Truing Wheels, SJ Odd Inclusions

[RickKrung]

After the farmers market work I've been doing, I thought it time to true the wheels.  SB and SG went fine.  SJ wheel is curious.  There is a very loud "crunching" or grinding sound as the truing tool traverses, seeming uncharacteristic for what should be a very fine stone. 
https://vimeo.com/291399304

Also, there are quite a few curious little bumps on the surface. The only thing that makes sense to me is these must be soft spots that flex under the truing diamond tip and the pop up when the pressure is off. 


I'll finish this using the grading stone and then a 1000 grit diamond plate and see what, if anything remains.  I think they won't matter to the function of the SJ wheel, I just find them curious. 

Rick

[RickKrung]

...snip...
I'll finish this using the grading stone and then a 100 grit diamond plate and see what, if anything remains.  I think they won't matter to the function of the SJ wheel, I just find them curious. 

Rick

Not surprisingly, the stone grader and the 1000 grit diamond plate smoothed out the SJ wheel very well.  There are a lot of small pockets, that look like air pockets.  The pattern and distribution seem consistent with the bumps mentioned earlier. 


Rick

[cbwx34]

That chipping on the edges is what would concern me...

Most regular waterstones are chamfered on the edges to prevent chipping... I did the same to my SJ wheel right off the bat.

I know you're not the first to bring this up... wonder what Tormek support would say........... 

[RickKrung]

That chipping on the edges is what would concern me...

Most regular waterstones are chamfered on the edges to prevent chipping... I did the same to my SJ wheel right off the bat.

I know you're not the first to bring this up... wonder what Tormek support would say........... 

The chipping has bothered me also.  And it seems to only get worse with use/truing.  At this point, I think a small chamfer would be be best, to try to stop the process and keep it chamfered as the wheel wears down to reach the deeper chips. 

How did you chamfer yours? 

The inclusions/pockets don't bother me as I don't think they adversely affect anything. 

Rick

[cbwx34]

The chipping has bothered me also.  And it seems to only get worse with use/truing.  At this point, I think a small chamfer would be be best, to try to stop the process and keep it chamfered as the wheel wears down to reach the deeper chips. 

How did you chamfer yours? 

The inclusions/pockets don't bother me as I don't think they adversely affect anything. 

Rick

I just turn the wheel on and hold either a small diamond sharpening stone or the fine side of the Stone Grader at an angle against the edge for a few seconds.

[RickKrung]

I just turn the wheel on and hold either a small diamond sharpening stone or the fine side of the Stone Grader at an angle against the edge for a few seconds.

Done.  I used the sides of the stone grader, first the coarse side and then the fine.  I think it will work eventually to eliminate all the chips.


I have two stone graders, one dedicated to the SB stone and I only use the coarse side on it, and I'm only grading the SG stone fine these days, so one grader would do, at this point. 

Rick

[Ken S]

We have had several reports of problems truing and dressing the SJ 4000 grit wheel. I have no doubt that there is a problem, be it with the wheel itself or the operator technique. I have not experienced it myself, although I rarely use the SJ.I will be interested in following this.

My one thought would be to ask how deep of a truing cut people are using. I only use half a microadjust number with each slow pass.

Ken

[DaveBlue]

In the Vimeo video it looked like the SJ wheel was being dressed without water, is this the case? From my experience heat can be an issue but vibration is a bigger issue even at these lower wheel speeds being used. I believe the dressing process would benefit from a smaller diameter diamond dressing tool. This would reduce dressing pressure and the amount of heat being created in the dressing process. Less dressing pressure would result in a flatter wheel periphery as well. I am not sure if there is a diamond dresser available from Tormek with a smaller diameter.

[RichColvin]

Dave,

I use water when dressing my SJ wheel.  No issues to date.

Kind regards,
Rich

[RickKrung]

Water was used while dressing the wheel.  In the video, if you look at the back/top surface of the wheel, after it has passed the dressing tool, you will see little jumps of light flashes.  That is light being reflected off of the water on the wheel. 

The truing tool cutter tip is wide, but the diamonds embedded in the surface do not cover the entire surface.  There are only a few diamonds actually doing the cutting.  I and others posted some photos of this in this thread: https://forum.tormek.com/index.php?topic=3647.msg23879#msg23879

I doubt seriously there is much of a heat buildup problem at as slow a rate of traverse as seen in the video.

Rick

[Ken S]

I generally dress the wheel very gently. I take multiple very shallow passes and traverse the wheel slowly. I have done deeper cuts and more rapid traverses successfully, but only when I was attempting to reshape with the SB.

