| [ Total Views: 917 | Total Replies: 13 | Thread Id: 85822 ] |
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 donn
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| posted on September 5th, 2010 at 01:17 PM |
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Not vw, 200mm bench grinder
I have a 200mm bench grinder that seems to be getting more and more out of ballance in that it vibrates all over the place when using it, when I first
got it it just sat on the bench and worked realy nice, now I have to bolt the damned thing down to stop it walking all over the bench. It's not a
cheapie, any hints on how to ballance the wheels?
I dream of a day when a chicken can cross a road without being asked for it's motive!
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annosL
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| posted on September 5th, 2010 at 01:40 PM |
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It may need the wheels refacing, there is a tool for this, has hardened star-wheels mounted on a handle and you pass the star wheels against the
grinding wheels which removes grit and makes the wheels more concentric, that could help with the balance.
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donn
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| posted on September 5th, 2010 at 02:56 PM |
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Yeah, was thinking along those lines but as I recall that only presents a new cutting face and the wheel doesn't seem to be out of round, you must be
getting on in years as I hadn't heard of those type wheel dressers for yonks, I've been looking at these, maybe it will do the trick
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=250687482318&ss...
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1500S
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| posted on September 5th, 2010 at 04:41 PM |
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| Quote: | Originally
posted by donn
Yeah, was thinking along those lines but as I recall that only presents a new cutting face and the wheel doesn't seem to be out of round, you must be
getting on in years as I hadn't heard of those type wheel dressers for yonks, I've been looking at these, maybe it will do the trick
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=250687482318&ss...
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The type annosL describes is a better type. http://cgi.ebay.com.au/Dawn-Grinding-Wheel-Dresser-No-0-/110580686557?pt=AU_H...
Go to any engineering supply place and you should pick one up at a reasonable price.
BUT! you should have the grinder fixed to a stand or bench anyway for your own safety.
DH
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Thinker
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| posted on September 5th, 2010 at 08:58 PM |
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for a 2oomm grinder dont bother with a star wheel dresser they only work well on 300mm + grinders your best bet to true the wheels is to try and get a
single point diamond.
diamond dressing sticks work well but will follow the worn contour of the wheel ( dressing)
you should be able to get a single point tool from any engineering supply company
https://www.bolt.com.au/product_info.php?manufacturers_id=54&products_id=...
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donn
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| posted on September 5th, 2010 at 09:11 PM |
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Ok fellas, I have a single point jobie but find it is very hard to keep it even across the face of the wheel, as I recall from my early days in the
trade the star wheels are kinda hard on a wheel but then the one we had in the workshop was kinda ancient. Dressing the wheel is for two things as I
understand it :-
1. to present a new cutting face to the job being ground.
2. to true a wheel that is out of round
Thing is that my wheel seems to be true, just out of ballance. Oh yeah, I agree that it should be bolted down but it should run fairly nice if all is
ballanced and that is not the case with mine now, it seems that the wheel or wheels are out of ballance, I seem to remember that there is some way of
rotating the wheels on the shaft in relatiuon to each other to get it back into ballance but can't remember how to go about it.
I dream of a day when a chicken can cross a road without being asked for it's motive!
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Thinker
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| posted on September 5th, 2010 at 09:23 PM |
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balancing grinding wheels is only done on surface grinders and cylindrcal grinders not on offhand grinders (bench) .
over time of using a grinder the wheel will self dress if you are using the correct grade of wheel for the material you are grinding but what can
occure is that the the bond that hold the grit in place can be removed unevenly and unbalance the wheel.
the best way to true a wheel on a offhand grinder using a single point tool is put a small clamp on the back of the single point tool and hold it
against the back of the work rest so you can keep it even. and dont be worried about removing alot of material you may need to take off 5mm to get it
right.
hope this helps
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1500S
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| posted on September 5th, 2010 at 09:36 PM |
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| Quote: | Originally
posted by Thinker
for a 2oomm grinder dont bother with a star wheel dresser they only work well on 300mm + grinders your best bet to true the wheels is to try and get a
single point diamond.
diamond dressing sticks work well but will follow the worn contour of the wheel ( dressing)
you should be able to get a single point tool from any engineering supply company
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The starwheel dressers are quite satisfactory on any wheel from 150mm dia to quite large. Two main reasons why they don't work is that they are not
used correctly as well as the disks being worn in the axle hole. Far too many users neglect to pull the toolrest out from the wheel to allow the
hooks to lock the dresser in place which in turn keeps the abrasive wheel concentric during dressing and truing.
To use a single point diamond you need it to be mounted in a block which can be guided along the toolrest to give a flat face on the wheel. The
problem is that each pass the diamond has to be adjusted in that little bit for each successive cut. To make the diamond last only small cuts should
be taken. Yes! on machine grinders the recommended depth of cut is only around 0.03mm max per pass!
The Bamford brand rotary abrasive dresser is also great but doesn't guarantee concentricity after a few dresses so the starwheel type is still
required to bring it back true.
See: http://www.pratco.com.au/dressers.php
You may always have out of balance problems with bench grinders as the wheels may be not uniform in density and there is no way of balancing them on
this type of grinder. There maybe a dense patch and as the wheel wears, the balance will move somewhere else as you dress through that area. You
could just try rotating each wheel to a new position and see if it gets better but generally not too likely.
