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Methods for parting off larger diameters

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accunlmtd

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#31
In looking at the history, I think you are parting way to slow rpm. That chattering is the tool bit coming out of the cut. Take the piece and try cutting again at a higher speed.
As they say, parting is such sweet sorrow.

But once you get everything right for your lathe, it will be a no brainer.
i part at the same speed i turn, just go for it.
 

Hukshawn

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#32
I think I parted it at 720 rpm. Normally I really don't get chatter. This time was odd. It was chattering right away.
I ended up playing with the tool geometry a bit, helped a bit. I just wound up hacking my way through. Still short tho....
 

BFHammer

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#33
Maybe crazy, but could you TIG enough to cover your shortage. Just pile it on and then turn, face it back to dimension. Might be easier than back to square one.
 

rgray

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#34
Anyone have any slick methods to glue aluminum back together?
I still have a chunk left, but not deep enough to remake this part.
There are plenty of two piece pulleys that thread together to offer a speed change.
The other day I took a snowblower apart to replace a belt and the pulley sheaves were individual pieces each with it's own key. They were held on with a bolt in the end of the shaft that when tightened held them together and fit the belt. If the center bolt couldn't be used then possibly three bolts could be used at a diameter larger than the shaft but smaller than where the belt rides.
 

Hukshawn

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#35
I had thought of that, but if you check out the drawing, there's a relief cut into the end of the pulley.
What I was going to try, since the piece is basically scrap, was to have the pulley body thread into the shoulder body. In a left hand thread.
 

Hukshawn

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#36
I had thought of that, but if you check out the drawing, there's a relief cut into the end of the pulley.
What I was going to try, since the piece is basically scrap, was to have the pulley body thread into the shoulder body. In a left hand thread.
 

Hukshawn

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#37
I had thought of that, but if you check out the drawing, there's a relief cut into the end of the pulley.
What I was going to try, since the piece is basically scrap, was to have the pulley body thread into the shoulder body. In a left hand thread.
 

Hukshawn

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#38
I had thought of that, but if you check out the drawing, there's a relief cut into the end of the pulley.
What I was going to try, since the piece is basically scrap, was to have the pulley body thread into the shoulder body. In a left hand thread.
 

Hukshawn

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#40
Jeez... someone delete those.
I'm in a basement and the connection is spotty. The page wouldn't refresh on my phone.
 

Mark Stonich

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#41
Ignore the following, but I can't igure out how to delete it. I hadn't noticed the relief in the drawing or the whole 2nd page of the thread.

Could you machine the larger pulley into the part and face it off. Then make the smaller pulley from a piece of plate. It looks like there should be enough metal to bolt the smaller pulley to the larger one. The through shaft should ensure centering when you drill the holes. Drill, tap and bolt the 1st hole before drilling the rest. Red LockTite between the mating faces.
 
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Hukshawn

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#42
Yeah, there's not a whole lot of meat on that outter pulley.



You can see there the relief is clearance for the retaining nut.
So, I don't think bolting anything on is going to be the key.
I haven't had time to work on this yet. What time I have had, has been used to hog out the dimensions of the motor mount. But I might try tonight as the lathe is quieter than the mill. So I can work after the kiddo has gone to bed. The last few nights I've just been zonked at the end of the day and just crawled into bed.
The part is pretty much a light aluminum paper weightritht now, so anything I do now will be an improvement. I have a big enough chunk left to redo the pulleys but not big enough to do the body. So, I'm gonna sit down and look at the drawing and see if there enough meat to do a left hand thread and thread a new pulley onto the already shaped body.
 

Hukshawn

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#43
Actually, I don't think it ever needs to be a left hand thread... someone correct me if I'm wrong.... if I do a male thread on the pulley and a female thread on the body, and the mill turning clockwise, a right hand will suffice... I do not have a reverse on this mill.
 

gheumann

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#44
I have cut 3" Al with a parting blade. It CAN be done but it IS a giant pain in the ass. Everything said above helps - perfect parting blade height, sharp blade, extend it as you go, start with very low RPM, keep a good flow of a good lube (WD40 works well on Al, "Tap Magic Aluminum" is the best.) But I finally bit the bullet and bought an el-cheapo (Harbor Freight) metal cutting band saw. It does the job, yes it wanders a little - and a single cut can take 10 minutes - but I can do something else while it is happening! That saw has earned it keep many times over. One of the best lessons from this experience is that "a way" isn't always the best way, next time plan for the parting operation so you CAN saw and face after, and "measure twice, cut once.". I doubt there's anyone here that hasn't cut off a part too short. The most common cause for that is referencing the wrong side of the parting blade for your measurement.
 

Highsider

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#45
I'd do the bore first. It's much easier deep parting to a hollow than a solid center. Also chapter from spindle brings shows up more on larger diameter.
 

Highsider

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#46
I should never try to do this from my phone------- 2nd sentence should read "chatter from spindle bearings.."
 

