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Posted by woodworker88 on July 21, 2008, 1:47 am
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I am working on restoring my 1918 Wade 8A Precision Toolroom Lathe and
I found that the worm gear which powers the longitudinal feed is
extremely worn and needs to be replaced. A steel worm rides with key
rides on the feedscrew, and is in good shape. The mating worm gear,
however, is brass and is extremely worn. The outer teeth are worn to
the sharp points, and the internal taper that forms a slip clutch to
engage the longitudinal feed is worn such that the clutch no longer
functions.
Replacing this gear would be no problem if it was a standard 24 DP 40
tooth brass worm gear, which is $37 from Boston Gear. However,
according to my best calculations, I have a 22 DP, 42 tooth gear. I
can't simply change to a standard, readily available gear because the
center distances between the feedscrew and the clutch mechanism is
fixed by the lathe's apron.
The options now are basically to have a custom gear made to match the
worn gear and the mating worm, or to attempt to make a replacement
myself. I have a Bridgeport with a large universal dividing head, and
I've made straight spur gears before. The problem is that I haven't
found any 22DP involute gear cutters, so I'd have to start with making
either a single point tool or a multitooth gear cutter first. Then,
because its a worm gear rather than a straight spur, each tooth is
actually concave to the OD. Thus, instead of simply feeding the gear
across the cutter for each tooth, you have to plunge the cutter into
the gear on the centerline.
Any ideas?
woodworker88
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Posted by Bruce in Bangkok on July 21, 2008, 4:17 am
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On Sun, 20 Jul 2008 22:47:02 -0700 (PDT), woodworker88
>I am working on restoring my 1918 Wade 8A Precision Toolroom Lathe and
>I found that the worm gear which powers the longitudinal feed is
>extremely worn and needs to be replaced. A steel worm rides with key
>rides on the feedscrew, and is in good shape. The mating worm gear,
>however, is brass and is extremely worn. The outer teeth are worn to
>the sharp points, and the internal taper that forms a slip clutch to
>engage the longitudinal feed is worn such that the clutch no longer
>functions.
>
>Replacing this gear would be no problem if it was a standard 24 DP 40
>tooth brass worm gear, which is $37 from Boston Gear. However,
>according to my best calculations, I have a 22 DP, 42 tooth gear. I
>can't simply change to a standard, readily available gear because the
>center distances between the feedscrew and the clutch mechanism is
>fixed by the lathe's apron.
>
>The options now are basically to have a custom gear made to match the
>worn gear and the mating worm, or to attempt to make a replacement
>myself. I have a Bridgeport with a large universal dividing head, and
>I've made straight spur gears before. The problem is that I haven't
>found any 22DP involute gear cutters, so I'd have to start with making
>either a single point tool or a multitooth gear cutter first. Then,
>because its a worm gear rather than a straight spur, each tooth is
>actually concave to the OD. Thus, instead of simply feeding the gear
>across the cutter for each tooth, you have to plunge the cutter into
>the gear on the centerline.
>
>Any ideas?
>woodworker88
I've made worm gears by making a cutter to match the worm in size and
shape and then using it to cut the gear. You need to design it to cut
both the top and bottom of the tooth to get the radius. I've made both
a multi tooth cutter by turning a "worm" with clearance and then
milling teeth, and a single point by grinding a large lathe tool into
a fly cutter type tool to machine both sides of the groove between the
teeth and the top of one tooth.
You will have to set the dividing head at an angle to match the pitch
of the worm though.
Bruce-in-Bangkok
(correct Address is bpaige125atgmaildotcom)
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Posted by on July 21, 2008, 12:06 pm
Please log in for more thread options > I am working on restoring my 1918 Wade 8A Precision Toolroom Lathe and
> I found that the worm gear which powers the longitudinal feed is
> extremely worn and needs to be replaced. =A0A steel worm rides with key
> rides on the feedscrew, and is in good shape. =A0The mating worm gear,
> however, is brass and is extremely worn. =A0The outer teeth are worn to
> the sharp points, and the internal taper that forms a slip clutch to
> engage the longitudinal feed is worn such that the clutch no longer
> functions.
>
> Replacing this gear would be no problem if it was a standard 24 DP 40
> tooth brass worm gear, which is $37 from Boston Gear. =A0However,
> according to my best calculations, I have a 22 DP, 42 tooth gear. =A0I
> can't simply change to a standard, readily available gear because the
> center distances between the feedscrew and the clutch mechanism is
> fixed by the lathe's apron.
