Diamond Grinding Wheel Balancing

[Journeyman]

Hi, seeking advice for truing up a diamond cup grinding wheel. Trying to make a small drill grinding set-up. Using one of the small 3" grinders that are available to provide the power but need to install a 4" diamond cup wheel. The grinder spindle is 10mm and the hole in the wheel is 20mm so I made an arbor to fit complete with a left hand thread flat nut to clamp the wheel in place. Everything fits OK, wheel is a good fit on the arbor, the arbor is a good fit on the grinder spindle and the nut works fine.

Problem is as soon as I start the grinder at it's lowest speed (1000rpm) the vibration is horrendous, not inclined to ramp it up to 9000rpm. Without the wheel in place there is no vibration at all. The arbor runs true with no discernable runout. A dti on the wheel shows the flat face to run true but the outer edge is a good .010" out. The sideways displacement can be seen even with my ancient eyesight!

Have trawled the interweb but with little success except one place that seemed to suggest a gap between arbor and wheel and using a mallet to centre the wheel? So over to you, I am sure that with the wealth of experiance here someone knows how it should be sorted.

Thanks in advance, John

 

[Swifty]

Can you clamp the wheel down and indicate the outside true, then rebore the centre hole. Just make a new bush to suit.

Paul.

 

[Blogwitch]

For a start John, how are you going to dress the finished wheel? You need to sort that out before truing up the cup.

Diamond wheels require special dressers as you cannot true them up with your normal grit wheel dressers.

To do it cheaply, you will require a correct dressing block for diamond wheels, then find a way of holding it rigidly and accurately as doing it like truing up a grit wheel won't work at all, the diamond will end up all shapes and sizes.

Because I have a lot of diamond wheels, I use a dedicated diamond wheel brake dresser, but they are usually very expensive, well over a grand (UK Pounds) if bought new.

A lot of people think that just fitting a diamond wheel will cure all ills, but nothing could be further from the truth.

John

 

[kiwi2]

Hi,
What about making an offset arbour to make the OD of the wheel run true?
Alan C.

 

[Journeyman]

Thanks for suggestions so far, keep em coming. I havn't got as far as thinking about dressing the wheel yet but the idea I am working on is a standalone 4/6 facet drill grinder by John Moran see about 2/3rds down the page http://www.gadgetbuilder.com/DrillSharp.html it has a traversing table and it should be possible to mount a dressing block securely to the table. I must admit I have never used a diamond wheel before and was expecting it to run true first time. I suspect that if I had bought a Norton wheel or similar well-known brand it probably would have done! The idea behind using a diamond wheel is that it will not wear too quickly and avoid adjusting the wheel to table distance too often, apparently a critical measurement in this design. An offset arbor sounds a possibility although measuring the exact offset of the wheel could prove tricky with my limited equipment. A bit of trial and error probably or in my case error and error...

Cheers John

 

[bazmak]

I recently had the idea to skim over the vice jaws in the mill
Bought a cheap 3" chinese cup wheel and its so far out of wack its unusual
Plan to set tue in the lathe an bore to suit holder.But as its been said you need to true the diamond face and edge,so you need a diamond trimmer.All new to me

 

[tornitore45]

Am I missing something? Running a 4" wheel at 9000 RPM? Is it not too fast?

 

[Journeyman]

I think mine is also Chinese or Indian there was nothing on the packaging, in fact there was nothing at all on the box. Seems odd to go to all the trouble of making something that at first glance looks reasonable but not bothering to put the hole in the centre!

Yes, 9000rpm is probably way too high it just happens to be the top speed of the mini bench grinder. I will try and find out the correct speed and then remove the "pot" on the grinder and replace it with a fixed resistor. Anyone here know the correct speed for a 4" cup wheel grinding HSS drill bits? CBN would be better but they are seriously expensive even the Chinese ones.

John

 

[tornitore45]

I do not have a mind image of such a wheel but suppose is mostly made of steel with a relatively low mass of diamond plating.
In such case, the imbalance is most likely on the steel part and may benefit from truing the steel in a lathe assuming you do not have to get into the diamond.

 

[bazmak]

The cup is usually alum,plan to skim that as well.9000 way too high
top speed on mill is2500 which should be much closer.Any info on trueing the diamond faces //

 

[doc1955]

I mounted mine on a removable arbor that mounts on my home made grinding head. It was dialed in true on the arbor and when it needs to be dressed I use a cleaning stick. http://www.use-enco.com/CGI/INPDFF?PMPAGE=234&PARTPG=INLMK3&PMITEM=391-5750
To use the stick I soak in coolant and then turn grinding head on let it get to speed then turn it off and basically stop it with the cleaning stick it will clean the wheel as it stops spinning. This has worked like a charm for me. I am planning on building a brake true unit eventually but for now this works for me.

