Turning speed

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glw20109

glw20109

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I've read many different posts on the optimum turning rpm for acrylic pens with different answers. I'm sure we have all read about the latest craze, chatGPT by Openai. Well I thought why not, so I asked chatGPT for the optimum lathe rpm for turning a .75 inch acrylic pen blank. This is the reply:

The suggested lathe RPM (revolutions per minute) for turning a pen with acrylic material can vary depending on the specific type of acrylic and the diameter of the blank. However, as a general guideline, a range of 2000 to 3000 RPM can be used.

It's important to note that different types of acrylic have different properties and may require different RPMs. Therefore, it's recommended to refer to the manufacturer's instructions or seek advice from experienced turners in your community to determine the optimal RPM for your specific acrylic pen turning project. Additionally, it's always a good practice to wear proper safety gear and adhere to all manufacturer's instructions and safety guidelines when operating a lathe.

The optimum lathe RPM for turning a .75 inch diameter acrylic blank can depend on several factors, such as the type of acrylic material, the desired finish, and the cutting tool being used. However, as a general guideline, you can use the following formula to calculate the ideal lathe RPM:

Lathe RPM = (Cutting Speed x 4) / Blank Diameter

Where Cutting Speed is the speed at which the cutting tool contacts the material, and is typically measured in feet per minute (FPM) or meters per minute (MPM).

For acrylic material, a recommended cutting speed is around 500-600 FPM (152-183 MPM). Let's assume a cutting speed of 550 FPM.

Using the formula above, the optimum lathe RPM for turning a .75 inch diameter acrylic blank would be:

Lathe RPM = (550 FPM x 4) / .75 inches = 2,933 RPM (rounded to the nearest whole number)

If you work the formula, the rpm gets higher as you turn the blank smaller, e.g. at .5 inch the speed is 4400 rpm and 5866 rpm at 3/8 inch.

Interesting answer. Not sure where to find the cutting speed for the different types of acrylic are. I can get 3200 RPM out of my lathe so that is what I will try turning at.
 
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Have to be honest I have no idea what speed I turn at but I turn all pen material with the same speed and that includes segmented metal pens. Have never changed belts on lathe. I use the VS switch to adjust speed within the range the belt is set at. Slow to fastests it can go I finish and sand with slowest and turn with fastest. It is not so much speed to tur acrylics as it is sharp tools. presenting tools the proper way and touch with tools. steady and slow will get you there.
 
InkyMike said:
This is the way. 🤠
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jttheclockman said:
Have to be honest I have no idea what speed I turn at but I turn all pen material with the same speed and that includes segmented metal pens. Have never changed belts on lathe. I use the VS switch to adjust speed within the range the belt is set at. Slow to fastests it can go I finish and sand with slowest and turn with fastest. It is not so much speed to tur acrylics as it is sharp tools. presenting tools the proper way and touch with tools. steady and slow will get you there.
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Actually, THIS is the way. Have never moved the belt. It spins somewhere between about 3200 and 100. Sharp tools and tool angle. YES!
 
Too complicated - I use about 2500 for pens. Works well for all materials. I also sand & polish at that speed.
 
ed4copies said:
I wonder how many pens that AI has turned?!?!?!
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Thing is, ChatGPT is just an advanced google search engine - it cribs all it's information from what it finds "out there" and munges it into some amalgamated whole. Kinda like the Poetic Edda when you think about it.


Odds are that some of what it came up with was based on what it found on this forum. :/
 
I think it is a decent answer with good explanation. Not that I would specifically follow it, but it looks like a good effort.
 
I noticed a few bowl turners in the early days coming over to IAP and turning pens. Some said the had been told 700 rpm MAX and a few others would say 800 or so. While that was a general good rule of thumb depending upon the size of the bowls, it certainly did not translate to pens. even now about once a year, someone will bring that up.

Gary, I occasionally use the simple mathematics that you used - to show how SLOW the cutting speed is at 700 RPM on a 3/4" diameter versus the cutting speed of 700 RPM on a 12" bowl. HUGE difference.

Below is a BOWL lathe speed as it relates to diameter. I would like to see another chart to include 1", 3/4", 5/8" and 1/2".
And That does not include special densities and material.
 

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I'm same as Todd. I run almost full speed. Laguna 12|16 has a top end of 3624 rpm. I generally run at 3500. Wood or resin.

I slow it down to the mid 2000s for sanding and about 400 for applying CA.
 
Let's not lose sight of the original post. The fascinating thing is that it came up with 2933 rpm and we all pretty much turn at about that. So, we are the real-world proof that Artificial Intelligence is accurate. That's kind of interesting on a few levels if you think about it.

So...We used our organic human intelligence to arrive at that number through practical application. What's wild is that Artificial Intelligence came up with the same number WITHOUT EVER TURNING A F**KING PEN!! That is impressive and scary at the same time.
 
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MRDucks2 said:
I think it is a decent answer with good explanation. Not that I would specifically follow it, but it looks like a good effort.
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ramaroodle said:
Let's not lose sight of the original post. The fascinating thing is that it came up with 2933 rpm and we all pretty much turn at about that. So, we are the real-world proof that Artificial Intelligence is accurate. That's kind of interesting on a few levels if you think about it.

So...We used our organic human intelligence to arrive at that number through practical application. What's wild is that Artificial Intelligence came up with the same number WITHOUT EVER TURNING A F**KING PEN!! That is impressive and scary at the same time.
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AI is only as accurate as the quality of the programs & data driving it. Since that data is derived from experienced turners, it would be surprising (and an indictment of its programmers) if it didn't produce those results.
 
Edgar said:
AI is only as accurate as the quality of the programs & data driving it. Since that data is derived from experienced turners, it would be surprising (and an indictment of its programmers) if it didn't produce those results.
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Agreed. I was taking it a few steps further with AI's ability to make seemingly rational human decisions for us in the future. Sorry. Off topic! :)
 
The biggest advancement of chatGPT is that it can present the information in a way that seems to have been written by a human. Honestly, if someone had posted that and claimed it as their own, the only way I would question it would be if the writing style was different from other posts by that user.
 
jttheclockman said:
Have to be honest I have no idea what speed I turn at but I turn all pen material with the same speed and that includes segmented metal pens. Have never changed belts on lathe. I use the VS switch to adjust speed within the range the belt is set at. Slow to fastests it can go I finish and sand with slowest and turn with fastest. It is not so much speed to tur acrylics as it is sharp tools. presenting tools the proper way and touch with tools. steady and slow will get you there.
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I think John nailed it here. Its more about the tool and how its presented to the blank.

I turn at maximum RPM for the belt setting I use, which has a range of 1000 - ~3600 RPM. I run slower for sanding, but pretty much max for turning. I use gouges for wood, and my easy wood tools with negative rake bits for resins. I will adjust the angle of the bit depending on the material. An angled round or square bit gives you more of a sheer cut, which can reduce the aggression a lot when you need to.
 
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