>
> The options now are basically to have a custom gear made to match the
> worn gear and the mating worm, or to attempt to make a replacement
> myself. =A0I have a Bridgeport with a large universal dividing head, and
> I've made straight spur gears before. =A0The problem is that I haven't
> found any 22DP involute gear cutters, so I'd have to start with making
> either a single point tool or a multitooth =A0gear cutter first. =A0Then,
> because its a worm gear rather than a straight spur, each tooth is
> actually concave to the OD. =A0Thus, instead of simply feeding the gear
> across the cutter for each tooth, you have to plunge the cutter into
> the gear on the centerline.
>
> Any ideas?
> woodworker88
This was a perennial subject in The Model Engineer, a British
magazine. Always someone having to cut odd worms and wheels in there
for various projects. Might be your local library would have back
issues. Two ways of going about it with the average equipment in the
home workshop. One is to make a flycutter and a brass blank, cut the
teeth out one at a time using whatever means for indexing at hand.
Some of the writers used the lathe for indexing and had a separately
driven cutter head mounted on the cross slide, offset at the correct
angle, some used the lathe for powering the cutter and held the blank
in an indexing fixture on the cross slide. Blank was usually held
between centers on a mandrel. The other method was to make a hobbing
cutter from "silver steel"(drill rod) same as the dimensions of the
worm, gashing that and backing off the teeth by whatever means
available, then setting that up to cut the blank. A little more work,
but the resulting teeth would probably better formed. Basically, the
hobbing cutter is mostly doing an Acme-style threading job. Pick your
poison! Going to take some effort no matter what you do.
Stan
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Posted by F. George McDuffee on July 21, 2008, 12:55 pm
Please log in for more thread options On Sun, 20 Jul 2008 22:47:02 -0700 (PDT), woodworker88
<snip>
> Thus, instead of simply feeding the gear
>across the cutter for each tooth, you have to plunge the cutter into
>the gear on the centerline.
>
>Any ideas?
>woodworker88
===========
Before you do anything, review _Gears and Gear Cutting_ by Ivan
Law. This is #17 in the Workshop Practice series [SI model
books) from the UK. All of these books that I have seen have
been very good.
# ISBN-10: 0852429118
# ISBN-13: 978-0852429112
It appears that you are about to discover why your lathe has the
capability to cut DP and module threads in addition to inch and
metric, and how to cut an Acme thread.
While thre are several suppliers of this book in the US two
sources are
http://www.amazon.com/Gears-Gear-Cutting-Workshop-Practice/dp/0852429118/ref=sr_1_1?ie=UTF8&s=books&qid=1216658833&sr=1-1
http://www.campbelltools.com/workshopseries.htm
(about 3/4 down the page on the left)
also
Good luck on an interesting project. Let the group know how you
make out and post some pictures to the dropbox.
Unka' George [George McDuffee]
-------------------------------------------
He that will not apply new remedies,
must expect new evils:
for Time is the greatest innovator: and
if Time, of course, alter things to the worse,
and wisdom and counsel shall not alter them to the better,
what shall be the end?
Francis Bacon (1561-1626), English philosopher, essayist, statesman.
Essays, "Of Innovations" (1597-1625).
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Posted by woodworker88 on July 21, 2008, 5:14 pm
Please log in for more thread options Thanks all very much for the advice. I talked to another machinist at
work today and we decided that a single point flycutter seems to be
the best bet. I have that book on order as of 15 minutes ago.
Thanks
Michael
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>I found that the worm gear which powers the longitudinal feed is
>extremely worn and needs to be replaced. A steel worm rides with key
>rides on the feedscrew, and is in good shape. The mating worm gear,
>however, is brass and is extremely worn. The outer teeth are worn to
>the sharp points, and the internal taper that forms a slip clutch to
>engage the longitudinal feed is worn such that the clutch no longer
>functions.
>
>Replacing this gear would be no problem if it was a standard 24 DP 40
>tooth brass worm gear, which is $37 from Boston Gear. However,
>according to my best calculations, I have a 22 DP, 42 tooth gear. I
>can't simply change to a standard, readily available gear because the
>center distances between the feedscrew and the clutch mechanism is
>fixed by the lathe's apron.
>
>The options now are basically to have a custom gear made to match the
>worn gear and the mating worm, or to attempt to make a replacement
>myself. I have a Bridgeport with a large universal dividing head, and
>I've made straight spur gears before. The problem is that I haven't
>found any 22DP involute gear cutters, so I'd have to start with making
>either a single point tool or a multitooth gear cutter first. Then,
>because its a worm gear rather than a straight spur, each tooth is
>actually concave to the OD. Thus, instead of simply feeding the gear
>across the cutter for each tooth, you have to plunge the cutter into
>the gear on the centerline.
>
>Any ideas?
>woodworker88