Selecting abrasive type(s)

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Stan Pope
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Selecting abrasive type(s)

Post by Stan Pope » Sat Mar 19, 2016 11:41 pm

A recent email question focused my attention on abrasive hardness, a topic to which I have paid only cursory attention. Specifically, I asked myself about regular MicroMesh and MicroMesh MX. Recent updates to a seller's summary sheet added text describing applicability: regular MicroMesh for wood and plastics, MicroMesh MX for metals!

The ability of an abrasive to polish an axle depends on the size of the abrasive grit and the hardness of the abrasive grit. Apparently the grit hardness in regular MicroMesh, e.g. MicroMesh 12,000, is not hard enough to reliably cut (i.e. polish) steel axles. Similarly, MicroMesh AO may also lack necessary hardness.

Does anyone have data that supports the use of regular MicroMesh and/or MicroMesh AO for polishing axles?


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MaxV
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Re: Selecting abrasive type(s)

Post by MaxV » Sun Mar 20, 2016 3:44 pm

I concur that you need Micromesh MX for polishing steel. However, if you are only polishing the zinc coating, then regular Micromesh works - zinc is much softer than steel. This would be the case for axles that do not have flaws that have to be filed offer. So official BSA officials need the Micromesh MX, while Awana axles, et al, can use regular Micromesh.



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Stan Pope
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Re: Selecting abrasive type(s)

Post by Stan Pope » Tue Mar 22, 2016 8:50 pm

The other side of grit hardness is the strength of the material that holds it against the axle. That means (to me) that if the backing is paper, the grit will not be very large. More likely the backing is a woven fabric with some healthy adhesive holding the grit in place!

An additional concern when using any abrasive is the final shape of the workpiece. Do we end up with a constant diameter cylinder? Or do we get something that could be a fancy leg for a miniature table ... the diameter rising and falling along the axis?

For instance, suppose that we start with a BSA Nail, fresh out of the box, and dress the ridges with a file down to within a 0.003" of the nail shaft. If the abrasive backing is flexible, it may follow the contours, although I think that it erodes more from the raised remnants of the ridges. The result, I think, is that the whole worked portion of the shaft becomes smoother, but that the are of the ridge remnants maintains a slightly larger diameter. Can the effect be mitigated by backing the abrasive with a stiffer material such as 1/8" thick leather? Or does it take something even stiffer? (I think that this concern applies mainly to the first (coarsest) abrasive which should be used until a good cylindrical shaft is accomplished.)

Thoughts?


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Selecting abrasive type(s)

Post by whodathunkit » Wed Mar 23, 2016 10:59 am

Stan,
I think your right about using a stiffer backing with the Micro mesh MX during hand applications.
(Most of the time this would be something like a firm foam block)
The cutting ability of micro mesh mx should also be increased by increasing it's rigidity of the back up material.

The floating action of the abrasive crystals in micro mesh mx
does not require high speed operation to achieve super finishes.
If higher speed rates are used, the feed rate an pressure should be reduced.

In general rule, higher speeds promote a faster cut, while lower speeds produce a better finish.

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