I sound like a bloody Toolmaker teacher don't I. 
DH
PS. 5mm to get it right!! I'd kill you!
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pod
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| posted on September 5th, 2010 at 09:45 PM |
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i like that last statement there 1500S,and yes go the star wheel
dresser 
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Thinker
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| posted on September 5th, 2010 at 09:57 PM |
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well i guess 5mm at 0.03mm well thats a weeks work
i makes sence why toolmakers are a dieing bread because they are just to bloddy slow.
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donn
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| posted on September 5th, 2010 at 10:20 PM |
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Thanks to all, that bit about
"You may always have out of balance problems with bench grinders as the wheels may be not uniform in density and there is no way of balancing them
on this type of grinder. There maybe a dense patch and as the wheel wears, the balance will move somewhere else as you dress through that area. You
could just try rotating each wheel to a new position and see if it gets better but generally not too likely."
which is simmilar to
"but what can occure is that the the bond that hold the grit in place can be removed unevenly and unbalance the wheel."
This may be the problem as I have a "white" wheel on one end at it does wear at a greater rate than the normal grey wheel. I'm thinking now that
this could be the problem. Love the admonishment, "PS. 5mm to get it right!! I'd kill you!"
Ha ha ha, I recently had to do almost that with my wet grinder, ages ago I accidently left the wheel standing in the water trough, after the water
evaporated it left a hard spot on the wheel that just didn't wear at the same rate as the rest of the wheel, eventualy I had to remove about 3-4 mm
off part of the wheel to get back into round. 
I dream of a day when a chicken can cross a road without being asked for it's motive!
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 helbus
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| posted on September 5th, 2010 at 10:37 PM |
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Just get a new wheel. Maybe $30?
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1500S
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| posted on September 5th, 2010 at 10:51 PM |
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| Quote: | Originally
posted by helbus
Just get a new wheel. Maybe $30?
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The wheel may only be worn down 10mm so why throw it away? It depends on how much use or in many cases abuse the wheel gets but for normal tool
grinding a 200mm wheel should last 10 years. If it's being used for a bit of light fabrication work it may reduce quite a bit if the wrong grade is
used.
| Quote: | Originally
posted by Thinker
well i guess 5mm at 0.03mm well thats a weeks work
i makes sense why toolmakers are a dying breed because they are just to bloody slow.
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The only reason that most of our metal trades including Toolmaking is dying in Australia is that most manufacturing has gone off shore for bigger
profits, not because a Toolmaker seemingly works slower than a general Fitter or Machinist and can't produce tooling at a competitive price! That we
can't argue with. As for any of the types of tooling and their usage I have quoted here are that of the manufacturers, not of some personal likes I
have.
Back on topic !!, for our friend on here who wants to dress an out of round or eccentric grinding wheel, make sure you give enough upward force on the
handle whilst holding the head of the dresser firm on the toolrest. The action is actually rolling the worn grit out of the face of the wheel. If
you see too many sparks, you are just grinding the dresser disks away with not enough pressure on the disks to keep them rolling.
DH
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1500S
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| posted on September 5th, 2010 at 11:23 PM |
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| Quote: | Originally
posted by donn
Thanks to all, that bit about
"You may always have out of balance problems with bench grinders as the wheels may be not uniform in density and there is no way of balancing them
on this type of grinder. There maybe a dense patch and as the wheel wears, the balance will move somewhere else as you dress through that area. You
could just try rotating each wheel to a new position and see if it gets better but generally not too likely."
which is simmilar to
"but what can occure is that the the bond that hold the grit in place can be removed unevenly and unbalance the wheel."
This may be the problem as I have a "white" wheel on one end at it does wear at a greater rate than the normal grey wheel. I'm thinking now that
this could be the problem. Love the admonishment, "PS. 5mm to get it right!! I'd kill you!"
Ha ha ha, I recently had to do almost that with my wet grinder, ages ago I accidently left the wheel standing in the water trough, after the water
evaporated it left a hard spot on the wheel that just didn't wear at the same rate as the rest of the wheel, eventually I had to remove about 3-4 mm
off part of the wheel to get back into round.
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Not quite the same or true. The most of the fixed (bench, pedestal) grinders use a vitrified bond. Generally good manufacturers mix the grit and
bond evenly but some overseas manufacturers can give us some questionable quality. Once the wheel is pressed to shape and fired it can't change
structure. As the wheel generally spins at around 1750 m/min, if you leave the wheel stopped and partly submerged in water or turn the wheel off with
coolant flowing, make sure you get it to speed slowly with a couple of on/offs as it will be extremely out of balance when restarted.
Also,as the wheel reduces in diameter, the apparent grade of the wheel is softer due to the slower surface speed, that is for the same pressure on the
grit it will break away from the bond easier which increases wheel wear BUT the bond strength can't physically change. To overcome this you have to
just use less pressure on the wheel from the work. No doubt with your wheel being left standing in the water, the crapp ( better described as steel
or iron particles which change to iron oxide, better known as rust ) mixed in the water would have soaked into the pores of the wheel and loaded a
section which would have ground different due to that part being filled with rusty metal.
Hope that helps.
DH
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