Citation rear upright being milled

[Dano]

It was a slow day at work today.... found this on You Tube

Citation Formula Car Rear Upright

[Wren]

Brandon Dixon put that up last week sometime I think. He had already shared it with a machining board we post to and we had been meaning to post it up here as well. This is out of the latest run of uprights, we had done some previously but we ran out.

I have a half-finished video on my computer of the lathe operations. I guess you have shamed me into finishing it now. I will link it here when I get it uploaded

[Wren]

Alright, I finished the video of the 2nd operation on the rear upright. This is the only lathe operation on the rear upright, the front upright has a similar operation performed on it.

http://www.youtube.com/watch?v=l5Qcrt3o2nk

not bad for a backyard shop

[Brian]

Very cool. I was totally disoriented when the lathe started spinning - it was running backwards! What RPM was that at, and did the RPM vary based on radius of cut? That would have taken me probably three hours in my backyard shop, running on a 1939 Southbend 16" by 60" toolroom lathe! But I could have eventually done it. I could have *maybe* done the front side on my Bridgie too, but that would probably have taken a month with the pocketing and taper sections and I don't think I could have done all of the radius cuts. I wondered about the bearing bores when I watched the mill video, I wonder if with the right tools it's possible to finish the bores on the mill (using an undercut tool for the rear bore?). Does it make round enough holes moving the table in two axis?

I make aluminium flywheels sometimes. It takes me a solid 10 hours of machine time to cut both sides of the aluminium disc, drill and tap all of the holes on the mill, make the steel friction insert and assemble it, and that is a very hard days work. I bet you could make a flywheel in an hour.

What was the material cost of the aluminium that turned into chips?

Another question - how do you accomodate workpiece temperature gain when you're doing the finish cuts for the bearing more right after hogging off the back of the piece? That chunk of aluminium must have been hot!

Brian

[R. Pare]

Bearing bores can be done on a mill if the mill is decent - no big deal, really. Still, a lathe is better.

The block would have cooled very quickly at the start of boring operation for the bearing when he had the coolant running, and should have easily gotten back to room temp by the time he got to the final pass.

There are 2 directions a lathe can turn - clockwise and counterclockwise. Neither is "backwards" unless you are using the wrong hand tools!

[Douglas Brenner]

What Aluminium is used?

[Mike Ahrens]

I see that the mill is a Sharp, what brand / model / vintage is the lathe? I have a bit of professional curiosity.

[Charles Bucknor]

Brian I guess backwards is when that big chuck decides to unscrew from the spindle, which door to run backwards to so you can keep an eye on it as you make the escape (joke).

[Brandon Dixon]

The material is 6061 T6 mostly. The parts were designed around that material, but I have occasionally run across 2000 series and 7000 series aluminum surplus pieces. I never turn down 7075 at a good price

The blank for the rear starts at about 28 pounds. 6061 plate runs between $3 and $4 a pound, so the material cost for that blank is around $120. It's enough that I don't like scrapping one!

As Richard said, doing the bearing bores in the mill is not a problem. I did my first run of front uprights exactly that way because Wren's lathe wasn't here yet. The lathe is just a more efficient and exact way to perform that operation.

As far as the part getting hot while machining, we normally run flood coolant all the time. I turned it off for that part of video, otherwise the video would just look like the inside of a cloud....The part never even gets warm with the coolant on.

Mike: The lathe is an early Sharp (model SLT-80) as well. It belongs to Wren and I'm sure that he would be happy to talk to you about it.

[Brian]

It's an instinct thing, hardwired in my brain...such as it is

My four-jaw weighs at least 50 lbs, is a screw on mount, and I disabled the reverse switch completely - I have absolutely no desire to have that thing chasing me around my machine shop!

Brian

[Wren]

I had to get used to running the lathe with the tool upside down, it still bothers me that I can't look at the insert while it is running. With the slant bed lathes, it does help control the chip a little better to have the tool upside down and sometimes the chip does fall directly to the conveyor.

I have a random selection of left and right handed tools, so most programs do turn the part both ways. It makes interesting sounds when you program the rotation incorrectly, which will really wreck a cutoff tool.

[R. Pare]

Using a RH holder as was in the face turning, the chips will shoot to the back of the envelope. This is good if you want to open the door a bit to watch what's happening, but unfortunately it means that the cutting forces against the tool are trying to lift the turret away from the bed, rather than into it. If the cuts are reletively light, this is not much of a problem, though if the cuts are heavy (or you crash) you can ruin/break the gibs that clamp the turret and slide in place - I've seen the gibs on a quarter-mil $$ machine break, which then allowed the slide to flex and break the casting at the ball screw nut mount. Not good! You really want the cutting loads to be fed towards the bed, not away.

Unfortunately, a lot of lathe manufacturers seem to want to have the turrets designed such that the holder offset will allow the use of only a single hand of tools, with the loads lifting the slide. I've never figured that one out!