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Tony
11-29-2011, 09:11 AM
Have an old tractor that popped its brake caliper on one side.
Two broken bolts. (caliper mounting bolts)
Inspection on the other side revealed 1 broken (but stuck in place)
bolt.. and one still hang'n in there.

So at the tractor supply (& auto parts store) I learn that these bolts
(for this tractor) aren't available as separate parts -- I'd have to get
the whole brake kit for both sides.

The bolts appear hardened.

I have a 10" piece of O1 that I could just get 4 bolts out of.

I could either home-heat-treat or send them out.

Question is, is O1 going to be any good for bolt? I'm afraid I might
get them too brittle in a homebrew torch'n'dunk treatment.

The lathe isn't ready yet so I have time to pick some proper stock.

I assume they're only hardened for abrasion resistance?

Thanks.

Tony

lazlo
11-29-2011, 09:16 AM
Question is, is O1 going to be any good for bolt? I'm afraid I might get them too brittle in a homebrew torch'n'dunk treatment.

It will be too hard as quenched -- around 65 Rockwell. Just put it in the toaster oven at 600 F for an hour, and you'll be at 56 Rockwell and very tough.

rkepler
11-29-2011, 09:24 AM
I think that it really depends on the failure mode of the original bolts - if they failed from brittle failure you'd want to go with something tougher, if they failed from yield or shear you might swap out some tough for hard. Brittle failure will leave a surface looking kind of crystalline on the break, yield usually has the bolt necked down on each side of the failure, shear can usually be seen by an offset to the join in the bolt.

If it failed on a thread root you might be looking at a difficult replacement - most bolts should have the threads rolled in for strength, single pointing in the thread will make a significantly weaker bolt with the failure point in the threaded section.

That being said I've got 'temporary' fixes holding up 20+ years later, so I'd just make the bolts from the O1 and try to hit the sweet spot in hard/tough.

lazlo
11-29-2011, 09:28 AM
most bolts should have the threads rolled in for strength, single pointing in the thread will make a significantly weaker bolt with the failure point in the threaded section.

Russ, most bolts are thread rolled for manufacturing efficiency, but as Carol Smith points out in his book, most threads are heat treated after thread rolling, which eliminates any strength benefits.

Bolts that have been thread rolled after heat treat are very expensive. Most aircraft (NAS) bolts are made this way.

Here's the How It's Made video of a French Canadian company making high-quality bolts. The threads are rolled at 2:17, and the heat treat process starts at 3:30. The bolts are heated to 870 C, quenched, and then annealed, after they're thread rolled:

http://www.youtube.com/watch?v=3kxcw08p_oY

MotorradMike
11-29-2011, 09:43 AM
You have a tractor with disc brakes?

rkepler
11-29-2011, 09:46 AM
Russ, most bolts are thread rolled for manufacturing efficiency, but as Carol Smith points out in his book, most threads are heat treated after thread rolling, which eliminates any strength benefits.

Bolts that have been thread rolled after heat treat are very expensive. Most aircraft (NAS) bolts are made this way.

There are 'hot rolled' bolts as well that split the difference.

But the point I was trying to make was that a bolt rolled and then heat treated will have better strength in the thread than a bolt that was single pointed and heat treated; so if the failure was in the thread area of a commercial rolled bolt then a single pointed replacement was not likely to be applicable.

(I'm skipping over a million caveats, mostly on the observed failure mode. If a determination was made on that and the original alloy {or bolt grade} then a replacement could be suggested.)

Tait
11-29-2011, 10:07 AM
Question is, is O1 going to be any good for bolt? I'm afraid I might get them too brittle in a homebrew torch'n'dunk treatment.

I guess the real question is how much of an issue would it be if they failed again? If it doesn't really matter, I would heat and dunk then temper.

If you want to avoid grain growth from overheating, which may make it break more easily, it might be worth sending out for a real heat treat. Unfortunately, the heat treaters around SoCal seem to not like treating O1.

Stepside
11-29-2011, 10:20 AM
If I remember correctly the J I Case 580 series backhoes had disc brakes. This would be the the models from the late 1990's. They were an arrangement of some discs with balls and ramps. Not only were they disc brakes, they ran in oil. So yes there are tractors with disc brakes.

The real point is they were noted for having the bolts loosen and then break.
So part of our check the oil and water service was to check the brakes for an oil leak. This was an indication of loose bolts. This is a fifteen year old memory so there could be some errors in actual facts.

hardtail
11-29-2011, 10:31 AM
Some late model International W6/9 models had disc brakes, these would be from the early 50's.........

SGW
11-29-2011, 10:37 AM
I think the first thing I'd do is check McMaster-Carr www.mcmaster.com and see what bolts are available off the shelf from them.

If I had to make some I think I'd use 1144, which has a tensile strength of around 100,000 psi or more. Another choice might be pre-heat treated 4140.

I wouldn't recommend O-1. I don't think it is particularly good for high-strength bolts.

cuemaker
11-29-2011, 01:08 PM
What size bolt?

Tony
11-29-2011, 01:20 PM
so 600* in toaster oven and then let cool to room? or quench?
temper after that? (just curious)

here is a pic of the bolt in question. I haven't been able to find it
locally. One guy told me he'd seen them before and I was going to
have to find a machinist who could make them but expect to "pay through
the nose" (!)

