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Dividing And Indexing Head Project

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A while back, I built an indexing head from aluminum and steel. While not an extremely heavy duty device (which it was not intended to be) it works well. BUT, I have decided to build a dividing/indexing head from steel as a more advanced and heavier duty unit. I would like to use a worm wheel and gear,but the price is just too high to buy them. I have seen some units made using a straight tooth gear such as a change gear in place of the worm wheel. I like this idea for cost and flexibility reasons but how do you make a worm to run the straight tooth gear. Does anyone have any insight into this?
 

John Hasler

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A while back, I built an indexing head from aluminum and steel. While not an extremely heavy duty device (which it was not intended to be) it works well. BUT, I have decided to build a dividing/indexing head from steel as a more advanced and heavier duty unit. I would like to use a worm wheel and gear,but the price is just too high to buy them. I have seen some units made using a straight tooth gear such as a change gear in place of the worm wheel. I like this idea for cost and flexibility reasons but how do you make a worm to run the straight tooth gear. Does anyone have any insight into this?
I think that the angle between the plane of the gear and the axis of the worm has to equal the lead angle of the worm. Thus your worm shaft does not come out quite at right angles to the gear shaft.
 
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I think that the angle between the plane of the gear and the axis of the worm has to equal the lead angle of the worm. Thus your worm shaft does not come out quite at right angles to the gear shaft.
You lost me at the bakery. I have no idea what that means, but thank you.



Edit: ooooh oooh , wait, I think I know what you mean. the shaft and worm won't be 90 degrees with the gear, right?
In all the photos I seen of these, they appear to be 90 degrees.
 
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John Hasler

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You lost me at the bakery. I have no idea what that means, but thank you.
Visualize a screw. Notice that the threads are not quite at right angles to the axis of the screw. That difference is the lead angle. Now imagine engaging those threads with the teeth of a matching straight tooth gear. The threads will now be parallel to the teeth of the gear and so the axis of the screw will not be parallel to the face of the gear but at a slight angle to it. That angle will equal the lead angle of the screw. The screw is your worm.
 

mws

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I believe what John was saying is that if your worm gear axis is angled relative to the straight gear teeth to match the helix angle of the worm's teeth you can pretty much drive the straight spur gear.

Have you considered buying a small reduction drive gear box and using the gears, bearings, body... from that. We have a surplus place here in Manchester, NH that has a shelf full of them for pretty cheap money. Probably a lot cheaper than buying the worm and gears new. And it wouldn't likely be 40:1.
 
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I believe what John was saying is that if your worm gear axis is angled relative to the straight gear teeth to match the helix angle of the worm's teeth you can pretty much drive the straight spur gear.

Have you considered buying a small reduction drive gear box and using the gears, bearings, body... from that. We have a surplus place here in Manchester, NH that has a shelf full of them for pretty cheap money. Probably a lot cheaper than buying the worm and gears new. And it wouldn't likely be 40:1.
I finally figured out what john was saying. To me not being at right angle is a slight problem. More cosmetically than a functional issue.

I believe any ratio can be successfully used if you design the plates around the ratio you use. I could be wrong as Dividing heads always baffled me. I believe 40:1 is the standard, but I have seen other ratios.

i am still working on understanding the plates and the setups.
 

John Hasler

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I believe what John was saying is that if your worm gear axis is angled relative to the straight gear teeth to match the helix angle of the worm's teeth you can pretty much drive the straight spur gear.

Have you considered buying a small reduction drive gear box and using the gears, bearings, body... from that. We have a surplus place here in Manchester, NH that has a shelf full of them for pretty cheap money. Probably a lot cheaper than buying the worm and gears new. And it wouldn't likely be 40:1.
The helix angle references the axis of the worm. It's the complement of the lead angle, which references a plane perpendicular to the axis of the worm. The angle between the worm axis and the spur gear axis would be the helix angle.
 
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If I figured this out correctly. It would take 40 turns of the crank to turn the spindle once And you have a plate with various hole patterns of different numbers. You select a plate with the pattern of holes to to equal the distance in degrees the handle gets turned to give you the correct divisions on the spindle. Am I in the neighborhood here?

So , if you used a 30:1 set of gears, you have to figure the hole patterns to do the same job with the new ratio, correct?
 

tomh

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Mark hope this makes sense

to make a very simple worm gear and wheel all you do is cut a disc mount it on the lathe compound so that it will spin freely but snugly and put a spiral flute tap in the chuck and move the compound against the spinning tap it will spin the disc cutting the tpi on it and then you use a bolt the same thread as the tap. It works very well and makes a very nice worm wheel and worm.
tomh
 

John Hasler

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You lost me at the bakery. I have no idea what that means, but thank you.



