Dividing Head / Rotary Table

[Surprman]

I have been posting my initial efforts in the "what did you do in your shop today" thread, but since I am getting farther along I figured I would put it in my own post. My motivation for making this stems from the fact my milling machine is small and even the poor quality Chinese dividing heads are pretty expensive - plus it seems like a fun project. I am focused on making the critical items first and then will design the rest of the unit around them. The critical items are: the worm/worm gear and the spindle. I've had some good luck with making the worm/worm gear. I've made a hob and tested it out on an aluminum blank. Even though I messed up the orientation of he slots in the gashing operation, it still came out good. I am waiting on getting a piece of brass from my friend to make the final gear. (I'm going with a 40:1 ratio).

Yesterday I figured I would create the final worm (since I still had the gears set-up on the lathe from making the hob). It came out great. I learned something in the process. I was turning the part between centers. Don't try to part off while turning in this manner. Luckily it only slightly marred the edge of the cut when it bent the remaining stump and halted the spindle (belt drives are my friend). Until my brass arrives I am going to work on my spindle. My plan is to kind-of replicate the design of my SB 9C lathe. I want to have the same thread so I can use my existing 3 and 4 jaw chuck plus a faceplate (when I eventually get one). I also have a nice set of 3C collets so I will be boring out the spindle to accept those. I want to be able to use this in the horizontal and vertical orientation, but if that is not doable, I will just make a separate rotary table later- on. I plan to be using some of the ideas that I have seen in some of the other posts on this site as I design this and I'll reference them as I go along.

 

[Bob Korves]

Nice job on the hob and the worm and worm gear! You are correct, parting when the part is trapped by a center is not a good idea!

 

[Surprman]

I am making the spindle for my dividing head now and had a lot of meat to take off. I decided to be a little more aggressive with the amount of metal I took off per pass. I went up to 0.150 depth of cut with the back gear engaged. Man - it took that off like it was nothing! It helps that I ground my tool properly and have it in my new Aloris tool post. My swarf looks almost like the examples in the SB "How to run a Lathe book". (Up until now I've been conservative and most of my swarf has been tiny shavings with lots of passes.). I like running the lathe even more now! I included a picture of the stock I started out with. (Got to use my HF 4x6 bandsaw to cut it to size - so nice. I had cut the stock on both sides previously with a bi-metal blade in a saws-all. I still remember how difficult that was! A little better than a hacksaw , but not much!)

 

[Surprman]

I finished my spindle yesterday. It came out pretty good. Next I will be making the worm gear out of brass. My plan will be to make the gear with the same shaft diameter as my lathe gears (and Al test gear) - so I can use my mandrel for the gashing operation. I will be making the gear with a flange on one side to put a grub screw in. The flange will have a large diameter and I will be using that flange later to re-mount it in the lathe to enlarge the hole so I can slide it into my spindle. I'm probably also going to put in a key way.

 

[Surprman]

Today I cut up the block of brass and turned it down on a mandrill. It came out nice - I put a shoulder on it to put a couple grub screws in later-on. I decided to go ahead and do the gashing operation today also. Because the gear is thicker than my Al test part, I will need to make a new, longer bushing for mounting on the lathe for hobbing. Here is a picture of the gashed gear, the spindle and the worm I've made so far.

Later!

Rick

 

[Surprman]

Well, yesterday I turned down a bushing to hold the gear blank on my lathe for the hobbing. It came out great. I put the blank on the lathe and started the hobbing operation. I learned two things:

1) I didn't gash it wide enough or deep enough. The result was a random tracking of the hob, leading to 41 teeth and not the 40 that I wanted. Blank ruined.

2) Brass likes to be processed at high speeds. Attempting to hob at slow speed like I did for the aluminum test part was awful - noisy and poor cutting. It may have contributed to the poor tracking in my weak gashes. When I boosted the speed significantly it worked much better.

I ordered a new piece of brass that I will gash more aggressively and process at high speed. I may still be able to salvage the original - I may turn it down in size and attempt a 36:1 worm gear (vice the 40:1 I was shooting for)

Not a total waste because I learned something I suppose.

Rick

 

[Randall Marx]

Looking good, Rick. I just found this thread and am looking forward to future installations. Thanks for sharing the journey with us.

 

[Surprman]

Ok - got my brass last week (I paid more for shipping than the brass cost ). Turned it down to size yesterday and gashed and hobbed it today. Used a larger width slitting saw and cut it deeper to force the hob to track properly. Ran the hob full-out on my SB9. Got 40 teeth this time! The wider, flat profile saw blade was not ideal ( would be better if it was a tapered, gear profile), but it came out really good. Boring the gear out to fit on the spindle was pretty easy. Here are the three main parts of the dividing head all together:

 

[Surprman]

After taking almost a year off to do other things, I got back to this project. I made two brass bushings for the spindle for the project. Next I will be designing the housing and building that- also earlier this year I was able to pick up two matched hole plates that I will incorporate into my design (I'll probably need to make a third, but it will be easy to replicate the configuration of the two I already have- since Ihave a machine shop!). Btw - the brass I made the bushings from was from the 41 tooth gear in my failed hobbing attempt last year!

Rick

 

[cathead]

Out of curiosity, how many teeth are on your brass gear now? I have been thinking along those same lines and
most dividing heads are 40-1. Nice looking parts! Keep it up. Maybe there are advantages to using 41 teeth that I am not aware of.