Check your platen

Justin Presson

Well-Known Member
#1
I'm gringing this large kitchen knife last night and one side by the plunge was giving me fits. Kept having this little ridge that I could not grind out and kept chasing it. Then the light bulb went off to check my glass platen and yep big chip out of the edge right where that ridge was at. I moved up to the top of the platen and it ground right out.
Lesson learned and time for a new platen.
Here is a pic of what it was leaving behind.

20190223_123748.jpg
 
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#6
Is the glass platen really the best option for flat and more importantly serviceable
What about a length of O1 heat treated and glued to the backer the same way the glass is. A friend has a HT D2 platen that has done many years of service without wear.
 

John Wilson

Well-Known Member
#7
Is the glass platen really the best option for flat and more importantly serviceable
What about a length of O1 heat treated and glued to the backer the same way the glass is. A friend has a HT D2 platen that has done many years of service without wear.
fair point. As to glass, I’ve been running this same piece of glass for about 4 years now.
 

Justin Presson

Well-Known Member
#8
I dont know Von, when I started this was the go to material. It's supposed to run cooler then steel and stay flat longer. This piece has been on my platen for about 4 years. Not sure when the chip happened but probably when I was changing the tool rest.
 

Daniel Macina

Well-Known Member
#9
I just got another glass Platten. I broke the first one putting it on when I was first using my grinder a while back. Now the grinder is almost up and running again looking forward to trying out the glass
 
#10
I have to say that I had two of the glass platens sent in the last package from my agent. Will get the present mild steel 3/8 platen milled to except the glass one this week when I also pick up the 3ph motor and vfd unit all wired and ready to go.
 

Jim Levite

Well-Known Member
#11
I put a small radius on all edges of my glass platen. Had them on previous grinders for years. But yes, like anything they can chip or break. Good heads up
 
#12
In my experience when I went to glass over the metal patten, the drag seemed to be cut in half. I used to taper and when I added the glass it seemed so much easier and had less problems.
 

BossDog

KnifeDogs.com & USAknifemaker.com Owner
#13
Using a glass platen cuts drag and heat build up from the belt by quite a bit. Glass will wear and have to be replaced. Hardened steel will wear and have to be replaced. I think glass wears at a slower rate but have no testing data to back that up.

I usually replace a glass liner every 6 months. I use JBweld. To get it off, heat with a torch, peel it off, flip it over and use the back side. Glass will generate some static sparks if the humidity is low. Spray the inside of the belt and the around the grinder with laundry static guard to knock it down.
 
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#14
My glass has some weird texture or ripples forming in it. Odd thing is, its above where the contact usually occurs. Mainly in the top couple inches. It makes me think maybe the belt is catching grit and bringing it around. Or, maybe the belt is bunching up right before the blade. Any of you ever seen this?
 

John Wilson

Well-Known Member
#15
My glass has some weird texture or ripples forming in it. Odd thing is, its above where the contact usually occurs. Mainly in the top couple inches. It makes me think maybe the belt is catching grit and bringing it around. Or, maybe the belt is bunching up right before the blade. Any of you ever seen this?
I have some of those ripples. I believe if someone were to set up a high speed camera, the belt probably runs a constantly ripple and the period between ripples probably gets very short as it encounters the platen due to compression. I also believe you are correct that the back of the belt brings grit around.

I have my platen proud of the rollers so that I can feed the blade up/down vertically without contacting the rollers.

The upper and lower corners of the glass have been radiused off by the belt backing over time. That radius is elongating a couple inches now, so it’s time for me to replace the glass.
 

John Wilson

Well-Known Member
#17
I don’t know that you can keep it even. I’d bet that every grinder needs a hair of tracking to one side. This is going to make the belt wear one side of the platen just a bit faster than the other.
 
#19
I have some of those ripples. I believe if someone were to set up a high speed camera, the belt probably runs a constantly ripple and the period between ripples probably gets very short as it encounters the platen due to compression. I also believe you are correct that the back of the belt brings grit around.

I have my platen proud of the rollers so that I can feed the blade up/down vertically without contacting the rollers.

The upper and lower corners of the glass have been radiused off by the belt backing over time. That radius is elongating a couple inches now, so it’s time for me to replace the glass.
I can neither confirm nor deny this is the cause, but Norton Abrasives notes that under-tensioned belts kind of stack right above the work. It seems a reasonable speculation that any belt even if properly tensioned may have the same stacking to some degree, and would account for that type of wear pattern. Just a thought.
 

John Wilson

Well-Known Member
#20
I can neither confirm nor deny this is the cause, but Norton Abrasives notes that under-tensioned belts kind of stack right above the work. It seems a reasonable speculation that any belt even if properly tensioned may have the same stacking to some degree, and would account for that type of wear pattern. Just a thought.
It makes sense to me, too. The fact that it’s so hard to sand a surface flat on the platen (blocks, scales) proves that the belt is not running as flat as it looks. The top edge of whatever you grind is encountering this stacking. I used to think it was the belt splice going around (and I’m sure that can be a part of it, too) but even gator belts do it.
 
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