Using die grinder for scraping stuff

[justin1]

Did a couple tests to satisfy some curiousity and questions from another post. Still don't think this is replacement for proper scraping just think it's viable for certain applications.

Feel free to make suggestions if my tests are not adequate and I can try a different approach. Tried to keep it quick and simple.

The test piece is chunk of W44 steel.

Spot measuring "scapes"

Sorta Measuring "scaped" piece

Blued up chunk

Die grinder I used and zip cut disc. I imagine a fine diamond zip cut would work better but don't have one to test.


@Mcgyver let me know what you think I'm curious on your opinion as someone who has done proper scraping.

 

[Janger]

Justin sorry what are you doing here? I don't get it. I understand the measuring but how did you create that .. what? cut?

 

[justin1]

Justin sorry what are you doing here? I don't get it. I understand the measuring but how did you create that .. what? cut?

Used a grinding disc on a air die grinder. I would of taken video of it in action but hard to film and grind at same time.

Video of someone else using this method to grind hardened ways

 

[PeterT]

Very intriguing. I think you kept calling the increments 'thou' like 4 dial ticks as '4 thou'. But its a tenths reading indicator so should be '4 tenths' = 0.4 thou? (A much lower number).
Tell us a bit about the test bar underside & your surface plate because you are holding the gauge stationary & moving the part relative to it. Is the underside known to be very flat like it has no rock on its own in any dimension? And your plate, is it a decent surface plate? I'm not disputing the numbers, just trying to help rule out any other deviation. I would have thought this might be a good way to hack down mountains like in the multi-thou before scraping, or no other option with hardened material. But this looks like it has potential. Maybe there can be even more depth control gained with select abrasives, RPM, wheel disc flexibility to give even more hand touch feedback.

 

[Arbutus]

Interesting! I would like to see some more details on the setup - more pix or your video?

 

[Dabbler]

@justin1 A very intriguing idea... I use 4 radii when scraping, from 2" radius to 6" radius. the smallest radius is used for roughing, as it takes 'scoops of metal' and for the same pressure, digs a little deeper than the largest radius. It is also used for Moore pattern scraping, or 'flaking' to improve oil retention after conventional scraping.

But that even needs a minimum of a 4" wheel - although at those angles, the depth is mitigated, a little. So I'm a little concerned about using such a small wheel. But I'm thinking about how that might help the roughing stage...

 

[Mcgyver]

@Mcgyver let me know what you think

My opinion? Not something I've thought much about so my views of as a scraping substitute are not deep or forged in experience: Interesting, less deviation that I expected but I wouldn't do it except for a hardened bed.

in more depth....

Its not a new thing, I remember this coming up a few times on PM. The general consensus (irrc) was no shame in doing so on a hardened way when you have to but it's sub-optimal on soft material. That consensus was from those who generally knew what they were doing (you get a sense of that being at place over the years).

The theory as I know it, and adds up based on my experience, .....

If one reads a tribology book (what a charmed life eh?), the ideal bearing surface is perfectly flat. Of course there is no perfect so between the parts you get protruding stalagmites and stalactites .... that's just my way of creating a visual, they are more properly call asperities.

Wear occurs when they collide. If the oil film is thicker than the dept of the asperities, there shouldn't be wear. After scraping, because you lighten up and are carefully hitting the high spots, you end up with s surface that doesn't even seem to flicker a tenths indicator. The reason is depth of cut is limited by how much force one can muster and fairly easily controlled beyond that by how hard you come at it - that will be sub-tenths as you lighten up and finish. With many iterations, the difference between high and low becomes max that DOC. You don't have that with a hand held grinder.

Maybe what you are doing will work well, but seems many times less "flat" (difference between and high and low) than you get with scrapping. Maybe as a roughing technique it would be good (i've also used files and milling)? I generally dislike "we've always done it this way" as an argument, but find myself thinking if this was good enough, its the ways machine tools would have been build already.

I also don't know why you are getting so much variance off the surface grinder. imo you should see not see even 1/2 tenth flicker form a part off the grinder??

PS ..... maybe the way to control DOC (so as to better replicate the results of scraping) is with grinder speed ....... that might be worth some experimentation.

 

[Dabbler]

I also don't know why you are getting so much variance off the surface grinde

He's using a die grinder with a zip disk.

no shame in doing so on a hardened way

that's my sense also.

But even on a hardened way, the finishing has to be done with a scraper or a diamond lap, to take off the highest spots.

 

[Mcgyver]

He's using a die grinder with a zip disk.

