Atlas milling machine refresh project

[34_40]

Congrats on the progress. I think a .010" cut with that shell mill in full contact is asking alot of the mill.
But that is based solely on my limited exposure / experience with my mill.

But you are getting a decent finish along the cut with yours.

 

[ogberi]

Very nice! The work envelope on these machines is about the same as a mini mill, but they're much more robust. Imagine swinging a cutter that size in an X2 or similar mill at that depth of cut...

I found my machine to be pretty picky about the gibs being adjusted just-so. I ended up using a piece of .002" flat spring steel between the gib and the dovetail, tightening the gibs so the table would barely not move, then withdrawing the shim. That worked for me, but I can't find the shim stock anymore. Probably used it for something... Also, the three bolts that hold each side to the knee's ways don't get torqued down, just snugged enough to let the knee travel but not bind. I used split type locking washers under mine to prevent them backing off under vibrations. I thought about loc-tite, the low strength type, but didn't have any on-hand. I may still do that.

If there's any slop in your ways, it'll probably be in the middle of the table. That's where most of the cutting takes place, same as on a regular mill, in the X axis. The knee shouldn't have much wear, and the Z axis (in and out towards the spindle) usually won't either. These machines tended to wear the middle of the tables out before anything.

Using backgear you can power through metal like mad. I always had the idea of buying some of those 4" diameter carbide-tipped saw blades, mounting it on a faceplate and turning the center hole large enough for an arbor and filing in a keyway. That'd make nice slots in a workpiece.

But I think one of the handiest things I used my mill for was turning short, fat drill bits. In backgear, with a silver and demming drill, I plowed a 1 1/2" hole in aluminum with no trouble at all. Much easier than the drill press would have done.

Awesome to see it making chips! Can't wait to see the finished fixture plate, I may need to make one myself too.

 

[VSAncona]

Well, I think I spoke too soon. I spent most of yesterday playing with the mill and I kept having problems. I've tried a bunch of different things and can't seem to get it to work right. I'm really frustrated.

It runs fine without any load. There is some vibration in the motor pulley setup, but nothing terrible. As soon as the cutter enters the metal though, it starts making a knocking sound, just like you get when making an interrupted cut on a lathe. It gets louder with deeper cuts. It does it in back gear and in direct drive. The pounding is bad enough that it keeps loosening the set screw on the spindle gear, causing it to separate from the spindle pulley when I use the mill in back gear. I'm not sure what is causing the knocking/pounding. I've tried tightening the belts, tightening the pre-load on the bearings, and making sure the gibs are tight. I tried checking the runout of the spindle and it's about half a thou on the outside boss and 1-2 thousandths inside the taper (not good, I know, but it is what it is). Even so, I can't imagine the runout would cause it to run so roughly. I think I need to take a break from it and come back to it later.

 

[ogberi]

If you have any MT2 collets, try using an endmill. Horizontal mills tend to have a "lope" to the cut, because it's near impossible to get the cutter on the arbor to have zero runout. brrrrRRRRrrrrrRRRRrrrr... that's what mine sounded like. I noticed a lot of noise when flycutting on it. The spindle pulleys look to be cast zamak, and the bull gear pin tends to hammer out the hole the drive pin sits in, by a little bit. I honestly have no idea how much knock is too much, which is one of the reasons I tore mine down.

If I am correct, you're talking about the ring on the left-hand side of the pulleys, with 2 set screws in it. My spindle has two corresponding blind holes in it that the set screws engage to prevent the collar from sliding on the spindle. If that's working loose, and you don't have the blind holes in the spindle, I would remove the spindle, put the bull gear, pulleys, and ring on it and bring them up snug. Then transfer punch the spindle through the holes in the ring and dimple it so the set screws have something to bite into. You *should* have the blind holes already, if it's a factor spindle (unless they got really lazy, it's a possibility).

Double-check your ring on the very left-hand end of the spindle. I had to run mine in until there was about .001 axial play, then I ran that ring down about 4 teeth to pull the tapered bearings together to eliminate all axial play in the spindle and get it tight. Despite seating the outer races with a tool and lead hammer, they "settled" in more when I cranked tension on the spindle. Mine is easily turned by hand, but without anything (belts, etc) on the spindle, it only turns about 1/2 a turn or so when spun by hand. *any* slop in the spindle bearings will cause no end of grief while cutting.

Don't get too discouraged. I'm not terribly far behind you (got my spindle back in, need to clean/paint the jackshaft mount this weekend), and if all else fails, have a cup 'o joe, a cigar, and stare at it for awhile. These are great little machines, and you'll figure it out.

Besides, you're making chips while I'm spending all weekend on the honey-do list. Vacuuming the house != fun. Plus about 80 sq ft of yard to turn into a rose garden. I could use a roto-tiller about now....

 

[wa5cab]

Also, the three bolts that hold each side to the knee's ways don't get torqued down, just snugged enough to let the knee travel but not bind. I used split type locking washers under mine to prevent them backing off under vibrations. I thought about loc-tite, the low strength type, but didn't have any on-hand. I may still do that.

Ogbert,

If you can't torque down the three 5/16"-18 hex head cap screws on each side of the knee, you need another M1-54 shim each side. The parts manual doesn't give the thickness but I would guess 0.002".

 

[VSAncona]

Thanks Ogberi, that gives me something else to check. I don't know if it's the collar with the two set screws or the set screw in the bull gear, but one of them is coming loose and allowing the parts to float apart from each other. I don't have any blind holes in my spindle for the collar set screws. This leads me to one other question. Should the collar/pulley/bull gear be positioned to the back of the spindle, or centered on it, or to the front?

I don't have any end mills yet, but I tried a shell end mill and it worked a little better. Still not as good as I'd like though. I think I'm going to stop messing with it for awhile. It's becoming like a sore that I can't stop picking at. I'll come back to it after a day or two and find something else to work on.

 

[wa5cab]

Position them so that the back gears and the pulleys (belt) line up.

 

[VSAncona]

Position them so that the back gears and the pulleys (belt) line up.

I tried that when I reassembled it, but the problem is that that back gears and pulleys can be positioned in various spots along theirs shafts too. So it's kind of a chicken or egg situation.

I tried a shell end mill yesterday and got a little better results. I'm still getting some chatter at the start of the cut, but I will take another look at the gib adjustment. These shoulder cuts are straight off the mill:

 

[wa5cab]

OK. I guess that I was assuming that the other two were still as-found. The general location of the bull gear is with its set screw centered over the Woodruff key. Put the bull gear in that location. Tighten up on the pulley and small gear (requirement here is minimum end float in the pulley but still free to rotate when the back gear pin is pulled out). Then adjust the position of the back gears and the countershaft pulley to match.

 

[VSAncona]

Okay, I'll try that and see if it makes a difference.

One more question about bearing preload. How freely should the spindle turn without any tension on the belt? If I spin it by hand, it will spin a couple of revolutions before stopping. I'm thinking that might be too loose.