Basic Tool Geometry and Tool info:

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RoutnAbout
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Basic Tool Geometry and Tool info:

Post by RoutnAbout »

This is the end view of a 4 fluted endmill with arrows and letters to help with the information to describe basic geometry and terminology for grinding purposes.

Legend:
a: Rake Greater degree of rake makes the tool more aggressive.
b: Core Diameter: Tool diameter minus flute depth times 2 equals core diameter.
c: Primary Land Angle on Margin: Greater degree of angle makes the tool more aggressive.
d: Heel of primary: Should be a smaller diameter that cutting diameter
e: Primary landwith on end:
f: Tool Diameter:
g: Flute Depth: Should be approx. 20% - 18% of total tool diameter.

I can come up with a chart of the dimensions of basic standard tool geometries if you need them
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Last edited by RoutnAbout on Sat Jul 15, 2006 7:17 pm, edited 6 times in total.
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RoutnAbout
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Post by RoutnAbout »

Important geometries when resharpening and buying new tooling:
(a)Rake
(c)Primary angle on diameter land
(g)Flute depth
(e)Primary angle of the land on the end (but not shown from the proper view point).
If you can keep these 4 items in relationship to each other as the tool shrinks in diameter you will have a long lasting sharp cutting tool

When resharpening tooling you can request certain changes to the geometry of that tool, providing there is enough material on the tool to make your changes. ( you can not turn a .400 inch (10.16mm) into a .500inch (12.7mm) tool)

Most of the time when a tool is being resharpened, only the diameter and end of the tooling are resharpened. You can also requst to the have the tool refluted and by doing so it will be as good if not better than the original tool. (Not all places can reflute tools.) By resharpening only the tool diameter, the Rake angle will decrease and so will the depth of the flute. By the time you've lost 1/2 of the original flute depth the tool is scrap and will not preform.
If the tool is refluted as well as the diameter, then this tool will preform basically until you can't sharpen the tool anymore. If I've explained this well enough, you can see you can take a .500in (12.7mm) tool and can resharpen it down to a .25in (6.35mm) tool and still cut like a new tool. Providing the grinder has changed all of the geometry as the tool grows smaller(such as the core diameter).


There are days during a manufacture job that everything goes good, once the program running and all tweaked in for the above said geometry and all I have to do is load and go, but that doesn't mean the work is done. Because there is things like wheel breakdown, the machine warms up or cools down, junk or trash on the tool blank. The operator has to make sure the tool is to print or customers request. And during the run of that order, the tool should be spot checked. Like every other job it becomes a job for some people and they lack in this department. So this is where some tools of the same size and geometry may out preform other like tools.

I hope this helps and was clear and descriptive enough to answer some questions and to spark new ones.
Last edited by RoutnAbout on Sat Jul 15, 2006 10:02 pm, edited 1 time in total.
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Post by dighsx »

Fantastic post Don! How does the quality of the carbide effect the resharpening? I worked with a guy who would go on and on about how CMT carbide was a better ‘grade’ (?) then most the others. Also when you get a tool resharpened do they tell you what the new dia. is or do you (the customer) have to measure that?

One final question for now, if you take a bit someplace to get resharpened, if you tell them to resharpen it, what would you get? I guess what I mean is do you have to know about all these things (rake, dia. land, flute depth, Pri. Angle) or will they just do all this for you by default?

Again great post.
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Jay (www.cncjay.com)

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Post by RoutnAbout »

Thanks Jay, and Good Questions, keep them coming

Jay
How does the quality of the carbide effect the resharpening?
The quality of the carbide don't affect the process of the manufacturing of the tool, but does have its place in how well the tool holds its cutting edge in differant types of material.

We do use different grades of carbide mainly for the companies that will be using their tools with the different kinds of metals. We tend to use the middle of the road grade for wood and plastics, because of cost. And the harder the carbide the more brittle it is.
I have been quoted a price on a .375inches(9.525mm) diameter by 2.500inches (63.5mm) long at 8 dollars each. Thats just the blank, it needs to be ground and sharpened on top of that.
Sometime this next week I'll get an idea of cost per blanks in a couple different grades to show a comparison.