In the first video he makes reference to the surface grinder finish, but in looking at it a second time, my comment was invalid; must have confused things as in fact where he mentions the SG finish he was getting next to no indicator hand movement, so the SG is performing well

 

[justin1]

Tell us a bit about the test bar underside & your surface plate because you are holding the gauge stationary & moving the part relative to it. Is the underside known to be very flat like it has no rock on its own in any dimension? And your plate, is it a decent surface plate?

The test bar was ground parallel. As far as the surface plate goes Its in rough condition but seems flat I picked a spot with least wear and ran piece under indicator before touching with die grinder to make sure there wasn't any movement. so I don't know how flat the plate is as a whole. I actually just got it yesterday on way home from airport. I can re do the test on my small Lee Valley B grade stone see if it changes much.

Ye I meant tenths I corrected my self closer to the end. I probly should of just re-shot the clip.

But I'm thinking about how that might help the roughing stage...

I think it would be fast way of roughing something you can't fit in mill or surface grinder. Just would leave enough material that you could finish it out with scraper.

@Mcgyver @Dabbler @Arbutus
I just like to hear peoples view points who have more experience then me as they see things differently then someone with no experience.

I found with my limited screwing around with die grinder on Chinese lathe and few test pieces that you can do some fine tuning withe the DOC with speed but the finish of cut is rougher vs just running at max speed seem to get less highs and lows in the cut. Most of the DOC comes from how hard you push and how you flick wrist.

In the video of guy using diamond when he noise dives zip cut into the metal that would probly produce the deepest cuts in soft metal anyways not sure about hardened as I have tried it on anything hard. I just start above were I want to cut and kinda flick wrist in C motion so I enter and exit the cut in more of a tear drop shape

Sorry about my poor narration I don't really film anything let alone talk to my self on camera lol. I'll get some more photos of how I was testing and maybe do a another video to address anything that has came up on this topic

 

[justin1]

The over view of my set up


The fine adjust on this mag base isn't very rigid and notice it does move around if I'm not careful so Ill try a different one on next test.


My surface grinder in in some of its glory just finished reassembling last days off after a deep clean after buying it few months ago. So far pretty happy with it just need more disc holders for it as the white disc I got now works but clogs up easy when I resurfaced mag chuck as it is lead and steel. And it's very easy to burn stuff I've found so I need a 46grit maybe not a 80grit I think it is.

 

[justin1]

More videos and now with more resolution thanks @Arbutus

This is done with same set up as before but now I'm using the B grade granite stone which is pretty much brand new and using the Helios .001mm dial indicator. I included blueing I used and the zip cut blade.




Video of testing the surface grinder finish to ensure piece is parallel

Video of the 3 different cutting pressures with die grinder with an abrasive zip cut disc

Video of me measuring 3 different cutting pressures with .001mm dial indicator

Video of die grinding in action

Video of blued up test piece

Video of measuring test piece
https://youtube.com/shorts/9V0zfe7pUQI?si=M0gQPsg0Bv38WqC8

 

[PeterT]

Again, very interesting. Most people have access to a mini grinder before they might have scraping tools & getting something within a 0.001" using grinder, blue & surface plate would be worth some experimentation. I'm not saying abandon classic scraping, but even as a means to get something rough into the territory where hand scraping could take over in its realm may have benefit.

I cant help but wonder if the grinder was somehow suspended on a rubber bungee type material from above where the net weight was then taken up to a high degree, would that result in an even better feel &of depth. Maybe the zip-way teardrop technique is partly to have a mental task pattern in your minds eye to spread the cut & kind of assist you from dwelling in a reduced area & cutting deeper. Maybe with partial 3D support you could feel it even better? At minimum it would reduce arm strain supporting the full weight of grinder. The cut is so shallow, even different types of grinder come o mind.

Also the grit & RPM must be a factor. Reducing grit & lowing speed must result in shallower depth all things equal. Ali inexpensive diamond lapping plates in all ranges of grits in a steel plate form maybe 1-2mm thick steel disc. I wonder if that could be more predictable in terms of wheel flex vs the buzz wheel? But maybe they have max speeds not sure there. Also if localized temp gets high with diamond, that's supposed to be a bad thing from altered material properties (same issue as HSS on diamond wheels). But you are taking so little off...

An interesting video to me is if you can stage it is with specimen blued beforehand off the surface plate (like typical inter-scraping stage) then as you grind target areas to correct geometry. I'm not sure that's your intent here but that would be useful.