Heavy counterweight driver hub machining

[Dale Grice]

All but four out of sixteen drives are now turned front and back with a roughed out tread and faced center/crankpin hub. The last four need the center/crankpin hub milled. These area meets the counterweight. The inside of the radius of the counterweight is 6". I am trying to figure out how to reduce the height of the hub area 3/16" per print and get a nice radius on the inside of the counterweight. A 6" fly cutter is not practical. The swing on the lathe will not allow a 6 inch offset. I could use my 8" rotary table, as shown. Or I could do the best I can and blend it in with a die grinder. Others must have a better or easier approach to take care of this on a manual mill. I am open to your suggestions and experience.

After these last four wheels - on to making a crankpin hole and key slotting jig.

Thanks,

Dale

[NP317]

I would leave them "connected." The driver will also be stronger, although that might not matter.
There are many prototype examples of small drivers made that way.
~RN

[10 Wheeler Rob]

Put a plate bolted to rotary table and mount wheel to it is best way I see to machine it.

[10 Wheeler Rob]

Or find a friend with a CNC mill to do it on.

[Steve Goodbody]

Hi Dale,
If it was me, I'd do it by hand as follows. This would just create a curved groove between the hub and the balance weight, it wouldn't reduce the hub thickness, but I don't think anyone would ever notice.

1. Grind up a small shaper / scraper tool from a small broken milling cutter (1/4 inch diameter or so). I wouldn't add any top rake, you don't want the tool to tend to dig in.

2. Make a stout pivot bar and a pivot pin, with the scraper tool mounted in the pivot bar at the appropriate balance-weight radius from the pivot and held in place by a cross-screw. The pivot bar would be nice and long, overhanging the wheel beyond the scraper, so that you can use the end of it as a handle giving you good precision on the rotation angle and cut speed.

3. Fasten the wheel to a sturdy block of wood with a couple of screws through the spoke gaps and with a tight hole in the wooden block for the pivot pin to be tapped into so that it can't move or shake.

4. Put the pivot bar on the pivot pin (I'd also add a hollow spacer to slip over the pivot pin between the block of wood and the pivot bar), and fuss with the wheel location until the scraper tool will scribe the arc at exactly the right place you want. You may want to add a couple of simple adjustable stops to limit the rotational angle and give a precise start and finish to the groove.

5. With the wooden block firmly mounted in a vice or screwed to the bench, apply a little downward pressure on the pivot bar with one hand while rotating the pivot bar with the other. Repeat as needed to scrape away a nice curved groove.

I'd use whatever scrap materials came to hand to make it a zero cost job needing only a small amount of time to make and a bit of patience to use.
Hopefully the above will be of some help - let us know what you finally do and how it turns out.

Best regards
Steve Goodbody

[Dale Grice]

10 Wheeler Rob gave me the necessary prompt. Thanks Rob. I had a plate that I had made to use on my lathe before I had a vertical mill. Made the plate, then within 3 months before I could use, I got the mill. That's the way things go.

So I centered the rotary table under the quill using an old turned down drill chuck arbor shown. Then I centered the plate using the short center shown and bolted the plate down. Turned a quick driver centering plug, third item shown in one of the pics, and moved over the appropriate amount and set the driver with the plug. Milled the hub faces and used the rotary table to do the radius.

[NP317]

Nicely done!
~RN

[10 Wheeler Rob]

Well done. Nice tooling plate, wish I had one of those handy items.

[Dale Grice]

Thanks
All you have to do is get a plate and start drilling and tapping holes. I got sick and tired of it. All on a bench top Craftsman drill press with a 3/8" chuck that belonged to my dad. Had it since about early 70's as far as I know.

Always figured I would get that plate surface ground. Just haven't done it yet.

Dale