Edit: ooooh oooh , wait, I think I know what you mean. the shaft and worm won't be 90 degrees with the gear, right?
In all the photos I seen of these, they appear to be 90 degrees.
Most worm drives have the teeth of the gear angled at the lead angle of the worm.
 

tomh

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Sorry reread your question, please disregard the above.
My ADD, ADHD, dyslexia, senior moment all kicked in at once. o_O
I would like to know that would work as well.
Tomh
 

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There is an article in HSM about fitting a worm drive to a mini lathe mounted indexer. The worm was to drive a module 1 gear - 20deg. pressure angle and tooth spacing approximately 1/8 inch. The lathe tool was ground to a 40deg angle instead of 60, and the threads cut at 8-TPI. The angle and TPI would have to be changed to match whatever gear you choose. While the best way to transmit power between a worm and a spur gear is to angle the worm shaft so that the faces are mostly parallel, a straight on drive will work for the small amounts of power involved.

The higher the ratio, the more tolerant the indexer is to hole place jitter. 40:1 for most indexers, but 90:1 for most rotary tables. If I was to do an indexer (and I probably will later this year), I would do 40:1.
 

rgray

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I think it's time to bite the bullet and build a worm drive... If there was a better gearing way to do it they would be available that way...I's just the smallest package high reduction gearing design available.

I've cut many a spur gear and angled spur gear...so my first thought was build spur gears with 45 degree angled teeth so then the shafts are at 90 degree. But it's just not as nice as a worm drive for a small footprint high reduction gear set.

Since you're gonna cut a lathe spur gear the big gear should be the easy part for you (and me) . basically an angled spur gear with the center of the tooth dished.....the worm is the part that has been intimidating me.
 
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I think it's time to bite the bullet and build a worm drive... If there was a better gearing way to do it they would be available that way...I's just the smallest package high reduction gearing design available.

I've cut many a spur gear and angled spur gear...so my first thought was build spur gears with 45 degree angled teeth so then the shafts are at 90 degree. But it's just not as nice as a worm drive for a small footprint high reduction gear set.

Since you're gonna cut a lathe spur gear the big gear should be the easy part for you (and me) . basically an angled spur gear with the center of the tooth dished.....the worm is the part that has been intimidating me.
I quite agree. This project has to be done inexpensively. And to go buy a worm gear set , it is just too costly. My goal is to make a decent dividing head that won't cost much, that the average hobbyist could build. I try to find ways to demonstrate to hobbyists that they can make quality tooling at a reasonable cost. This is going to be another one of those projects. I have been studying photos of some old dividing heads that were kind of simple and many use a straight tooth gear, I just haven''t figured out how they made the worm fit. ( I need to look at some in person) and some used worm gears. Some of the old heads I have been studying were not 40:1. they vary in the ratio. I think if you design the hole plates to go with the ratio you use, the ratio is not that important. ( at least that is what it seems at the moment) There is an article on Harold Hall's web site that gave me a lot of good information. This head is also not going to be a big honking monster. I want it to fit smaller mills also, and it will tilt to work vertically or horizontally. I have most of my design. The gearing is what is holding me up at the moment.
 
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There is an article in HSM about fitting a worm drive to a mini lathe mounted indexer. The worm was to drive a module 1 gear - 20deg. pressure angle and tooth spacing approximately 1/8 inch. The lathe tool was ground to a 40deg angle instead of 60, and the threads cut at 8-TPI. The angle and TPI would have to be changed to match whatever gear you choose. While the best way to transmit power between a worm and a spur gear is to angle the worm shaft so that the faces are mostly parallel, a straight on drive will work for the small amounts of power involved.

The higher the ratio, the more tolerant the indexer is to hole place jitter. 40:1 for most indexers, but 90:1 for most rotary tables. If I was to do an indexer (and I probably will later this year), I would do 40:1.
I have a rotary table that was made ( where else ) in China and I know it is not 40:1. They make a kit consisting of plates and crank and fingers to replace the hand wheel and convert it to a dividing head. Now since they are NOT using a 40:1 ratio, this was what convinced me that as long as you design the hole plates to work with the ratio you have , it doesn't really matter what the ratio is to a point.

I am looking at using 30:1 as it is what is available.
 
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Another thought I had is to use a piece of acme screw for the worm and cut a gear like I did for the thread dial I made that rides on the acme lead screw of the lathe. that should work .
 
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OK..... I have most of this figured out ....... it's on now.... we gonna make a dividing head anyone can build!
 

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I have a rotary table that was made ( where else ) in China and I know it is not 40:1. They make a kit consisting of plates and crank and fingers to replace the hand wheel and convert it to a dividing head. Now since they are NOT using a 40:1 ratio, this was what convinced me that as long as you design the hole plates to work with the ratio you have , it doesn't really matter what the ratio is to a point.

