Group Project: Dividing Head - Organization and Design

[Flyinfool]

I can see using a hole saw to rough out the holes, I never saw one that gave near a nice enough surface finish compared to a bored hole. That saw will be chewing thru 7 inches of steel for this project. I will be curious to see how it performs when more rigidly mounted.

 

[ttabbal]

As @Flyinfool said, the OD isn't really critical, but the shoulders that mate to the base are two of the more critical dimensions, I would think. And the exact dimension isn't so critical as that the two match.

I bought a Milwaulkee hole saw with carbide teeth. It comes with an innovate arbor that I can build an adapter directly into an MT3 taper for super rigidity. If it tests out with as good a finish as I think it will give, I'd like to drill a hole in a scrap plate and mail that to @ttabbal. Until this project is finished, that hole saw will be dedicated to that job.

Sounds good to me. A gauge is always welcome. I'll do some testing as well to verify stress doesn't cause any problems. I don't think the wife will take well to me stress relieving it in the oven.

 

[Flyinfool]

As I mentioned in another post.
Do it when she is not home or learn to duck.......

 

[ErichKeane]

I noticed an odd dimension with the shaft and worm-wheel. It looks like the area for the worm wheel + washer is supposed to be .938 long. However, the worm gear itself is 1" long (plus .150 for the washer). Are we expecting the bolt to go through both and then be 'free' between the two for 200 thou?

If i opt to instead change to just threading the shaft (or press fit or loctiting or etc) on the worm gear, is just 1" off the .70 shoulder fine?

Also, of interest, the difference in size between the OD of the shoulder and the OD of the washer is interesting. .70 for the shoulder, and .700 for the worm


Additionally, I was thinking I could start ordering materials. What to you guys thing about them? Due to the gear-hobbing I was sort of hoping to make the worm-wheel out of aluminum, but if that isn't going to work, thats fine too. Are we worried about the teeth getting broken if it is just aluminum? Or should we do 1018/12L14/etc?


For the shaft + worm, I would think 1018/12L14 would be fine whether we did aluminum or steel for the wheel.

 

[Flyinfool]

I noticed an odd dimension with the shaft and worm-wheel. It looks like the area for the worm wheel + washer is supposed to be .938 long. However, the worm gear itself is 1" long (plus .150 for the washer). Are we expecting the bolt to go through both and then be 'free' between the two for 200 thou?

If i opt to instead change to just threading the shaft (or press fit or loctiting or etc) on the worm gear, is just 1" off the .70 shoulder fine?

Also, of interest, the difference in size between the OD of the shoulder and the OD of the washer is interesting. .70 for the shoulder, and .700 for the worm


Additionally, I was thinking I could start ordering materials. What to you guys thing about them? Due to the gear-hobbing I was sort of hoping to make the worm-wheel out of aluminum, but if that isn't going to work, thats fine too. Are we worried about the teeth getting broken if it is just aluminum? Or should we do 1018/12L14/etc?


For the shaft + worm, I would think 1018/12L14 would be fine whether we did aluminum or steel for the wheel.

The bolt and the washer serve no purpose other than to mount the worm to the shaft. The shaft is shorter than the worm to be sure that it all clamps solid. There is nothing special about the 1/16 clearance. Just a number pulled out of thin air that would allow me to put a very loose tolerance on the dimension and be sure it will still work. IF you decide to single point the thread, the washer and bolt will be gone and the shaft will end at the gear.

.70 vs .700 is part of the checking of fits and tolerances that I have yet to do.

If the driven gear was made out of aluminum my biggest worry will be wear. especially if you happen to be indexing a steel gear and those chips will easily damage an AL gear. You could probably get away with 7075 or 2024 AL, I think 6061 will be to soft. I have never machined 7075 so I do not know how it is to work with. If the gear is made from steel, I think the hob will need to be properly heat treated to hold up to cutting steel. The ideal material would be brass. it is harder than AL but still machines easily and is purdy. BUT brass ain't cheap. 12L14 and 7075 AL are about the same cost.

I would not use 1018 for the worm + shaft, it usually does not leave a nice surface finish as machined for a precision part with bearing surfaces.

 

[ErichKeane]

The bolt and the washer serve no purpose other than to mount the worm to the shaft. The shaft is shorter than the worm to be sure that it all clamps solid. There is nothing special about the 1/16 clearance. Just a number pulled out of thin air that would allow me to put a very loose tolerance on the dimension and be sure it will still work. IF you decide to single point the thread, the washer and bolt will be gone and the shaft will end at the gear.

.70 vs .700 is part of the checking of fits and tolerances that I have yet to do.

If the driven gear was made out of aluminum my biggest worry will be wear. especially if you happen to be indexing a steel gear and those chips will easily damage an AL gear. You could probably get away with 7075 or 2024 AL, I think 6061 will be to soft. I have never machined 7075 so I do not know how it is to work with. If the gear is made from steel, I think the hob will need to be properly heat treated to hold up to cutting steel. The ideal material would be brass. it is harder than AL but still machines easily and is purdy. BUT brass ain't cheap. 12L14 and 7075 AL are about the same cost.

I would not use 1018 for the worm + shaft, it usually does not leave a nice surface finish as machined for a precision part with bearing surfaces.

Thanks! That all makes sense. Brass ends up being silly-expensive for this I think... Even the aluminum and steel are both ~$150 as far as I can tell, unless there is some way to get this from some other material (or from another source, hints welcome!).

As far as the shaft, I'm leaning toward 12L14, it is both cheaper and much nicer to work with

 

[Shotgun]

The gear isn't supposed to be taking any real stress. Right? It is just supposed to dial the spindle to the correct position while not under load, and then the spindle lock is engaged? Even if someone is making a spiral cut, there still isn't much load on the gear.

The one I made was out of 7075. Got the material from eBay for approximately $2/lb. It now looks like the price is ~$2.50/lb. Do a search for "aluminum scrap drops". I did have to round off the square stock.

 

[ttabbal]

Hey, if I'm using uranium, I expect you to use at least titanium! Maybe plutonium, should give a nice glow with the uranium parts.

I don't see any issue with 12L14. I don't think there would be a ton of stress on the parts. 7075 is nice to work, but I don't think it would hold up nearly as well. Sure you don't want to use iconnel?

I haven't tried it with a gear, if @Shotgun thinks his is up to it, I'm good.

 

[Shotgun]

I haven't tried it with a gear, if @Shotgun thinks his is up to it, I'm good.

I think I mailed that part to @ErichKeane? Chip ingress is an important point that I hadn't considered.
I only had a second for a quick search, but it looks like brasses have a Brinell hardness in the high 70's, while 7075 is in the high 80's.

Edit: Found better source. The best bronze is aluminum bronze with a rockwell-b hardness of 77. 7075 aluminum's rockwell-b is 75. I'd say that choice is a to-may-toe/to-mah-toe sort of thing.

 

[ErichKeane]

I think I mailed that part to @ErichKeane? Chip ingress is an important point that I hadn't considered.
I only had a second for a quick search, but it looks like brasses have a Brinell hardness in the high 70's, while 7075 is in the high 80's.

Yep, I'm doing that part I have the blank you made. The thickness is about right, but the diameter is too small (it is spec'ed at 3.600 diameter, which is part of what makes it so expensive).