I have not encountered any problems with my gentle technique, even with the SJ, although I rarely use my SJ.

For a while, I used the electrical wiring ties on my TT-50. I never had the bouncing problem, however, since Ionut recommended using the ties, I tried it. I recommend using them as an inexpensive, quick and easy possible solution.

I have used an inexpensive 1000 grit diamond plate to grade my SG fine. It left a very nice surface and was dead flat. I need to do more testing with the diamond plate, both with the SG and SJ. I think it looks very promising.

I have started working on "phase II" of this project. I purchased a set of three DMT credit card size diamond thin plates. I glued them to metal plates measuring 2"x6"x1/8" (50mmx150mm x 3mm.) I hope to see if I can reliably produce 220, 600, and 1000 grit on the SG and gently dress the SJ.

Regarding pressure when truing, dressing, and grading wheels, I believe using a lighter touch will be the key. We know that diamond wheels require a light touch all the time. We also know that using a light pressure for the last few passes helps smooth the surface with the Original grinding wheels.

Diamond cutting technology is a fairly recent development.

Ken

[DaveBlue]

When dressing small grinding wheels that contain fine abrasive grit it is key to have the right size diamond grain in the dressing tool. The table below is an extract from something i have used for many years in relation to multi-point dressing tools very similar to the Tormek tool. The tool should only be 4 mm diameter with a carat content of 0.6 carats for this wheel size.

Grinding wheel grit size        Diamond Grain Size
320 - 600                                 D76
220 - 320                                 D107

Are the diamonds in the Tormek tool this fine?

I personally have problems with dressing using the jig and find it difficult to get a good dress on the Tormek, i am new to the Tormek grinding machine and very interested in the comments in this thread. I have tried using the cable ties and to some extent this as helped.

[RickKrung]

When dressing small grinding wheels that contain fine abrasive grit it is key to have the right size diamond grain in the dressing tool. The table below is an extract from something i have used for many years in relation to multi-point dressing tools very similar to the Tormek tool. The tool should only be 4 mm diameter with a carat content of 0.6 carats for this wheel size.

Grinding wheel grit size        Diamond Grain Size
320 - 600                                 D76
220 - 320                                 D107

Are the diamonds in the Tormek tool this fine?

I personally have problems with dressing using the jig and find it difficult to get a good dress on the Tormek, i am new to the Tormek grinding machine and very interested in the comments in this thread. I have tried using the cable ties and to some extent this as helped.

A photo of the business end of my diamond dressing tool is show in this thread.  Can you estimate or calculate the grain size by knowing the diameter of the copper base in which the diamonds are embedded = 5.2mm?  What are the units of the diamond grain sizes that you reference above? 

Also, wouldn't the speed of the diamond cutter traverse matter?  I didn't like the manual operation of the truing tool so motorized it using a gear motor and model train speed controller, mentioned in this thread.  I've measured the traverse rate at 4 minutes for a single pass.  That leaves a very fine surface but I don't recall if I used anything that slow when truing the SJ stone.  Judging from the pattern on that first photo I posted, I does not appear so fine.  It is time to true it again as it was not very flat when I used it on a plane blade today, so I'll be sure to run it as slow as my truing tool will go and see what difference it makes. 

Rick

[DaveBlue]

The diamond grain size D76 is an average of 0.076mm 76 microns and D107 is an average of 0.107mm 107 microns. This as you can imagine looks a lot finer than the diamond grain used in the dressing jig. You are correct the speed at which the diamond travels across the wheel is important and this is called the overlap factor. A conglomerate style dressing tool needs to travel farely fast and the overlap factor is normally based on diamond travel per wheel revolution. I will try to estimate the diamond size used in the pictures and update the thread. I will also try to source the dressing i describe. Incidentally you mention the depth of cut taken when dressing, i would recommend no more than 0.01 to 0.015 mm which would be difficult to measure.

[Ken S]

The easy way to try different diamond grits is to purchase a set of three DMT credit card size diamond cards and a length of 1/8" x 2" steel or aluminum plate. I cut three eight inch lengths and used epoxy or JB Weld to glue on the diamond cards. Mount one of these in your square edge jig. Mark the grit on the plates.

I have mounted these, but have not had a chance to use them. I plan to use all three grits with my SG and just the fine grit with the SJ.

I have used another 1000 grit diamond plate with my SG with good success.

Here is a lnk:


https://www.amazon.com/DMT-D3EFC-Dia-Sharp-Extra-Fine-Diamond/dp/B00006IIO3/ref=sr_1_2?ie=UTF8&qid=1539129506&sr=8-2&keywords=dmt+diamond+cards

Ken