[ame]https://www.youtube.com/watch?v=qY_shjNIsUc[/ame]

 

[Blogwitch]

Bazmak,

This is about the cheapest brake dresser available new at this time.
Looks to be an import jobbie.

http://www.absimporttools.com/diamond-wheel-brake-truing-dresser.html

A genuine Norton one would most probably cost at least 3 to 4 times this much.

I was lucky and picked my Norton one up off Ebay for about 40 bucks, with a spare new wheel. The chap didn't know what it was.

Here is a second hand one if you are quick

http://www.ebay.com/itm/NORTON-Brak...0&pid=100005&rk=2&rkt=6&sd=261930919849&rt=nc

Dressing sticks for diamond wheels are fairly cheap, but difficult to hold and feed to get the wheels perfectly square without removing too much material.

A change of direction now, and maybe something to be considered if you just want to resharpen tools rather than grind them to shape.

I have been playing about with diamond coated wheels for resharpening, especially tungsten tipped tools (and replaceable tips), coupling water dipping the disk with a very slow speed (about 100 rpm). More of a lapping sharpening system rather than a grinding process. The basics have been proven, it is now awaiting a simple build. It will look very similar to the disk sanders on the side of a normal benchtop belt sander.

This is where I get my bits and pieces from. I will be using an 8" system, and works out very cheap.

http://richontools.com/index.php?main_page=index&cPath=1_9&sort=20a&page=3

The backing plates are here.

http://richontools.com/index.php?main_page=product_info&cPath=45&products_id=798

BTW, this is also where I buy all my cheapo mill tooling from, at these prices they really are throwaway tools.

John

 

[Journeyman]

I have ordered some dressing sticks, I was surprised how cheap about GB£1 each and will make suitable holder to clamp one to the table when I eventually get it built. Did a bit of research on the speed front and Norton recommend a speed between 2756 and 3543 sfpm for dry grinding with a cup wheel. As the wheel is roughly 4" diameter the circumference is conveniently 1ft so a speed in the region of 3000rpm should be good. I think I will try to make an eccentric bush for the wheel once I have worked out exactly how much off centre it is.

Will take a note of Richon Tools and wish I had seen them before buying a wheel in the UK much cheaper although coming from Hong Kong you can always get hit for import duty and VAT!

John

 

[Blogwitch]

Never been hit for any duty in the many years I have been using them. But the bits do usually take 2 to 3 weeks to get here.

BTW, if there is anything wrong with the order or items are missing or damaged, the owner will bend over backwards to put it right.

John

 

[Swifty]

I'm always surprised by people wanting to grind steel with diamond wheels using normal grinder speeds, laps at much slower speeds are another thing. Diamond wheels are for carbide, if you are sharpening a brazed toolbit, use a normal grinding wheel to relieve the steel base, then use the diamond wheel for the carbide. Over the years I have used cup wheels, 7" diameter wheels on surface grinders and 14" diameter wheels on cylindrical grinders, all diamond wheels only used on carbide. The heat generated grinding steel, lack of material removal etc will ruin a diamond wheel. We used oxide sticks held against the diamond to clean the face of the wheel.

Paul.

 

[Journeyman]

You shouldn't have told me about Richon Tools I was looking through their website and came across a CBN cup wheel for GB£13.19... Couldn't resist, it's on the way who knows it may even have the hole in the middle!

John

 

[Swifty]

That's a good choice for steel, just take light cuts.

Paul.

 

[Journeyman]

Well I made an eccentric bush to fit the wheel. Set a length of 25mm aluminium bar in the four jaw and turned the end down to 20mm, made it a good fit in the wheel so that the wheel wouldn't spin easily. Set the inside of the wheel to run as true as I could get it using DTI then marked the end of the collar and the wheel so I could get them aligned again. Removed the wheel and machined the bore of the bush 10mm to fit the grinder spindle. Parted the bush off to length. Reassembled on the grinder and... Just as bad as before.

Tried again but this time setting the outside of the wheel to run true. Much better, still some vibration but probably useable, may improve when the wheel is dressed. The only other thing I can think of now is to set it up on the lathe and try and true up the inside of the cup. I don't know if this is acceptable or a good idea, any thoughts appreciated.

John

 

[Swifty]

If the outside of the wheel is not running true to the inside, sound like a badly made wheel to me. I had one of those small bench grinders years ago, it was very noisy, most likely due to bad bearings. It may pay to check the bearings in yours.

Paul.