Milling chipper knives

PassNCrash · Nov 18, 2020

Hi,
Does anyone have recommendations for tooling to mill chipper knives.
I normally grind about 20 per month.
These are the knives that tree services use for chipping branches etc. on the roadside.
They normally feed about 1 rock for every 3 branches. So they sometimes have large chips.
I often have to remove over 0.100" so it takes a long time on the grinder. (knife type)
I have a bridgeport type mill with only a R8.
If I could mill first it could save a lot of time.
One supplier told me the knives are RC56.
They average about 5/8" thick by 3" by 8" long with a 30 to 40 bevel.
They would be ground after milling so finish does not matter.
Thoughts on a R8 tool and inserts?
Anything I have tried just destroys the insert.
Local suppliers have not been much help.

Thanks

ChipSplitter · Nov 18, 2020

PassNCrash said:
Hi,
Does anyone have recommendations for tooling to mill chipper knives.
I normally grind about 20 per month.
These are the knives that tree services use for chipping branches etc. on the roadside.
They normally feed about 1 rock for every 3 branches. So they sometimes have large chips.
I often have to remove over 0.100" so it takes a long time on the grinder. (knife type)
I have a bridgeport type mill with only a R8.
If I could mill first it could save a lot of time.
One supplier told me the knives are RC56.
They average about 5/8" thick by 3" by 8" long with a 30 to 40 bevel.
They would be ground after milling so finish does not matter.
Thoughts on a R8 tool and inserts?
Anything I have tried just destroys the insert.
Local suppliers have not been much help.

Thanks

Short answer: Yes.

Long answer: Yeeeeeesssss, very carefully.

Mike1974 · Nov 18, 2020

Not rigid enough for inserts in this application, and hardened steel. Are you face/end milling, or side milling? First thing I would try is a moderate cost/quality 5 flute 1/2" end mill and side mill with it. Experiment with cut amounts and I think you will find some kind of decent compromise between tool life and time savings vs all grinding. Also, use the entire flute length if possible.

DDoug · Nov 18, 2020

What kind of grinder ?
H.P.?
Wheel size ?
Coolant ?

kenton · Nov 18, 2020

I milled some for a friend when I was in school. I got an old 1/2 inch 4 flute carbide end mill with chipped corners and side milled the blades off the back of the mill table. If I remember correctly I ran around 100 rpm, full axial depth of cut, and took .015-.020 radial depth of cut per pass. I had to remove about .060 per side so it didn't take long. The tree cutter said he really liked the extremely fine serrations that side milling them left.

Hobby Shop · Nov 18, 2020

Why not weld the .100” chips first and grind them back to original?

gbent · Nov 18, 2020

I don't like the idea of an impact loaded, high speed rotary part that is hardened having an arc strike. Incredible stress riser.

It would be interesting to know the material. I'm guessing S7, but if its D2 that would explain a lot of the grinding difficulty.

DDoug · Nov 18, 2020

gbent said:
I don't like the idea of an impact loaded, high speed rotary part that is hardened having an arc strike. Incredible stress riser.

It would be interesting to know the material. I'm guessing S7, but if its D2 that would explain a lot of the grinding difficulty.

Better yet....weld them up with some hardfacing….

Gordon Heaton · Nov 18, 2020

digger doug said:
Better yet....weld them up with some hardfacing….

That's what I'd do, and with a TIG. The 'arc strike' can be as gentle and spread as much as you want, and it isn't going to be that much stress for such a small relative surface. I mean, they're 5/8" thick and the weld is on a beveled edge, then ground.

Jeff_M_PA · Nov 18, 2020

Unless things have recently changed, these kind of knives most commonly D2.

Street · Nov 18, 2020

I think interrupted cut is going to kill the tips that can do it...you can try then you will know.
May cost you some dollars to find out.

Yep D2 and the place i worked at ground every blade no matter how bad it was, ie chunks missing etc.

don't think you can weld it, HAZ is going to be brittle i would think so blade will grenade.

dian · Nov 19, 2020

dont they use an intermediate layer so this can be done?

DDoug · Nov 19, 2020

dian said:
dont they use an intermediate layer so this can be done?

