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Posted: Fri Jul 05, 2019 9:34 am
by rich89
I've been cutting 16mm porcelain tiles with a bridge cutter and 200mm diamond blades.
I've tried 3 different manufacturers blades and all, eventually, start to cut in a slight curve.
Initially all cut dead straight, to 0.4mm on a 900mm cut.
After maybe 30-50 cuts, the blades suddenly start to head off sideways in a slight curve so the end of the cut will be 2-3mm off centre.
I have been dressing the blades and they are not going 'blunt', they cut fine but for some reason the blade just decides to start cutting to one side.
The machine is still on the line, so the blade flexes more and more off line as the cut continues.
Any ideas why this happens?
Posted: Fri Jul 05, 2019 11:54 pm
by S jackson
Is your blade perfectly in line with the line of the machine?
Try putting a metal rule along the blade to accentuate any discrepancy.
If it’s not totally in line it may be wearing one side of the blade more than the other which may be causing your drift??
Posted: Tue Jul 09, 2019 10:42 am
by Tony McC
It could be 'cupping' of the blade, where it distorts ever so slightly in one direction, so inbstead of being a perfectly flat 'plate', it becomes a very, very shallow 'bowl' or cup.
This usually only happens with blades formed using a cheap steel disc, but you're experiencing it with different blades/manufacturers, which is very unusual.
All I can suggest, as someone more at home doing the cutting than maintaining the machinery, is to have the hub of the saw checked out by a proper service engineer. If the alignment is even a micrometre out of track, that would cause a twisting force to be applied to the blades over time, and *that* could be the culprit.....best guess!
Posted: Tue Jul 09, 2019 7:25 pm
by Vikinggroundworker
I would hazard a guess that the saw runs on some sort of bearings or runners along the inside of the arm - and they may be loose, full of crud or need adjusting. Just like a radial arm saw. Is there any movement or play at all on the motor assembly other than back and forward?
Posted: Wed Jul 10, 2019 10:14 am
by rich89
Thanks for all the suggestions.
I have clocked the blades for runout on the motor axle, so this will show any warping. Some are slightly warped with 0.2mm runout radially.
I have also checked runout linearly across the blade. This was initially very very bad, 0.7mm! This caused a lot of issues to start with.
I have since shimmed the motor to get it square to the bridge rails to within 0.1mm.
The machine is capable of making pefect cuts, with a nice new blade. It can cut a slither off a 1200mm tile to 0.4mm variation - pretty good I think.
I am fairly confident that the machine runs true.
It's the blades that are trying to cut off line.
Once the blade starts to go off, you can see it ping back into line at the end of the cut when the offcut is released from the tile.
If you run the blade along the edge of an new tile, which is dead square and straight, it tracks the edge perfectly.
If you run the blade along the egde of a tile this it's just cut, off line, you can see the cut gradually getting further and further from the side of the blade.
I think that the egde of the blade is not wearing evenly for some reason and on a long cut this is enough to give is a bias to the left or right.
I have since worked out how to regrind the edge of the blades to get them square instead of rounded and this seems to help a lot. It involves spinning the blade in a pillar drill while grinding the edge with an angle grinder, edge on at 90 degrees.
I have probably ruined a couple of blades, as cutting with them, when they are flexing sideways so much probably warps them.
I have 5 blades to play with. 3 from ATS (cheap). 1 Rubi TVH, (a little more expensive) and 1 from Marcrist. (Expensive).
They all exhibit this issue eventually, the Marcrist kept going the longest.
I have send the Marcrist blade back to them for analysis along with a tile to test.
I think this porcelain is particularly hard and very non abrasive so the blade needs a lot of dressing between cuts to keep the diamonds exposed.
Montolit have suggested a blade for this type of Porcelain, needless to say it's 6 times more expensive than the ATS blades, but maybe it will cut 10 times longer! I'll wait to see how I get on with the blades I have until I pull the trigger on a £180 blade.
I've checked the machine very carefully with dial gauges, squares etc. I am confident it runs true now.
The blades never get warm and I let them cut at their own pace.
You can tell the tile is hard on the blade as the first cut goes through like butter. After one or two more cuts, you can feel there is slightly more resistance. After a load of cuts, the blade takes 3 times longer to get through the tile.
