[AT] Drill size for bolt tap question

Cecil Bearden crbearden at copper.net
Sun Apr 16 18:30:44 PDT 2017 

Mounting for a sickle mower sounds like what wobbled the holes out.   
Those old mowers vibrated the entier machine.  I remember mowing with an 
old IHC sickle mower that was supposed to mount to the Old tractors with 
the drawbar that mounted at each wheel gearbox.  Dad took off the mower 
drawbar and put lift pins in it, and we used it as a 2 point  hitch 
behind a TO-35 Massey Ferguson, the grey one.  If you sat on it all day, 
you were still vibrating when you went to bed.  It usually broke 
something about 2 rounds before finishing the field.  Drive shafts and 
pitmans were the usual casualty.  I remember my uncle, the cabinet maker 
& carpenter, making spare pitmans out of leftover Ash from cabinets he 
had torn out.   The ones he made lasted a lot longer than the IHC ones.

Cecil in OKla


On 4/15/2017 6:27 PM, Al Jones wrote:
> Charlie,  that is an important thing to think about.  I >>think<< the
> holes are in the right place.  I'm going to do some measuring before I
> start buying supplies.....There are remains of threads in the holes, I
> think somebody stripped them out and got carried away trying to go to
> a size bigger.
>
> The holes correspond to the bolts that hold the fertilizer attachment
> on a Super A, except they're on the other side.  Chances are nothing
> will ever be attached there, but if I ever get a wild hair I want them
> right.  The po said their uncle had some sort of sickle mower on it
> and I think part of it mounted there.  Looks like they didn't keep
> stuff tight......
>
> By the way, the holes on the other side are also bad, but I think
> they'll hold a 5/8" helicoil.
>
> Al
>
> On Sat, Apr 15, 2017 at 6:24 AM, charlie hill
> <charliehill at embarqmail.com> wrote:
>> Al,  I like your solution and particularly John's suggestion of
>> using a bolt as an insert.  I only have one question.  What is
>> this hole for?  Does something mount to it?  If so you are going
>> to have to be very careful to get it properly centered to the old
>> location relative to the rest of the torque tube and other holes
>> that might be involved in whatever attaches.   Since the original
>> hole is now somewhat wallowed out you don't know where the old
>> center is..... do you?  You could easily be off by as much as 1/4".
>>
>> If that is an issue, you might need to put the plug in place (bolt or
>> whatever you use) and then drill and tap it in place.   You might
>> have already addressed this issue.  If I missed it just ignore me.
>>
>> Charlie
>>
>> -----Original Message-----
>> From: Al Jones
>> Sent: Friday, April 14, 2017 3:05 PM
>> To: Antique tractor email discussion group
>> Subject: Re: [AT] Drill size for bolt tap question
>>
>> I've been doing some more checking.  The helicoil kits I found online
>> are insane expensive.
>>
>> It looks like I could take the hole out to 63/64" without messing up
>> the boss on the side of the housing.  That would accommodate a 1 1/8"
>> coarse thread.  I found solid threaded inserts in that size, but
>> they're fine thread which requires a slightly bigger hole, etc. etc.
>> etc.  Plus they're also insanely expensive. My notion is to see if I
>> can get a machine shop to make me an insert with 5/8" internal threads
>> that will screw into a 1 1/8" threaded hole.  The question is if I'd
>> just be better off to take it to a machine shop and let them do it
>> all:  The cheapest 63/64" bit I could find was around $40, a 1 1/8"
>> tap is on up there too.
>>
>> Al
>>
>> On Fri, Apr 14, 2017 at 1:18 PM, charlie hill
>> <charliehill at embarqmail.com> wrote:
>>> A 1" -8 heli-coil requires a 1 1/32" hole.
>>>
>>> https://www.carid.com/images/heli-coil/pdf/heli-coil-catalog.pdf
>>>
>>> -----Original Message-----
>>> From: John Hall
