How large of a part can safely be parted off.

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737mechanic
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How large of a part can safely be parted off.

Post by 737mechanic »

I have a 5in diam. x 2.5in long piece of aluminum and I would like to cut off about 1.25in of it but can not clamp it in my horz. bandsaw. I will need a 5/8 diam hole in the center and I was wondering if I would be able to part this off without much problem. I have a 12x36 g4003g lathe. Seems like a lot of part off blade to have sticking out.

I was thinking of doing it in steps, stick the blade out about 3/4in and part as deep as I can then pull out and stick out another 3/4in and keep doing this, that way the deep cuts would help support the blade as it got longer.

Any tips?
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ctwo
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Re: How large of a part can safely be parted off.

Post by ctwo »

I did a 3" diameter SS solid rod on my little Logan with a 3/32" thick blade, and it seemed fine. I did the last 1/4 or so with a hacksaw though. I'd of liked a 1/8" blade, I think...
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SteveHGraham
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Re: How large of a part can safely be parted off.

Post by SteveHGraham »

I guess this will be a bummer, but I suppose you could part it as far as possible and then finish with a hack saw. You should have no problem using a parting tool to reduce the diameter by 3", leaving you with less than 2" to finish by hand.
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SteveM
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Re: How large of a part can safely be parted off.

Post by SteveM »

737mechanic wrote:I was thinking of doing it in steps, stick the blade out about 3/4in and part as deep as I can then pull out and stick out another 3/4in and keep doing this, that way the deep cuts would help support the blade as it got longer.
That's exactly what I did to part 3-1/2" steel on an Atlas.

The sequence was:
Hang the tool out 1/4"
Part in back gear with really slow feed
When you run out of tool, back out the carriage and advance the tool.
Repeat

Image

Note that I had a center in the end. NEVER PART WITH A CENTER. I got to within 1/4" and then hacksawed the rest.

The pain-in-the-butt part about using the Aloris-style parting blade holder is that the tool is on an angle, so when you pull the blade out more, it goes up, so you have to reset the height EVERY time.

Steve
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mcostello
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Re: How large of a part can safely be parted off.

Post by mcostello »

In a long ago issue of The Home Shop machinist someone wrote an article about parting off 11" bronze. He said His personal best was 18". Parting blade was bucked up from below with a thin strip of steel tapped into place under the parting tool. Never seen it done but would like to watch standing behind the Guy. :)
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ctwo
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Re: How large of a part can safely be parted off.

Post by ctwo »

Steve, that is a tid-bit gem... Why the concern for the center?

Chip evacuation seems to be a concern, but I found it to be tool-bit grabbing.
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
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spro
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Re: How large of a part can safely be parted off.

Post by spro »

Parting tool depth has been an issue for a long time. There are parting blade holders which extend way out under the blade. I saw one used on a big old lathe in an old book. This was back when the dials were smaller and the compound could be parallel to the cross slide. The extension below the cutting blade was supported by a pair of roller bearings, rolling over the cross slide ways? or supported by rails attached to the saddle slots. More to the present; ISKAR has inserts and a blade type holder for deep cut.
SteveM
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Re: How large of a part can safely be parted off.

Post by SteveM »

ctwo wrote:Why the concern for the center?
When the parting is completed, the center will prevent the part from dropping, and it will cock sideways and jam.

My guess is that the blade will snap off and the part will be ruined at best. Worst case, the compound or other parts on the lathe could get damaged.

Last night I had to part off 1" steel 6" from the chuck (piece was too big to fit thru the spindle and I didn't want to waste the stock), so I used a live center until it was just about done, then I did the rest VERY slowly.

Steve
piedmontg
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Re: How large of a part can safely be parted off.

Post by piedmontg »

Hi

A couple of questions first so I understand your goal.

You are cutting it in half ie 1.25 sort of as you will only have about 1.125 of usable material left over is that a correct interpretation?

Is your final part to be 1.25 or did you allow for cleanup and you need a part thinner?

If I actually needed a nice 1.25 with a .625 hole I would not bother with the aggravation of parting it off just to have a small leftover piece. Yes I have parted off some wild stuff so it can be done if necessary. I would face one side nice, turn it around and machine it to the width I wanted. Then I would bore or ream a nice round hole.

Just another approach.

Bob
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737mechanic
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Re: How large of a part can safely be parted off.

Post by 737mechanic »

Ok so I got the job done and it was easier than I anticipated. Parted off the entire 5in piece and have 1.25" left. Took about 15 min to get through it but went smooth and left a great finish.


(piedmontg) Thought about that but didn't want to face off 1.25" worth of material that I paid for, besides I wanted as much left over for other projects down the road.
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Re: How large of a part can safely be parted off.

Post by spro »

So you did it but there was something more than extending the cutting tool. You are keeping secrets! Just kidding. Glad it worked. Pretty durn deep.
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737mechanic
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Re: How large of a part can safely be parted off.

Post by 737mechanic »

This is what I made with the piece. it is a poly-rib pulley for the lathe. I am putting a brake and changing the dual v belts with a single 10 rib belt. I will be sure to show the finished project once I get it done.
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