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10-12-2013, 06:21 PM #1
aluminum setup in the lathe for a pulley
Good evening. I have a newb question. I am trying to make a pulley probably the hardest way possible. I had 2 pieces of rounded plate with lips on one side and small collars on the other, both center drilled to the same size already. I put a mandrel through the two plates and plug welded them together to make a thicker piece of stock for my pulley.
Next I chucked it up in the lathe and put a live center in it and began to work it down to size. I pulled it out of the machine to do something else and came back to it a few days later. I chucked it up the same as before, and went to cut one of the lips off the OD. It did not run very true, but the lip came off as a ring as planned. But it is not running true . I put a dial indicator on it and it was a little less than .010 out of round. I removed it and re chucked it and now it is much worse, about .030 out, and the live center is dancing around quite a bit.
This is where I have stopped. I looked at the surface I am chucking on and it is chewed up a bit from I guess over-tightening the chuck. I will try and put up some pics. I know it is ugly, but this is a learning project for me.
My question is what would be the best easiest way to get this back running true.
The end product is going to have a ID of a little under an inch, which I was planning to set on the shaft with 2 set screws, or make a much bigger project out of this and try and cut the splines to fit the driver shaft. This is supposed to be an extra pulley on a small diesel engine crankshaft so I can run airconditioning.
my chuck will not be able to get small enough to grab the ID. the OD of the little collar/lip is where the problem is, so I don't think I can chuck up there again.
Should I try a tapered mandrel?
The plan was to cut the center a little deeper than needed, and then cut the pulley walls, then weld a bead in the center of the pulley for extra strength to hold the halves together, then cut the center weld back down to finished size.
I did look for a store bought pulley, and I could not find anything that would not need almost as much work as making it from scratch.
any help is appreciated
10-12-2013, 06:50 PM #2
I'd disregard the OD/Face of the part for now, and concentrate on getting a good bore in the part. After that, turn up an arbor that fits very close (think .001) to the ID. DO NOT REMOVE IT from the lathe. Drill and tap the end for a countersunk bolt, and put a countersink in it. Get in there with a hacksaw and slit it in two directions, axially. Now you can put the part on, snug up the screw, and have it running quite well for any operations you must do. If you don't want to fuss with shims or a 4 jaw, dont remove the home built mandrel until you're done with the pulley. Take light cuts, and you can use a center drilled piece of plate or round to push against the face of the part with the tailstock while you do your turning on the OD. Good luck.
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10-12-2013, 07:07 PM #3
Also, no offense, but your welds kind of make me think about how loud and exploding pulley hitting the hood would be. I applaud your efforts, and I'm sure you don't weld AL day in and and day out. Just go over em one more time with the heat cranked up to make sure she isn't going anywhere.
10-12-2013, 07:13 PM #4
I think the bore is pretty good . it is just under .5", and both halves are lined up.
so If I understand correctly instead of a tapered mandrel to set up on the ID I have now. Make an arbor shaft that fits the current ID, and use the tapped cross slit center hole in the arbor to expand the arbor in the ID of the pulley. That sounds reasonable. but I would only be turning on the arbor, and would not have any support from the tailstock . is that what you are saying? I am guessing the arbor is steel not aluminum correct?
10-12-2013, 07:22 PM #5
yes those welds are just temporary to hold the thing together while I get the outside dimensions done and the pulley walls made, Then I was planning to cut the groove extra deep and put a nice bead in the middle, machine that down to size, and then YES re- do the plug welds.
I was having trouble getting my wire to get to the bottom of the plug hole. I was pretty cranked up on a 250 amp mig. Those were my first plug welds ever. If I were to do it again I would have used a bigger diameter hole to start with, or a smaller nose piece on my mig gun, or maybe larger diameter wire
Thanks for the comment though. I do realize the plug welds are pretty ugly, but they are doing there job for this portion of the project
I am also a bit concerned for the groove weld. I was planning on NOT using the lathe to spin the piece for welding, I am going to have to make up a turning positioner for that
10-12-2013, 07:26 PM #6
Do what you said in post 4, but put a center drill a center in the end of the mandrel so you can support on both ends, and take light cuts.
