Group Project: Dividing Head - The Build

Shotgun-I reread your post. You are suggesting the end cap being used as an expanding mandrel of sorts. The end cap OD would be 3"0 inches and expand slightly when tightened down? I have never seen this type of setup so I am not sure if you would get enough clamping action.
 
Now you're getting it, @rwm
Have you ever used a mandrel? How about an adjustable reamer? This sort of arrangement is all over the machine shop. The external taper on the trunnion drives into the internal taper of the cap, forcing the cap to expand. Sure, it's only a few thou of expansion, but that's all that needed, since the cap will already be a slip fit.. And it will be more secure since you'll have the screws and the taper ramp as a force multiplier.
 
I have certainly used a mandrel and collets but they have much longer "arms" to flex. I'm not convinced that this thin cap is going to expand adequately. If the cap were an inch thick with slots cut most of the way through I could see that working as planned but that's a whole nother animal. If it can fit in the design it may just be better to go up to a 3 inch trunnion?
EDIT:
I did a quick trig calculation. To get radial expansion of .004" you would need to flex a .5" thick disc by about 1 deg across the face. That doesn't sound like a lot but it could be a lot for a disc this size?
You could not use 4 perimeter screws to attach the disc to the trunnion. You would probably have one screw in the center so the disk could flex or "dish." I think you would want to mock this up as see how it works practically?
 
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Just to back up for a minute. Regardless of the above discussion, this pic shows an interference problem with the aux base if we have a 3" hole for the trunnion. Maybe Jeff has a work around?
 

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I have an idea. Need a bit to draw it up to see what you think, From what is sloshing about between my ears right now I think it will save the base.
 
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In other news, I ordered an Acme tap to try as a hob. I hope to get the gear teeth a little deeper to get closer to the 2.028 spacing called out in the plans.
 
Cool, I hope the tap helps.

I now have several ideas floating around in the mush betwix my ears.

The seemingly best ones will need changes to the trunion but I do not know all the abilities of @Ianagos to create them.

In no particular order....;
1. weld a ring to that end of the trunion to make the diameter big enough to work and then machine it to final dimensions and you will never know it was welded on.

2. put a 15° taper on the end of the trunion and have a split tapered ring between the for the cap to push into the taper. (This will put a significant thrust load on the other plate and may (will) cause it to deflect some.)

3. Make 2 split rings that will nest to allow the current diameters to work. this would be pressed together by the cap. With that small of taper there may be an issue separating them once tight.

4. Make a new end cap, with a split tapered ring as part of it, to engage a taper on the trunion similar to #1 but with the ring as part of the cap. This could then have a tapped hole in the center to break the taper fit if necessary.
 
It would be useful to know if Lanagos has already acquired the trunnion material and what it's actual OD is.
I see your locking solutions above but isn't the real issue the 3" hole already cut in the base (see post 404.) If we can fit a 3" trunnion, why would we not just leave the design alone but make the end caps 3.125" in diameter? Keep in mind the trunnion angle will only be adjusted occasionally (not like the spindle.) Maybe I am missing something?
 
That is what I addressed in option 1. With a 3 inch bore and a 3 inch trunion the trunion would just side thru and never tighten up, it needs that shoulder.
 
Yes I see that. The welded ring would certainly solve that problem. A flange bushing would as well. What about the intersection of the 3 inch hole and the .750 radius arc in the auxiliary base? I'm assuming shotgun has not finished the auxiliary base or he would have had a problem with these two features intersecting or at least having very little material there.
 
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