Downunder Bob

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#47
That's an option for sure. I had done that before and didn't pay attention and the band saw made a horrible mess..
That would significantly reduce the cutting time as I can't get blades less than 20 tpi in that (Chinese) size saw.
Have you asked a local blade maker, I think you'll find most cities have them, some of them usually only make blades for wood working machines, but you could get an oversize metal blade of the profile and teeth configuration you want and get the blade guy to cut and rejoin it for you. That's how I get mine.
 

Hukshawn

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#48
Threaded the body. I'll cut a chunk for the pulleys and thread that on then turn the whole thing as a whole again. That's a 24tpi, maybe too fine..? Am I complicating it with such a fine thread? I was concerned with it having good holding power... don't need the threads to be a weak point.


IMAG0899.jpg
 

Reeltor

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#49
Since no-one mentioned this I hesitate to post because it might be unsafe?
On edit: removed unsafe practice,


Mike
 
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JimDawson

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#50
Since no-one mentioned this I hesitate to post because it might be unsafe? Before I bought my Enco Band Saw I would chuck the work up in the lathe, have it set on a real slow RPM and use a handheld hack saw to cut the work. This worked for me, using plenty of cutting oil. I cleaned the cut of chips and the hack saw blade often and went slow. Hasn't anyone else done this or is it just me? Is this something really stupid that I got away with or acceptable with precautions?


Mike
You are correct, it's not safe. :eek 2:

What I have done it to put a good groove where I want to make the saw cut, and then use the hacksaw with the lathe turned off. Lathes make a pretty good vice for doing that.:)
 

David S

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#51
This may be obvious to all you pros, but I thought I would mention it. I have always cut off large diameters with my hacksaw. The cut was less than pretty. It was just the ordinary simple hacksaw with the wing nut to secure the blade. Then I discovered high tension hacksaws, perhaps from someone on this forum. What an amazing difference! I recently cut a end off a 2" diameter aluminum rod. I hardly had to face much off to get it trued up in the lathe.

David
 

Hukshawn

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#52
So as mentioned above, I threaded the body at 24tpi to thread a new pulley on.

So, I actually did the math on this one. Threaded the body, pretty much without looking at a caliper or dro, cause frankly, it didn't matter. But from that male thread, I mathed the female side...... it's f****ing perfect! First try! No test fit, only boring to diameter with an boring gauge and the calipers, then sorting out the major/minor thread diameters from the chart I have. BAM, perfect first try. No slop, it's not tight. I can't believe it! Hahaha.

So, I screwed up by cutting it short, then knocked it out of the park with an awesome fix. Now I'll chuck up the body with the big chunk threaded on and cut the pulleys.

IMAG0903.jpg
IMAG0902.jpg


The neighbours must think I'm crazy. When I threaded the pulley on I started laughing hysterically. Lol. Things don't ever work out perfect on the first try........
 

MetalMuncher

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#54
So as mentioned above, I threaded the body at 24tpi to thread a new pulley on.

So, I actually did the math on this one. Threaded the body, pretty much without looking at a caliper or dro, cause frankly, it didn't matter. But from that male thread, I mathed the female side...... it's f****ing perfect! First try! No test fit, only boring to diameter with an boring gauge and the calipers, then sorting out the major/minor thread diameters from the chart I have. BAM, perfect first try. No slop, it's not tight. I can't believe it! Hahaha.

So, I screwed up by cutting it short, then knocked it out of the park with an awesome fix. Now I'll chuck up the body with the big chunk threaded on and cut the pulleys.

View attachment 226224
View attachment 226225


The neighbours must think I'm crazy. When I threaded the pulley on I started laughing hysterically. Lol. Things don't ever work out perfect on the first try........
Way to go!! Looks like someone was watching over you, feeling sorry for your mistake, and helped you make up for it in a superb way!

I've had my share of parting woes on my 7x10 as well. I finally read enough advice about it to ignore the convention of "how to grind a parting tool" and redesigned mine so it cuts much better. The top edge, viewed from the side, would look like the cross section of a teaspoon if you sawed it down lengthwise through the middle of the handle and on through the spoon part. A nice "C" shaped upward sweeping cutting edge. It works very well shaped like that.

BTW, I got the idea for that shape from how I grind fly cutter tools to do aluminum. Visualize the "paddle" style ice cream scoop scraping across the top surface of a bucket of ice cream and rolling up a scoop of ice cream, and you get the idea.

Glad you were able to find a solution! :)
 

MarkM

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#55
Use your lathe to face and cut to length the riser blocks and I would add a set screw to your threaded fix. Machine will be run in reverse at times. Have the set screw thread into your male portion but don t penetrate.
 
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Doubleeboy

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#57
I come to this thread late. When parting diameters that are larger than your comfort zone, sometimes a machinist jack supporting the underside of parting tool can take a lot of chatter out and allow you to keep the pressure on the feed and go to town. A machinist jack could be as simple as a hardware store coupler nut and a bolt with lock nut.
 
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