Todays Project - What did you do today?

[wrustle]

(12-29-2013, 08:20 PM)PixMan Wrote: I went to the shop and remade the blank for the 70T Mod 1.75 change gear I need for my lathe. I made one out of "scrapbinium" and it cut a lot like 1018CRS. The guy who's going to cut the teeth for me said it would not hob to a decent finish, so I went to a local steel supplier (Peterson Steel, Worcester MA) and got a Ø6" x 7/8" thick round of annealed 4150. I figured I might as well make a new one because I went .0012" oversize on the 20mm bore on the crappy material one.

Here's the stock as I faced off the sawn side. It was out of being parallel by almost .040" (1mm).


Here's the finished front side, it came out quite nice and the bore in now right at 20mm.


Now I've turned it around to finish the back side. Too thin to simply snug it up against the chuck jaw faces and the bore too small to get in there with an indicator. So what I did was use an indicator on the cross slide and "zero out" the DRO in Z axis. By retracting the cross slide just enough to velar the 6" diameter, I could move the carriage out to index between the jaws and then return the carriage to zero and run the cross slide back in. If anyone has a better way of doing it I'd like to hear it. The blank came out parallel within a "couple of tenths".


Finish turning done, now I need to figure out a good way to get the 6mm keyway in it before shipping to the gear hobber.

Ken,

On thin parts like that where you can't locate the piece off the jaw face, just grab three drills the same size that are small enough in diameter to get the holding stock faced off while still being able to hold the OD with the jaws. Lay the drill shank across your jaw face, place the piece against it, and then do the same with the next jaw, and then the one after that. Clamp your part lightly and check that your drills are being held. If not, tap the part to seat it but do it lightly. Once all are seated, remove the drills by pulling them out from between the jaws and the part and clamp your part solidly.

I've done that many times over the years, and it works great! Just remember to pull the drills out before you turn the machine on!! The face will come out as good as the face of your jaws are square to your spindle center line.

Oh, and while I'm thinking of it, be sure to actually measure the shanks of your three drills. There can often times be a .001 difference in diameter. New drills work the best as they do not have battle scars on them from drill chucks, and jobbers drills are eaisier to use because they have a longer shank and are easier to remove because of the length as well.

Part looks good by the way.

You know where to get them broached. You just need a broach, a shim, and a 20mm bushing, I've got the press.

Happy New Year!
Russ