[AT] Drill size for bolt tap question

[Al Jones]

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
>>>>
>>>>
>>>> _______________________________________________
>>>> AT mailing list
>>>> http://www.antique-tractor.com/mailman/listinfo/at
>>> _______________________________________________
>>> AT mailing list
>>> http://www.antique-tractor.com/mailman/listinfo/at
>>>
>> _______________________________________________
>> AT mailing list
>> http://www.antique-tractor.com/mailman/listinfo/at
>
> _______________________________________________
> AT mailing list
> http://www.antique-tractor.com/mailman/listinfo/at
>
> _______________________________________________
> AT mailing list
> http://www.antique-tractor.com/mailman/listinfo/at