It's a finish mower aka pasture clipper.Two or three blades belt driven off a right angle gearbox which is driven by a tractor's PTO.

The design is a bit weak,but it was done for a reason.It's a safety factor designed to save an $80 set of belts should the machine hit something while mowing.The lefthand bolt is all that holds the blade on.It over-tightens and shears dropping the blade and saving the belts.

Most times the remaining threads in the spindle bore can be spun out by hand and the blade re-installed with a new bolt.It's not the best design,but it does work so long as you don't run over stumps and lightered knots.

Being foreign made they used a metric bolt,John Deere made a similar model,which was made here,but features a LH SAE bolt.It shears at a higher torque,but since it's a 1/2-20 it usually chomps the threads in the spindle.

Making a bolt would be a bad idea,not because it would be dangerous,but because it would shear off easier.

We all should know by now that roll threaded bolts are 40% stronger than cut thread bolts.Why would anyone want to make a bolt that is 40% WEAKER than the OEM which is shearing now?

12mm 1.75 LH taps and dies can be had,so can all-thread,so can nuts.Bolts that's another story,believe me I have looked.

J Tiers
07-17-2009, 09:08 AM
Wierd, you are just confirming my idea. Use the OEM part.

if you install a high strength screw, maybe it will NOT shear , at least not immediately. Then something else gets broken, or maybe the thing doesn't break, but is damaged, and later on it throws the now-unbalanced blade......

My point was that the manufacturer put that screw in for a reason, and if you decide to change it, you are rejecting their reasoning.

Odds are it was made in that particular thread precisely because it is less common (I didn't find any, although 2mm, or 1,25mm pitch are findable), and thus you would be back to them to get a screw which is correct.

rotate
07-17-2009, 10:01 AM
We all should know by now that roll threaded bolts are 40% stronger than cut thread bolts.Why would anyone want to make a bolt that is 40% WEAKER than the OEM which is shearing now?


40% refers to the strength of the thread and not the shear strength of the bolt, and since the "bolt" and not the thread is designed to shear it would seem doubly important that the thread be strong enough to sustain the shearing force of the bolt.

Having said this, I don't see any reason why you shouldn't machine one yourself. Just make couple of spares and swap it out when it breaks. If anything, by having something weaker than OEM part you stand to benefit unless the damn thing keeps shearing during under normal operations.

GKman
07-17-2009, 12:25 PM
I don't believe anybody designed the thing to shear a bolt off to save expensive belts. I can't explain it, I just don't. I want (and have several) with a threaded shaft with a self-locking nut that slips if overloaded so the blade stays on the shaft. The other design that works safely is the blade keyed or splined to take the torque and a bolt to hold it on.

Take this and $3.50 to Starbucks and see if it will get you a cup of coffee and report back.

wierdscience
07-17-2009, 10:28 PM
40% refers to the strength of the thread and not the shear strength of the bolt, and since the "bolt" and not the thread is designed to shear it would seem doubly important that the thread be strong enough to sustain the shearing force of the bolt.

Having said this, I don't see any reason why you shouldn't machine one yourself. Just make couple of spares and swap it out when it breaks. If anything, by having something weaker than OEM part you stand to benefit unless the damn thing keeps shearing during under normal operations.

The bolt is failing in tension not in shear,when the mower hits and object or the blade digs in the ground the spindle torques up and basically over tightens the bolt popping the head off and dropping the blade.

They do shear in normal operation,it's safety feature,unfortunately it's to safe.

wierdscience
07-17-2009, 10:33 PM
I don't believe anybody designed the thing to shear a bolt off to save expensive belts. I can't explain it, I just don't. I want (and have several) with a threaded shaft with a self-locking nut that slips if overloaded so the blade stays on the shaft. The other design that works safely is the blade keyed or splined to take the torque and a bolt to hold it on.

Take this and $3.50 to Starbucks and see if it will get you a cup of coffee and report back.

I never said it was a good design,it's just what they came up with.$2.00 for a bolt is better than $80 for a set of belts that take an hour to change.JD does it,Howze does it and several others.Sadly they don't all use the same blade as the mowers with the threaded spindle.If they did it would be a simple conversion.

I had a Linze spindle walk in this afternoon,same design,but 9/16-18 LH.Cocked up threads and shot bearings,it's on tap for tomorrow AM.

tattoomike68
07-17-2009, 10:56 PM
just drill and tap the crank 1/2-13 LH and go mow grass, thats easy to do, its olny a crankshaft.

If I was slow and lazy I could make that job last a week too.:D

wierdscience
07-17-2009, 11:01 PM
just drill and tap the crank 1/2-13 LH and go mow grass, thats easy to do, its olny a crankshaft.

If I was slow and lazy I could make that job last a week too.:D

That's been done,doesn't work either and the 1/2" bolt won't fit through the blade bore.

It's also not a crankshaft,it's a steel spindle mounted in a cast bearing housing.

I also average a $100/week just spinning bolts out,get your own racket:p :D

Earache
07-18-2009, 04:22 AM
Try:

Utterback Supply
1714 W Morris St
Indianapolis, IN
Phone: (317) 637-6468

I make motorcycle parts and have been surprised at what they can get for me in terms of metric bolts.

Good luck!