Properly made platen attachments

Matthew Gregory

Matthew Gregory

Chief Executive in charge of Entertainment
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As I'm sure many of you have seen, I've had quite a few issues with my KMG grinder. Some of that I've done to rectify things can be seen here:

https://www.bladeforums.com/threads/converting-a-kmg-to-direct-drive.1351035/

Brian Fellhoelter touched upon other bits in this thread:

https://www.bladeforums.com/threads/kmg-grinder-tweaks-thread.831688/

There are plenty of others, but I think you get the point.

As a result of my modifications, and my friend Joe selling a LOT of the direct drive kits shown in the thread above, I've fielded a lot of questions regarding troubleshooting these machines. One issue pops up quite a bit...

Although I freehand grind everything, I use a LOT of different attachments. All have their own tool arms. Many of these I've made, but some are just bone stock, like the platen attachment. The stock platen body is 1/2" thick plate 6061 aluminum, and one of the issues I think is how they're manufactured. I don't know this as a fact, but it's my guess that the 1/2"-13 threaded holes for the 1/2" hardware store bolts Rob uses for axles aren't spot drilled, bored, and cut with threadcutting endmills in a cnc, but rather just sloppily drilled and tapped. IT IS THE EXCEPTION, not the rule, for these to not be skewed. I own three of these platens, and none of them are square, and some are as far off as 3º. To help place this in context, the crowning applied to most drive and tracking wheels is 1º.

...and we wonder why the belts charge all over hell and high water.

I've toyed with the idea of drilling all of mine out and installing new inserts like helicoils or Acme keylocking threaded inserts, but I'm wondering if there's a better way, or if I'm just better off making my own damn platen attachment.

I'm always striving to improve my skills. For me, making a knife isn't necessarily about finding ways to increase efficiency, or doe things faster or easier. I want to make HAND MADE knives, meaning made with my two hands. I don't begrudge anyone doing things with rests, or jigs, or any other such methods - I just enjoy the challenge of working to the best of my ability. It's gotten to the point where many of my problems are due to the limitations of the machines I use, and this misalignment is a bit part of that.

Have any of you guys thought about this?
 
I have made 6 platens 3/8" plate and tossed the original. I have the equipment to precision machine and ensure proper bolt alignment and yes I feel your pain. Why 6 you ask...3 are radiused and 3 have pyroceramic glass not only back ups but I have 3 machines so 2 platens per machine. Make new ones get them machined and drilled properly don't waste time fiddling with misalignment!!!!!
 
For a platen I use a 2" right angle steel stock that is bolted to the platen attachment. This insures it is parallel to the axis of the wheels, that is if the wheels are on straight to begin with.

I then mount a glass platen or a harden steel platen to it.

I run a GIB so I am aware of just how important everything needs to be square in a grinder build.
 
I feel your pain. :)
I keep toying with the idea of a precision platen mount.
I use several platens, radiused and what-not. I am thinking of something that let's me screw in two bars or steel rods straight out the back of the platen that line up with the mount holes there.
Then run these into a block mounted on the arm that allows them to be clamped into the block.
This gives a quick change for platens without changing out arms and the need for several platen assemblies. Just one with several platen attachments. I hope that makes sense, but I can draw it up if not.

The thing I want to add to this quick change platen system is a micro-adjustment ability for alignment. We have this for the belt, we need it for the platen.
I keep thinking everything in knives is so down to the 1/1000, but our platens are built like a cave man banging rocks together.
 
IMO there is nothing more frustrating than trying to do nice work with junky tools. When the tool won't do the job, you have a continuous fight to overcome its shortcomings let alone your own abilities. I feel you pain.
 
I look at it this way. The KMG grinder at the cheapest price they sell w/no motor or VFD is $850.. There is less than $200 in materials, wheels, springs, bearings and fasteners....... And that's at full retail price for the parts to make it. If I'm paying basically someone for $650 in labor, the damn thing had better play a damn good tune!!! If it didn't I'd drop the crap back on their door step and get my money back..
 
I get it, Marc. I try to stress to new guys that are looking into machines to avoid the KMG, that's for sure, but there are literally THOUSANDS of these things out there, and someone that already owns one may have to deal with it, and many are finding that there's not a whole heck of a lot of service after the sale, so to speak.
 
This is part of the problem.20170912_103042.jpg



A well set up grinder can run in forward or reverse with good tracking, without the tracking wheel. People, you should try this with your grinder and see if it works. If it doesn't something is wonky.

Part of the problem is the wheels will tend to be perpendicular to the surface of the flat platen attachment. That's just a piece of extruded aluminum. That top picture is my most recent KMG, it's out of flat .020" which means the wheels aren't perpendicular to the grinder or parallel to each other which means that belts won't stay true. This has to be corrected for the best results, or to stay in position when you reverse (or just to run well in reverse at all).

