Gears and Gear Cutting on the Milling Machine?

[CharlieW]

Paul,
A 12 DP is a pretty big tooth profile. I think your teeth may be smaller than 12DP. The Logan QC I made gears for recently, had 20DP, 20 degree PA gears in it. The change gears on the end were 18DP. I have this 1880's Prentise Brothers lathe that has a few broken teeth in one of the back gears which is a fairly coarse tooth gear and it is a 14 DP.

I determined the DP size with a gear pitch gage.




I forgot to mention that I used an 8" rotary table mounted on edge of my Bridgeport. I placed a #3MT arbor in the center hole in the R-table and held it tight with a draw bolt. The arbor had a 1/2-20 thread extending from it. I stacked my gear blanks on it and tightened the nut on the end of the arbor to hold the blanks. I had no keyway to hold the blanks.


Charlie W.

 

[8ntsane]

Hi Charlie

I have the manual for the lathe that covers the 14 & 16 inch swing lathe and the 18 to 20 swing. According to the manual, it is 12 DP and 20o PA . This manual isnt the run of the mill owners manual. This is more of a service type manual, thats gives the complete tear down of the complete machine. This includes all gear tooth counts DP & PA for all gears. This thing gives all part #s for all bearings as well, its pretty detailed except the metric gearing. They show the drawings of the metric gear train , with tooth counts, and set up. They didnt go into detail about DP & PA like the rest of the lathe.

Sidney Lathes of that yr could be ordered with the full metric gearing, and all the screws where in mm metric as well. The drawing for the metric version was totally different as well.

Now being you had mentioned the gear pitch gage, I called around today, and found a company local to me that said they could easy tell me what I have. So, Im going to bring them in a gear , and he said with in a few mins, they could tell me exactly what I have. I did go to that site that you posted a link for. Apparently the formula is (tooth count plus-2, divided by DP) will give the diameter of the gear. I did that test on the gears , and it comes up 12 DP. If I calculate in for any other DPs, the diameter of the gears change. So, Im going to have the gear makers have a look, and see what they say. I suspect the gears are 12DP, and they had a different DP for the metric gear train.
This is a heavy duty machine, so I can figure the manuals infro being right. Even the 18-20 inch Sidney Lathe had the same DP.

Here is a pic of the lathe







Thanks fo the infro given, the links have helped

Paul

 

[CharlieW]

Wow, that is quite a lathe. I'm glad I didn't have to move it. Looks like a great machine.

 

[GK1918]

what a sweety, even better look at his floor. I should have had two girls instead of boys.!

 

[8ntsane]

Well, its official
I had the gear checked today, and the gears are 12 DP, and a 20oPA. So I guess the manual is correct. I did show the guy the page from the factory drawing, and he looked at it for a few mins, and said the coversion gears for metric, can,t be 12DP , He said the 60T gear that connects to the 48T gear box gear would have to be 12 DP, but the 127T, the idler, and the stud gear are no doubt a different DP. He did say its going to be a bit of futzin around to figure out what DP the metric conversion gears are, but doable if I spent the time.

So now Ive got to figure out what will fit calulating DP & tooth counts to figure out the diameters, and just what will fit inside the cover. Oh man, this sounds like a slow painfull process. He did say to figure out the diameters for a few different DPs, and cut out the sizes in card board, and slip them over that shafts. It should give me what will go, and what wont. I suppose thats what im doing this weekend.

Huge
Do you think a rotary table would be accurate enough to cut a 127t gear? I know my dividing plates dont show anything pas 99 divs.

The search for the mystery DP continues.
Thanks to all the replys guys, it all helps

Paul

 

[8ntsane]

Hugh
Thanks for the reponse.
I will send out a copy of the manual tomorrow, and I will get some pics of gear train with the cover opened up. I will get it all to you tomorrow.

Yes the metric conversion was factory option, They also sold the same machine with all metric screw, and dials too. The manual will make that all clear.

Thanks Paul

 

[toolingjim]

I know this thread is old, but I haven't been on here for awhile and as a previous advise-thrower-outer was wondering how the gear cutting is coming along for some of the posters.

8ntinsane, did you ever get your metric gears sorted out? Was bytewise able to help you work out your gear train?

I have seen some gear trains that changed gear pitches by having gears with two different pitches compounded together on a common keyed shaft. This allowed one part of the gear train to be one pitch, and the rest to be another. Perhaps this is what they did on your lathe. It is also true that the 127 tooth metric conversion gear often did not fit under the guarding on some lathes. Yours might have been one of these.

BTW, I have found that it actually is practical to cut gears with a rotary table, just slow and requiring concentration and a lot of calculating. On the flip side, many dividing heads made nowadays do not seem to have the index plates to do a full set of divisions. The old Brown and Sharpe dividing heads and their Chinese clones could do virtually any divisions you wanted, but really require you to pay attention to what you are doing.

So, any news on the gear front?

 

[benmychree]

Fact is that you cannot accuratly cut a 127 tooth gear with a normal dividing head or rotary table; 127 is a "prime" number and cannot be evenly divided by any factoring; a universal dividing head is used, where the spindle is geared to the dividing plate, so that while you turn the crank, the dividing plate also turns an corrects for the lack of theoretically correct hole circle. It is called differential indexing. This I did many years ago when I made metric transposing gears for my lathe; I first made a 127 T that fit my automatic gear cutter, as it took a finer pitch and consequently smaller diameter gear that would suit the swing of the dividing head, then cut the coarser and larger gear in the automatic gear cutter. If one looks in the tables in the Brown & Sharpe Practical Treatise on Milling and Milling Machines, in the table on indexing, that there are a good many numbers of divisions (prime numbers particularly) that must be done by differential indexing. Fewer numbers of division are able to be done on Cincinnati dividing heads due to their use of high number indexing plates.

 

[Bill Gruby]

Gear cutting is fun once you get the hang of it. I did well here. My rotary table converts to a dividing head with a 90:1 ratio not 40:1 as a dividing head does. That is 316 Stainless being cut.

"Billy G"