It's called "buttering".

Bill in PA · Nov 19, 2020

digger doug said:
What kind of grinder ?
H.P.?
Wheel size ?
Coolant ?

When I used to grind machine knives, .100" was just a nick (normal wear). On a 35hp grinder with a segmented grinding head it would have been silly to do anything but let it grind. Set the amount of downfeed and come back in a few minutes. Even on the low 10hp machines, it did not take long. Always worked on something else while it was running.

20-25 years ago, we charged $1.00 per inch per edge to resharpen chippers. So, three 9" chippers would be $54.00 for the set. Target shop rate at the time was $100/hr.

Bill

BSCustoms · Nov 19, 2020

This sounds like a costly experiment. Can you rough them down with a 7" angle grinder?

PassNCrash · Nov 19, 2020

Bill in PA said:
When I used to grind machine knives, .100" was just a nick (normal wear). On a 35hp grinder with a segmented grinding head it would have been silly to do anything but let it grind. Set the amount of downfeed and come back in a few minutes. Even on the low 10hp machines, it did not take long. Always worked on something else while it was running.
20-25 years ago, we charged $1.00 per inch per edge to resharpen chippers. So, three 9" chippers would be $54.00 for the set. Target shop rate at the time was $100/hr.

Bill

Thanks for all the replys,

Bill it sounds like what you used to do is what I am doing.
My grinder is 10HP but takes a long time.
Maybe I need to learn to be more aggressive with the grinding.
My feed is currently fixed at 0.01mm (0.004")per full pass (left and right)
There are times when 1/4" has to be removed.
So it could take 500 passes. (even at 25 seconds thats 3hrs)
Maybe downfeed on both ends?
Using a 60 grit resinoid cylindrical stone 10"
Sounds like my rates are 25years behind the times!!
weld build up is not an option.
The grinding is not difficult, just time consuming on damaged blades.
I did try milling with a TMX 3 insert 1-1/4" dia cutter with TNG inserts.
They chipped quickly.

Thanks
Glen

DDoug · Nov 19, 2020

PassNCrash said:
Thanks for all the replys,

Bill it sounds like what you used to do is what I am doing.
My grinder is 10HP but takes a long time.
Maybe I need to learn to be more aggressive with the grinding.
My feed is currently fixed at 0.01mm (0.004")per full pass (left and right)
There are times when 1/4" has to be removed.
So it could take 500 passes. (even at 25 seconds thats 3hrs)
Maybe downfeed on both ends?
Using a 60 grit resinoid cylindrical stone 10"
Sounds like my rates are 25years behind the times!!
weld build up is not an option.
The grinding is not difficult, just time consuming on damaged blades.
I did try milling with a TMX 3 insert 1-1/4" dia cutter with TNG inserts.
They chipped quickly.

Thanks
Glen

Coolant ? You should be flooding it on.

Resinoid 60 grit ? I'm not a grinder person but that sounds "not good".

tdmidget · Nov 19, 2020

Agreed, wrong wheel in every way. Get a vitrified wheel no finer than 46 grit. Itb sounds like this a traverse type surface grinder. If the surfaces are flat then a Blanchard would just the ticket.

kenton · Nov 19, 2020

If you want to use your mill you will need to side mill with an end mill, a face mill will not work. Like I posted earlier it is a good way to get the last bit of use out of endmills with chipped corners.

That said it sounds like a large grinder and someone who knows how to run it is probably faster.

PassNCrash · Nov 19, 2020

Thanks for the reply,

Any feedback on the grinding process appreciated.
I was using a 46 grit vitrified at one point.
The reason I changed was for other items I am grinding.
For those items sharpness and surface finish are important.
The chipper knives are probably less than 15% of the work for this machine.
Is the difference with a 46 Vitrified enough to warrant changing stones?
When I changed from 46 vit to 60 res I also changed the mounting hub from 12" to 10"
It seems much easier to get what you want in 10" stones.
I would have to buy a new stone to go back to vitrified.(I am a small shop)
The 60 res was recommended by the supplier (Gockel USA)for the bulk of what I grind.
It seems for work really well for most items.

Glen

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