This may not be important for many makers, but if you're like me and go back and forth between forward and reverse a lot it needs to be right.
 
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Bowed platen. Ha!

So, if you sweep it, is it torqued as well as bowed, too? Cold rolled ain't exactly unstressed...
 
Well what Nathan is showing is basically the problem with every "c" shaped platen cut from plate steel or extruded aluminum. None of it is flat as cut. Cast mic6 tooling plate would be better, but I just straightened mine when it caused me grief initially.

Another issue is the stacking of run out between the platen, tool arm, the side plate the tool arm is constrained against and the drive wheel and tracking wheel run out from perp. Meaning, you could have perfectly flat platens and axle bolts square to the platen face, but still have accumulated run out that causes issues ( though if both plates wheel axles are true this is probably minor impact imo unless it's really wonky)

Ideally the platen plate would be machined parallel, the holes perp to that surface, one edge of the tooling arm machined flat and that's the same surface the platen bolts against as well as being the surface pushed up against the main side plate of the grinder.

This would be the main reason I don't like having the tool arm lock bolt on the right side of the grinder convenient as it is, on my grinders at least, because my cface motor mounts on the right plate, so I want my tool arm pushed against the right plate as well.

Maybe the easiest way to straighten axles on an already tapped platen would be to grind the washer/spacer that goes between the platen and pulley bearing with a very slight angle on one face, and then rotating it under a little bolt tension until the axle is true. I think that would work.
 
I think you have the right idea with drilling them out for a threaded insert (short of making a new one from scratch). Another option is just through drilling with a 1/2" bit and then sticking a nut on the other side.

If there's any bow, I'd see what Niagara would charge you to put it on that big old surface grinder they have. ;)
 
You could set it up in a mill from the surface that touches the arm and deck it.

Ream it out .499 on an accurate machine, run a precision shoulder screw through it from the left (making a stud spindle), replace the 1/2-13 nut with a precision spacer like a thrust bearing washer and put the nut on the right side (outside). That'd fix it, it'd be square. Or scrap it and start over with a fully machined piece, they're not that complicated.



---Or---

We're going to set up here to make a few for a TW90 length platen (we need the length) we could also make a few in the standard dimensions if there was enough interest. They'd be accurate. I'll keep an eye on this thread. If it looks like there is interest we'll put together a run. We have a space in our schedule coming up and we're planning on a run of radius platens (haven't done those in a while) we could add this to it if enough people want it. :thumbsup:
 
Nathan, that "correct grinder tracking" video shows what tracking can be like. I do wish my grinder did that good. I can be running in forward, switch to reverse and the belt will move over 1/2". I've been dealing with it, but staying true like your grinder sure would be NICE!! I'll have to do some looking and checking to see just how good I can get.

Ken H>
 
Nathan the Machinist said:
We're going to set up here to make a few for a TW90 length platen (we need the length) we could also make a few in the standard dimensions if there was enough interest. They'd be accurate. I'll keep an eye on this thread. If it looks like there is interest we'll put together a run. We have a space in our schedule coming up and we're planning on a run of radius platens (haven't done those in a while) we could add this to it if enough people want it. :thumbsup:
Click to expand...

I could be convinced to buy a tw90 length platen attachment, perhaps...
 
I will 100% be standing by for the opportunity to order a flat and/or radius platen if the opportunity were given Nathan.
 
If you are saying you'd be making the "C" platen plate, I'm interested. I'd really love a longer one than I currently have, especially for kitchen knives.
 
As for axles, I originally tapped mine, but I found the limitations of my tapping ability when it wouldn't track as well as I wanted. I just through drilled them and used a nut. Since my platen wheels have spacers in them, i could snug them down (not super tight, just snug) and it should be about as perfectly perpendicular as I could hope for. My grinder tracks very well now. I don't see any benefit to drilling and tapping these over through drilling. Unless I'm missing something.
 
OK, did a bit of work on my grinder getting it to run true - it's better. Note the video is a mirror image of the grinder. Not sure what the deal is, the video uploaded is correct, but once it was uploaded, it's mirror image. BUT - you can still see when switching from forward to reverse the belt stays steady.

 
Nathan the Machinist said:
We're going to set up here to make a few for a TW90 length platen (we need the length) we could also make a few in the standard dimensions if there was enough interest. They'd be accurate. I'll keep an eye on this thread. If it looks like there is interest we'll put together a run. We have a space in our schedule coming up and we're planning on a run of radius platens (haven't done those in a while) we could add this to it if enough people want it. :thumbsup:
Click to expand...


I'd definitely buy a platen chiller.
Any chance you'll make some 36" or 72" platens?
 
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