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Resurecting a B&S rack milling attachment linear dividing unit.

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benmychree

John York
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About 30 years or so ago, I acquired a B&S linear dividing unit to be used with the rack milling attachment; it laid around for all those years until I found information describing the attachment and the calculations for determining the change gears for it, with a list of change gears required and a chart of diametral and circular pitches, this was in a very old Machinery Magazine that came up online; mainly it was a tutorial of the use of continued fractions to determine gear ratios, using the B&S attachment as an example. Having that in hand, I spent about a week part time to make all the gear blanks and cutting the teeth, which were 24 DP and 3/8" wide; this amounted to 1007 teeth, not including a couple of mistakes due to indexing errors and misreading the number of divisions for one gear blank; 98 and 89 look pretty much the same upside down!
Here are some pics of the completed job, although I may have to make a taller bracket to mount the unit on the machine table so that there is sufficient slot height for all the gear combinations.
In the last pic, I show the rack milling attachment, I would like to find one for my machine, which would look a bit different than the one shown, it would have holes on top to fit the twin overarms of a #2 universal light type milling machine.

rack milling attachment 007.JPG

rack milling attachment 008.JPG

rack milling attachment 009.JPG

rack milling attach 001.JPG
 

ThunderDog

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Crank, engage, cut, crank, engage, cut... Oh, the feeling of getting to the end and realizing you missed on the count.o_O
Nice job.
 

benmychree

John York
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The next chapter will entail making a new bracket; I found that the height is too short and does not allow all the larger gears to be used, this is due to it being made for a different model of milling machine.
 

T Bredehoft

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I feel embarrassed that I had never heard of or even imagined a machine that would to that. Now that I'm enlightened I'll be dreaming of uses for it.
Thanks for bringing it to our attention.
 

benmychree

John York
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Its use is described in B&S's book " Practical Treatise on Milling and Milling Machines, around page 75, depending on what edition one has; Also described is the method of doing linear dividing with the dividing head geared to the table screw, that method is capable of a wide range of finely subdivided movements, with tables to detail them with no calculations necessary; I used that method to divide several blacksmith's hook rules that I made for friends, in that case, 10 turns of the dividing head worm shaft equaled 1/16", which should give an idea of the fineness of graduation possible. For the purposed of graduating rules, the rack attachment would speed up that operation quite a bit.
 

ThunderDog

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Having never even used a proper dividing head (saving the pennies to purchase one) would this allow you to make helical gears? The idea being that the rotation of the dividing head is "timed" to the table movement.
 

benmychree

John York
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Having never even used a proper dividing head (saving the pennies to purchase one) would this allow you to make helical gears? The idea being that the rotation of the dividing head is "timed" to the table movement.
Yes, if the dividing head is of the "universal" type, that is if it has a method of driving the worm shaft from the table screw via a gear train. Also required is that the mill has a means of swiveling the table on the saddle or has a "universal" spindle attachment so that the cutter can be oriented to the spiral angle being cut; this is the mission of the "universal milling machine". I have cut a number of spiral gears on mine over the years, most recently a pair of timing gears for a 1 cyl marine engine; the gears had axes at 90 degrees, they were the same diameter with a ratio of 2:1, I am still trying to wrap my head around how that would be possible, but it worked!
 

Janderso

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(Waking up this thread)
""""" I have cut a number of spiral gears on mine over the years, most recently a pair of timing gears for a 1 cyl marine engine; the gears had axes at 90 degrees, they were the same diameter with a ratio of 2:1, I am still trying to wrap my head around how that would be possible, but it worked! """""

I would really like to see that set-up.
 

Superburban

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most recently a pair of timing gears for a 1 cyl marine engine; the gears had axes at 90 degrees, they were the same diameter with a ratio of 2:1, I am still trying to wrap my head around how that would be possible, but it worked! """""
Great! Now I'm going to be thinking how that works, Until I figure it out. Were they different tooth count?
 

benmychree

John York
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Great! Now I'm going to be thinking how that works, Until I figure it out. Were they different tooth count?
Yes, one gear had twice the number of teeth as the other.
(Waking up this thread)
""""" I have cut a number of spiral gears on mine over the years, most recently a pair of timing gears for a 1 cyl marine engine; the gears had axes at 90 degrees, they were the same diameter with a ratio of 2:1, I am still trying to wrap my head around how that would be possible, but it worked! """""

I would really like to see that set-up.
Unfortunately, I did not take any pictures.
 

benmychree

John York
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The job is done by gearing the table screw shaft to the dividing head input shaft, so that the dividing head rotates while the table is feeding, this at a ratio that provided the desired lead for the spiral angle of the gear to be cut. The table of the mill is then swiveled to match that spiral angle, and the teeth cut, one after the other.
With the pair of gears cut, the spiral lead was 4X on one than the other, making it necessary on the one with the shortest lead to use the short lead attachment, and because the table will not swing to such an extreme angle, to use the universal spindle attachment (call it a vertical attachment, but it swivels in all planes) to drive the cutter rather than the main (horizontal) spindle. If you can find a copy of B&S book, "Practical Treatise on Milling and Milling Machines" there are illustrations showing these setups.
 

benmychree

John York
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My go-to copy that I have owned since 1964 is in the process of being rebound by DH, one of his many diverse talents; it has many pages, especially in the tabular data that are afflicted by "mechanic's tan". It is well used to say the least; it was one of several reference books required for our after hours apprentice classes.
I'm sure that as with many other things, it is easier to ask for forgiveness than permission --- I only ever asked and was granted permission to post an article from American Machinist regarding niter bluing, it was posted on HM some time back.
 
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