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Gerhard Gerber

Platten woes

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As an honorary Vulcan I cannot deny the truth when I hear it...

Saturday morning early over coffee a fellow knife maker told me " I use the same belts, I built my grinder myself and I don't have this problem"......

No arguing with that.

Apart from low grit ceramic belts I have and use Klinspor JFlex belts.  Anything higher that 100 grit the belt bump becomes very noticeable and it eats a horizontal worm into the blade that can't be sanded out, so I've been chasing my tail for the past few months basically burning belts backwards & forwards through the grits.

I've complained about this before (here) and got good advice, but I've realized maybe I did not convey the severity of the problem, and photos are difficult.

I realized I didn't used to have this problem, or this severe at least, but several things have changed:

- Instead of swapping wheel and platten I got another frame, motor and VFD, different make and model but also 1.5kW.  The supplier was out of stock so I got a larger drive wheel on this grinder.

- The platten was also meant for another model where it mounts on the left side of the tool arm, on mine the platten was upside down so I swapped everything over to the other side of the platten base plate so everything was upright. 

I was using the grinder with the wheel more so I did not realize when this became an issue, but it very much came to light recently working on broad bladed cleavers.

What I've tried so far:

- my platten was dished out, 3 or 4 very deep vertical scratches down the face, and a horizontal mirror of that worm I get on the blades near the middle.  I've sanded that 90% back towards flat and smooth.....good enough for testing.

- I made sure the platten was flush with the wheels and tested, no noticeable change.

- adjusted the platten so it stands proud of the wheel the thickness of a belt, no noticeable change

Yesterday I managed to snap 5 belts, might just be my MIA mojo but something seems very wrong.

What I intend to try next:

- recess the platten the thickness of a belt.

- try the platten on the original grinder, not that I think the motor or larger drive wheel could be the cause(?)

- last option would be to flip the platten back to the upside down configuration.

 

I would appreciate any ideas......

 

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Belt bump happens because of varying thickness of the belt, they are thicker at the seam because of the tape and there could be glue as well.

Does the platten have sharp edges? I rounded mine so it wouldnt catch the belt seam/tape. 

My 1x30 sander seems to have this problem pretty bad.

Ive had plenty of belts die early, wish I could fix em. I had a dull 80 grit belt with some water dripping on it do a good bit of work for me, it was a 2x72 decent quality belt but the tape snapped. 

Maybe belt bump comes from the grit side of the belt, are you snapping the tape or ripping the belt? I have ripped a few belts, it could be uneven grit at the seam.

I only have a trizact belt for my 2x72, but its working fine. I would imagine a thicker backing might have less bump.

I was thinking you could grind down the grit at the seam, just read it somewhere else too. That might work.

If you are tearing belts it could be from the belt catching a sharp edge, you can damage the belt this way at the seam on the grit side and it will raise a slight bump.

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Quote

I only have a trizact belt for my 2x72, but its working fine. I would imagine a thicker backing might have less bump

Zero problems with the thicker belts, should be the same with trizacts but I don't have any (yet)

Quote

I was thinking you could grind down the grit at the seam, just read it somewhere else too. That might work.

I got that advice from a maker in South Africa, the results were disastrous......turned the horizontal worm being eaten into the blade into something next-level.

That kinda proves something in the setup is accentuating the belt bump.

Had a client over yesterday afternoon and quite frankly still need to think about troubleshooting MO a bit.... 

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Flattening and smoothing the platten has turned it into a belt cutter, chewed through an old 40grit belt that I've been using for wood and micarta for more than a year in minutes.... :(

IMG_20190603_151827[1].jpg

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Try rounding over the top and bottom edges of the platen so the belt cant catch on it.

Its been a couple years but I used to never have problems with my cheap 1x30, then it started killing my belts.

I suppose the variables would be: 

Belt quality, doesnt seem to matter to me but I havent used many different belts.

Platten condition, I think rounding the leading and trailing edge helped me some, but that was a while back and I cant quite remember.

Platten height, most people have the platten in contact with the belt. Not sure if this helps/hurts the belt.

Belt tension, I have read that you should be able to pluck the belt like a guitar string and get a sustained vibration.

Leaving the belt on or taking it off and proper storage,  this is probably a big deal, you should take the belt off when not using it and hang it up for storage.

Aggressive grinding, grinding on a sharp corner can cut into the belt and give you a flappy belt or just rip it. A sharp platten could do the same.

 

I made the mistake of hating my 1x30, it made me much more hesitant to use it and meant I got less done. I should have stuck with it and fixed the thing. Something similar happened with my bicycle innertubes, ive had close to ten flats this year, my valves get cut or rip out so I dont like pumping up my tires. The tires get low and get flats when I bottom out the tire anyways and I start to hate something ive done for 20 years. Turns out bicycle rim manufacturers dont deburr the valve hole and a two minute fix cost me $70 and lots of confidence.

Sounds like youre really burning through belts, hopefully you will get it sorted. You can get a lot of work done with a contact wheel and it should be much easier on belts if you have the option, mine is just a longboard wheel. I still clean everything up on the platten.

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On 6/8/2019 at 10:20 AM, steven smith said:

 

Belt tension, I have read that you should be able to pluck the belt like a guitar string and get a sustained vibration.

 

I had stuff to get done and this troubleshooting process is not fun.........only tried one thing: Longer tensioner spring, considerably slacker belt and for the limited grinding I did it seemed better.

To try the other motor/VFD/frame I'll have to reposition the drive and idler wheels.

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From my perspective, it looks like the edge on the top (in the photo - side of platten when installed) has two distinct areas that seem notched and sharp.  Like others have said, round the top and bottom edges but I also make sure the sides of my platten are not only perfectly straight and smooth, but also very slightly rounded, your one side looks rough.  Maybe that is part of the issue????

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Those photos were taken while I was flatting it, they were very sharp and that stage but I have rounded them.

The roughness on the side is bad welding of the platten to its bracket, was always like that.

I know it doesn't look great but the belt just goes over it, nothing ever contacts the platten right there.

 

Frustrating thing is it worked fine, and I missed the issue grinding smaller blades, so I don't know when what went wrong....

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7 hours ago, dragoncutlery said:

are you getting butt joined or lap joined belts?

I have no idea, however Klingspor make the JFlex belts....

 

I realised I might as well make a replacement platten  with some angle iron, unfortunately the 5160 bar stock I have is only 40mm wide or I'd make a hardened platten.

 

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well im not familer with the jflex per say but a butt joint is were the abrasive butts up to its self and a lap joint the abrasive over laps its self and makes for one hell of a bumpy ride and should be avoided at all costs

 

there used to be a few places that sold a like graphite covered strip that you could cover your platen with that had enough give to maybe deal with a bit of bump and reduce running friction

 

i have been running a 01 platen unhardened for about 15 years now just needs to be trued up from time to time

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Well, I'd say butt joint, and the little piece of red tape at the back holding them together.

I was using the slack belt in both directions yesterday and picked up some funny difference.

This VFD came wired the wrong way around, so when the motor is running in the normal grinding direction it indicates a negative number.

This feels like paranoia because surely the direction of the VFD and motor can't influence how the machine runs......?

 

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