New Hit & Miss Build

[George_Race]

After building a couple of very small simple runners, it is time I tried something a bit more challenging. For my next project, which I will document here, I am going to build the Brian Rupnows Improved Hit and Miss as described here on HMEM. There are a lot of ways to build something, I am sure, and you will find that I am not a machinist so I do not always do things in the proper or more conventional ways of a machinist. My approach will always be to do what ever I can to make a part that works for the applications it is used in. The bottom line, I am here to build, enjoy, and share with others.

The very first step, find the center of a round piece of aluminum and start the governor flywheel.

Next take a couple of passes off the top of piece to level the surface.

Now time to pocket out the center of the flywheel and make the hub.

That operations is now done and it will now fit in my lathe for further machining.

Mount it in the lathe chuck and get ready to finish the perimeter and other side.

 

[JackBat]

I for one am looking forward to your build, keep it coming.

 

[George_Race]

Thanks, the piece is still in the lathe, just waiting for me to get back to it.
Maybe tomorrow!
George

 

[George_Race]

Well I am back, finally got some time to devote to the new project. As always this is a learning experience, and this time it is a disappointing experience. But, having said that, it is also a good experience and I will go on from here and do better next time.
My last pictures showed the flywheel blank in the lathe, ready to face off. The first thing that I did was use a center drill to mark the center of piece. I then drilled it with a number drill just slightly below the 1/4 inch target. I then put a chucking 1/4 reamer through the hole and cleaned it up. I felt the reamer cutting about half way through the piece, it then kind of acted like it was already reamed from the other side. That should have been a clue, but I pressed on and finished to face off the piece to the proper thickness.

When I removed it from the lathe, I put a piece of 1/4 inch brass rod through the center hole. From the side I drilled it, it was a very nice tight fit. But, turning the piece over, it was obvious that the hole was larger on the back side! What I think happened is that the drill bit actually went through the piece at a slight angle, making the hole larger where it came out thru the back of the piece.

I forged on, the next operations to be done on my little CNC. I pocket milled the new side of the flywheel, being very careful to make sure I was on dead center. I then turned it over to do the cutting of the several holes on the hub side of the flywheel. Because the hole was larger, and slightly egg shaped, it was difficult to find the exact center to work off of. Anyway, I proceeded and the first two larger openings were perfect, meeting exactly at the hub on both the top and bottom cuts.

Next on to the .22" recessed openings in the hub. Using my Mach3 DRO's I carefully indicated the exact location. As soon as the cutting started, it was obvious that something was not right as it was milling out the side toward the center hole. I carefully moved to the other side and had the same results, expect the tool milled out the outside of the hub this time. I then indicated and milled the two remaining holes at the bottom of the pockets, just to see how accurately I could do it. They both came out on center, looking good.

The lesson I have learned here is to not trust drilling in my little HF lathe. I get excellent results when I pocket mill holes in flywheels and other pieces, instead of drilling with twist drills. I am going to start a new piece, and this time it will probably all be done on the mill, with just a slight touch up of the outer edge of the flywheel on the lathe.

Here are a couple of pictures where you can see just how far it is off.

Tomorrow morning off to the metal shop to get a couple more blanks cut and start over. Next time it will be perfect!

 

[ianjkirby]

Hi George,
I may well be wrong, but your description of the drilled hole sounds to me like the drill bit "filled" with aluminum in the flutes, and the back portion of the hole was not cleanly drilled, but "bulldozed" out.
I have always, when drilling aluminum, used several sizes of drill to sneak up on the finished size, and also used lots of RP7, or WD40, or whatever is in your area. Plus lots of backing out to clear the drill flutes.
Have another go, you'll get it!
Regards, Ian.

 

[ShedBoy]

Dam shame that. Ian has the right idea with sneaking up on it. As for the broken bit that seems perfect to go into a furnace and be recycled. Keep at it. I am like you, not a machinist so I can pull out some beauty set ups, not all work. If unsure just ask and you will get more ideas.

Brock

 

[Lesmo]

Bad luck George, I have had similar problems with ally, and found Ian’s take to be the best approach. The only other thing I would add, is that I found using a much lower speed than you would normally use for such a soft material helped a lot

Les

 

[bearcar1]

Hi George, sorry for your troubles. Have you 'clocked' your tail stock to see if it is straight? It won't matter much what method you use to drill out the hole if the tailstock is out of alignment.

BC1
Jim

 

[George_Race]

I do appreciate all the comments and suggestions.

I did "sneak" up on the hole that I drilled on the lathe. Started with 1/8 inch and worked up with three different sizes, as I remember. I will check the tail-stock again to make sure it is on center, but I did do that a while back and it was very close.

I am going to do all the holes with the mill next time, and I am sure that I will get it much better on my next try.

Every time I make a bad part I learn something, and all of your suggestions and comments really are a big help to a fledgeling machinist like me.
Thanks,
George