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Old 01-26-2012, 10:57 PM   #1
PerryRT
 
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Default Lathe Tool Nose Radius?

So I've been fiddling around with grinding my own HSS lathe bits lately mostly using the old South Bend pamphlet that I got here:

http://dale.chatham.org/Interests/MetalWorking/HowToGrindLatheTools.pdf

It's been something that's been on my "list" for years - inserts are great, but I like to know about lo-tech methods too... and I suspect that the price of inserts won't be dropping any time soon. I've intentionally been making some "bad" ones so I can tell the difference between bad and good cuts in different metals.

Actually, I'm finding the "bad" ones easier to make, at the moment!

One thing's got me stumped, though. Nose radius. For the life of me, I can't seem to get a uniform nose radius on my tools - they generally come out... well..... lumpy. Non uniform. And certainly not to any specific radius known to man.

Barring some sort of jig, is this just one of those "experience things" I'll get better at? Or is there a trick to it?

Also, is it better to grind the nose radius parallel to the angle of the front clearance (i.e. after the front clearance, so that the nose radius can be seen down the relieved front edge of the bit?) Or before the front clearance so that the nose radius is only at the very top edge and fades as you move down the bit?



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Old 01-26-2012, 11:24 PM   #2
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Default Re: Lathe Tool Nose Radius?

I grind all flats then hone all flats on an oil stone. then hone the radius on the same oil stone .

this thread explains and shows with pictures how I hone radii

http://www.homemodelenginemachinist.com/index.php?topic=15493.0
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Old 01-26-2012, 11:41 PM   #3
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Default Re: Lathe Tool Nose Radius?

Interesting! (Great pictures, btw) So you don't even radius on the grinder at all!

I have a set of Arkansas stones, but wasn't too worried about using them yet until I could get a feel for the angles and basics.... I'll try that!

Thanks!

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Old 01-26-2012, 11:58 PM   #4
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Default Re: Lathe Tool Nose Radius?

Quote:
So you don't even radius on the grinder at all!
If i am doing a small radius for regular turning I just stone by hand .
A bigger radius grind your flats then turn the grinder off and do two or three quick passes on the turning wheel to rough out the radius. then hone as mentioned before.
For a forming tool say a 1/16 inch radius on an 1/8 tool bit or larger then rough in on the grinder or belt sander then finish on a hone.
Also keep in mind the better grades of tool steel will last a lot longer in use but also take a bit more work to grind.
more info on HSS steel here
http://www.arwarnerco.com/warner_materials.html
Good people to deal with they support the hobby and quality is top notch made in USA Latrobe PA do not expect enco import prices but a good value I am a satisfied customer have never been disappointed in any of there products. I use there tools on a regular basis.
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Old 01-27-2012, 05:47 AM   #5
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Default Re: Lathe Tool Nose Radius?

Quote:
Originally Posted by PerryRT

Barring some sort of jig, is this just one of those "experience things" I'll get better at? Or is there a trick to it?
Without a jig the "experience" or practice is the thing

Quote:
Also, is it better to grind the nose radius parallel to the angle of the front clearance (i.e. after the front clearance, so that the nose radius can be seen down the relieved front edge of the bit?) Or before the front clearance so that the nose radius is only at the very top edge and fades as you move down the bit?
I like to run mine all the way down the front edge so the is no chance of unwanted rubbing.

If you are right handed, the left hand holds the bit at the required angle to the wheel and the right hand rotates the tool using the thumb and forefinger of the left hand as the pivot point. (Well that's my way, developed unconsciously over the years, I only really thought about it when I tried to write it down )

On our size machines these radii are usually not much bigger than 1/16"

Hope this helps.

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Old 01-27-2012, 07:12 AM   #6
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Default Re: Lathe Tool Nose Radius?

I do it the same way - and I'm left handed!

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Old 01-27-2012, 09:24 AM   #7
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Default Re: Lathe Tool Nose Radius?

@ PerryRT

Read the South Bend tool grinding pdf and was quite surprised to find that it advocates having the tool height above centre (top of pamphlet page 6), by 5 degrees or 3/64 (1.2mm or about 0.5mm per cm) per inch of diameter when working with steel or cast iron.

I have never come across this before. Has anyone tried it and does it make a difference ?

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Old 01-27-2012, 09:42 AM   #8
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Default Re: Lathe Tool Nose Radius?

I grind nearly all my tools on a belt sander and simply tip the table down a few degrees and grind the flats and radius at the same setting. The only tools that get honed are of the woodworking variety

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Old 01-29-2012, 04:28 PM   #9
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Default Re: Lathe Tool Nose Radius?

The little diamond stones sold to sharpen knives - the solid ones, not the ones with holes in them - are perfect for putting a radius by hand on a HSS lathe bit.

Quote:
Read the South Bend tool grinding pdf and was quite surprised to find that it advocates having the tool height above centre (top of pamphlet page 6), by 5 degrees or 3/64 (1.2mm or about 0.5mm per cm) per inch of diameter when working with steel or cast iron.

I have never come across this before. Has anyone tried it and does it make a difference ?
I have always set the tool dead center for all operations, and it works fine. I cannot see that the recommendation you found would make much of a difference in a home shop. So much of that stuff, especially speed & feed recommendations, can be really baffling, but it's good to keep in mind that a lot of that data is created for a business machine shop where the absolute highest metal removal per unit time can be important for profitability.
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Old 01-29-2012, 11:41 PM   #10
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Default Re: Lathe Tool Nose Radius?

Quote:
Read the South Bend tool grinding pdf and was quite surprised to find that it advocates having the tool height above centre (top of pamphlet page 6), by 5 degrees or 3/64 (1.2mm or about 0.5mm per cm) per inch of diameter when working with steel or cast iron.

I have never come across this before. Has anyone tried it and does it make a difference ?
You know, I read that and decided that perhaps that was advice for a rocker toolpost and didn't apply when using a QCTP....

I've always gone with square on the center line, and it seems to work OK both on my Sherline and my 9x30.

Thanks to everyone for the advice. I cut a new bit this afternoon and spent a couple of minutes rounding it by hand (as Tin Falcon) suggested.

Easy enough, and a lot more controllable than doing it on the grinder. I may try that again in the future, but this works for now.

Thanks!


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