The pics look like the chuck jaws slipped and did a little machining of their own. May want to tear down that chuck and clean and lube it.
10-12-2013, 07:40 PM #7
If this picture doesn't confuse you more than I have already, nothing will. Please excuse my use of Paintbrush, and the acid-trip color scheme.
Yes, slit the arbor lengthwise for a little bit on the end, in a cross shape. Go right into the threads. You're only expanding a thou or two, it won't strip out. It's limited by the pulley bore anyway. Use any material you want for the mandrel, aluminum is fast and easy to machine, and expands easily, too. Make sure she's tight and you take light cuts, if it spins it'll gall your bore. Open up that .5" bore to your finished size (.999 or whatever), and turn the arbor .001 or .002 smaller. I really hope this helps...
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10-12-2013, 07:45 PM #8
I guess I am a bit confused on the cross slit arbor. if I cross slit the arbor after it is drilled and tapped. How will it expand the arbor if it is drilled and tapped for the same size as the expansion screw? I can see it if I put a bigger screw in the cross slit hole.
I like the tapered mandrel that puts the pulley on a friction fit on a tapered steel mandrel, and I really like the center drill on the tailstock end of the mandrel for a tailstock center.
If I use a tapered mandrel. Which end of the taper should be where? does the tailstock get the fat end of the tapered mandrel?
Also how much taper for example sake lets say the ID section of the work piece is 1" wide, and bored to .5" ID.
I have never used a tapered mandrel before, what keeps the skinny mandrel end of the piece from wobbling on the mandrel?
10-12-2013, 07:47 PM #9
Perfectly good drawing. It makes sense.
Thanks, I learned something new.
10-12-2013, 07:49 PM #10
The countersunk head is doing the expanding, not the threads. As you tighten the screw, the tapered head is trying to expand the countersink in the mandrel, thus expanding the mandrel into the bore.
10-12-2013, 07:53 PM #11
your illustration is very helpful. I now understand the pursher plate. If I use a steel arbor tapped to say 1/4-20, will that expand enough? I sure thought I should work the ID to final size after I cut the pulley walls
so you think I should go to finished ID for the bore before I start cutting the pulley walls and the center part?
How hard is if for a Newb to cut internal splines on the lathe. I saw a picture of a guy doing it a little bit at a time with a boring bar used like a broach.
Or should I put it in a rotary table on the mill.
I think the spline may be a bit advanced for me, but I do want to learn
10-12-2013, 07:58 PM #12
In regards to tapered mandrels, fat end goes towards chuck. All turning happens towards the chuck, effectively keeping the part tight. The taper is very slight. IE, I think a 1" would be about 1.001ish on the big side, .998ish on the little end. Don't get me wrong, they're great. However, they require you turn between centers, and they also require you to have a perfect bore size. If you end up with .996 or 1.005, too bad, so sad. I think making an arbor and leaving it in the chuck, while a bit more work, will cut down on your struggles in the end. Again, get your bore to size before you do any more turning work, let the pilot bore be your reference for all subsequent machining. Please do report back with your results
10-12-2013, 08:02 PM #13
1/4-20 would work, 3/8 would have a bigger tapered head and a little more outward squeeze. Use what you have.
Get the part bored, then turned and faced, and we'll talk about shaping the splines in the lathe. You most certainly can do it, I recently cut an 11/16 hex into a tool with a flat toolbit on the lathe, because we didn't have a broach, and the hole was blind anyway. Layout, tool grinding, and machining time was under 1 hour, and this was in heat treated 4140. Hex came out within .002, cutting to scribe lines and cleaning up with a file.
