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Methods for parting off larger diameters

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Hukshawn

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#1
i have a 3" aluminum part I need to part off the lathe. My 3/32" parting tool isn't gonna do it... I don't have a stationary band saw, I have a hand held band saw. On larger diameters it tends to wander and I don't have a whole lot of meat to play with to allow that wander and just face later...
Ideas?
 

mikey

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#2
Why won't your tool work? Is it an inserted tip tool with limited travel or some other issue? A 3/32" T- or P-type tool should make that cut. The only other real options are to hacksaw it and face it or flip the part, indicate it square and face off from the other end.
 

Hukshawn

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#3
It's a parting blade in a qc tool holder. Last time I had more than 1 1/4" of blade sticking out there was a shocking amount of flex, and obviously chatter. The diameter of my part is 3.100" and that's in a shoulder from a 4.500" piece of stock. I'm just not comfortable with that much blade sticking out.

I might hack it off with the saw and do it from several directions to not give the blade a chance to deflect as much as if I were cutting right through. Then just face it. There should be enough material. I just have one shot at this...

Here's what I'm making. I was going to bore the hole after I parted it off to avoid having to drill out and bore a blind hole.
IMG_0187.JPG

I am making the piece backwards first. With the smaller diameter shoulder being cut first in the end of the stock. Then once that's finished and parted off, I will set up that shoulder in the jaws and start cutting the pulleys.
 

higgite

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#4
.... I have a hand held band saw. On larger diameters it tends to wander and I don't have a whole lot of meat to play with to allow that wander and just face later...
Ideas?
How about partially parting (grooving) the piece with your parting tool as far in as you feel comfortable and then finish with the bandsaw, giving it less time to wander during the cut?

Tom
 

Hukshawn

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#5
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.
 

mikey

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#6
Okay, I see. I wonder if you can part in part of the way and stop the lathe and slow the speed down a bit to complete the cut. If the lathe is tight and the parting tool is on center and perpendicular with the ways, a 3/32" blade should be able to make the cut. However, as you approach the inner third of the part the SFM picks up and that can cause issues; slowing down may allow you to complete the cut without under drama. Why not try it and if it fails, hacksaw the thing from there.
 

Hukshawn

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#7
I haven't much choice. I will give it a try.
 

Bob Korves

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#8
Okay, I see. I wonder if you can part in part of the way and stop the lathe and slow the speed down a bit to complete the cut. If the lathe is tight and the parting tool is on center and perpendicular with the ways, a 3/32" blade should be able to make the cut. However, as you approach the inner third of the part the SFM picks up and that can cause issues; slowing down may allow you to complete the cut without under drama. Why not try it and if it fails, hacksaw the thing from there.
Mike, SFM decreases with a smaller radius. I am sure you know that. Am I missing something?
i have a 3" aluminum part I need to part off the lathe. My 3/32" parting tool isn't gonna do it... I don't have a stationary band saw, I have a hand held band saw. On larger diameters it tends to wander and I don't have a whole lot of meat to play with to allow that wander and just face later...
Ideas?
I have parted off 3"+ steel with my 3/32" T shaped HSS parting tool in a BXA holder without problems. Aluminum should be much easier. Get the details correct: blade absolutely square to the work, cutting edge on center or very slightly below, carriage locked and everything tight, lower than normal speed (perhaps 300-400 RPM for your aluminum 3" job). Feed at a steady but not aggressive pace, try to keep the tool cutting continually if all keeps going well, you can use a cutting fluid like WD40 or kerosene to keep the aluminum from welding to the parting blade. If it starts going bad, just stop and go with a hacksaw or band saw. I do not power feed when parting off, l like to feel the cut in progress...
 