>>> Sent: Thursday, April 13, 2017 9:54 PM
>>> To: Antique tractor email discussion group
>>> Subject: Re: [AT] Drill size for bolt tap question
>>>
>>> Biggest form tap I stock is about 1/2" or 12mm. I wasn't suggesting
>>> using one, just pointing out to use the correct calculator. I posted
>>> this link because it actually works.  There are a LOT of tap charts with
>>> bad info--they round the hole sizes to aprox. 5% increments. I have even
>>> found charts that just flat out missed the hole sizes. The best chart I
>>> have ever found was one put out by Cleveland 30 years ago--it lists
>>> actual percentages. I'm anal about threads as most everything we do has
>>> to be gaged.
>>>
>>> Biggest cut tap I have ever used was an M30---hit it heavy with
>>> Moly-Dee, shut the doors and backed way up. We had enough HP fortunately
>>> to get it done.
>>>
>>> John
>>>
>>>
>>> On 4/13/2017 8:15 PM, Stephen Offiler wrote:
>>>> OSG is excellent stuff.  We use a lot of OSG and Emuge.  But for CF taps
>>>> (CF stands for "cold-forming" meaning they force metal into the shape of
>>>> a
>>>> thread without creating any chips) I can't imagine a 1"-8 even being a
>>>> thing.   Judging from experience up to 3/8" CF taps into aluminum, a 1"
>>>> CF
>>>> tap would take a stunning amount of spindle HP.
>>>>
>>>> SO
>>>>
>>>>
>>>> On Thu, Apr 13, 2017 at 4:32 PM, John Hall <jtchall at nc.rr.com> wrote:
>>>>
>>>>> This is what I use all the time at work--be sure to use cut taps, not
>>>>> form taps!!!!!!!!!!!!!
>>>>>
>>>>> http://www.osgtool.com/Technical.asp?tid=1&id=1
>>>>>
>>>>>     For most threads 67-75% is about average. A couple notes--drill bits
>>>>> almost always drill oversize--especially being used in a hand drill.
>>>>> Stainless steel and tool steels can be hard to tap so use a lower
>>>>> percentage. Some thread sizes calculate to the point there is no "good"
>>>>> drill size--sometimes metric/english drill is substituted, or the hole
>>>>> is milled or bored as needed. Having said all that, a 1"-8 hole with a
>>>>> 15/16 drilled hole will produce only 39% of thread--absolutely horrible.
>>>>> No amount of Loctite will remedy that. You will need some sort of epoxy
>>>>> to take up the slack.
>>>>>
>>>>> There are some threaded inserts that use a larger than normal drill
>>>>> size--I think McMaster Carr carries t
>>>>> hem.
>>>>> John Hall
>>>>>
>>>>> On 4/13/2017 2:23 PM, Al Jones wrote:
>>>>>> I've got some wallered out holes on a Farmall Super A torque tube that
>>>>>> I
>>>>>> want to fix.  They need to be 5/8" coarse thread, but somebody stripped
>>>>> 'em
>>>>>> out, then did some sort of funky drilling, and now my holes are 15/16"
>>>>>> in
>>>>>> diameter.  I'd like to fix it myself but the longer I look at it the
>>>>> more I
>>>>>> fear a machine shop visit is in order.
>>>>>>
>>>>>> My notion is to try to tap the holes for a threaded insert.  If I drill
>>>>> the
>>>>>> holes out any larger for a larger tap, it's going to eat away the
>>>>>> square
>>>>>> boss on the side of the torque tube, so I want to avoid that. Now, the
>>>>>> chart I am looking at says you need a 7/8" hole for a 1" tap. That
>>>>>> means
>>>>>> the existing holes are 1/16" too big.  Can I still tap it with the 1"
>>>>> tap,
>>>>>> Loctite the daylights out of the insert, and get it to hold? These
>>>>>> holes
>>>>>> are on the left side, and there weren't many implements that used these
>>>>>> holes, plus it's going to be mainly a show/plow day tractor.  But I do
>>>>> want
>>>>>> them functional and they have to "look good."
>>>>>>
>>>>>> I have a good torque tube, but this is an early (probably built the
>>>>>> first
>>>>>> or second day of 1950 production) white demonstrator tractor, so I'm
>>>>> trying
>>>>>> to keep the castings original.
>>>>>>
>>>>>> thanks!
>>>>>> Al
>>>>>>
>>>>>>
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