Question on using a Hardinge Universal Divding head

Pretty simple question I think, but couldn't find the answer in the recent thread, "Universal Dividing Head" or a search of the archives.

I recently aquired a Hardinge universal dividing head. The question I have is how to engage the spiral drive on the dividing head. In other words, when I turn the manual handle of the dividing head to turn the spindle, the input power shaft used when cutting spiral gears doesn't move. It's like it's in "neutral". It's like the manual input shaft and the power input shaft are disengaged.

I would think these two shafts are connected inside the dividing head, perhaps with some sliding gear which locks and disengages the two inputs? I don't know how to lock or unlock them.

Here is a pick of the input power shaft.

The spiral drive is permanently geared to the indexing plate. Loosen the clamp ring that surrounds the plate and you will see that now the spiral drive shaft will cause the plate and the spindle to rotate. I have one of the UM dividing heads, but have never used it, so I can only say that there is an instruction book on them that you should look up.

Larry

Thanks so much Larry. I did what you mentioned and of course it worked as you indicated. I wouldn't have thought that the spiral drive is geared to the indexing plate, but it makes sense once one really thinks about it. The spiral drive turns the index plate. The manual input crank locks in the index plate, which then turns the spindle. Then one indexes to cut the next gear tooth by advancing the manual crank to the next correct hole on the index plate, as with regular indexing. Makes perfect sense.

Of course I can see the clamp ring would be removed (rather than loosened) when actually using the spiral drive.

I'd like to get the manual. I see reprint for sale for 30 bucks on the internet. I understand it used to be available as a free download, but I don't think it is anymore.

Thanks again for the explanation. Extremely helpful.

I have a photocopy of the dividing head manual and it is not worth $30. PM me your address and I will mail a copy to you.

Larry

I ran into another issue on this dividing head. The 3 screws which fasten the index plate to the dividing head were apparently missing at some point. So the person who owned it before me, stuck some smaller diameter screws to hold the plate on. Fortunately he used brass screws so the internal threads of the dividing head are still good.

However, I'm apparently having the same problem the guy before me had. Namely, I can't find these screws anywhere. They are 12-28 flat head screws. They are the standard 82 degree heads. Googling for an hour or so, I can't find where to buy them, unless I buy in wholesale quantities. Many websites list these screws, but looking closely they show they are out of stock.

I've checked all the usual suspects like McMasterCarr, MSdirect, etc. Nothing, no matter if it's flat head slotted, flat head phillips, or flat socket head. I wouldn't think 12-28 would be so hard to find, but I can't find any.

Any ideas on where I could get a few of these would certainly be appreciated.

Btw, thanks again Larry for sending that manual. I haven't received it yet, but will be looking for it in the mail, and will remunerate accordingly.

The OEM screws are machine made and hardened with slotted heads. The heads are not standard diameter or thickness. If I had to have some, I would make them from O1, but not harden them. I just took a look at my heads to check the screws. The only one with no plate mounted at present is also the cleanest and newest looking, though the serial number is not high. Anyway, the plate screws look like 12-28 x 1/2" flat head hex socket cap screws with under size 3/32" hex that had the heads faced off to fit the plate countersink. The hex socket appears to be deep enough to work OK. Now I wonder if these screws were a Hardinge replacement part made from a special order screw or made by a previous owner. Anyway, 12-28 flat head screws are hard to find.



This is supposed to be a source of 12-28 x 1/2" flat head hex socket cap screws, with 1240 on hand. They probably have the standard 1/8" hex. You have to contact them and see how many they will send for their $25 minimum sale. If you get a handful, maybe you could sell me a few.
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You asked about the indexing plates. Hardinge lists the seven plate part numbers for a set, but you have to ask them how many thousands of bucks for them to make one. The last two digits of the part number is the number of holes in the smallest circle, usually there are three circles. So the first plate is marked PA-17 and has 17, 18 and 19 holes.


Larry

A word to the wise about force used to clamp the dividing plate when the head is used in the regular fashion: Do NOT over-tighten the clamp screws at the top. The cast-in bosses at the bottom are more fragile than you think. It's not unusual to see these heads with one of the bosses snapped off, typically the thinner one.

Thanks Larry!

I'll give them a call this week. If I can get some 12-28 screws, I will send you some. I had noticed these screws had custom made heads. Actually I have two Hardinge dividing heads (one universal and one semi-universal) The semi universal one has the correct flat socket head screws shown in your pictures 2 and 3. What I had intended to do is if I can get some flat head 12-28 screws,I planned to face them off so that they were flush with the index plate, then cut a slot in them, exactly as shown in your first picture.

If I can't get any 12-28 screws, I was thinking of taking some regular zinc coated 5/16 flat head screws, turn them down to the correct size to accept a 12-28 die (0.212 to 0.216"). Thread them, then face off the heads to fit the index plate countersink, then slot them. That was my thought anyway. I've never made screws before, so I don't know if it takes special dies to thread completely up to the head of the screw. I assume since dies have an internal taper on the thread cutters, a standard die won't cut correct threads completely up to the head of the screw?

jim rozen said:

Do NOT over-tighten the clamp screws at the top. The cast-in bosses at the bottom are more fragile than you think. It's not unusual to see these heads with one of the bosses snapped off, typically the thinner one.

Click to expand...

Thanks Jim, I had read that before, and I too have seen at least one Hardinge dividing head on ebay with the lower boss snapped. I've been pretty careful because of this. Just barely snug the clamp screw with an allen wrench. I'm sure it hardly takes any torque to hold the index plate in the clamp ring. Probably twisting the knurled socket head cap screw by hand would be enough.

Larry, thanks for the info on the plates. I'm missing plate PA-27 out of one complete set to use for both dividing heads. I thought I remember reading some people made even more plates so they could have more than 360 divisions, which, as you know,is the max number with the standard set of Hardinge PA plates.

Just happens there is ONE original screw on ebay right now...

Hole Plate Screw for Hardinge Dividing Head (12-28) | eBay

Irby

Some time ago some kind soul, likely a PM member, sent me a print of the screw. I tried to post it, but it is too large. Pm me, and I can email you a copy.
John

Thanks Irby. I see the seller wants $20 for a screw. These things must really be valuable!

Thanks to you John Allan for the kind offer. Actually I have 3 of the original screws in my other Hardinge dividing head, so I have a pattern of what they are supposed to be like.

Larry, I did get a hold of that business you mentioned and ordered 100 screws. The guy I spoke with said 12-28 flat head screws haven't been made for a long time. The only ones he had were longer than 1/2". Of course that's no big deal. The screws he had were not black oxide, but a zinc finish, but I still plan to use them after I face them off to fit the countersink of the index plates.

Instead of reslotting the screw heads, I may go ahead and put a 1/8" flat hex socket head,when I get more time this winter. My guess is the reason Hardinge originally went with a hex socket head was because a slotted head screw would compromise the faced off head of the screw.

In that sense, what size endmill would you recommend for milling out an 1/8" hex? Or if I decide to go with the original 3/32 hex, what size endmill would you recommend for that?

Btw, I received the manual you sent. Thank you very much. I will be sending you an envelope back. Then when the screws come in, I'll drop a few of those in the mail to you too.