I am looking at using 30:1 as it is what is available.
I have one of those Chinese tables, too. It is 36:1. 10deg. per turn of the handle. The bearings are bad, the backlash ridiculous, and the center recess not in the center. I don't use it. I keep it as a monument to my unwise thriftiness.

Looking forward to the project.

Larry
 
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The requirements for this dividing head so far are:

1. I will have a spindle that has a 1 1/2-8 thread to match my lathe tooling which also matches my little manual rotary table. This makes tooling interchangeable.
2. The head will tilt 90 degrees so it can be used vertically or horizontally. This is a challenge but I think is do-able with some planning.
3. The spindle will also accept 3C collets. ( 5C are too large to fit in the 1 1/2-8 spindle. however, an ER 40 chuck can be fitted to the front of the spindle.)
4. The plates will also fit on the the spindle for manual indexing and there will be an indexing pin that can be installed . ( I hope). The worm will be removable for this set up.


If there are any ideas for features I have missed , suggestions are welcome.
 
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I have one of those Chinese tables, too. It is 36:1. 10deg. per turn of the handle. The bearings are bad, the backlash ridiculous, and the center recess not in the center. I don't use it. I keep it as a monument to my unwise thriftiness.

Looking forward to the project.

Larry

Wow! mine is nice. It had some backlash , but it adjusted out really well. everything else is good on mine. ( it came from CDCO ). the only thing I think was stupid on their part is if you use it vertically it needs a 1/4" shim under it to keep the hand wheel from hitting the table.
 

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I'd forgotten about the handle! I got mine on the auction site. It was an introductory one for a stupid low price. I have a 6" Phase II on a larger mill now. Got it from the same auction site. The Phase II is sweet. Sometimes it makes sense to pay more.
Larry
 
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Why don't you cut your own worm gear. This guy does it here and build a rotary table.

http://madmodder.net/index.php?topic=7488.0
I have tried that and failed miserably.

The other thing is I want this build easy for any hobbyist to be able to do. I don't think making the gears will accomplish that. for this reason, using acquired gears will be the plan. getting gears from an old gear box seems the best idea to keep the simplicity desired.
 
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Once this build starts, this project will move to a new thread in members projects. I will let you all know when this happens.
 

benmychree

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If I figured this out correctly. It would take 40 turns of the crank to turn the spindle once And you have a plate with various hole patterns of different numbers. You select a plate with the pattern of holes to to equal the distance in degrees the handle gets turned to give you the correct divisions on the spindle. Am I in the neighborhood here?

So , if you used a 30:1 set of gears, you have to figure the hole patterns to do the same job with the new ratio, correct?
It may be worth it to buy the worm and worm gear in the standard ratio of 40:1, because the tables that give the info. for turns and holes on the dividing plate are easily available in most machinist's handbooks. The other common ratio, especially in larger units is 90:1, and this table of info is much less available. A good reason not to select a straight toothed spur gear is that there is only a slight line contact between the worm and gear, hence much faster wear to the gear and worm resulting in backlash. To further complicate things, the spur gear you would select will be of diametral pitch, while it would need to be circular pitch, which is not available commercially, and which you would not be able to cut the worm to match it without a stack of odd change gears, some probably prime numbers not available commercially, and not possible to cut with a dividing head that does not have a differential indexing feature, which most do not.
Using a commercially available gearbox is problematic due to most of them being not of even ratios because of the need to use odd numbers of teeth to avoid the same teeth meshing over and over at nearly every revolution, that is odd ratios are used to cause a "hunting" action so that wear is spread over all the teeth in the gear train.
 
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I have done a lot of research on the dividing head lately and you are somewhat correct that ideally , 40:1 would be the way to go. You are missing the point of the project. This will be how any hobbyist can make a pretty good dividing head at a MINIMAL cost and not be too difficult. Yes, I could go to Boston gear and order a worm set for 150 to 250 dollars, but then I might as well go the extra couple hundred and buy a Chinese dividing head.

I have found dividing heads with many different ratios. some of the really old simple ones had odd ratios. some of the new imports have a ratio other than 40:1. I am guessing that is why there are so many plate sets that work on various heads. If the 40:1 was a standard (which it sort of is) you would only need one chart. All the companies do something to make their plates proprietary, be it the mounting method, the size or where they get mounted. My plates will be proprietary because of the ratio. It is all a mute point. There is absolutely nothing wrong with the 30:1 ratio. I have already figured the needed hole patterns for most of the common hole circles encountered and they will also cover many more. I intend to keep developing the needed plates to cover most divisions. There is no problem as long as the plates and chart made are used on a 30:1 dividing head.

This thread is done . there will be a new thread started in members projects to cover the building of a simple dividing head.
 

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