Radius / Ball Turning Fixture

[David Kirtley]

Based on Ralph Patterson plans for mini lathe. Work in progress.
. 2.5 in body. 3/8 "x 2,5 in X 4" mounting plate. All aluminum. Still need milling of body, mounting to plate, drilling of body and plate. Also need handle with ball on end. Will make the ball with this fixture.

Base of body piece. Not drilled, tapped or milled yet.


Pocket turned in base.


Just held in by tailstock so I could check fit. Pretty happy with it so far. Didn't want to invest too much time in the base before I fitted the body. Still needs some cleanup. and drilling the mounting holes for the saddle.

 

[David Kirtley]

It is a fun project and none of the dimensions are critical. The rotating parts just have to fit together. The only other critical thing will be tool height. I am going to use a carbide insert.

One thing I did figure out that would have made things faster would have been to make the plate first. It is a lot easier to do plain turning to dimension the body than the boring to depth and sizing the pocket for the rotating body.

 

[PurpLev]

looking good. definitely one of the upcoming projects for me.

any benefits of using carbide inserts as opposed to HSS tooling that made you go that route?

 

[David Kirtley]

Just the fact that I have never made a carbide insert tool holder.

I actually have been thinking about making two tool holders so I can have a HSS one as well.

This one is really a prototype/ learning experience. I have not done much boring before and this was the first time I have used my faceplate.

I don't know that the AL will hold up in the long term. It is odd for moving parts. The oxide film is so abrasive and the fresh metal is so soft that bad things can happen. It could last 50 years or it could self destruct quickly.

 

[David Kirtley]

Small progress. I went ahead and drilled a through hole on the body because I don't have a bottoming tap for the screw size. No big deal. It will be under the sliding tool holder anyway. 3/8-16 flat head screw. I think I will run in some lapping compound to let it wear in a bit. Without any loctite on the screw, it will tighten up if I turn it with it running too closely. I might need to run a set screw as well. I went with a bit larger screw to give it more bearing surface. Well, more friction is a by product. Drilled and put the countersink in on the plate. I might countersink it a little bit more but I don't have the world's best countersink for this size. The only big one I have is a single flute. I have more on the way but they are not here yet. The screw might be a tiny bit proud of the base and I want to make sure it turns freely when mounted on the saddle.



Here they are put together. The screw is loose in the hole there. When I tighten it down a bit more, it is pretty close to below the surface of the plate. Again, waiting until I make final fitting. It is a lot easier to take more off than put more on.



Yes, I didn't get the whole surface when I fly cut the base. Non-critical dimension and I will just hit it with the belt sander for a finish.


Next will be the mounting holes and to start milling the rotating body.

 

[David Kirtley]

Mounting holes drilled


Countersink done for pivot. Some lapping done. Will do final lapping when body is finished.



Test fit of mounting holes



Test with body assembled.



Considering options for milling. One is to make as specified in the plans I am working from. The other is just to put t-slots in the body and mount things from there. Will have to sleep on it.

 

[mech1]

Just the fact that I have never made a carbide insert tool holder.
I don't know that the AL will hold up in the long term. It is odd for moving parts. The oxide film is so abrasive and the fresh metal is so soft that bad things can happen. It could last 50 years or it could self destruct quickly.

Have you tought about anodizing the AL parts?

Werner

 

[David Kirtley]

Hi Werner,

For direct bearing contact, anodizing the parts really wouldn't help. The thickened aluminum oxide layer is harder but it also makes the part it is rubbing against harder as well so there is no appreciable net gain. It would be a lot better to use a washer made of dissimilar materials between the parts. Brass, delrin, or UHMW polyethylene would be good candidates.

Sometimes a light duty prototype makes a lot more sense than building something much more substantial (and expensive.) This is more an exercise in machining and finishing rather than getting a long lasting fixture. This has less than $10 of materials in it. I am making this light duty one knowing that I will most likely only occasionally use it. If I really enjoy using it and it wears out, I will see about making one that is much more robust.

If I were making one to last, I would just use a couple bearings for a shaft and needle bearings under the rotating part. For less than $10 of additional parts, it would be able to be refitted with new bearings and last indefinitely.

 

[mech1]

Hi David,

Thanks for your toughts, I agree with them.

Hi Werner,
For direct bearing contact, anodizing the parts really wouldn't help. The thickened aluminum oxide layer is harder but it also makes the part it is rubbing against harder as well so there is no appreciable net gain.

On, maybe, interesting thing: we benchmarked the hydraulik block of a dual clutch gearbox from AUDI. Block and valve spool made of (hard) anodized aluminum for better wear behavior. Let's see, if I have te time to test it once, I will post my findings. Sure there is a dependency between layer thickness and wear behavior.

Werner

 

[David Kirtley]

Just as an update, I got my turner but together mostly except for the cutter. I am not that happy with it. Mainly due to the size limitation over the saddle with it. Have not decided what to do yet so it is on the back burner.