Boring was the task in the shop today. My next piece of aluminum to make was the Y-axis ballnut mount. It's not a terribly complicated piece, but it gets a large hole in it that's not centered on both axes, just on one. After my experiences cutting out circles on the Sherline I was looking for a better way to do it, and decided I'd try boring it on the lathe. Because of the shape of the part, I couldn't use the normal three jaw chuck, but could use the four jaw. A three jaw is a scroll chuck, more or less like a really big version of a drill chuck in that when you tighten it, all three jaws converge at the center to clamp whatever you're working on. The four jaw has independent jaws and it's more involved to setup than a three jaw scroll chuck. I've only done it a few times, and never on the big lathe, so it took a few minutes.
A picture may be worth a thousand words, so here's the part after boring the big hole. Notice that the jaw at the top right is at the outermost ring? The two middle jaws are inside the inner ring and the bottom jaw is around the inner ring. The part isn't centered on that hole, but you move that hole to the center on the lathe for boring. Lathes make things symmetrical around the centerline of the chuck; the axis of rotation.
The other thing I needed to do was make some pins for the X-axis piece I talked about a few weeks ago. I have some pieces of 1/4" brass rod so it was a simple task to cut them to length and make them two different diameters. Here's all of the last couple of work sessions in one picture.
Have you ever tried the French hamburger buns from the Publix bakery for your BBQ sandwiches? Highly recommended.
ReplyDeleteTerry
Fla.
I haven't. Noted and thank you!
DeleteThat looks very challenging to center.
ReplyDeleteI originally had drilled a hole where that big one goes, with plans of using a 3/8 EM and G-code to cut circles from that center. The hole was the next size bigger than 3/8 in the set I was using, so 25/64? I had a short piece of half inch diameter aluminum rod and turned one end down to press fit into that hole. Then I used the dial indicator to indicate on that shaft instead of the edge of the hole. I got the wobble under plus or minus .001", which seemed good enough.
DeleteI had the exact same question, and that seems like a quite elegant solution.
DeleteI guess the only other solution would be fixed dial indicator indicating on the perimeter + rotation + math, but that wouldn't work in this case as the part doesn't extend above the Chuck jaws, and the stroke required to either follow the whole perimeter or even the relative stroke to all 4 corners only is pretty substantial.
Here is where a tool-holder mounted non-contact distance measurement device with sufficient precision would be really nice (especially if it interfaced with hardware/software to give you a radial map of the part)
Hmm...that plus DRO on the long axis = precision 3-D mapping
I started out going in the direction you mention, of a dial indicator touching the edge of the drilled hole. I have a nice Mitutoyo indicator I picked up at one of the model maker's shows that indicates in .0005" per division. Unfortunately, its needle wouldn't touch the hole when held in the tailstock. On top of that, it has a small range, .030 total, and when I first put this on the bigger dial indicator, it was only eyeballed in and was like .075 on the long axis. It would have never showed up on the fine-reading indicator.
DeleteI tried the drill bit that made the hole, but you know how drill bits always drill larger than they're marked, and it wobbled around. A single layer of masking tape was too tight to fit, so it was too loose by itself, wouldn't fit with tape. I figured the thing to try was to make a press fit plug and that worked first time.
Looks like you got a great surface finish in the bore. I heard that a little pork fat with a hint of woodsmoke makes the perfect cutting oil. (snort)
ReplyDeleteGood work!