Negative rake carbide tool mounted on a mini metal lathe. Amazing finish on Acrylic.

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More4dan

More4dan

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So I mounted my negative rake carbide holder on the quick change tool post on my mini natal lathe. I wanted to test the concept for finish on some Acrylic cut offs. After rough cutting I made a few light passes with the negative rake carbide holder. The carbide is a $2 insert. The AA was not sanded at all. I only ran some Mequires auto polish on a paper towel. This has the potential of saving me much sanding. I would likely run thru the MM pads but the as turned finish is about 95% complete.

Danny

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Looks great Dan. I'm curious if you are using a square or radius cutter, and if you are presenting if for a cut using the left and right corners, or a straight approach.

However, looks like fun!
 
mark james said:
Looks great Dan. I'm curious if you are using a square or radius cutter, and if you are presenting if for a cut using the left and right corners, or a straight approach.

However, looks like fun!
Click to expand...

It's has a 2" radius. I'm presenting it square to the blank as a finishing cut only. Cuts of about .005". At 0.010" it whines and wants to chatter. I will try rotating the post to catch the corner with a deeper cut like I do by hand.


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Last edited:
More4dan said:
It's has a 2" radius. I'm presenting it square to the blank as a finishing cut only. Cuts of about .005". At 0.10" it whines and wants to chatter. I try rotating the post to catch the corner with a deeper cut like I do by hand.


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Click to expand...

Gotcha, thanks for the info. I have several Magic skews, and frequently use them on an angle for the negative rake approach vs a straight carbide. I have been very pleased with the versatility after altering the angle. As I explore more materials/timbers, more options are very nice. Yea, I hate whiners ;).

I have bought some true negative rake carbides, but have not had any meaningful shop time the past 6 months.
 
Would you mind showing the entire lathe? BTW...my favorite blank. Nice choice. What are you putting together?
 
WriteON said:
Would you mind showing the entire lathe? BTW...my favorite blank. Nice choice. What are you putting together?
Click to expand...

I'm working on my first kitless clicker. I'm using carbon fiber for the body and acrylic for the transition between the CF and the finial and the CF and the nib section for a bit of color.

Also one of my favorite blanks.

I'll take a photo of the lathe when I get back to my shop. It's a Harbor Freight 7x10.

Danny


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Awesome post Dan, you always seem to have some great ideas. I have learned a lot from reading your posts.

Just so just so I am clear. This is not a true negative cutter insert, rather becomes a negative cutter because of the angle that the holder presents it. So, I could accomplish the same thing on my metal lathe by using a normal holder and a true negative rake cutter? Mostly because I do not have a mill yet to make the holder, but it is easy enough to make with files if it is flat.

I could just put my tool in the tool post holder like you did, but I am already an accident waiting to happen anyway, and I don't want to push the envelope.
 
Michael, I don't have a mill either. I just marked a piece of 1/2" square rod and ground on my belt sander to the line. I then drilled and tapped for the insert screw. Didn't take very long.

My goal was to use a lower cost standard cutter that I could sharpen with the same effect.

I got the idea looking at old metal lathes that held the tool bit at an angle to create a positive rake with the cutting edge ground flat, easier to grind. I just reversed it. My boring bar set mounts the insert with a negative rake to get a better interior finish.

Next I'll try a round cutter.

Thanks for the kind words.

Danny


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Last edited:
Dan, where do you get your cutters for $2.00. I need to see about getting some for my metal lathe. I find that using it I can do slime line pens faster and with less work than on a wood lathe. Also, what size is the holder?
 
I found the carbide inserts here:
m.banggood.com

[US$21.99~29.99 19% OFF] 10pcs Wood Carbide Insert Cutters For Wood Turning Tool Woodworking Lathe Tool Woodworking Tools from Tools on banggood.com

10pcs Wood Carbide Insert Cutters For Wood Turning Tool Woodworking Lathe Tool
m.banggood.com m.banggood.com

I've made about 20 orders through their site. Shipping takes 2-4 weeks but I've received everything and have been impressed with the quality. Great options for ER32 collets and chucks too.

I made the holder with some 1/2" square mild steel bar, from EBay.


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I did adjust the tool to cut at the centerline. I had similar results with Inlace acrylester too. This one done by hand.

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I'm not sure why it works but it does. I'm guessing it is a less aggressive cut than shearing with a positive or neutral rake. It would have less stress in the plastic reducing the stretching/deformation of the surface. Only a guess.


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