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Old 11-25-2007, 12:11 AM   #1
Murray Kish
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Sharpness...

I feel stupid.

I've been having a heck of a time getting my cutoff blade to work the way I *think* it should work. I've been trying to cut small 1 or 2mm hex rod, and it just hasn't been working well at all.

So, today, I decided I needed a bench grinder (cuz every good machinist has a bench grinder, right?). I sharpened up a few things, and then ran my cuttoff blade under it a couple of times.

Wow, what a difference.... cuts like butter now.... I know they're supposed to be sharp when you get them, but I must have worn mine down somehow (not exactly sure, since I haven't cut much with it??)

Murray
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Old 11-25-2007, 06:42 AM   #2
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Re: Sharpness...

Quote:
Originally Posted by Murray Kish
I feel stupid.

I've been having a heck of a time getting my cutoff blade to work the way I *think* it should work. I've been trying to cut small 1 or 2mm hex rod, and it just hasn't been working well at all.

So, today, I decided I needed a bench grinder (cuz every good machinist has a bench grinder, right?). I sharpened up a few things, and then ran my cuttoff blade under it a couple of times.

Wow, what a difference.... cuts like butter now.... I know they're supposed to be sharp when you get them, but I must have worn mine down somehow (not exactly sure, since I haven't cut much with it??)

Murray

Murray, My cutoff tool came with two blades and both them were totally useless out of the box even though they looked sharp. What kind of grinding wheel are you using?
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Old 11-25-2007, 10:19 AM   #3
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Re: Sharpness...

Cutting metal creates wear, even though you're cutting a soft metal with a hard metal, while the soft metal is visibly removed, the hard metal will be losing its edge too.

It's kind of like the fact that you use an Xacto only to cut plastic or card, yet eventually the Xacto becomes dull too.
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Old 11-25-2007, 10:34 AM   #4
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Re: Sharpness...

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Originally Posted by cinqster
What kind of grinding wheel are you using?
I believe it's a 60 grit Alum Oxide wheel on there right now. The other side has a brass 'brush' wheel, which I may replace with a different grit stone wheel.

Murray
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Old 11-25-2007, 10:40 AM   #5
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Re: Sharpness...

Grinder basics....

How in the ($@&%(* do I measure/set the angle of my steady rest to the grinding wheel? My rests are almost infinitely adjustable, but I have no idea how to set it to get a specific degree of cut?

ie. I have one of those cutoff 'bits' that are typically used on heavier/bigger lathes, and I want to thin it down to make thin/narror grooves (like 1mm or less). I would like to set the table so that the wheel takes slightly more from the bottom of the cut, than the top (to give it some relief).

The only way I've figured out so far is by trial and error? Is there a way to set up the table so that it will cut a specific angle?


Thanks

Murray
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Old 11-25-2007, 02:07 PM   #6
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Re: Sharpness...

Quote:
Originally Posted by Murray Kish
Grinder basics....

How in the ($@&%(* do I measure/set the angle of my steady rest to the grinding wheel? My rests are almost infinitely adjustable, but I have no idea how to set it to get a specific degree of cut?

ie. I have one of those cutoff 'bits' that are typically used on heavier/bigger lathes, and I want to thin it down to make thin/narror grooves (like 1mm or less). I would like to set the table so that the wheel takes slightly more from the bottom of the cut, than the top (to give it some relief).

The only way I've figured out so far is by trial and error? Is there a way to set up the table so that it will cut a specific angle?


Thanks

Murray
Murray, any good lathe book will give you very specific grinding angles for each kind of tool, and there are different recommended angles for each material you want to cut - which makes things even more complicated. I've got some diagrams somewhere if you want them scanned.

I've got the same problem and my grinder has THE most useless tool rests (a bit of old 1/8 steel sheet bent at 90 degrees) I've seen accurate tool holders that adjust in 3 planes on tool sites but can't an example to hand right now. If I get my milling machine sorted I may make something up instead. In the meanwhile I've got a couple of those old angled wooden kitchen knife holders knocking around the garage, so I may fashion a guide from them! Yeeeehaaa!

An alternative is to use a small griding wheel in the lathe chuck and put the tool in the tool post to grind - a lot of people seem to use this method but there's no way I'm having grinding grit all over my lathe!
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Old 11-25-2007, 02:46 PM   #7
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Re: Sharpness...

Sharp cutting tools are absolutely crucial for cutting metal. But a 60 grit grinding wheel is not really a sharpening tool- it's for shaping only. Sharpening has to be done in addition to shaping, and any improvement in your cutting edge using a coarse grinding wheel is really by luck.

These are what I use for sharpening my cut off blade and lathe bits-



Diamond lapping tools. They do a very nice job- the only trick is holding a consistent angle while sharpening. Someday I'm going to make a jig for holding and sharpening bits....
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Old 11-25-2007, 08:49 PM   #8
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Re: Sharpness...

Thanks for all the help/advice guys.

MPWR - I actually have a set of those diamond lapping tools (the exact same ones in the picture).... I'll dig em out and put them with me 'machining' stuff...!!


cingster - Thanks for the offer. I have a few books and some info on grinding lathe bits already. What I'm really struggling with is how to actually grind that specific angle (which it looks like you can identify with). Even if there was a jig, I assume it would have to sit on the rest, which assumes that it was pre-set at some angle already (90 deg?). I just don't know how to measure/set that angle. Maybe it's just not that critical???

Thanks guys.

Murray
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Old 11-26-2007, 04:03 AM   #9
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Re: Sharpness...

Murray, either this guy is very, very good at the freestylie...or mad!

http://tinyurl.com/3dhhb8

The holder that I've seen had degree scales on it so you could gauge the angles accurately but I still can't find it. This guy's made a solution here:

http://tinyurl.com/yvvcce
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Old 11-26-2007, 08:01 AM   #10
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Re: Sharpness...

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Old 11-26-2007, 08:33 AM   #11
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Re: Sharpness...

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