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2x72 budget build completed, tracking issues


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I've mostly completed my budget build except for a project box to house my controller and switches and some motor protection.

I've run into a problem with the tracking.  I bought a decent set of machined aluminum wheels.  I've tried to be extra careful with alignments and although things appear to be aligned I'm still having tracking problems.  Specifically inconsistency across multiple speed ranges.  Meaning my tracking at wide open is different than my tracking at 50% speed.  I'm not sure if this is normal or not as this is my first build.  If I adjust the tracking to work in the mid ranges it will need readjusted at higher speeds.  Typically as I increase speed the belt will tend to wander off the wheels and fly off unless uncorrected.  Then when I tune for full speed the belt will move back toward the grinder and hit the tower arm when the speed is decreased.  

Its also inconsistent between belt types.  If I tune for a Norton Blaze belt and then switch to a trizact belt the setting aren't correct.  This may be normal but again I'm unsure.

Lastly, I've noticed than if I really hog into a piece of steel the belt wants to wander off the platen.  

Anyone have any tips or advise on how to diagnose the tracking issues?  I've used a square straight edge to try my best to get the wheels true.  But obviously something is off.

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Welcome aboard... have you read the sticky about tracking above? It is a good detailed write up about  tracking problems even though the picture has been lost. In your picture it looks like there are two crowned wheels which may be part of the problem, our KMG came with only one crowned wheel and it tracks just fine at all speeds.

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I see that two rollers are cambered, you usually only need one of them to be cambered and it dosent take much either only about 1deg. How do you tension the belt? insufficient belt tension may be part of the problem as speed should not be an issue, If everything is setup correctly turning in either direction should not change how it tracks or speed/ type of belt. A ridgid machine frame with no flex is important as flex as tension or load from a heavy cut will make the belt throw off 

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21 hours ago, Irondragon Forge & Clay said:

 In your picture it looks like there are two crowned wheels which may be part of the problem, our KMG came with only one crowned wheel and it tracks just fine at all speeds.

Really?  Most of the wheels sets I see for sale have crowned drive wheels and tracking wheels in the same set.  Including those from Origin Blade.  Seems odd that they would sell complete sets like that if it wasn't an acceptable setup.  

As for the belt tension, it uses a 44lb compression spring inside the riser tube.  To change belts you press down on the riser with the tracking wheel.  Seems adequate but with this being my first grinder I don't have a feel for what the proper tension should be.  The grinder is a very common design that many builders have used so its been battle tested by the knife making community.  

As for the rigidity, the grinder is build from 2" and 1.5" tubing that's .25" wall thickness and fully welded to a 12x24" .25" steel plate.  It's very heavy.  I don't think flex is an issue.  It feels like a tank.

I'll go back and read the sticky that was mentioned and see if I can learn anything.  Maybe I'll get a laser out.  Haha

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All of my wheels are dead flat, no crown at all. With crowned wheels- any slight misalignment, vertical or horizontal misalignment will drive the belt crooked. Especially if you have two crowned wheels that are fighting each other for tracking. It's entirely possible to run them- it will just mean they have to be dead on perfectly trued.

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7 hours ago, Jarlberg said:

As for the rigidity, the grinder is build from 2" and 1.5" tubing that's .25" wall thickness and fully welded to a 12x24" .25" steel plate.  It's very heavy.  I don't think flex is an issue.  It feels like a tank.

The motor is mounted on what looks like just flat plate thats not that thick, It only takes a small amount of movement to affect the tracking and I though that could be one of the places the actual frame is indeed strong looking

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I just went and checked the KMG. It uses a compression spring that takes 40 pounds to compress it so I don't think that's the problem. The only crowned wheel is on the motor drive wheel all the rest are flat. I really think the two crowned wheels are causing the problem like BeaverNZ & Welshj said.

I know the spring is a 44 pound spring, but are there 44 pounds of tension when the belt is installed? With the KMG it takes 40 pounds to release the belt. If your spring is short it may not reach 44 pounds at the belt. Easy to fix with spacers under the spring.

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I'll have to measure the tension with the belt installed.  It's a fair amount of effort to depress the tracking wheel.  I would think it's close to 40 lbs.

