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Prokop
01-23-2008, 10:15 AM
I tried to look it up, but with no luck.

Anybody could enlighten me with the basic of grinding my own bit for thread cutting?
I bought inner and outer tool holder (carbide) from Grizzly, but they are too big for a thread I am trying to cut. Now I am thinking about grinding an old bit to the proper shape.

Thank you.

Carld
01-23-2008, 10:21 AM
I don't have a clue what you are talking about in refference to the "tool" you bought.

I prefer to use 3/8" cobalt steel tool bits with the 60 deg angle ground on them. If you don't have a lathe tool grinder then you have to do it free hand and use a tool called a fish hook. It's a thread tool for setting the bit angle and set up the bit in the tool holder.

Do you have a book on lathe opperation?

Prokop
01-23-2008, 10:28 AM
I should have use a link:

http://www.grizzly.com/products/Threading-Tool-Holder/G7030
http://www.grizzly.com/products/Internal-Threading-Tool-Holder/G7033

my book is too general on that topic:(

Carld
01-23-2008, 10:34 AM
Are you doing internal or external? Those look like good tools and should work.

SGW
01-23-2008, 10:52 AM
There's nothing particularly magical about it. Grind an included angle of 60 degrees. Be sure there is enough clearance on the leading side to clear the helix angle of the thread.

Willy
01-23-2008, 11:21 AM
Here's a couple of links to some simple thread grinding jigs.

http://www.dogcreek.ca/Thread_grinding_jig/threading_tool_grinding_jig.htm

http://www.gadgetbuilder.com/ThreadingTools.html

smiller6912
01-23-2008, 11:54 AM
Grinding the bit is the easy part. Any bit ground to a 60 deg included angle with a decent relief (5-10 deg.) will work. The real trick is technique. It does take some practice. I have cut some nice looking #4-48 threads with a 3/8 HSS tool that I ground on my belt sander (of all things). DO get a tool called a center gauge (fish tail) you will need it both for cutting the bit and for setting it up in the lathe.
(also, try doing a Google on "single point threading" , you should get some good reference material like, http://www.lathes.co.uk/latheparts/page6.html )

outback
01-23-2008, 10:46 PM
Below is a toolbit grinding fixture I came up with years ago. Made it mostly to utilize the coolant available on surface grinders. I grind all my toolbits with the fixture.
http://img.photobucket.com/albums/v30/jglass/Shop%20Demonstrations/CAD%20Drawings/bitfixture0001.jpg

Machine ground toolbits.
http://img.photobucket.com/albums/v30/jglass/toolbits0001.jpg

outback

Lew Hartswick
01-24-2008, 12:00 AM
Here is another version.
http://i233.photobucket.com/albums/ee238/LewHartswick/sameforthreadingtool.jpg
...lew...

Your Old Dog
01-24-2008, 06:55 AM
There's nothing particularly magical about it. Grind an included angle of 60 degrees. Be sure there is enough clearance on the leading side to clear the helix angle of the thread.

I was having a lot of trouble with threading till my neighbor made me a bit at work. I use it as a pattern bit to set up my grinder. I tilt the table 10 degrees and then shoot for the included angle of 60 degrees (30 degrees each side) as I run the cobalt bits across the wheel and it works great. Dog can now cut threads, aint' it great? LOL I didn't have near enough clearance before and it caused chattering and muddy cuts.

I actually went through the trouble of making a slide kind of like the letter "k" with 30 degrees on each side. It works great but looks whimply but hey, I'm a backyard machinist with an emphasis on the backyard!