Tool Diamond wheel truing dressers

[TorontoBuilder]

I have previously used a molybdenum stick in a grinding vise to true up diamond wheels.

Thanks to Rob Renzetti, and his video which I'm sure you've all seen.

I'd call it my favourite method, since it's my only experience trying to true a resin bond diamond wheel. It seems to work well enough but I paid over $50 for the stick.

I wanted to try the other options, a skewed type wheel dresser, and a brake type dresser as an option, and see how well they worked. The wheels are about $15USD each from mcmaster carr.

I figured I'd 3D print a shell with a 3mm thick wall, using loop setting and zero infill... whcih is better alternative to trying to fiddle with vase mode to make thin walls. Then I'll fit my threaded inserts and fill the cavity with epoxy and gravel mix. A 1/4" steel plate the bolts to the bottom to allow the use of magnetic chuck.

Two caps hold the spindle to the base. The spindle is 3/8" precision ground shaft, a hub will spin freely on a pai of bearings. Pretty simple.

 

[PeterT]

I figured I'd 3D print a shell with a 3mm thick wall, using loop setting and zero infill... whcih is better alternative to trying to fiddle with vase mode to make thin walls. Then I'll fit my threaded inserts and fill the cavity with epoxy and gravel mix. A 1/4" steel plate the bolts to the bottom to allow the use of magnetic chuck.

Interesting. I have zero surface grinder experience. I've only dressed my toolpost grinder with a traversing single point diamond. Maybe this wheel based dressing principle is a thing but my gut instinct is that it looks sketchy. One tiny bit of loosening or play or distortion or runout anywhere in the dresser assembly & the whole affair could blow up in your face with disasterous consequences. I cant tell by the video but his wheel holder looks like solid steel. I'm apprehensive that if your base distorts by whatever mechanism it could be the infeed jam point. Yes epoxy/aggragate mix would make a stiffer composite sandwich product vs 3DP alone, & aggargate makes excellent vibration dampening. But its actually not that stiff or strong. And the composite sandwich of 2 materials entirely depends on adhesion to the 3DP wall which... I wonder. Plastics are very offstandish to most all resins. In fact I've cast epoxy parts in 3DP molds the odd time completely forgetting the release agent & (with a bit of difficulty) the part pops out. If you have any micro-parting between the 3DP surface & aggragate you basically have nothing for mechanical stability IMO. It becomes a core rattling around inside a shell. If it was any kind of part where consequences were not so dramatically catastrophic I'd say go for it. But 2 spinning wheels, the dressing wheel going at 2-4x faster due to ratio... Yeesh.

 

[TorontoBuilder]

Interesting. I have zero surface grinder experience. I've only dressed my toolpost grinder with a traversing single point diamond. Maybe this wheel based dressing principle is a thing but my gut instinct is that it looks sketchy. One tiny bit of loosening or play or distortion or runout anywhere in the dresser assembly & the whole affair could blow up in your face with disasterous consequences. I cant tell by the video but his wheel holder looks like solid steel. I'm apprehensive that if your base distorts by whatever mechanism it could be the infeed jam point. Yes epoxy/aggragate mix would make a stiffer composite sandwich product vs 3DP alone, & aggargate makes excellent vibration dampening. But its actually not that stiff or strong. And the composite sandwich of 2 materials entirely depends on adhesion to the 3DP wall which... I wonder. Plastics are very offstandish to most all resins. In fact I've cast epoxy parts in 3DP molds the odd time completely forgetting the release agent & (with a bit of difficulty) the part pops out. If you have any micro-parting between the 3DP surface & aggragate you basically have nothing for mechanical stability IMO. It becomes a core rattling around inside a shell. If it was any kind of part where consequences were not so dramatically catastrophic I'd say go for it. But 2 spinning wheels, the dressing wheel going at 2-4x faster due to ratio... Yeesh.

A couple of points to address the concerns you raise, and see if the design addresses the concerns.

Firstly, the PLA-CF is mostly just a shell mould to contain the epoxy granite. I could have altered the shell setting to make the mould completely removable but though why bother for a one off design.

That said, epoxy bonds very well to PLA and the rougher the surface texture the better the bond... The CF reinforced PLA has a texture that lends itself to mechanical keying but orca slicer also has a fuzzy skin setting that I can apply to the internal walls to make an even better surface for bonding.

The majority of the forces are compressive forces which epoxy handles very well.

This method of skew angle truing is tried and true. The driven diamond wheel speed, the size ratio and the skew angle is what determines the speed of the dressing wheel. Typically ~2000 rpm with full contact at 15 degree offset on a surface grinder.

The shaft has far more influence on vibration than the actual base. The originals are much thinner parts of cast iron because that was common material and technical plastics were not. I expect this to have less vibration that can be transferred to the diamond wheel than the moly stick method.



The forces acting on the base are downwards compression and some minor shearing force from the driving diamond wheel shearing across the skewed dressing wheel face

 

[PeterT]

I'm going to do some epoxy aggragate + 3DP experiments for some machine type accessories which would normally be CI, so we will have to compare notes. Actually you can take this mechanical locking of epoxy even further than relying on surface roughness alone with 3DP riblets or ledges. Just have to mitigate any open air bridging issues, usually resolved with vibration or vaccum depending on the part.

