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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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#1
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.
 

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ThunderDog

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#2
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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#4
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!
 
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