[AT] Drill size for bolt tap question

[Stephen Offiler]

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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