Jay
I worked with a guy who would go on and on about how CMT carbide was a better ‘grade’ (?) then most the others.
My guess that he feels that CMT tools are giving him better results are because that maybe CMT make their tool grinders hold tighter tolerances, thus providing a better quality tool.

Jay
One final question for now, if you take a bit someplace to get resharpened, if you tell them to resharpen it, what would you get? I guess what I mean is do you have to know about all these things (rake, dia. land, flute depth, Pri. Angle) or will they just do all this for you by default?
There are standard settings for all the geometry.
A good grinder will look at the tool and make a judgement call on his part to make that tool sharp. If it don't have many chips along the diameter of the cutting edge he may choose not to resharpen inside the flute. ( which will reduce the rake angle a little but not noticeable ) But if there are several chips on the cutting edge, Its best to grind approx .010-.015 off of the diameter and approx .008-.010 inside the flute. By doing this brings it back to the original cutting defaults with the exception of the size. (Its now at least .010 smaller because you hit that drywall screw that your using to hold down your part)

You don't need to know what these parameters are to have them regrind your tooling. They should have all of this info (that is if they want to stay in business). But what I'd do is when I take my tooling in to have resharpened is let the right people know that you've been having some trouble with them cutting correctly and they should pay closer attention to how they are grinding your tools.

Usually the grinders don't tell you what they have ground your tool at. But if you want them to, just ask them to mark the shank with a marker. We do have a very large customer ( approx 700 peices a month of the same tool) that have requested us to do this for them.

I've went out and purchased a 6inch calipers and measure my own. ( unless i use my micrometer)

Again great questions Jay, keep them coming
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Post by Burchtree »

Hi Don
I have been touching up my V bits and small dia. round over bits, cove bits, etc. with a diamond file. I don’t do large dia. Bits because of balance issues. What advice could you give us on proper honing of bits? The best diamond files to use? What jigs or fixtures we could use?
Thanks
Dan
P.S. Your knowledge of tooling sure is a blessing to this forum

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RoutnAbout
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Post by RoutnAbout »

Hi Dan,

Diamond files are pretty good and have their place for knocking burrs off, but they are much more coarse than a diamond honing stone. I get my diamond stones through work, but a few weeks ago I ran across the same diamonds stones at the Woodcraft store.

As far what kind of fixture to hold the tool while honing and sharpening by hand is hard to find.
This may sound kind of crude, but I've clamped down on the shank with a small pair of visegrips to help hold the tool, and then used the honing stone on the flate face of V-bits and round-over bits ( this will work on all flat faced tools.) Be real careful to not round over the edges of these faces where it meets the diamter as it will make it more dull. By using a flat stone on a flat surface and keeping the stone flat to the surface you will be able do a pretty good job and should get you through the job.
Dan here is small portable indexer that uses 5C collets and could be used to hold the tool while honing, you being a machinist, have probably seen and used something like this.

Here is a small manual grinder. Its made by Cutter Master. Be sure that you forward to the next page at that site as they have several good pictures of the setup. They also have couple attachments you to do most tools. Its pricey, but not out of reach.
I've used this type of machine and its pretty accurate. As you can see from all the pictures, you can grind the ends, diameter and even resharpen the inside of the flutes. Someday I'm going to duplicate the machine. We all get in that pinch of we should have could have bought or had that tool sharpened last week if we had only known. This will take care of that.
Hope this helps
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Post by Goodoil »

All very interresting
Since i've moved I had to source a new saw sharperner and i'm allways praising him on how sharp the router bits are after he is done no mater what the brand even a cheap Chinese brand cuts sharp.
So its because he sharpens the flutes!
Paul

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RoutnAbout
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Post by RoutnAbout »

Paul, I'm glad you've found a grinder that knows what he's doing.

Yes he's probably regrinding the diameter, and the flutes with the proper rake.
By any chance do you know what he's using? Anca? Walters, Schutte?? If you don't know, its not a big deal. Just curious.

I wonder if the name on his shirt was " Sparky "
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