roughing radius on scraper blade carbide inserts?

metalmagpie · Jun 8, 2020

I now have two quality scraper carbide inserts. One is made by Sandvik and the other was sold by Biax. Both are roughly 1" square.

I am aware of Rich King's suggestion to grind 4 different radii on the 4 sides of each insert. I may do that and I may not.

I know that green grinding wheels are sold for grinding tungsten carbide. I have never used one, nor do I own one. I do own several bench grinders, a surface grinder and a 1750 rpm motor set up to run Chinese diamond lapping plates. Plus, I have a buddy with a Baldor model 500 "carbide grinder", although I don't know if he has any green wheels.

It seems to me that trying to rough in e.g. a 40mm radius on one of those little Chinese lapping plates is not a very workable solution.

So I'm thinking about picking up a 6" regular type 1 wheel to put on a bench grinder. I have a Darex M-series base and motor, which make up a pretty good quality bench grinder.

Can you suggest a particular grinding wheel I should use?

metalmagpie

CarbideBob · Jun 8, 2020

I will cry if you use a "green" wheel on carbide.
The worst EL-cheapo import diamond wheel so much better. Check E-yuk.
Green wheels do not grind carbide, they chip it away like a chisel and hammer.
Scraper blades in volume are normally finished with a 600 to 1200 grit and the wheel must flow into the carbide.
A 1200 grit wheel will not like stock removal, roughing who cares, 180 grit the go to for me.
Four sided presents fixture problems for my machines but a nice $600,000 Wendt or Agathon will do it all in one clamp but what is there of grind lines in the wrong plane.
Bob

gbent · Jun 8, 2020

if you are going to scrape, just spend the money now and buy an Accu Finish. Any money you spend on anything else is pissed away. You will understand after you use an Accu Finish.

CarbideBob · Jun 8, 2020

Accu Finish nice and it seems well loved, what happen to the old "Cold-Grind" machines?
Does Accu Finish make a swing attachment for producing normal sized cutting tool radii?
Bob

Paolo_MD · Jun 9, 2020

Generally people (myself included) prefer to use a diamond wheel of some sort run at lower RPM (~200-350), since the rate of material removal is still decent, it produces much less heat, and it is easier to keep it wet without too much mess.

In hand-scraping blades it is not extremely critical to obtain a perfect radius. Therefore, I believe that most of us free-hand it, rather that building some sort of custom swinging fixture with a feed mechanism for the blade.

Said so, Stefan Gotteswinter has a Youtube video of cutting the radius using a Deckel-style T/C grinder:
YouTube

Paolo

michiganbuck · Jun 9, 2020

A diamond wheel is best for grinding carbide. Green wheels are hard enough but often don’t give the smooth sharp edge. 120 grit is Ok, 320 better/good, 500 near a mirror and good, 1200 and finer best. The finer the wheel the longer to grind and the more heat. Dry grinding can make fine fractures in the edge, wears the wheel faster, makes breathig dust, and can wear the wheel faster. (Running a 500 to 1200 dry is tough on the wheel and on the carbide.)
Wet is best and a small aquarium pump and a bucket is enough with a 1/16” or 1/8” hose to the wheel, and a catch tub under. A milk bottle cut plastic washer on your motor /grinder shaft flush to the grinder case will keep coolant out of your motor. kill the coolant before you kill the grinder. *Must have a three-prong plug and an extra ground wire is good/safer when you use coolant on any machine..
Plate mount or type 1 wheel can be used but both should be indicated and made to run true (<.001 to .003) at start of use. Best to try to grind/travel along wheel so you avoid wearing a hole/dent in your wheel, so work/part is acting like it is also a wheel dresser.

metalmagpie · Jun 9, 2020

michiganbuck said:
A diamond wheel is best for grinding carbide. Green wheels are hard enough but often don’t give the smooth sharp edge. 120 grit is Ok, 320 better/good, 500 near a mirror and good, 1200 and finer best. The finer the wheel the longer to grind and the more heat. Dry grinding can make fine fractures in the edge, wears the wheel faster, makes breathig dust, and can wear the wheel faster. (Running a 500 to 1200 dry is tough on the wheel and on the carbide.)
Wet is best and a small aquarium pump and a bucket is enough with a 1/16” or 1/8” hose to the wheel, and a catch tub under. A milk bottle cut plastic washer on your motor /grinder shaft flush to the grinder case will keep coolant out of your motor. kill the coolant before you kill the grinder. *Must have a three-prong plug and an extra ground wire is good/safer when you use coolant on any machine..
Plate mount or type 1 wheel can be used but both should be indicated and made to run true (<.001 to .003) at start of use. Best to try to grind/travel along wheel so you avoid wearing a hole/dent in your wheel, so work/part is acting like it is also a wheel dresser.