I'm still really surprised to hear that two crowned wheels are wrong.  The ones I bought are shown here at grinder-2x72-wheel-section .Remove commercial link  Origin Blade is one of the most popular grinder supply companies out there and all of their sets include crowned drive wheels and tracking wheels.  And those kits are sold on eBay with near perfect reviews from thousands of purchasers.  So ai don't think it's too uncommon to have two crowned wheels in a setup..

Edited by Mod30
Remove excessive quote and link.
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You might want to edit your post and remove the quote as outlined here. The quote feature

Also links to commercial sites are not allowed, you can mention the name of the company but no link per TOS.

Have you called them about it, maybe when they filled the order they inadvertently included two crowned wheels, or they may have an idea of what's wrong. I can't tell from their picture if two wheels are crowned. From looking at their wheels, the only one they show crowned is the drive wheel.

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Sorry about that.  I overlooked the commercial link requirement.

The manufacturer also lists all of their products on an auction sight where they include more information.  They are definitely sold specifically with two crowned wheels in the set.  The auction pictures are very clearly crowned.  

Regardless, I have some tweaking to do.  Guess I could take the tracking wheel to a machinist and have them flatten it.  But I'd rather use them as they are if I can correct the tracking through tuning the grinder.

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I have been making and selling industrial linishers locally on and off for about 25 years and I make them very ridgid to stop tracking variations when put under load. The motor mounting plate though longer than yours is 25mm thick and the latest mod is the tensioning screw is now in line with the drive pulley to cut down on flex even more. You can lean on these as much as you like and the belt does not track off more than a few mm. The last pic is my new 2x72 and it uses a strong gas strut and the motor is foot and flange mounted and the plate on the flange is 10mm thick. The blue machine is 2.2Kw or 3Hp and the smaller one is 1.5Kw They are both 2 pole 3 ph. I found a pic of the 2x72 and the amount of camber on one roller is just a small amount of insulation tape, I will do something better as I am going to put some rubber lagging on the drive and tracking wheel to complete the machine.I do that as over a long time the rollers wear out of round.

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In my opinion the tube in tube tensioning system may be the issue with the OP grinder.  I know this is a common design used online by a lot of folks, but the bottom line is that there is a fairly large tolerance to allow the tubes to telescope.  I expect that each time you put a new belt on there is a chance that the tracking wheel will end up in a slightly different alignment to the drive and platten wheels.  I have heard that it is easier to align a grinder with only one crowned wheel, but have to check further in my files to find the correct reference.  Perhaps the others using grinders of this design are less particular.

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Yes I agree if a thumb screw or bolt was put into a corner of the outer tube to force the inner into the corner to give repeatability may help. I use ball race bearings on the arms for free movement with zero freeplay

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Yes I did install plastic shims on 2 sides to take up the little bit of sloop. But the fact is mine also has 2 crowned pulleys as a lot of people said would cause problems. All I know is this was my first build also. I did make sure that all the pulleys line up because that can be critical as far as tracking goes. This information is only from my own experience as not to disagree with anyone else. 

Thanks, Gaylan

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Thanks for posting your grinder build.  That's encouraging to see how well yours operates and tracks.  Can you discuss the plastic shims you used?  Does the plastic stay in their permanently or do you have to wedge it in each time you change belts?

Without a belt in-place the riser has very minimal amount of movement.   I will try cutting a strip of plastic from a milk jug and see but I don't think it would fit.  Or maybe an aluminum shim from a strip cut out of a pop can.  One thing I noticed is that my riser appears to be longer than yours.  I cut mine to 13" just like it was mentioned in the plans  I could try shortening it and compensating by extending the platen arm out from the vise. 

I still suspect it more of an alignment issue but I've been so busy I've not been able to sit down and retune it. 

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So the way I shimmed the sides was I cut the sides of a gallon jug into strips that went the full length of the upright. On mine that worked just right there is now movement and the belt tensioner pushes down and comes back up no problem.  My spring is about 40lbs with the belt on.I did put some dry graphite on the plastic before I installed them. So my bottom tube of the riser is 10’’ , the riser that goes in that tube comes up to the top 16’’ with the belt in place. From the base plate to the top of my tensioner pulley is 15. 1/2’’. I used a long straight edge to line up all the pulleys. 

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I used a cheap UHMW plastic cutting board from Wally World for shims. They are: thin, flat, large and come in different colors. The only crowned pully on mine is the tracking pully as shown in your pic.

Frosty The Lucky.

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