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15th Mar 2019, 09:40 PM #1Member
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Speed calculator on a dial for a lathe
As you do on a rainy Friday night I was perusing through the used lathes on ebay and came across a Swedish lathe with a great idea, I have not seen one before but it does imperial feet/ minute and metres/ minute.
You move the dial to the diameter and cutting speed for the metal, rotate to suite and it tells you on the bottom how fast to have the machine.
Being the novice I am I think it is a great idea.
Screen Shot 2019-03-15 at 20.37.35.png
Maybe the picture didn't come out but here is the link to the Ebay page
If you zoom in on the left you will see what I am talking about.
Big Metal Lathe - BOSS says SELL CHEAP | eBay
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15th Mar 2019, 10:06 PM #2Pink 10EE owner
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The Macson 18/21" swing lathes had a dial thing on the headstock. I think it was some sort of spindle speed calculator.
Gold, the colour of choice for the discerning person.
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15th Mar 2019, 11:13 PM #3Golden Member
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If you like it you could maybe make one out of two pieces of paper or cardboard and keep it beside your lathe.
I've seen another graphical calculator you might find useful with material type, cutting speed and diameter shown on three straight parallel lines knowing any two you can draw the line connecting two points to estimate the third
https://vanhack.ca/lib/exe/fetch.php...ting-speed.png
Am sure it is in one of the basic beginners turning books but cannot find it on my shelf, the above link shows a version of it.
This sort of graph is called a nomogram. Have done some googling but cannot find the version I am thinking of.
Bill
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16th Mar 2019, 07:03 AM #4Philomath in training
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Here's another one
Speed calc.jpg
At one stage I was going to make a copy but I find (especially with my lathe) that just because you can run work that fast does not mean it is practical - flex, chatter, shape all conspire to mean that you need to cut speed.
Michael
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17th Mar 2019, 01:54 PM #5Most Valued Member
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That's a good point Michael, but for a beginner, it's a good starting point, as it would vary according to the lathe, overhang of the tool, and many other variables.
KrynTo grow old is mandatory, growing up is optional.
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18th Mar 2019, 04:50 PM #6Most Valued Member
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- Aug 2011
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- Melbourne
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When I first started turning I felt I really needed a quick and easy spindle speed guide, so I made up an excel spread sheet and printed it out. The horizontal rows had the desired speed in M/min, the vertical columns had the diameter of the material and the corresponding cell contained the required RPM for the correct surface speed.
I hardly use it now. I go by initial guess and then feel.
SimonGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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18th Mar 2019, 05:37 PM #7Gear expert in training
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- Melbourne
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Here's the nomogram from the standard TAFE textbook "Fitting and Machining"
IMAG3239.jpg
What I really want is a feed chart; I can usually pick a good speed, but getting the chips to break nicely and leave a good finish as well is still very hit-and-miss for me.
It seems to be affected by tip radius as well, are there any rules-of-thumb?
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18th Mar 2019, 07:55 PM #8Most Valued Member
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Don't exceed the nose radius.
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18th Mar 2019, 08:00 PM #9Gear expert in training
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But the only way I'm getting a bright finish is by going deeper than the nose radius
0.5-1.0mm deep on a 0.4 rad comes up better than grinding, but 0.2 deep on the same tool comes out chewed up and horrible.
EDIT: Never mind, that's depth, not feed.
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18th Mar 2019, 08:07 PM #10
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18th Mar 2019, 09:14 PM #11Most Valued Member
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18th Mar 2019, 09:17 PM #12Most Valued Member
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- Nov 2007
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- melbourne australia
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Speed calculator on a dial for a lathe
I did similar to Simon when I started out. Fitted a tacho to the lathe and made a table of RPM vs stock diameter for various materials. Not long after I removed the tacho and threw out the table. I now make an educated guess of RPM based on the type of material, its diameter and the tool doing the work. Set the VFD and start cutting. Adjust RPM as required to give a nice finish or stop the chatter when parting off.
I actually found some of the recommended speeds and feeds didn't work. I suspect they are designed for much more rigid machines than my Hercus 260.Chris
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18th Mar 2019, 10:12 PM #13Most Valued Member
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It's theory.
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19th Mar 2019, 12:27 AM #14Golden Member
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- Nov 2010
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- Gippsland Victoria
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I often get a very good finish by turning the knife tool around to present a flat edge to the workpiece and take a tiny fluff cut. Sometimes doc can be as little as pushing slightly on the toolpost with my hand.
If you want to be geometrical about it that is an infinite tip radius and a microtadge depth of cut.
Bill
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19th Mar 2019, 03:48 AM #15Senior Member
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- Aug 2007
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- Saskatoon, Saskatchewan, Canada
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- 292
Search for machining apps and download one or two to your cell phone. Some basic ones are free and the better ones cost a few bucks. Now you have the info for lathes, milling, drilling, tapping and shop math in your pocket. They are designed for industry and carbide so you may want to be less aggressive depending on your machine but they get a newby like me in the ball park.
Pete
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