Sorry for the long post, but hopefully there is some light at the end of the tunnel and I have a lot more tiles to cut. I've made a bit of a rod for my own back by using a different layout pattern, so I need to 'make' two smaller tile sizes from the really large 1200x600 tiles that I'm not using any more.
Posted: Wed Jul 10, 2019 10:16 am
by rich89
Tony McC wrote:It could be 'cupping' of the blade, where it distorts ever so slightly in one direction, so inbstead of being a perfectly flat 'plate', it becomes a very, very shallow 'bowl' or cup.
This usually only happens with blades formed using a cheap steel disc, but you're experiencing it with different blades/manufacturers, which is very unusual.
All I can suggest, as someone more at home doing the cutting than maintaining the machinery, is to have the hub of the saw checked out by a proper service engineer. If the alignment is even a micrometre out of track, that would cause a twisting force to be applied to the blades over time, and *that* could be the culprit.....best guess!
Could be. I will check the bad blades and see if this has happened. Cutting with a cupped blade will force it to flex more and therefore make the cup worse and worse...
Posted: Thu Jul 11, 2019 9:03 am
by Tony McC
I'm *genuinely* surprised that the Marcrist blade has given you problems. That's like claiming the Bentley is running a bit rough! 
I'd be *very* interested to hear of any feedback you receive.
Posted: Fri Jul 12, 2019 9:32 pm
by rich89
Tony McC wrote:I'm *genuinely* surprised that the Marcrist blade has given you problems. That's like claiming the Bentley is running a bit rough!
I'd be *very* interested to hear of any feedback you receive.
Not heard the whole story, but they say the tile is 'quite thick' for a 200mm blade and it was polished.
Will have to phone them Monday to get all the details as they won't commit to an email for some reason...
Done a load of cuts with the Rubi blade after revitalising it with the angle grinder. It behaves itself for quite a while but as soon as the egde rounds off or goes unsymetrical, it starts cutting curves.
So need to hit it with the grinder again to get a nice square edge on it.
Posted: Mon Jul 15, 2019 1:26 pm
by rich89
Spoke to Ian at Marcrist today. Saying the blade is polished and the steel may be compromised by overheating due to polishing.
This is despite running wet and dressing the blade...
He says that a 200mm blade is not really big enough and a 900W motor is not really powerful enough, but that's not too helpful for me! I am not aware of the blade bogging down at all, but I guess that if the cutting speed is too slow, the blade can micro heat and polish over?
He recommended dressing the blade dry (which I'd have thought would definately overheat it) and using a soft but abrasive material to dress it. Breeze blocks or soft ceramic tiles were mentioned.
They are going to send me a new blade and a dressing stone to try! So can't compain about that.
So looks like I need to up my blade dressing to maybe every third cut. Maybe just run the blade through a ceramic tile or breeze block once after every cut.
He said when dressing the blade to pass it 10 times through the dressing stone... That would get through a lot of dressing stones!
Posted: Tue Jul 16, 2019 10:16 am
by Tony McC
I hadn't realised it was a 200mm Ø blade - that is a bit small, so even with a water feed, the risk of overheating is very real.
Excellent customer support from Marcrist, though. That's why they are so often recommended.
Posted: Wed Jul 17, 2019 9:12 am
by rich89
Tony McC wrote:I hadn't realised it was a 200mm Ø blade - that is a bit small, so even with a water feed, the risk of overheating is very real.
Excellent customer support from Marcrist, though. That's why they are so often recommended.
I haven't noticed any warmth in the blade at all, but maybe it can suffer micro heating right where the diamond particals are?
Cutting is going fine now, with a cheap ATS blade, dressed dry using a grindstone wheel for a bench grinder. I just chop it into slices, as soon as I notice cutting speeds drop slightly.
I always draw a line on the tile so I can watch for any sideways drift, as it seems to just suddenly happen. If it does, I take the blade off and grind the edge off square with the angle grinder.
So far so good.
The key is obviously lots of blade dressing, after every 3 or 4 cuts (about 2m of cut), a couple of passes through a lump of grindstone.
That's after getting the machine trued up and square.
Posted: Wed Jul 17, 2019 7:10 pm
by Tony McC
Good advice there, about the blade dressing. I attended a training day last autumn presented by a guy with decades of experience in cutting porcelain, and that was something he stressed, but it seems to be a rare occurence out on site.
Better training is obviously required!