Setting the compound at 0* or 30*

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GlennW
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Re: Setting the compound at 0* or 30*

Post by GlennW » Sun Jan 06, 2019 1:46 pm

Look at your tool overhang in relation to the center line of the cross feed slide.

That creates seriously unbalanced loading on the carriage and cross slide under heavy cuts.

That's one way to break the end off of the compound slide if a tool digs in!

I only turn the compound like that when absolutely necessary.

I also never leave the compound slide extended past it's base for the came reason, and also leave the slide locked until it is needed.
Glenn

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Re: Setting the compound at 0* or 30*

Post by tornitore45 » Sun Jan 06, 2019 2:00 pm

Look at your tool overhang in relation to the center line of the cross feed slide.
Glenn, i suppose you are referring to RSG picture and the CCW torque on the compound slide resulting from cutting forces.
You imply the compound slide should be backed off to bring the tool tip close to the compound center of rotation?
Mauro Gaetano
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GlennW
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Re: Setting the compound at 0* or 30*

Post by GlennW » Sun Jan 06, 2019 3:53 pm

Yes, sorry I wasn't very clear.

Not necessarily backing the cpmpound slid up, but rotating it to an angle closer to the cross slies and keeping the tool closer to the cross slide center line.

Over hang like that can also induce some pretty good chatter as well.

There are times when a large diameter part will not swing over the cross slide or carriage and you have to use the compound like that to reach it, (which may be exactly what RSG was doing) but if not needed, I personally wouldn't use a setup like that for general turning.
Glenn

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RSG
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Re: Setting the compound at 0* or 30*

Post by RSG » Sun Jan 06, 2019 9:04 pm

GlennW wrote:
Sun Jan 06, 2019 3:53 pm
There are times when a large diameter part will not swing over the cross slide or carriage and you have to use the compound like that to reach it, (which may be exactly what RSG was doing) but if not needed, I personally wouldn't use a setup like that for general turning.
This is why I am asking these questions, to learn the best practice. I typically turn aluminum around 6" dia., if setting the compound at 29* is inherently more rigid then I will start the practice immediately.
Vision is not seeing things as they are, but as they will be.

John Hasler
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Re: Setting the compound at 0* or 30*

Post by John Hasler » Sun Jan 06, 2019 9:28 pm

In the photo the base of the toolpost has nothing under it so the force on the tool can bend the topslide down. It's best to get the entire base of the toolpost over the compound so that it is fully supported. It doesn't really matter what combination of toolpost position, topslide position, and compound angle you use to get there.

Sometimes, though, you have to let it stick out because that's what works for the job at hand.

whateg0
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Re: Setting the compound at 0* or 30*

Post by whateg0 » Mon Jan 07, 2019 9:51 am

RSG wrote:
Sun Jan 06, 2019 8:55 am
GlennW wrote:
Sat Jan 05, 2019 9:11 pm
I seldom set my compound slide to zero as it blocks my view of the cross slide dial...
Perhaps 0* on my machine and yours are different then Glenn? Setting mine at zero aligns it perpendicular to the top slide which is completely out of the way of the cross feed dial, unless I am miss understanding you.
Many people use the compound in that orientation so as to use the compound's dial for measurements in Z. I have a DI on the ways for that purpose.

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liveaboard
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Re: Setting the compound at 0* or 30*

Post by liveaboard » Mon Jan 07, 2019 12:09 pm

I have no way to measure carriage movement; so I keep the compound at zero so I can use the dial to measure the length of a cut or bore.
Since it won't be very accurate, I use the carriage for cutting once the dimension is established.
this gets me to within +- 0.2mm quickly, which is usually close enough [lengthwise] for the work I do

John Hasler
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Re: Setting the compound at 0* or 30*

Post by John Hasler » Mon Jan 07, 2019 1:16 pm

liveaboard wrote:
Mon Jan 07, 2019 12:09 pm
I have no way to measure carriage movement; so I keep the compound at zero so I can use the dial to measure the length of a cut or bore.
Since it won't be very accurate, I use the carriage for cutting once the dimension is established.
this gets me to within +- 0.2mm quickly, which is usually close enough [lengthwise] for the work I do
I use a micrometer carriage stop for that.

RSG
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Re: Setting the compound at 0* or 30*

Post by RSG » Mon Jan 07, 2019 3:10 pm

John Hasler wrote:
Sun Jan 06, 2019 9:28 pm
In the photo the base of the toolpost has nothing under it so the force on the tool can bend the topslide down. It's best to get the entire base of the toolpost over the compound so that it is fully supported.
I was always under the impression that it was best to dial the top slide in as far as it could go to increase rigidity, sort of locking it by tightening the dial to its max. So what you are saying is, that's incorrect? Should I be backing off the top slide so the base is underneath that. If so is there a chance it could move under machining operations?
Vision is not seeing things as they are, but as they will be.

