[AT] Drill size for bolt tap question

Fri Apr 14 21:57:37 PDT 2017

A 1in tap from wholesale tool co.  www.wttool.com is $43.90 plus 
shipping.  A 7/8 in bit reduced shank is $22  Most farm supply stores 
have grade 2 bolts.  You could drill and tap for the 1inch bolt, and 
drill the bolt for whatever size you need.   A lathe would be preferable 
to drill the bolt with, but It can be done on the tractor with a hand 
drill.   I would definitely use loctite. Also if using a 7/8 to drill 
the hole, be very careful and use lots of tapping fluid when tapping./  
I usually go at lease 1/64 larger than the recommended size to prevent 
breaking taps.   This looks cheaper to me than going to a machine shop.  
Their minimum charge will exceed the price of tap and bits.

Cecil in OKla

'

On 4/14/2017 2:05 PM, Al Jones wrote:
> 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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