Suggestions on cutting acrylics and such

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Henry

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Hello all

So I recently picked up a metal lathe from Craig’s for cheap and am wanting to learn how to make kitless pens with it. It’s the harbor freight brand I believe. I’m experimenting but having little luck making clean cuts. In fact some cuts looks as though it’s causing the acrylic to heat up and melt. My questions are thus:

A. How fast should I make the cuts?

B. How aggressive can my cuts be and what amount of material is recommended to remove per pass?

C. Tooling? Carbide vs HSS

D. Any resources that you can recommend? I’ve been watching a lot of YouTube but putting it in practice is another story.

IMG_1421.JPG

This is what my attempts have been looking like FYI.

Thanks!! Take care


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1shootist

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Are you using a quick change tool post or the 4 sided clamp style that comes with the metal lathe ?
I can turn pens, acrylic, wood whatever on my metal or wood lathe so it can definitely be done so don't give up.
I use carbide on either type lathe, from my experience I've found I use the metal lathe at approx 1500 to 2000 rpm while the wood lathe is higher at 3400 rpm. The amount of cut is basically the same on either.
I'm assuming you have a mini metal lathe and ifso you can purchase a adapter from littlemachineshop.com that clamps on to the 4 sided clamp that is a tool post so you can use your wood turning tools with it. But you don't absolutely need to have this, you can still make pens with your metal tools...I used it both ways for a while til I decided to get a wood lathe.
Theres really no short answer I can give..just keep at it.
 

bmachin

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Hi Henry,

If you want to make kitless (or any kind of) pens, you should buy this book:


Richard Kleinhenz was a member here a number of years ago.

Go to this channel on YouTube: https://www.youtube.com/user/Steve4948/videos
The videos are old and things go wrong, but Steve explains what he's doing and why. In addition some of his Toastmaster's speeches are quite funny.

As far as your current metal lathe experience is concerned I'm reduced to making a few guesses and comments:
1. In my experience, you should be able to turn almost any plastic at almost any speed as long as the speed is sufficient and the tool is sharp.
2. Carbide or high speed steel makes no difference although it is easier to make a tool which is better adapted to the properties of the specific plastic you are turning if you make your own hss tools.
3. What sort of tool are you turning with now? is it something that came with the lathe when you bought it? It's quite possible that it's just totally dull and acting like a scraper, or that the geometry is just totally wrong for turning plastics or at least the plastic that you are working with.

Hope this helps

Bill
 

Henry

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Thanks for the reply !

I do have a quick change tool post that came with the lathe. My current tools are HSS and are 1/4 in I think. I’ve only been playing with it for a few days so experience is definitely a factor. Thank you for the links. I’ll check them out.

How do you prevent the overheating? Cutting lube maybe? Although I never thought to use that on acrylic. I’ll probably invest some money on proper cutters and see how that goes.

Thanks again




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More4dan

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Sharper cutting tool with a more aggressive cutting angle than a metal cutting bit. Metal cutting bits are usually ground at 8-15 degree angle. For wood and acrylic I would use 20-30 deg and grind to a knife like edge using high speed steel. Think shaving sharp. Touch up the edge occasionally with a diamond card.

The carbide cutter designed for metal would be too dull for tuning wood and acrylic. The wood turning carbide is ground to a sharp edge with a steeper angle.

Sharp will cut cooler and you shouldn’t need cooling media or cutting fluid for acrylic. I will make roughing cuts of 20 thousandths and finishing cuts of 5-10 thousandths. If interested, I can show you a simple mod to be able to turn by hand so you can get tapers and curved surfaces.

Danny

Hope this helps.




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Henry

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Sharper cutting tool with a more aggressive cutting angle than a metal cutting bit. Metal cutting bits are usually ground at 8-15 degree angle. For wood and acrylic I would use 20-30 deg and grind to a knife like edge using high speed steel. Think shaving sharp. Touch up the edge occasionally with a diamond card.

The carbide cutter designed for metal would be too dull for tuning wood and acrylic. The wood turning carbide is ground to a sharp edge with a steeper angle.

Sharp will cut cooler and you shouldn’t need cooling media or cutting fluid for acrylic. I will make roughing cuts of 20 thousandths and finishing cuts of 5-10 thousandths. If interested, I can show you a simple mod to be able to turn by hand so you can get tapers and curved surfaces.

Danny

Hope this helps.




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I’m very interested thanks!


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magpens

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@Henry

I have been using a metal-working lathe to make pens out of acrylic for over 8 years.

Different Acrylics differ greatly as to what speed they will tolerate, both for drilling and for machining.

I never go over 1000 rpm with any acrylic. . I use, mainly, tungsten carbide cutting tools for machining and HSS drill bits for drilling.
The key thing is to use sharp tools, if you can ... but well-used tungsten carbide tools often work OK at lower speed.

For some acrylics, I limit my speed to 500 rpm or less, based on my experience at the time with that particular acrylic.

WD-40 works pretty good as a lubricant for both drilling and machining.

I see that you are getting a wide variety of answers. . I offer my comments based solely on my own experience.
 

Henry

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@Henry

I have been using a metal-working lathe to make pens out of acrylic for over 8 years.

Different Acrylics differ greatly as to what speed they will tolerate, both for drilling and for machining.

I never go over 1000 rpm with any acrylic. . I use, mainly, tungsten carbide cutting tools for machining and HSS drill bits for drilling.
The key thing is to use sharp tools, if you can ... but well-used tungsten carbide tools often work OK at lower speed.

For some acrylics, I limit my speed to 500 rpm or less, based on my experience at the time with that particular acrylic.

WD-40 works pretty good as a lubricant for both drilling and machining.

I see that you are getting a wide variety of answers. . I offer my comments based solely on my own experience.
Thank you for your reply. Anything helps ! My initial thought as to why my cuts are not as clean is because my tool is dull. But also I was thinking I was going too slow. You kind of debunked that theory lol. I feel more confident at slower speeds anyhow given that it’s all new to me.


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More4dan

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High speed and sharp HSS. High speed and dull will overheat for sure. Also check that you’re cutter is hitting the blank on center. Too high and you won’t cleanly catch the cutting surface rubbing below and building heat.


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Henry

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So I was browsing the inter webs some more and found that people can cut a square blank to round to roughly the desired dimensions with one pass !! It’s incredible. I’m beginning to think my feed rate maybe too fast on this lathe. Not sure though as I am just doing a visual comparison between my progress and the videos. And I’m at the slowest setting it seems. Just got to practice more I’m sure. Thanks for the great feedback!!


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More4dan

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So I was browsing the inter webs some more and found that people can cut a square blank to round to roughly the desired dimensions with one pass !! It’s incredible. I’m beginning to think my feed rate maybe too fast on this lathe. Not sure though as I am just doing a visual comparison between my progress and the videos. And I’m at the slowest setting it seems. Just got to practice more I’m sure. Thanks for the great feedback!!


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I’m guessing it wasn’t with a mini lathe. I’ve seen some full size engine lathes do similar with steel. I’ve tried with wood once and the blank came apart, Dramatically!


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Henry

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You’re probably correct. I’m not brave enough to try that on my mini lathe anyhow. For my square blanks I think I’m going to round them to tough dimensions on my wood lathe first then do the machining phase over the mini lathe. All this requires some patience and I’m notoriously impatient lol.


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More4dan

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Henry I do the opposite. I round on my mini lathe cutting half a turn on the cross per pass (20 thousandths). I use a 1/4” HSS bit I ground just for acrylics and wood. I turn between centers with a 60 degree dead center with a straight shaft clamped in my chuck. I’ll move to my wood lathe to drill and turn to final shape.


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