13mm head, 10mm shank, 8mm threads: (about 1.25" long)

http://img.photobucket.com/albums/0903/knucklehead/bolt1.jpg

here's the end view of the break. Looks like failure in tension. Were these
tightened too much perhaps?

http://img.photobucket.com/albums/0903/knucklehead/bolt2.jpg

ignore the deformation on the tip.. that was from trying to get that little
bit out.

-Tony

cuemaker
11-29-2011, 01:31 PM
That head is similar to or the same as a "Wheel bolt"

The fact that the shank is bigger than the threads throws a monkey wrench into the whole shebang.

Steve Steven
11-29-2011, 01:47 PM
That looks a lot like a "shoulder bolt", except for the chamfer under the head. Look in McMaster-Carr at shoulder bolts and see if they have metric ones.

Steve

Carld
11-29-2011, 01:52 PM
If you can get a shoulder bolt that would work you can make a washer with the taper on it, shorten the shoulder to the right length and then shorten the thread if needed and rethread to the shoulder.

A little creative engineering is needed here. Never make what you can buy and modify.

lazlo
11-29-2011, 02:47 PM
so 600* in toaster oven and then let cool to room? or quench?
temper after that?

That's temper. You quench it first, then 500 - 600 temper, depending on what final hardness you want. You can't really over-temper -- just turn the oven off after an hour and let it cool down.

But like Steve and Carl say: it would be much easier to modify a Metric shoulder bolt.

justanengineer
11-29-2011, 02:48 PM
I say go visit your local Cat dealer, buy a bolt with matching total length and thread size, then machine a steel bushing to create the necessary thickness, chamfer/shape etc for the thicker part. You want the bolt's strength first, and its shape is a secondary worry.

Never make something that will likely fail, possibly cause injury (brakes), and be a PITA to remove (broken bolt). You will only be creating needless work for yourself and adding cost, not value.

gwilson
11-29-2011, 03:00 PM
I don't recommend 01 either.

Tony
11-29-2011, 03:58 PM
engineer -- interesting proposition. However my 'bushing' would end up
only 1mm (~0.040") wall thickness.

What if the O1 were professionally heat treated? Would that change this
situation? I'm fine with pro heat treat.

re: modding a shoulder bolt -- that had crossed my mind. but this thing
appears to be hardened.. and I don't believe a shoulder bolt is. and if
I could find a hardened shoulder bolt, I wouldn't be able to modify it.

rklopp
11-29-2011, 04:12 PM
If you are not worried about safety and liability, I'd modify an existing Grade 8 bolt that is not of doubtful pedigree. This could include taking a bolt with shank diameter larger than the distance across the points of the the desired hex head, and simply using the big bolt as bar stock. Grade 8 bolts machine just fine. Keep your cutting surface speed down if using HSS tooling.

mike4
11-29-2011, 05:59 PM
I got beaten to the suggestion of grade 8 or better bolts as a starting point .
.The tapered shoulder on the bolt is it completely enclosed,as I have managed to turn the shoulders down to get so called "specialised" bolts replaced in forklift wheels and axle mounts.
It doesnt need to be full depth as if you dont overtighten the bolt there will be no problems.
Is the stepped thread really necessary or is it used to hold parts at a specific distance apart?
I'll probably be blasted for this but if the manufacturers didnt try to protect their parts by slightly changing what could be readily purchased items to some hard to obtain part only manufactured for a model by some obscure company which has long gone out of business by the time the parts require replacement life would be a whole lot easier.
Michael

Carld
11-29-2011, 08:57 PM
Tony, it doesn't matter how thick the cone washer will be. It's trapped on the bolt and in the tapered hole. It's much better to start with a bolt of known grade and modify it as needed.

lakeside53
11-29-2011, 10:23 PM
I'm betting that's an "off the shelf" item. OK, some dusty obsure European or aerospace shelf, but...

Apart from the cone, it's just a metric hex head shoulder bolt. For tough, 12.9 is the rough equivalent of grade 8. Call one of the specialty Metric importers.

Peter S
11-30-2011, 05:29 AM
As Lakeside said, a socket shoulder screw might do the job. (Edit: Lakeside, oops I see you said hex head, I have not seen those before).

According to my Unbrako catalogue, a 10mm shoulder screw (i.e. M8 thread) is available in the following lengths (i.e. length of 10mm diameter portion): 16, 20, 25, 30, 40mm etc.

Threaded portion is 13mm long.

Head is 16mm diameter x 7mm long with 5mm hex.

They do have a fairly generous undercut where your taper starts though.

BTW, Unbrako shoulder screws are Rc 36-44 (or perhaps Rc 39-43). They are not much fun to machine, but you should be able to machine the taper as per photo (and reduce head OD if required for clearance, 13mm AF is about 15mm diameter I think). If the available lengths match your bolt of course....perhaps if space allows, a slightly longer shoulder bolt with seperate cone machined and slipped on...

Should be available from tool & die or toolroom supply shop.

lazlo
11-30-2011, 10:19 AM
BTW, Unbrako shoulder screws are Rc 36-44 (or perhaps Rc 39-43). They are not much fun to machine,

Yes, but Unbrakos are considerably stronger and harder than stock Grade 8 (or 12.9) bolts. They're the gold standard of fasteners.

Regular grade 8's are in the Rc 33 - 39 range, not much worse to machine than pre-hard.

M_C
11-30-2011, 01:12 PM
What tractor is it?

I've dealt with bolts just like that before, but I can't remember where!