accunlmtd

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#11
Try going part way in with your tool, then back out, slide the parting tool, over a bit to make the groove wider. You make be getting a lot of side friction. May be basic info, but on deep cuts, it is hyper-critical to make sure that the blade is perfect in alignment.
As mentioned above, good steady feed.
I have made 3 to 4 in. cuts on my old Atlas (lantern style) at 500 rpm. On my SB Heavy 10, it is a breeze
 

royesses

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#13
I part 3" aluminum 6061 T6 on my little 7x16 HF with 3/32" t type blades regularly. Batten down the hatches first ah I mean tighten the gibs, lock down the saddle and set the parting tool for just enough stick out to get about 1/4" deep into the victim. Don your protective head gear and apply oil and set the spindle speed very slow. I start out at 30 rpm. Then advance the tool to get a nice curl going and as you get further in you can set the stick out deeper and slightly speed up the spindle. Keep dripping oil on it. Also if it starts to chatter get more aggressive with the feed. Works great for me. The chips come off in these tiny little curls. It has actually become a fun thing to do. I don't know what lathe you have but the procedure should be adaptable to it. Then again I might be crazy.

Roy
 

Hukshawn

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#14
I don't have any issues parting normally. I have a 10x28 lathe. It is reasonably well set up, decent rigity. I don't usually have any issues parting 0ff. I've been doing a lot of it lately since I've been making this belt conversion or the mini mill. But I hadn't parted of such a big item before. I assume my previous attempt to part off a large diameter with lack luster results was due to the blade not being straight. I have thought about that but forgotten.

I usually just part off at speed. Works fine. I do like the little curly bits. I had picked a few out one day and wanted to do something with them as they looked neat... as soon as I opened the gear head lid to change the pulley, I lost them. Lol.
I'll give this a shot tonight. See how it goes. I hope I don't screw it up. It's my only piece of stock for this pulley. Pressures on.
 

Billh50

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#15
I have parted off 5 inch aluminum with a 3/32 tool... I started with the blade fairly short, cut as far as I could, then extended the blade and cut more. I parted the 5 inch diameter in 3 steps like this.
I have done this also with great success.
The few times I haven't done this I have bored the hole so I don't have to cut as deep. If done right a bottomed hole can be bored deep enough to be in the middle of the cut off.
 

Bob Korves

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#16
Two more things. When cutting, keep it cutting, don't let it rub without cutting. Also, don't even think about parting off with a tailstock center pushing on the work...
 

Hukshawn

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#21
Anyone have any slick methods to glue aluminum back together?
I still have a chunk left, but not deep enough to remake this part.


The part that too short (referring to the drawing) is the .630" needed for the pulleys. I have .493" left. I don't think there's enough to try and salvage the pulleys. But I wonder if I can figure out a method to thread the pulleys on to the shaft portion...
 

Hukshawn

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#22
Oh frig... I'll just go across town tomorrow and buy more stock... Uhhg


Classic Shawn move...
 

Hukshawn

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#25
I'm so annoyed. Lol
Starting out in machining is really frustrating. I gave up on the lathe for a while, I'm on the mill now. Making the riser blocks for the motor mount. Just rectangular blocks. Faced them then was milling them to size. The only sharp end mill I have is a 1/4" that's only 5/8 long. I have to flip the piece around 4 times to face the ends. But a longer tool would save all sorts of time... Annoying... I know the tools I need to do what I want... they're all just so damn expensive!
 

Bob Korves

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#27
Sometimes the parting tool will cut a cone and make the part too small. It is always worth having an allowance for the cut to be less than square across the face and then face it to length after parting it off.. A parting blade that is not square with the work, or not ground square on the parting blade itself sometimes causes that, and I think a loose carriage can also cause that problem. Sometimes it just happens anyway, even with a good technique...
 

mikey

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#29
I'm so annoyed. Lol
Starting out in machining is really frustrating. I gave up on the lathe for a while, I'm on the mill now. Making the riser blocks for the motor mount. Just rectangular blocks. Faced them then was milling them to size. The only sharp end mill I have is a 1/4" that's only 5/8 long. I have to flip the piece around 4 times to face the ends. But a longer tool would save all sorts of time... Annoying... I know the tools I need to do what I want... they're all just so damn expensive!
Why not use your fly cutter to square and dimension the part?
 

Hukshawn

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#30
I bought a 1/2" 2 flute end mill with a 1 1/4 cutting surface. More than enough to face and dimension anything I'm doing right now. I have a bunch of other end mills from the old tool box but the only one that's sharp was a 1/4" 4 flute.
 
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