How to Use a Dividing Head

hi everyone today I'd like to talk a little bit about dividing heads dividing heads are used when making any feature that involves dividing up the circumference of a part or the face of a part such as gears splines graduated dials wrench flats bolt hole circles or complex angles they work by using a combination of gear reduction and dividing plates which contain circles of holes that allow you to make partial turns of the spindle most of the time you see a Chuck mounted on them that they could have a center and a tail stock on the other end you have a crank handle here that has a pin that drops into our dividing plate and this can be moved up and down in this slot to go between the different circles of holes now this is actually attached to the worm that drives the worm gear that turns the spindle lastly you have these sector arms here and these are two pieces you can undo the screw here and you can slide these apart the sector arms are used to mark which holes are going to be used so you don't have to count every single time which could of course lead to an error there are three different ways to use a dividing head to index a part you have direct indexing which I've talked about in my videos on the spin indexer and the horizontal vertical collet indexer differential indexing which allows you to make a gear or spline or various other things basically it allows you to divide up the circumference of a part or the face of apart and then angular indexing moving apart a specific angle to the next feature indirect indexing you use the holes that are in the spindle of the head itself rather than the gear reduction on the dividing plates most dividing heads are going to have a direct indexing capability and most of them are going to have a row of 24 holes on the spindle different dividing heads will have different numbers potentially 24 seems to work pretty well but I've seen other dividing heads that have multiple rows so that you can get different indexing possibilities the important thing to remember is that you can index to any factor of the number of holes so if you had 36 holes like the spin indexer that I showed in one of my other videos you can index 2 3 4 6 9 12 18 and 36 divisions some dividing heads have an allowance where you can disconnect the worm drive and that allows you to spin the chuck freely and makes it a little bit faster this head doesn't have that capability but it does allow you to lock the indexing pin on the handle in the up position which lets you just turn in which case you would use this pin to find an available hole just like that you would make your first cut and let's say you wanted 12 divisions you would go to every other hole on the plate and drop the pin back in and then you'd make your second cut and it would go exactly the same as the other direct indexing devices that I've shown in previous videos for differential indexing the first thing you need to know is the gear ratio of the dividing head most dividing heads use 40 to 1 reduction meaning it takes 40 turns of this crank to make one turn of the spindle 60 to 1 is also used occasionally and there's also a couple of brands out there that use 72 to 1 you might also find dividing plates on rotary tables and those almost always have ninety to one gear reductions if you buy a dividing head and you don't know what the gear reduction is it's pretty easy you can just put a mark at the top of your Chuck and then turn the handle and count how many times it takes for that mark to return to the top position once you know your gear reduction you can use it to find how many turns of this handle and partial turns you need in order to get that number of divisions on your part to do this you're going to have to use 4 actions Braca hmm excuse me fractions to do this you make a fraction using the gear reduction and the number of divisions you want to make so the gate reduction goes in the top number the numerator and the number of divisions you want goes in the bottom in this case we have a forty to one dividing head so 40 will be in our top number and the number of divisions we want will be in the bottom for example if we were trying to cut two hundred graduations on a dial the fraction would be 40 over 200 the next step would be to reduce that fraction to its lowest common denominator right off the bat you can drop zeros and you get four twentieths which can be further reduced to 1/5 you need to make 1/5 of a turn on this handle in order to get 200 evenly spaced divisions around the circumference of your part in order to do that we need to use our whole plate to make partial turns in this case this plate does not have a circle that's divisible by 5 so we would have to swap this out and go to a plate that does let's say one of our circles though had 15 holes in it we can get 1/5 of a turn out of 15 holes and 1/5 of 15 is 3 so if we were doing that we would set this up we would not count the hole that the pin is in and we would count 1 2 3 from there and we would move our sector arms up so that it marks the 3rd hole once we have this set up we could go ahead and start making our cuts we would make our first scribe line on the part move our three holes move our sector arms make our second cut and so on so forth until we got two hundred equal divisions and this is just for illustration purposes because again this circle is not divisible by five and I don't have one that is on the plate in another example let's say we wanted to machine a hex on the end of a bolt our fraction would now be 40 over six which would reduce to six and four sixths which reduces further to six and two-thirds this means there will be six complete terms of this handle and then two thirds of a term between each division in this case we have holes that are 33 27 and 21 in here and all of those are divisible by three that means we can get 2/3 of a turn out of 21 1/3 is 7 so 2/3 is going to be 14 holes the hole that I'm in right now is a circle of 27 so 2/3 is going to be 18 holes in that one and then if we were in the 33 whole circle just by moving the slider up 2/3 would be 22 holes like I said I'm in the 27 whole circle so let's go ahead and mark this out for 2/3 of a turn of 27 like I said before you don't count of the hole that the pin is in so you would start immediately to the right of that and we would have 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 so right there that is 2/3 of the 10 and now we tighten up our sector arm again the screw just keeps the sector arms moving as a unit they are two pieces that overlap now that we have that set up we would have our part in the chuck we'd make one cut across it to make our first flat we'd make six complete turns there's one two three four five six and then we'd bring it on up to here and I like to start dropping it in a little early so I don't accidentally move too far these do have backlash in them once you drop your PIN in move your sector arms around so that they mark the next hole and you would take your second cut and then repeat the process don't forget to move your sector arms that's probably the most common mistake besides math errors you would continue this process until you finally have a hex on the end of your bolt for angular indexing you need to know how many degrees the spindle turns with each turn of the handle that's found by dividing 360 the number of degrees in a circle by the gear reduction so on this 42:1 head that would be 9 degrees per turn of this handle 360 divided by 40 if you had a sixty to one head it would be six degrees 360 divided by sixty seventy two to one gives you five degrees per turn and ninety to one gives you four degrees per turn now that you have that information you can make another fraction except it's a bit different this time it's the number of degrees you want over the number of degrees per turn of the handle if we wanted to make two holes that are 22 degrees apart we would use the fraction 22 over nine that reduces down to two and 4/9 so we need to do to complete terms of the handle and 4/9 of a turn the rest of the procedure is exactly the same as differential indexing in this case we're in the 27-hole circle so we can get 4/9 of a turn we just have to figure out what 4/9 is we know that 1/9 of 27 is 3 so 4/9 to 27 would be 12 holes so we'll loosen up our sector arms again they can move now we just count out our holes again we're starting to the one to the right of the pin not the one that the pin is in uh power sector arms now stuff to move the handle out of the way a little bit and we're ready to go I'll go ahead and get it set up over here in that example we would do two complete turns one two and then move it up to our sector up once it drops in we move our sector arm and we make our next cut I'm going to put a couple of links down in the description one of them is going to be the handout that I give my class on dividing heads and other indexing tools and the other one is a little practice sheet that I give them it's just a table set up in word that tells you what the gear reduction is and gives you some random division numbers and the types of holes that you have available to you if you have any questions about how these things work or you just don't understand what I said and need some clarification drop me a line down below in the comment section also please consider liking and subscribing if you haven't done so already thanks for watching and I'll see you next time

Channel: Stuart de Haro

Views: 51,400

Rating: 4.9133129 out of 5

Keywords: Machining, Machine Shop, Machinist, Milling Machine, Metal Lathe, Machine tools, Dividing head, indexing head, indexing, gears, splines, hex

Id: 9phmqh1jYPs

Length: 11min 40sec (700 seconds)

Published: Tue Oct 22 2019

Reddit Comments

[u/M3at_Waffle]

I just finished making this video for my class at the community college and thought some of you may be interested in it too. Cheers!

[u/kpidhayny]

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