Anyway, back the wheel dresser, does it even need to have a wheel well & axle at some an angle relative to rectangular body footprint? You need a steel base plate for mag vice anyway. So two vertical ears pinned & bolted on either side, or welded if you have one with a resultant U-shape. Same bearing holes & you are done, no? I mean you are going to set the device at some angle to the main grinding disc, I feel if it was a rectangular plate U you can now set a specific & repeatable angle relative to edge of mag vise if there is some sweet spot?

 

[TorontoBuilder]

I'm going to do some epoxy aggragate + 3DP experiments for some machine type accessories which would normally be CI, so we will have to compare notes. Actually you can take this mechanical locking of epoxy even further than relying on surface roughness alone with 3DP riblets or ledges. Just have to mitigate any open air bridging issues, usually resolved with vibration or vaccum depending on the part.

Anyway, back the wheel dresser, does it even need to have a wheel well & axle at some an angle relative to rectangular body footprint? You need a steel base plate for mag vice anyway. So two vertical ears pinned & bolted on either side, or welded if you have one with a resultant U-shape. Same bearing holes & you are done, no? I mean you are going to set the device at some angle to the main grinding disc, I feel if it was a rectangular plate U you can now set a specific & repeatable angle relative to edge of mag vise if there is some sweet spot?

I could make a simple u shaped bracket and be done... but I'm experimenting at the same time.

I like to kill two birds with one stone.

That and I don't have to leave the house to do this job if I buy off the shelf threaded inserts.

I want to make a few grinding fixtures that use similar construction.

I was planning on both vibration and degassing.

I'm also going to experiment to see if I can get a nice 1.2mm wall section that can work if I mix a little more fluid epoxy mix

Oh and I plan on making concrete experiments too.

 

[jorogi]

TB, with all due respect I think we have to recall the first three rules of machining. Rigidity, Rigidity, Rigidity. Oh yeh, and something about safety too.

I have no experience with 3dp-ing but I do have some with grinding. My dressing wheel is of steel construction with two bearings and it works well. It is a solid hunk, very rigid.

I also have a single experience with a grinding stone exploding. When I first got my grinder I was happily grinding away one day when the power failed thus instantly turning off my electric mag chuck. I can't remember the nitty gritty details but the cut was probably 2-10ths deep, 20 thou step over with a 3/4" wheel. Not aggressive at all. Explode is an accurate description, you certainly don't want to get in the way of your flying work piece or a chunk of wheel, they're lethal. Also it happens instantly, not enough time to even shit yourself.

Also I would disagree with your assessment of the direction of the force (my drywall will support me on this). You should be on the back side of your wheel and grinding in a conventional cut not a climbing cut. The force is tangent to the wheel, so in my case horizontally right to left and ever so slightly up. Any lifting of the dressing wheel (and again we're talking 10ths here) and it could get ugly before you know anything is going on.

I might not have it right, and perhaps one of the 99% of brighter people on the group here could correct me if I'm reading my experience wrong. What I'm saying is I don't approach many things in life in a pussy like fashion but I respect my grinder more than any tool in my shop. Please be safe my friend.

 

[TorontoBuilder]

@jorogi thanks for the feedback and the reminder on safety.... you are 100% right that grinding wheels demand total respect, and a failure is catastrophic.
However, my setup is mechanically different from a standard surface grinder workpiece on an electric mag chuck, which changes the force vectors entirely.

Because my dressing fixture is located past the 6 o'clock centerline on a clockwise rotating wheel, the tangential force actually pushes the fixture up and away from the wheel center, creating a natural conventional cut rather than a climbing cut.

It can't naturally suck the dresser under the wheel, and I have a purely mechanical magnetic chuck so a power failure wont result in detachment of the fixture and the following explosive contact with the wheel.

That said, there are massive compressive forces at play here.

Every time you lower the wheel head to index the cut, the infeed force pushes directly down into the diamond and the fixture body.

When you combine that downward compression with the upward/sideways tangential drag of the wheel, the resulting net force travels diagonally down through the fixture. It's force vector physics.

This is exactly why I am focusing so heavily on rigidity and looking into epoxy granite rather than 3D-printed plastics or standard concrete. Epoxy granite has incredible compressive strength to handle that downward infeed, but unlike steel, it has massive internal vibration damping. My design is much beefier than the old Newman cast iron versions, and uses low carbon steel bottom plate to match the magnetic flux capabilities and holding power of a solid steel version without saturating.

The goal is to absorb those high frequency harmonics from the diamond fracturing the grit so it doesn't micro chatter and ruin the dressed wheel profile.

 

[jorogi]

Every time you lower the wheel head to index the cut, the infeed force pushes directly down into the diamond and the fixture body.

Ah, I don't plunge the grinder. I lower the wheel behind the work and then traverse across the piece.

 

[TorontoBuilder]

Ah, I don't plunge the grinder. I lower the wheel behind the work and then traverse across the piece.

That still puts downward compressive force on the dresser, and the diamond wheel contacts the dresser on the trverse

 

[TorontoBuilder]

It occurred to me that I also have a tool post grinder...


I can mount this to the left of the magnetic chuck, with an additional set of riser blocks... and bob's yur uncle.