Harold_V
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Re: Setting the compound at 0* or 30*

Post by Harold_V » Mon Jan 07, 2019 4:24 pm

RSG wrote:
Mon Jan 07, 2019 3:10 pm
I was always under the impression that it was best to dial the top slide in as far as it could go to increase rigidity, sort of locking it by tightening the dial to its max.
That's exactly opposite of reality. When you dial the compound to the end of its travel, the T slot will be well past base support, so it offers a greater opportunity for chatter, and leaves the compound at risk of being broken if there's a crash.
So what you are saying is, that's incorrect?
From my perspective, yes, using your lathe as you suggested is not in your best interest. It most likely isn't much of a problem for you, however, as you're not really loading your machine because of the nature of your work. Try turning a rough piece of steel with that setup, especially using positive rake, where tool loading is at its greatest, that might not be the case. It's also risky if you're running excessive positive rake, where the tool has the potential to hog.
Should I be backing off the top slide so the base is underneath that. If so is there a chance it could move under machining operations?
Yes, a good chance, especially if the gib is loose. That's why I said I keep the compound on my lathe locked unless the slide is in use. I do that by tightening the gib. It takes but seconds for the gib to be adjusted, with the benefits of the tightened gib outweighing, by a HUGE margin, the small effort to do so.

H
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Harold_V
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Re: Setting the compound at 0* or 30*

Post by Harold_V » Mon Jan 07, 2019 4:28 pm

liveaboard wrote:
Mon Jan 07, 2019 12:09 pm
I have no way to measure carriage movement; so I keep the compound at zero so I can use the dial to measure the length of a cut or bore.
Since it won't be very accurate, I use the carriage for cutting once the dimension is established.
this gets me to within +- 0.2mm quickly, which is usually close enough [lengthwise] for the work I do
It's dead easy to build a bracket to hold a long travel indicator. While my Graziano has a calibrated dial on the carriage feed, I still use such a setup. It's far more reliable, and lightning fast to adjust to the desired location. My setup allows for the use of longer than 1" travel indicators, too. I recommend it highly, especially if you face multiple lengths of cuts that demand precision. By recording positions once established, you can do multiple parts in far better time.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

pete
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Re: Setting the compound at 0* or 30*

Post by pete » Mon Jan 07, 2019 8:01 pm

Strangely it seems to be more of a UK or mainland Europe practice to use the top slide for parallel turning. Many of my books and magazines are published in the UK and it's very common to see that shown or mentioned. North America it seems much more universal to use the carriage and that dial indicator trick. I tried using the top slide a few times and it seems more logical, quicker and easier to use the carriage that was designed for and the lathe built to follow a straight parallel path down the lathe bed.

It took me far longer to figure out that a high rigidity situation while machining is much more important than it should have. In a 3 dimensional space there's 6 degrees of freedom for the work piece that have to be restrained. The cutting tool tip also has exactly the same requirement. Compounding the problem for that tool tip is every component on the lathe that both supports and allows the tool to move has minor and unavoidable clearances and varying amounts of rigidity or deflection under the cutting loads. I have no idea of how to provide a link to the actual video since the title and his user name is in Russian Cyrillic. But there's a Russian language video on YouTube where he ran an exhaustive series of tests on what looks to be roughly a 16" - 18" swing heavy duty professional quality lathe. He checked multiple areas with indicators under less than excessive cutting loads that showed fairly high deflection and movements in the lathes parts that directly affected the tool or work position. A great many of those tests were for areas I'd never considered would move as much as they did. Even not understanding a single word in Russian his demonstrations and force vector diagrams were more than a bit educational.

There's a few professional machinist's on YouTube that went to a lot of trouble to both build and lock down riser blocks on there lathes cross slides that accept the quick change tool post so the top slide wasn't needed or used for most turning operations. ROBRENZE to use as one example did so for his Hardinge HLV. And that lathe isn't known for being a very flexible or inaccurate machine. I'd also have to judge his intelligence and abilities as being the very best on YouTube. He did mention that his second lathe would be used for any taper turning or threading that was required so his riser block was semi permanent. For most of us it would depend on just how much single point threading and taper turning was being done on average to justify if the change over time is worth it when that top slide is needed of course. I seem to recall he mentioned better accuracy and part finish just from using a riser block and removing his top slide.

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