3M Surface Conditioning vs Harbor Freight

[jacoby]

I did a little test on the 3M 07515 Very Fine surface conditioning discs vs the Harbor Freight 61504/99985 Fine discs.

Price-wise the 3M pads run about $1.40/ea. HF run $1.20/ea normally or about $0.96/ea with a 20% off coupon.

General impressions. The 3m pad is thinner, flatter, and does not have any sort of binder visible like the HF disc. The fibers with the 3m disc are finer and there appear to be more of them. Most importantly, the 3M disc is a more pleasant color of blue (they look a bit green due to the lighting in my shop).



First off, the 3m disc. Right two holes were hit with the pad and nothing else. Left two holes were followed up with a couple swipes of the maroon 3m hand pad.



And now the HF pad. This time from left to right there are two untouched holes and then two followed up with the maroon hand pad. The right-most is a comparison with the 3m disc.



They both seem to perform acceptably. The 3m pad seems higher quality and leaves a finer finish though.

As for the amount of material removed, I don't have anything sensitive enough to tell. The ?-2 seconds it takes to deburr the hole removes less than I can measure within the 0.0001" accuracy of my Starrett mic. My understanding is the alclad is ~5% of the nominal thickness, per side, so it's nowhere near breaking through, even on the thin 0.020" material. Notice the cleco left more of mark on the surface than either of the discs did.

[BMC_Dave]

Good stuff! I was wondering about those HF pads, great to see a comparison.

[JonJay]

Use them until they load up and are no longer useful. See which one clears better/lasts longer.

[jacoby]

Originally Posted by JonJay

Use them until they load up and are no longer useful. See which one clears better/lasts longer.

3M is on the right. Both have done approximately the same number of holes but the HF has done more time (I was using it to see how long it would take to break through the alclad).

One thing that you can't tell from that pic is the 3M has taken on a nice convex shape that's easy to control. The HF is still slightly lumpy and concave. You can kinda tell from the even loading and wear on the 3m vs the bits at 12 and 5 o'clock that haven't really touched anything on the HF.

(ignore the spar backdrop; i haven't deburred its holes)

Either way, they will both go a pretty good distance.

All in all, I really like using these discs to deburr. I've tried various options and these leave the crispest hole and go the quickest. After a pass I'm showing about 0.0015"-0.002" difference from the base material, which is inline with what I get with 100? 3-flute, 120? 1-flute, 80-something? 1-flute (don't use this one) countersinks or a drill bit. At this point I assume the punching and drilling process is what's moving the metal and not a result of the deburring.

I've also tried a glove and the maroon pad. Neither of those really removed all the burr. I could catch a fingernail on probably 20-30% of the holes.

The drill bit has done the worst of all my testing (a 2 flute drill will naturally try to make a tri-lobe shape and it shows during deburring). I found that surprising since it's listed in 43.13 (4-58).

[David Paule]

A couple swipes with a flat mill file, held flat on the surface, does an outstanding job with those burrs and does no other damage.

It's quiet, too.

Dave

[Radioflyer]

I wonder if you would agree? It seems to me that by using these pads, you are simply bringing "burrs" down to the level of the holes. The very edge of the hole may have sharp stress risers. To my custom, true deburring is done with an edge tool running into the edge of the hole and thus leaving a slightly beveled edge entering the hole. For example, lightly using a countersink bit would result in a full deburring. Would't the discs be better for deburring the edges of sheet metal parts rather than holes?
Meanwhile, thank you for the comparison between these two brands of disc. It is great seeing product comparisons and tests.

[DanH]

Originally Posted by jacoby

I did a little test on the 3M 07515 Very Fine surface conditioning discs vs the Harbor Freight 61504/99985 Fine discs.

There's a difference, but forget about it. Instead look at what you're doing to that spar.

Surface finish has a large effect on fatigue life. It becomes particularly important at edges which form the the most distant fiber in a beam.

Look at these photos. The process is cutting gouges across the corners at the edge of the spar. In the context of fatigue, those illustrate bad practice.





Surface scratches are directional. When using abrasives for surface finish, the key is to finish with the least possible scratch depth, and with all scratches parallel to the load vector. Here's an example. The "scratches" are greatly exaggerated, but the principle is clear. A scratch/gouge/cut across the stress is bad, while the same cut parallel to the stress makes almost no difference.



Edge gouging aside, the trouble with using a surface conditioning disk on a highly stressed part is that the finish scratch alignment tends be 360 degrees. Optimum is with all scratches aligned with stress.

As for the amount of material removed, I don't have anything sensitive enough to tell. The ½-2 seconds it takes to deburr the hole removes less than I can measure within the 0.0001" accuracy of my Starrett mic.

The flat surface away from the edge? The mic is not measuring the depth of the scratches. It's measuring the peaks between the scratches, which tells nothing about the depth of cut.

[jacoby]

DanH,

All good points. I should mention that piece was scrap due to my countersink betraying me. I was only demonstrating the difference between the two discs, not proper final surface prep. I am an amateur, nobody should listen to me or do what I do.

That said, I was throwing the kitchen sink at it to see what damage I could do, including that bit you see on the chamfering. I believe that bit was chatter from trying to use the edge deburring tool. It would have gotten cleaned up with a bit of draw filing.

For what it's worth, here is the replacement piece as it'll go to primer. I may chamfer the edges a bit more. All the marks the discs leave disappear with some touchup from the maroon pad.

[jacoby]

Originally Posted by Radioflyer

I wonder if you would agree? It seems to me that by using these pads, you are simply bringing "burrs" down to the level of the holes. The very edge of the hole may have sharp stress risers. To my custom, true deburring is done with an edge tool running into the edge of the hole and thus leaving a slightly beveled edge entering the hole. For example, lightly using a countersink bit would result in a full deburring. Would't the discs be better for deburring the edges of sheet metal parts rather than holes?
Meanwhile, thank you for the comparison between these two brands of disc. It is great seeing product comparisons and tests.

My understanding is that a square edge is more desirable than a beveled one, for riveted joints. Bolted/screwed should get the countersink deburr treatment.

See this thread: http://www.vansairforce.com/communit...ad.php?t=68311, specifically post #29 on page 3

[rvbuilder2002]

Originally Posted by jacoby

My understanding is that a square edge is more desirable than a beveled one, for riveted joints. Bolted/screwed should get the countersink deburr treatment.

See this thread: http://www.vansairforce.com/communit...ad.php?t=68311, specifically post #29 on page 3

Since it is my post you are referencing, I thought I should clarify.....

When I wrote "That is why the one with sharp corners will be stronger", it was in the context of comparing the two examples in the the diagram that was attached to that post.

That should not be taken to mean that sharp corners on fastener holes are good (they aren't), just that the sharp hole shown in the diagram would be stronger than the one with excessively deburred holes. Particularly with bolt fasteners because of the improved baring area of the hole interior on the bolt shank.

Holes should always be deburred... just not excessively so.