1. ## A unique B&S Dividing Head

For years I’ve had a Brown and Sharpe that I’ve primarily used for regular dividing head work. Rarely have I done any helical or spiral indexing. And in all reality, as I think on it, I primarily use my K&T and Cinci dividing heads, there’s only a couple jobs I do on the brown & sharp.

To the point of the story, this week I needed to cut a specific lead on a part, and setup the brown and sharpe. I couldn’t get anything to work out. Part of it was my ignorance in spiral milling, some of it was lacking some pieces parts for the setup.

After a day of making another bracket for a idler gear, messing with gear arrangements and beating my head against the wall trying to get something useful to come out, I finally realized my ignorance.

My dividing head is a 20:1 ratio.

I’ve never heard of a 20:1, let alone a Brown & Sharpe.

2. Then its "master lead" will be 5" when geared 1 to 1 to a four pitch table screw

Sounds like someone's "low lead" work around

3. Yes, I figured that out in a rather backwards manner.

With the part not matching up correctly I started backtracking to figure out what I had done wrong. Everything was correct, and even after trying some different setups, always resulted in the same error.

I ultimately setup an indicator on the chuck face, made one full revolution, and then using a stack of gauge blocks off the chuck face, I found I had exactly half of my expected lead.

Then re checking my setup, everything checked out with one component remaining. The dividing head.

Problem now, is I need 3 of the same gear, to get the correct lead and to reverse the direction.

I can only imagine why someone would special order a 20:1 dividing head, and I can only imagine it served as an easier way to get desired lower leads?

If I remember correctly the gentleman I bought it from said it came out of the Cleveland Twist factory in Cleveland.

4. Say it gives some lead for the gear you want. That 20 to 1 will shorten it by one half. So you gear up for twice the given lead

The "other hand" mate always requires ANOTHER idler in train

Thumbnail is handy page from Mr. Earle Buckingham's amazing books

Originally Posted by Fal Grunt
Yes, I figured that out in a rather backwards manner.

With the part not matching up correctly I started backtracking to figure out what I had done wrong. Everything was correct, and even after trying some different setups, always resulted in the same error.

I ultimately setup an indicator on the chuck face, made one full revolution, and then using a stack of gauge blocks off the chuck face, I found I had exactly half of my expected lead.

Then re checking my setup, everything checked out with one component remaining. The dividing head.

Problem now, is I need 3 of the same gear, to get the correct lead and to reverse the direction.

I can only imagine why someone would special order a 20:1 dividing head, and I can only imagine it served as an easier way to get desired lower leads?

If I remember correctly the gentleman I bought it from said it came out of the Cleveland Twist factory in Cleveland.

5. John, would you mind helping me understand the helix angle a little? From the supplied information, my cutter would have a 12.85 degree angle for using a machine with a fixed spindle. Since I am cutting this on my B&S #2 with a universal head, I offset the spindle to shy of 6.5 degrees. This makes a part that very closely matches the original.

However, I can not match this to any of the math given in Machinery's Handbook. I have another similar job that does not have any supplied information for, that I would like to calculate the correct angles for.

Appreciate the input!

6. It comes from tooth count(s) and center distance. Its always in relation to the pair of gears - they will both have the same angle (one left, one right), but the leads change with the tooth count

Originally Posted by Fal Grunt
John, would you mind helping me understand the helix angle a little? From the supplied information, my cutter would have a 12.85 degree angle for using a machine with a fixed spindle. Since I am cutting this on my B&S #2 with a universal head, I offset the spindle to shy of 6.5 degrees. This makes a part that very closely matches the original.

However, I can not match this to any of the math given in Machinery's Handbook. I have another similar job that does not have any supplied information for, that I would like to calculate the correct angles for.

Appreciate the input!

7. I guess I am not understanding the relationship as to how it applies to what I am cutting. Since I am cutting a helix, or spiral I am not seeing how it applies to the relationship shown by the gears. I understand, and have seen pictures, showing the table offset to match the helix being cut, typically from a gear tooth cutter, or other form cutter. That portion I understand

I know when cutting threads, such as a square thread, or buttress, or other form thread, that you have to match the cutter or work to the helix angle of the thread. I am hoping to figure out how to calculate this for the helix I am working on, to then apply it to future projects. In this current example I was given the answer along with the documentation of the part. The documentation did not include anything as to how they reached that answer. When I do the math in Machinery's Handbook, either Helix Angle or Lead angle of a screw, neither seem to match the numbers provided?

I am clearly missing something but I don't know what IT is to ask the right question.

8. The angle is something you set the swiveling table to (on a Universal) or the company supplied spiral milling attachment (if a Plain)

It has very little to do with successfully milling a helix

To put this another way, if that is all you did you would NEVER get a helix cut

Think of that angle setting as something to ACCOMMODATE what has gone before in getting the DH and its drive set up

You gear this device to travel a very particular distance to make one turn on the DH spindle

This amount of table travel is named LEAD

Lead combined ( in Trig) with (circumference of) pitch diameter of of what ever gear or whatever is being cut is the GENESIS of the angle in question - as far as the machine tool is concerned. We have seen above where the angle came from as far as information - look at Post # 6

Easy to see smaller or larger pitch diameters directly affect LEAD length

Cincinnati published TABLES OF LEADS with over 2800 differing four gear set ups for the DH - and you still only come as close as you can to the LEAD actually wanted.

Originally Posted by Fal Grunt
I guess I am not understanding the relationship as to how it applies to what I am cutting. Since I am cutting a helix, or spiral I am not seeing how it applies to the relationship shown by the gears. I understand, and have seen pictures, showing the table offset to match the helix being cut, typically from a gear tooth cutter, or other form cutter. That portion I understand

I know when cutting threads, such as a square thread, or buttress, or other form thread, that you have to match the cutter or work to the helix angle of the thread. I am hoping to figure out how to calculate this for the helix I am working on, to then apply it to future projects. In this current example I was given the answer along with the documentation of the part. The documentation did not include anything as to how they reached that answer. When I do the math in Machinery's Handbook, either Helix Angle or Lead angle of a screw, neither seem to match the numbers provided?

I am clearly missing something but I don't know what IT is to ask the right question.

9. I understand the lead itself, I’m trying to understand the cutter that is specified for cutting that lead. Since it is a basic helix, not a gear, any cutter can do the required work, why or mathematically how, do you need a tapered cutter(or in my case to offset the head)?

I can only guess, as you showed with the mating gear, it has something to do with getting the two angles to match correctly, but my question remains, where does that number come from? None of the equations I have tried from Machinery’s Handbook give me an angle matching the angle specified.

So either the original designers did something different, or I’m not calculating the numbers correctly, or I’m really not understanding!

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