Drill Press Repair

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Subject Author Date
Drill Press Repair John L. Weatherly 04-22-2008
Posted by John L. Weatherly on April 22, 2008, 5:03 pm
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 My father-in-law has well broken in drill press that he wants me to repair.
He told me it was built in 1918. It says "CANEDY OTTO MFG CO" on the side
of the column. Flat belt driven. Has a counterweight inside the column
with a chain attached to the quill. Has all kinds of open gearing on it.
Has been retro-fitted for an electric motor.

The problem is the gear that engages the rack gear on the quill is stripped.
That means no feedy up or down. The shaft the gear is machined on is in
good shape. It looks looks like they machined the entire shaft and
shouldered up to the gear. Weird.

Two questions:

1) Should I build up the gear with weld and machine it down, or machine the
gear separately & silver solder it on? I have lathe capabilities as well
as a 25" Smith & Mills shaper with a dividing head on the way (generous
payment [gift] for the job.

2) How the hell do I reverse engineer the worn gear? I can count the teeth,
but that's about it. The rack gear on the quill is in decent shape. I'm
sure there is an equation three pages long for it, I'm just ignorant about
gears.

What do y'all think?

--
John L. Weatherly

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Posted by Jim Wilkins on April 22, 2008, 5:52 pm
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 On Apr 22, 5:03=A0pm, "John L. Weatherly"
> My father-in-law has well broken in drill press that he wants me to repair=
.
> He told me it was built in 1918. =A0It says "CANEDY OTTO MFG CO" on the si=
de
> of the column. =A0Flat belt driven. =A0Has a counterweight inside the colu=
mn
> with a chain attached to the quill. =A0Has all kinds of open gearing on it=
.
> Has been retro-fitted for an electric motor.
>
> The problem is the gear that engages the rack gear on the quill is strippe=
d.
> That means no feedy up or down. =A0The shaft the gear is machined on is in=

> good shape. =A0It looks looks like they machined the entire shaft and
> shouldered up to the gear. =A0Weird.
>
> Two questions:
>
> 1) Should I build up the gear with weld and machine it down, or machine th=
e
> gear separately & silver solder it on? =A0I have lathe capabilities as wel=
l
> as a 25" Smith & Mills shaper with a dividing head on the way (generous
> payment [gift] for the job.
>
> 2) How the hell do I reverse engineer the worn gear? =A0I can count the te=
eth,
> but that's about it. =A0The rack gear on the quill is in decent shape. =A0=
I'm
> sure there is an equation three pages long for it, I'm just ignorant about=

> gears.
> John L. Weatherly

I think the angle of the sides of the rack teeth is the pressure
angle. Common values are 14-1/2 and 20 degrees.

An old technique for copying gear teeth is to make a crude oversized
gear out of thin lead and roll it against the good gear until the
center distance is correct. Then grind a shaper bit to fit the gap
between lead teeth.

Jim Wilkins


Posted by Ned Simmons on April 22, 2008, 6:14 pm
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On Tue, 22 Apr 2008 14:52:32 -0700 (PDT), Jim Wilkins

>On Apr 22, 5:03 pm, "John L. Weatherly"
>> My father-in-law has well broken in drill press that he wants me to repair.

>>
>> 2) How the hell do I reverse engineer the worn gear?  I can count the teeth,
>> but that's about it.  The rack gear on the quill is in decent shape.  I'm
>> sure there is an equation three pages long for it, I'm just ignorant about
>> gears.
>> John L. Weatherly
>
>I think the angle of the sides of the rack teeth is the pressure
>angle. Common values are 14-1/2 and 20 degrees.

Yes. And the number of teeth per inch is the pitch. If you're lucky
it'll be a standard spur gear. In which case I'd buy the proper gear
from Boston Gear, Union Gear, or Martin. You can verify you've picked
the right gear by comparing the center distance between the shaft and
rack with the catalog value. The numbers are also in Machinery's
Handbook.

Turn down the shaft a bit below the teeth of the old gear, bore the
new gear for a shrink fit onto the shaft, and taper-pin it in place.
Or some variation based on the actual design of the shaft.

>
>An old technique for copying gear teeth is to make a crude oversized
>gear out of thin lead and roll it against the good gear until the
>center distance is correct. Then grind a shaper bit to fit the gap
>between lead teeth.

Cute!

>
>Jim Wilkins

--
Ned Simmons

Posted by John L. Weatherly on April 23, 2008, 12:03 pm
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Ned Simmons wrote:

> On Tue, 22 Apr 2008 14:52:32 -0700 (PDT), Jim Wilkins
>
>>On Apr 22, 5:03 pm, "John L. Weatherly"
>>> My father-in-law has well broken in drill press that he wants me to
>>> repair.
>
>>>
>>> 2) How the hell do I reverse engineer the worn gear?  I can count the
>>> teeth, but that's about it.  The rack gear on the quill is in decent
>>> shape.  I'm sure there is an equation three pages long for it, I'm just
>>> ignorant about gears.
>>> John L. Weatherly
>>
>>I think the angle of the sides of the rack teeth is the pressure
>>angle. Common values are 14-1/2 and 20 degrees.
>
> Yes. And the number of teeth per inch is the pitch. If you're lucky
> it'll be a standard spur gear. In which case I'd buy the proper gear
> from Boston Gear, Union Gear, or Martin. You can verify you've picked
> the right gear by comparing the center distance between the shaft and
> rack with the catalog value. The numbers are also in Machinery's
> Handbook.
>
> Turn down the shaft a bit below the teeth of the old gear, bore the
> new gear for a shrink fit onto the shaft, and taper-pin it in place.
> Or some variation based on the actual design of the shaft.
>
>>
>>An old technique for copying gear teeth is to make a crude oversized
>>gear out of thin lead and roll it against the good gear until the
>>center distance is correct. Then grind a shaper bit to fit the gap
>>between lead teeth.
>
> Cute!
>
>>
>>Jim Wilkins
>

I appreciate all the replies. Here are some photos:

http://b.imagehost.org/view/0594/mvc-383f.jpg
http://b.imagehost.org/view/0594/mvc-384f.jpg

I had thought about the boring an existing gear idea, but as you can see,
the whole depth of the gear is only slightly larger than the shaft
diameter. I like the shrink fit idea. Maybe I could make it in three
pieces? The good news is there is one good tooth profile left.
--
John L. Weatherly

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Posted by spaco on April 22, 2008, 7:53 pm
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It looks looks like they machined the entire shaft and
> shouldered up to the gear. Weird.
---------------------------------
>
It might be worth taking a closer look. And maybe asking some more
specific questions about this part. I would think that even back then
they'd have wanted to use a different material for the shaft and for the
gear.
Take the machine apart, clean up that shaft completely and look at it
for a couple of days. Take some pictures and post them.
You might find a pin or two that were strategically placed . The
head may have been carefully filed to match some other feature, making
it hard to see under a lot of grime.

These machines are often called "camelback drill presses". Searching
for such a thing may shed a little light on the subject, or give you a
clue as to where to go next.

Pete Stanaitis
---------------------

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