All respect, michiganbuck, but when I say "roughing out the radius" I am NOT looking for a mirror edge, or even one with a negative 5 degree rake. I am just talking about taking a carbide blank shaped like a postage stamp and knock away most of the excess. Then it's time for the diamond wheels and aquarium pumps.

I notice they make diamond wheels for 4.5" angle grinders now. Maybe I'll try one of those.

metalmagpie

lucky7 · Jun 9, 2020

When someone like one of the above posters, who has spent a good part of their life working as a grinder hand says something, I listen.

L7

Btw, I’m also a happy user of accu finish slow speed grinder for both roughing and finishing. Works very well.

michiganbuck · Jun 10, 2020

Guess one can rough in with most any wheel green or a cement grade diamond wheel. Might get .020 or so chips in the rough-in edge.

Back when diamond wheels were sky high, we did a lot of green wheel finishing. That took frequent dresses because green wheels break down a lot ..and the grind had to be toward the fine/cutting edge to make sharp.
Now a days a good set-up makes Diamond wheels more cost effective than green wheels..

Still, I remember the difference of the whisper smooth grind if natural diamond wheels.
Seems they went whoosh/woosh across carbide. And manufactured diamond wheels went rat,tat,tat,tat
Natural is D, and manufactured diamond is MD. I know you don't even see that on wheels anymore.

Larry_D · Jun 10, 2020

You can get electroplated diamond discs for $15-20 each. Stefan Gotteswinter is where I learned of them. Those coupled with a disc sander is what I did. I just threaded the shaft on the disc sander and can swap out the diamond discs in a minute. Use the low grits to rough in shape, but mostly the 1200 grit stays on it for re-sharpening once I've got the shape established. The disc sander table allows you to set the rake angle you want and grind it accurately. Whole setup cost me an afternoon and maybe $100. Biggest issue is most disc sanders run faster than necessary, I keep intending to slow mine down but it hasn't been an issue so far. I just keep it misted with water with a squirt bottle.

Mark Rand · Jun 10, 2020

I use a resin bonded diamond wheel on the surface grinder. Drill a hole in the blade carrier at the radius you want from the edge. Then pivot it around a vertical post on the mag-chuck to grind the radius on the blade Support the carbide end of the tool with another block mounted on the mag chuck to keep it all horizontal. A suitable wheel height gives the desired relief angle at the same time.

Once you've done that, a lapping disk on the lathe with an angled rest, keeps the edge mirror sharp.

Richard King · Jun 10, 2020

From now on your going to have to buy a used Glendo as the factory no longer makes them. Here is a recent letter I received from them:
Hi Rich,

Hey I need to let you know that we have dropped the Accu-Finish line recently. The stake through the heart was the motors were getting some expense and they wanted us to by a 1000 at a time. It just didn’t make sense to continue. We will continue to sell wheels and most of the parts. It is sad for me because that was my main product line when I started her 19 years ago. The GraverHone on our GRS Tools product line is the only thing that would come close to the Accu-Finish. I have had a few of the automotive guys buy them to lap their Serdi style cutters in. I will send a GRS tools catalog to you.

Aaron McMichael | Sales Representative

Glendo LLC

p: 800-835-3519 | 620-343-1084

w: grs.com e: [email protected]

a: 900 Overlander Rd. Emporia, KS 66801

Richard King · Jun 10, 2020

As far as the sharpening, the way the diamond wheels have come down in price you can get a better or sharper edge with a diamond wheel or disc then goofing around with a green wheel. I used a green wheel 50 years ago... If someone brought a green wheel to a class I would kick him in the arsch. lol...not really..... it is so easy to make a diamond lapper...
Alternatives to Glendo / Accu-Finish style Diamond Lapping Wheels

Paolo_MD · Jun 11, 2020

metalmagpie said:
All respect, michiganbuck, but when I say "roughing out the radius" I am NOT looking for a mirror edge, or even one with a negative 5 degree rake. I am just talking about taking a carbide blank shaped like a postage stamp and knock away most of the excess. Then it's time for the diamond wheels and aquarium pumps.

