[AT] Drill size for bolt tap question

Sat Apr 15 16:27:49 PDT 2017

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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