10-12-2013, 08:09 PM #14
ok the lights are starting to turn on . Now I understand the countersunk head doing the expanding. That makes a lot of sense.
But with the aluminum being so soft, I am concerned about going to finished ID first?
How about the splines, it would be very nice to have this fit the spline on my crankshaft?
So now I like that arbor Idea better than the tapered mandrel
I have done some reading on welding in your lathe. I am not sure I want to try it. My lathe is no great piece of kit. it is just a almost worn out Standard Modern 13x40.
I have not had this machine running very long. but it seems to be doing the job.
thanks for the help so far
10-12-2013, 08:12 PM #15
So if I want to try for the spline, I should take the ID bore to the minor diameter of the spline? that is the smallest dia. in the depths of the cuts correct?
So at a minor dia. of close to 1", with a steel arbor, 3/8 sounds like a good threaded hole
Last edited by diesel-xj; 10-12-2013 at 08:16 PM. Reason: more additions
10-12-2013, 08:15 PM #16
Yes, ID of the spline. Better a couple thou big than a couple thou small. You'll see why later. Not sure why you'd weld in the lathe, finish up your welding before any more machining, so you can correct for warp with skim cuts.
10-12-2013, 08:22 PM #17
I wanted to weld a good bead deep in the center of the groove, then machine it back down.
Yes welding in the lathe sounds like a good way to screw up my lathe. I wanted to make the deep center cut, then make up a slow speed rotary welding positioner . I think I have a variable speed gear motor in the shop somewhere, I am hoping it will be simple enough to set that up
So I need to make the center groove bigger now I thought
it sure would have been easier to start with a nice thick enough piece of stock
Last edited by diesel-xj; 10-12-2013 at 08:23 PM. Reason: more
10-12-2013, 09:10 PM #18
The way this is done in industry is (and I've made about a zillion sheaves):
1) chuck one side and profile the side and spigot and drill the center hole through undersized.
Leave the OD oversized.
2) flip the part around and chuck from the finished side and profile the second side. Then
bore the center hole to finish size.
3) set up a straight, tight fitting mandrel in the lathe spindle. Set up a rotating
pusher block in the tailstock. Fit the sheave onto the short mandrel and bring the
pusher block to bear on the outboard side of the sheave. In this setup now
turn the OD to size and then profile the groove(s).
This way the OD is exactly concentric with the bore of the sheave.
Sandpaper glued to the flat surface of the mandrel helps to drive the part
in the third op if needed.
10-12-2013, 09:22 PM #19
Jim - I would do it the same way, but it seems the OP is having some runout or gripping issues re-grabbing the part. Perhaps his chuck isn't so good, perhaps he's at the limit of the scroll, who knows. I'm hoping he can get everything true to the bore this way, giving him the least runout axially and radially as possible, and allowing quick and easy re-mounting should he have the need to remove it. Start with your most critical dimensions/features first, giving later ops an accurate reference.
10-12-2013, 10:00 PM #20
thanks guys. So I know this is probably a total Newb question.
What should I chuck up on to turn the ID to finished or near finished size for the spline? Can I just chuck it back where I had it?, or on the flip side which is also not in very good condition. and bore the ID to finish size, then make the arbor with the countersunk screw and the press block. Now I have a good arbor in the ( near finished) ID, Now all the rest should be good and centered on the near finished ID. I then can finish the one side and add enough of a lip (spigot). then flip to the other side and I could either chuck on the spigot, or re-install the arbor on the finished side. Then finish the last side, and finish the OD,
I don't know if that was followable. but the idea is to get a good ID bore and then I can work from that Good ID.
When you guys say light cuts. how is .010-.015 per pass?
Yes the chuck is a cheapy, it is pretty new but not high quality. it is a D1-4 direct mount 8" 3 jaw scroll chuck.
I have been cutting this at 500 and 350 rpm. I don't know which was better speed. Also I don't know if you can tell from the picture but the finished ID is going to be about 6.5" dia.
thanks again for your help