I notice they make diamond wheels for 4.5" angle grinders now. Maybe I'll try one of those.

metalmagpie

If you insist in using a green wheel, do yourself a favor: bring the grinder outdoor, wear a mask and Tyvek suit or clothes that you can throw away after the (extremely messy job).
A few years ago I did this mistake. When you could get Sandvik inserts cheap on eBay I got a few and set up to grind them at different radii. The green wheel was completely gone after roughing no more than ten inserts. On contrary, on a different carbide grinder I do have two resin-bond diamond wheels: 150 and 600 grit. They still look almost like new after shaping and honing numerous inserts.
Of course, as soon as I got a chance and the money, I bought a KK-Calamar carbide grinder. I made an adapter with embedded magnets so that I can swap electroplated wheels in second (right now I also have a Glendo, which is more compact and portable, and am building a similar adapter for that machine as well).
I generally use WD-40 on the electroplated wheels.

Paolo

lucky7 · Jun 11, 2020

Does the occilating spindle of a KK Calamar really help? The cynic in me thinks it’s a gimmick but maybe I’m wrong.

L7

Paolo_MD · Jun 11, 2020

I think it helps at least to not digging grooves in the wheel.

I see it more useful when sharpening a lathe tool/indexable insert to a specific geometry, but it also works well when freehanding.

If it annoys you, you can stop the oscillating motion by just by moving a lever.

If I were to choose between a Glendo Accu Finish and a KK-Calamar, I'd simply go for the cheapest of the two. If the price is the same, probably, I'd get the KK-Calamar. But, given that I haven't played around much yet with my Glendo, I could be biased.

Paolo

metalmagpie · Jun 11, 2020

I remembered I have a couple of round 6" diamond wheels. One is 1/4" wide and the other is 1/2" wide.
I put them on an old Craftsman block grinder (3450 rpm) and took a scraper insert and tried just grinding on it. I should mention the 1/4" wide diamond wheel's edge is resin bonded 100 grit.

The insert had a tiny nick on its surface. Maybe it was from someone putting it to a green wheel, don't know. :-) Anyway, I decided to just take the edge back until the nick was gone. If the insert had been steel and I'd been on my 2x72" belt grinder, the job would have taken 20 seconds. As it was, it took a very long time. Maybe 25 minutes. And that wasn't even reshaping the edge, just taking it straight back. Maybe I'm just impatient? But it seems to be very very slow to me.

And let me be clear - I am not advocating a green wheel, or waterjet, or EDM or any particular technology. I am simply asking what is the effective way to reshape a square insert edge into a radiused one in a reasonable amount of time.

I already have the Stefan-type Chinese 6" lapping wheel set. I'm hoping for something at least an order of magnitude faster.

metalmagpie

michiganbuck · Jun 11, 2020

Running with coolant a diamond wheel often grinds twice as fast, and with not getting hot one can stay in the grnd until done.
Dry grinding also can cause chipping in the edge going off the carbide..so if you want both edged sharp you are out of luck.

gbent · Jun 11, 2020

metalmagpie said:
I remembered I have a couple of round 6" diamond wheels. One is 1/4" wide and the other is 1/2" wide.
I put them on an old Craftsman block grinder (3450 rpm) and took a scraper insert and tried just grinding on it. I should mention the 1/4" wide diamond wheel's edge is resin bonded 100 grit.

The insert had a tiny nick on its surface. Maybe it was from someone putting it to a green wheel, don't know. :-) Anyway, I decided to just take the edge back until the nick was gone. If the insert had been steel and I'd been on my 2x72" belt grinder, the job would have taken 20 seconds. As it was, it took a very long time. Maybe 25 minutes. And that wasn't even reshaping the edge, just taking it straight back. Maybe I'm just impatient? But it seems to be very very slow to me.

And let me be clear - I am not advocating a green wheel, or waterjet, or EDM or any particular technology. I am simply asking what is the effective way to reshape a square insert edge into a radiused one in a reasonable amount of time.

I already have the Stefan-type Chinese 6" lapping wheel set. I'm hoping for something at least an order of magnitude faster.

metalmagpie

Are you positive your wheels are diamond? That time would be about right if they were CBN wheels.

metalmagpie · Jun 11, 2020

gbent said:
Are you positive your wheels are diamond? That time would be about right if they were CBN wheels.

Yes, they're diamond.

roughing radius on scraper blade carbide inserts?

Titanium

Diamond

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Stainless

Diamond

Titanium

Titanium

Diamond

Plastic

Diamond

Diamond

Diamond

Stainless

Titanium

Stainless

Titanium

Diamond

Diamond

Titanium

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