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The Newbies Arena Are you new to knife making? Here is all the help you will need.

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  #1  
Old 04-28-2013, 12:21 PM
thinwater thinwater is offline
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New plasma cutter grinder

I have been wanting to make knives again so I make up a grinder. The sides are 1/4" steel plate cut on my cnc plasma cutter. I made the wheels on my lathe and have upgraded the drive wheel to a 4" from the 3" I started with. I need to get a bigger motor. The 1/2 hp 1750 motor is to easy to stall. It works very well for flat grinding.

I just bought the steel to make up a KMG type grinder. I will have that done within a few weeks as I have time on the machine center. I made up a bunch of the wheels and sold them on ebay. They more than paid for the entire project.

I tried to post a picture of it but the forum said I cant post attachments.

Now to get to work on some knives...
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Old 04-28-2013, 12:45 PM
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Ray Rogers Ray Rogers is offline
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We definitely want to see the pictures. You'll be able to post them after you get through your probation period. Until then, keep us updated with a description of your progress...


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Old 04-28-2013, 03:22 PM
thinwater thinwater is offline
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Originally Posted by Ray Rogers View Post
We definitely want to see the pictures. You'll be able to post them after you get through your probation period. Until then, keep us updated with a description of your progress...
I will do a build log of the new KMG style grinder and post the pictures when I am allowed. I have a large cnc machine shop as my primary occupation so making the machines wont be a challenge, the knives are my challenge.

It is tempting to just machine the knife blades in my machines but that would be cheating!
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Old 04-28-2013, 04:17 PM
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WynnKnives WynnKnives is offline
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Depends on who you ask as far as the cheating part goes, but I can't see it being nearly as rewarding as doing it by hand.

Also interested in seeing pictures of the grinder, I'm surprised the 1/2 hp motor does the trick for you. I used a 3/4 hp for a very long time and it just didn't quite cut it, but my new 1.5 hp is perfect.
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Old 04-28-2013, 05:24 PM
thinwater thinwater is offline
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Pictures!

This is the plasma cutter grinder. The top tube is 24" long, 3" x 3/8" thick steel box. The side plates are 1/4" steel. I made the wheels at my shop. I made the drive wheel and two contact wheels by hand on a manual lathe, the tracking wheel was done on a cnc lathe.

I made the platten, platten mount, side plates, front and back plate, all on the cnc plasma cutter.

I will be making a better tracking arm assembly for this on my cnc mill next week. This one works well but is ugly and I made it on a drill press.
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File Type: jpg painted grinder prototype.JPG (152.8 KB, 61 views)
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Old 04-28-2013, 05:29 PM
thinwater thinwater is offline
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Originally Posted by WynnKnives View Post
Depends on who you ask as far as the cheating part goes, but I can't see it being nearly as rewarding as doing it by hand.

Also interested in seeing pictures of the grinder, I'm surprised the 1/2 hp motor does the trick for you. I used a 3/4 hp for a very long time and it just didn't quite cut it, but my new 1.5 hp is perfect.
The 1/2 hp motor is very week and frustrating. I think I will get a 1 1/2 hp like you did. What RPM are you using? I am using about a two to one incresae in RPM with a pully and V belt to drive it with the 1750 rpm motor. This should give me around 3600 fpm with a 4" drive wheel. I think 5000 -6000 is a better number to shoot for and the 3400 rpm motors would get me closer using a slightly speed reducing pully set up.

Last edited by thinwater; 04-28-2013 at 05:32 PM.
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Old 04-28-2013, 05:51 PM
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Ray Rogers Ray Rogers is offline
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I don't see any crowning on your idler wheel. They are usually made with a slight crown in the center which improves the tracking considerably.

After you have some practice grinding you'll probably want to go in the other direction speed wise. Those high speeds work pretty well for rough hogging but as you move to finer belts being able to slow way down is a big advantage. The fine belts will wear out quickly and all belts will generate more heat at higher speeds. Not to mention the difficulty of holding a straight grind line on a supersonic belt. All my grinding is done at 1800 sfpm or less (often much less) ...


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Old 04-28-2013, 06:00 PM
thinwater thinwater is offline
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Originally Posted by Ray Rogers View Post
I don't see any crowning on your idler wheel. They are usually made with a slight crown in the center which improves the tracking considerably.

After you have some practice grinding you'll probably want to go in the other direction speed wise. Those high speeds work pretty well for rough hogging but as you move to finer belts being able to slow way down is a big advantage. The fine belts will wear out quickly and all belts will generate more heat at higher speeds. Not to mention the difficulty of holding a straight grind line on a supersonic belt. All my grinding is done at 1800 sfpm or less (often much less) ...
Thanks a lot! I dont know how fast to move my grinding belts and that information will be a big help.

The tracking wheel is crowned. It is a perfect arc done in a cnc lathe. My new drive wheel is 4" and domed also. I have a 3 step pully on the motor and grinder so I can slow it way down when needed.

I am loving this forum, the knives members make are awesome. I have a dozen or so I have made so far but they are just getting past the jail house shank quality.
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Old 04-28-2013, 07:43 PM
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WynnKnives WynnKnives is offline
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I really like my 1.5 hp motor but its a 3450 rpm (got it for super cheap) but I wish I had a 1700 so my step pullys could speed up if needed. I have it on the slowest setting with about a 4" drive wheel, I'm looking into smaller drive wheels to slow it down. I haven't done the math at my sfpm (I just finished my new grinder a few weeks ago) but its too fast for my slowest setting.

And your build looks solid and simple... very nice, I don't know all what you have but I would get some decent contact wheels for grinding they really make it nice to make hollow grinds and such, there just isn't enough cushion in metal.

Last edited by WynnKnives; 04-28-2013 at 07:45 PM.
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Old 05-01-2013, 02:08 PM
dwc34205 dwc34205 is offline
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Nice job! I built my own also. I forked out a little more and got a VFD instead of going with step pullies. I have a used 2hp 1720 rpm motor that I bought from a local electric motor shop. The speed range on it is from 0-60 Hz and I rarely go over 20 Hz. I think the pulley ratio is 2:1 so at full speed I would be running 3440 rpm.

The only thing I would reccomend on your build is rounding the corners of the plate that the two wheels are mounted on the flat platten. I had mine done the same and if you track the belt over too quick or too far it will dig in and ruin the edge of your belts. At least with mine; the domed tracking wheel can make it move/jump position pretty quick and have that happen.
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